1. BLEACHING, or BLANCHING, (Blanchiment, Fr.) originally signifies the art of whitening any substance by other means than painting; but it is more particularly applied to a branch of trade or manufacture exercised by persons called bleachers, who, by certain processes of a chemical nature, give to woollen, linen, and cotton stuffs, &c. the greatest degree of whiteness of which they are susceptible.
2. Till lately this art had not occupied any considerable share of attention, except to those who were more immediately concerned in the practice of it. Its processes were few, and though exceedingly tedious, were simple and easily understood. The late rapid progress of chemical science, has however thrown so much light on the theory of the art, and contributed so materially to the improvement of its processes, that it is become a most pleasing field of investigation, and demands a much more considerable space in a modern encyclopaedia than it has hitherto obtained.
3. We propose, therefore, to treat of bleaching in the following article more fully, and more in detail, than is usually done, and to bring, as far as possible, into one point of view, every thing of importance which has been lately written on the subject by Berthollet, De Charmes, Rupp, Kirwan, Higgins, Chaptal, O'Reilly, and other eminent chemists.
4. The improvements made by these gentlemen have been so rapid in their succession, and so important in their consequences, as to have rather created a new art than ameliorated the old. It will hereafter be scarcely credible, that in the space of about twenty years, the whole of an ancient system of bleaching, which had prevailed from time immemorial, should have been entirely overturned, and replaced by one of the most scientific accuracy, and expeditious management.
5. The origin of this art, like that of many others which are subervient to the comforts or conveniences of man, is involved in great obscurity. We find that a desire for rich and brilliant colours, and for garments of the purest white, has prevailed in civilized society from the earliest periods of which we have any accounts. This was more particularly the case in the eastern countries, as appears from the earliest writers, both of sacred and profane history. It is, however, probable, that the art of dyeing was antecedent to that of bleaching; but the effects of the sun and air in whitening garments, and in discharging the less permanent colours imprinted by the dyer, which must have been very observable in those climates, would soon lead an ingenious people to imitate or increase the action of the atmosphere, and turn to advantage as a luxury what in many cases must have been considered as an inconvenience. Of the methods employed by the ancients in whitening or scouring their various stuffs we are almost entirely ignorant; we know, however, that the Egyptians were accustomed to use some kinds of clay for these purposes, and that they availed themselves of the bleaching powers of the atmosphere. Pliny informs us, that a plant to which he gives the name radicula, was employed for scouring wool*; this is probably the fame with what we call sapwort. The acridix c. 3. juice of some species of euphorbia, especially the pellus, is said to have been used in France for whitening linen. 6. The art of bleaching is very extensive, and comprehends a variety of objects, whether we consider it as a distinct branch of trade, or as an art called in to the assistance or completion of several of our manufactures. It is essential to the perfection of the linen, the cotton, the filken, the woollen manufacture; it is in many cases a necessary step in preparing stuffs for the dyer and the calico-printer; and to it the paper-maker and the wax-chandler are indebted for the beauty of their productions. To this art belong the scouring of clothes and stuffs, the removal of colours, spots, and stains, the cleaning of books and prints.
7. We shall in the following pages describe the various methods employed to answer these several purposes, and shall endeavour to trace the steps by which bleaching has arrived at the high degree of perfection which it has lately attained. In detailing the processes of the artist, we shall, however, avoid as much as possible his technical language, so as to render this article not only a useful assistant to the practical bleacher, but an interesting object to the philosophic chemist.
8. As the methods of bleaching animal and vegetable substances are different, we may properly divide this article into two parts; in the first of which we shall describe the processes for bleaching wool and silk, and in the second the methods employed in the bleaching of linen, cotton, paper, and other materials furnished by vegetables.
PART I. BLEACHING OF ANIMAL SUBSTANCES.
9. THE substances which are derived from the animal kingdom, and which we more particularly employ as articles of clothing, differ essentially from those which are the produce of vegetables. The art of bleaching depends very much on an exact knowledge of those peculiar characters, which form the line of separation between these two classes of bodies, and it is therefore of importance to him who is desirous not only to be master of the several processes in this art, but to understand the theory of the subject, to be acquainted with the nature and properties of each.
10. The animals from whose spoils we obtain our principal clothing are nourished by vegetables, which as they pass through their organs lose their former properties, and acquire others more akin to animal bodies. In particular they are found to contain a new element, azote, which is but sparingly found in the vegetable kingdom, but constitutes one of the most abundant products of animal bodies. They also contain sulphur and phosphorus, as appears from the examination of those pungent exhalations which always accompany the decomposition of animal matters.
11. It is found that animal matters are more easily separated into their component principles than vegetable, owing to the weaker degree of their mutual attraction. Hence the action of acids and alkalies is much more violent on the former than on the latter, and consequently much more caution is requisite in their employment.
12. In bleaching animal substances recourse must be had to the united action of the fixed alkalies, soap, ammonia or volatile alkali, and sulphurous acid, the choice, preparation, and uses of which will be presently described. The animal matters with which the bleacher is more immediately concerned are wool and silk.
CHAP. I. Of Wool.
13. WOOL, like hair, of which it is a variety, is composed of filaments or tubes filled with a substance of an oily nature. The surrounding surface of these tubes is pierced with an infinite number of small holes which communicate with the internal cavity. By chemical analysis wool is found to contain carbonat of ammonia, and a considerable quantity of oil. It is very little altered by exposure to the air, and undergoes no change from the action of boiling water. It is of great consequence that the bleacher should attend to this circumstance, as will appear immediately.
14. A solution of caustic alkali, or caustic ley, destroys it altogether, and forms with it a soap, for the discovery and application of which we are indebted to Chaptal; it is but little acted on by acids, but the application of a violent heat reduces it to a state of fusion. From all these circumstances it appears that wool is nearly allied to oleaginous substances.
15. The examination of these chemical actions is of consequence to direct the bleacher in his operations on this substance: the trifling action which acids exert on wool, and its inalterability in water, even when assisted by heat, show the necessity of having recourse to alkalies or soapy matters; while at the same time the violent action which these exert, will point out the propriety of being cautious in their use.
Of Bleaching Wool.
16. The wool as it comes into the hands of the manufacturer usually contains a large portion of the natural greasy matter, from which it must be purified before it can undergo the process of bleaching. Sometimes the farmer cleans it from most of its oil, so as to diminish its weight by 50 or 60 per cent. in order to enhance the value of the article; but care is taken to leave some portion, as the natural fat is found to be the best preservative against the attacks of moths and other insects.
17. The first object then is to carry off the whole of the oily matter, which is called the operation of scouring, and is performed by means of an ammoniacal ley, which is thus prepared. Five parts of river or other soft water are to be mixed with one part of stale purified urine, which is found to contain a large quantity of ammonia (A).
(A) The detergent property of urine has been long known, and it is frequently employed in washing to lave Chap. I. BLEACHING.
Animal This mixture is to be boiled for a short time, and into substances, this, at about the heat of 56 degrees, or so that the hand of the workman can be easily held in it for a considerable time, the wool is to be thrown. Four or five pailfuls will generally be sufficient for 20 pounds of wool. After steeping for a short time, the wool is to be stirred about in the mixture continually for about a quarter of an hour or 20 minutes, according to the quantity of greasy matter. It is then to be taken out and drained into a basket, so that the drainings may drop into the vessel in which it was steeped, that nothing may be lost. It must now be completely rinsed by exposing it in baskets to a continued stream of clear water, while a workman is perpetually employed in stirring it with a pole, till the water passes off perfectly clear. The wool is then removed, and a fresh quantity put into the basket, which is to be treated in the same manner. The steeping and rinsing are to be repeated till the wool has attained as great a degree of whiteness as it is capable of receiving from this operation. It is necessary, in order to conduct this process to the greatest advantage, that the workmen should attend to the following circumstances.
18. 1/3, A quantity of fresh ley must be from time to time added to the bath, as the immersion of the wool is found to weaken its power; but it is better not entirely to renew the bath, as the grease abstracted from the wool during its immersion, forms with the ammonia of the urine a kind of soap, which much increases the cleaning quality of the bath.
19. 2d, Increasing the temperature of the bath will augment its deterring powers, and may sometimes supply the want of an addition of stale urine; but both these circumstances require caution, as too great a degree of heat hardens the greasy matter, and renders it more difficult of solution; and again, too much urine makes the wool harsh.
20. 3d, After being much used the bath becomes too foul, and must be entirely renewed.
21. The wool which has properly undergone the process of scouring should be white, soft, elastic, and open; whereas before it was hard, stiff, and greasy. By this operation the wool loses much more of its weight, so that 100 pounds of raw wool, when completely scoured, will not yield more than 30 or 40 fit for the manufacture of cloth.
22. After scouring, the wool is sometimes carried to the fulling mill, in which it acquires an additional degree of whiteness. The above is chiefly employed for the coarser wools, and wool that has yet to be carded for the making of broad-cloth, but for the finer kind it is better to employ a bath in which soap has been dissolved. This method is more expensive, but the expense is compensated by the superior quality of the wool which is thus treated. This operation is performed by the comber, and is thus conducted. The wool is divided into parcels containing each about fix pounds and a half. A bath is prepared with two pounds and a half of green or black soap dissolved in a sufficient quantity of boiling water; and in this bath a parcel of the wool is to be washed for a longer or shorter time according to its foulness. It is then wrung by means of a hook, and hung in the sunshine or air to dry. Before it is combed it must undergo a second scouring, which clears it of all the natural oily matter.
23. This quantity of wool is not to be washed all at once, but in successive portions, and fresh hot water is to be added from time to time in order to free the wool more easily from the grease. For wringing it there is a hook fixed at each end of the washing-tub, on which the wool is fastened and turned round by means of a handle or winch, fixed to one of the hooks. As economy should be consulted in every manufacture, a method of scouring wool without soap, would be of considerable advantage. Fullers have long been in the habit of employing a species of clayey earth, called from them fullers earth, which has the property of combining with the greasy matter and rendering it more soluble in water. A new earth has lately been found on an estate belonging to Lord Warwick, which by certain processes is made to answer the purpose of soap, and a patent for its preparation has been granted to Mr John Vancouver. It is not distinguished by any particular name, and is disposed or situated in the ground in different strata or layers. The first or uppermost layer is of a greenish or grayish colour; the second layer is of a beautiful lilac or light purple; and the third or undermost is generally white, although the white is found intermixed with the purple. The stratum on which the earth lies, is indurated red marl, and it is superinduced by a bed of gravel. The thickness of the entire stratum of this earth is from four inches to one foot, and its general position is very even, regular, and level. When first taken out of the earth, its colours are very fine, particularly the lilac, which, on exposure to the sun's rays, or to the influence of frost, soon becomes white. On chemical examination, it appears to contain clay, siliceous sand, and the oxide of iron; but a more studied examination would probably shew the existence of other peculiarities, from which the detergent property of this earth might be found to arise.
The processes for manufacturing this earth are performed as follows:—After digging it out of the vein, it is dried by means of stoves or otherwise; then pulverized, and sifted through fine sieves; a size is then prepared from white shreds of leather, and the dry sifted earth is beaten up with the size; after which it is formed into convenient parcels or cakes, resembling those of soap, and of such sizes, figures, and dimensions, as are best adapted to the purposes of its intended application. The use of the size is to keep the parts of the earth together, and to moderate the effect of its absorbent quality, which is so extreme, as to cause it to become pulverulent, like quick-lime, when water is added to the dried earth; and, on this account the patentee does not confine himself to the use of
save soap. At sea, where fresh water cannot be spared for the purpose of washing, the sailors are accustomed to scour their foul linen in stale urine, which so far cleanses them that a subsequent rinsing in salt water renders them tolerably pure and sweet. of size made of leather, but applies other animal and vegetable mucilage to the same purpose, giving the preference to such, as by their cheapness and adhesive quality are best adapted to the purposes of the manufacture. The most distinctive property of this earth is that of cleaning wool in a manner much superior to soap; because it makes it equally white and clean, without robbing it of what manufacturers call its nature, as soap does; for, it is well known, that when wool is washed with coarse soap, it undergoes some change, either in the polish of its surface, or in the elasticity of its fibres, or in some other respects, which causes it to feel less full to the hand, so that it will not rise and spring up, after the pressure, in the same manner as it did before such washing. Whereas, on the contrary, wool, when treated with the washing-earth, becomes equally white and clean, at the same time that it remains in possession of all its original fulness and elasticity, which are of great consequence and value in the manufacture of this important article of produce*. Before the wool is quite dry it is combed, as this operation is found to succeed best when it is a little moist, it being then easier to form it into proper lengths of three or four feet. Considerable nicety is requisite in the conducting of these first processes, as much of the success of the succeeding operations depends on their proper management.
24. After combing, the wool sometimes undergoes two or three farther washings, especially when it is required of a very delicate white.
25. It is known that the wool has been properly scoured, by its filaments being smooth, long, and slender, white, and perfectly free from foreign substances, and not having lost their natural tenacity. The Dutch wool is generally the purest: the English is next in quality, but is much harsher and fouler. The German wool is still harsher than the English, and the French is inferior to them all.
26. The loss sustained by the wools in scouring is proportional to their impurity. Thus the French and German lose about a third of their weight, while the Dutch and English do not lose above a fourth.
27. But this scouring, whether it be performed with urine, soap, or earth, is seldom sufficient to bring the wool to that brilliant whiteness which is desirable for some manufactures. This is given it by means of the vapour of sulphur, or by steeping it in sulphurous acid, which is called by the manufacturers sulphuring.
28. The usual method of sulphuring goods is to expose them in a very close apartment to the vapour of burning sulphur. The goods are hung on poles so disposed that the vapour can readily pass between the pieces, and when the chamber is filled, a quantity of sulphur, placed in very flat and broad dishes, is set fire to, and allowed to burn away gradually in the chamber, while every aperture by which the vapour could escape is carefully closed. The acid vapour generated by the combination of the sulphur with the oxygen of the air of the chamber, penetrates to every part of the cloth to which it can get access, destroys the colouring matter, and thus completes the bleaching. Every thing is allowed to remain quiet till it is supposed that the effect of the sulphureous vapour has fully taken place, which requires from 6 to 24 hours.
29. The action of the sulphureous vapour leaves a roughness and harshness on the cloth, which are removed by passing it through a bath slightly impregnated with soap.
Such was the usual method of sulphuring woollen cloth; but it was soon found to be very imperfect, as the effect of the vapour scarcely extends beyond the surface, and thus there is often a necessity for renewing the operation. O'Reilly has lately proposed to employ the sulphurous acid dissolved in water, and he thus describes the method of preparing and using it.
30. "The sulphurous acid, or that acid which is produced by the imperfect combustion of sulphur, differs from the sulphuric acid (oil of vitriol) in containing less of the acidifying principle, and constituting, as we may say, the mean between sulphur and sulphuric acid.
31. "Sulphurous acid combines very readily with water. In this state of combination it may be employed for the bleaching of wool and silk. We may procure it in this state by making the gas pass through water, in an apparatus similar to that which is employed for obtaining the oxygenated muriatic acid. The most economical mode of preparing this acid is by decomposing the sulphuric acid by means of some combustible substance which is capable of depriving it of a part of its oxygen. In the nice experiments of the laboratory, where the chemist wishes to have it in the greatest purity, it is obtained by means of metallic bodies, and especially mercury; but for our purpose, where we must confine economy, we shall recommend the most common materials.
32. Take chopped straw, or saw-dust, and put it into a matrafs; pour over it some sulphuric acid, and apply a moderate heat. Sulphurous acid gas, or sulphureous vapour, will be disengaged; which may be combined with water by means of the following apparatus.
33. A matrafs with a long neck is placed in a furnace, and made to communicate with a tubulated bottle in which a little water has been put to absorb the small quantity of sulphuric acid which might pass through the first reservoir without being decomposed. Care must be taken to place a small tube within the bottle, so that one of its extremities is immersed some way below the surface of the water to prevent absorption. A tube with a double curvature conducts the gas into the vessels in which it is to combine ultimately with the water. We propose to make a hollow cylinder of lead, or white wood, bound with varnished iron, of a pretty considerable height, and surmounted with one of Wolfe's bottles, the bottom of which has been removed, and which must be made to fit into a collar in the mouth of the leaden cylinder; and care must be taken to make it firm by means of wax, but so as to render the joining impervious to fluids. This capital of glass will allow us to see the number of bubbles which are disengaged on the surface of the water, and thus to ascertain the progress of the saturation, while the weight of this narrow and high column of water, pressing on the bubbles of sulphurous acid gas, as it is disengaged from the end of the tube at the bottom of the cylinder, will facilitate its combination with the water, and will accelerate its dissolution in that fluid. That nothing may be lost, we may have a series of two or three of these cylinders connected together, and they will then comprise the whole of the apparatus which we are describing. A cock fixed in the bottom of each cylinder will facilitate the discharge of the liquor into the tub for immersion.
34. "The apparatus which we would recommend for the immersion of the woollen and silken goods in the ley of sulphurous acid perfectly resembles what will be described hereafter for the immersion in oxygenated muriatic acid, and which we have constructed after the principles of Rupp. From conversing on this apparatus with Cit. Widmer of Jouy, we have conceived the design of the present, which is now making at the manufactory of Effonne. Let us suppose an oblong box, divided by a partition in the middle; on each side of this partition is a large reel, on which the stuffs are to be rolled; at each angle is fixed a roller, over which the stuffs pass before they proceed through the partition to be drawn over a similar number of rollers which conduct them to the second reel. The object of this disposition is to make the stuffs pass through the bleaching liquor, and expose it to the greatest possible surface.
35. "For the purpose of turning this reel, we make use of an axis or column of glass which passes through a collar of leather, and has one of its extremities, which is square, fixed into the reel, while the other is fixed to a winch, which gives it the rotatory motion; and in this way we may entirely avoid employing any metallic substance within the vessel. To prevent the escape of the gas, the cover of the tub is made with a ledge which fits exactly into the rim of the box, and of which at least an inch should pass into the deterring liquor.
36. "I propose the following method of bleaching woollen stuffs: We are first to scour them by immersion in a ley slightly alkaline, in the proportion of a pound of potash to 50 pounds of wool. The bath is heated to the temperature of 30 degrees (B).
37. "The old method with stale urine may also be employed. Urine is preferred because it holds in solution a quantity of salt, which is not sufficient to injure the wool.
38. "When the grease is dissolved, and the wool has been well purified, it is to be washed in warm soapy water. This part of the process is sometimes performed in the fulling mill, sometimes by beaters, and sometimes by treading in the tub. In every case the grease must be separated by repeated washing before the sulphuring is employed. If we wish to obtain a brilliant whiteness, it would be proper to make the stuffs undergo heat a second, or even a third time, always in water slightly impregnated with soap, in the proportion of two ounces of this substance to a pound of wool. It would be better to repeat this operation, turning the stuffs about with a stick for half an hour, than to endanger injuring the quality of the stuffs by employing too strong a ley.
39. "After scouring with the greatest care, the stuffs are carried to the tubs for steeping in the liquid sulphurous acid, or, as it may be called, the sulphur water; the pieces are rolled upon the reels, and by turning the winch, are made to pass through the acid, till it is observed that they are sufficiently whitened. They are then taken out, and suffered to drain on a table covered with a cloth, that the action of the sulphurous acid on the wood may not injure them; they are afterwards walked in river water, and, if necessary, Spanish white is used. This is done by steeping the pieces in a tub of clear water, in which about eight pounds of Spanish white have been diffused. Two sulphurings are usually employed to obtain a fine white; but in our process, a single immersion, with turning for two or three hours, should be sufficient.
40. "Before recommending the employment of the liquid sulphurous acid, I have made a great many experiments on woollen threads and stuffs, varying the manipulations, and always with the most complete success*."
41. Besides the whiting mentioned in the above extract, it is usual to pass the stuffs through water impregnated with blue, or, what is generally practised, after the whiting has been used, the stuffs are taken out, and to the same bath of Spanish whiting and water is added a pail of water, in which about an ounce and a half of fine indigo, or of Prussian blue, have been diffused, the blue being pounded, sifted, and tied up in a little bag, which is stirred round in the water. When the blue water has been added, the bath is well stirred, and the piece of cloth is again passed through it. It is afterwards laid on a packing cloth, and subjected to the fuller's thistle, to raise the nap, it being wetted from time to time with the liquor of the bath. It is then dried, and well beaten with twigs, to carry off the superfluous whiting.
42. Manufacturers have an idea that bad smells, such as foul breath, are capable of producing some change on the bath of blue and white, and thus render a repetition of the process necessary. It is certain, that without attention the white and blue will not be intimately diffused, and that thus a kind of vegetation will be produced on the cloth. When this happens, it must be washed by plunging it into hot water, and then the bath must be repeated.
43. It is chiefly to cloths that are to be of the finest quality that all these processes are adapted. For ordinary flannels, especially such as are intended to be worn next the skin, sulphuring and soap baths are less proper; and the soap especially diminishes the absorbency, which is so desirable a property in these flannels. They are usually prepared by scouring with bran and water, and subsequent rinsing in fair water.
CHAP. II. Of the Bleaching of Silk:
44. SILK is a substance possessing some degree of transparency, and is spun by a caterpillar from a matter contained within its body, which has the property of hardening when exposed to the air. The silk-worm is an inhabitant of the southern climates, being originally brought from Asia, and naturalized in the south of Europe about the period of the decline of the Roman empire.
(b) About 100 degrees of Fahrenheit. 45. The filaments of silk, as left by the silk-worm, are rolled together into a kind of ball or clew, and in their natural, or what is called the raw state, are covered with a yellow varnish or gum, which obscures their lustre, and gives them an unpleasant roughness.
46. Water has no effect on silk at the boiling temperature, and no change is produced on it by alcohol; but alkaline leys, when tolerably strong, attack, and are capable of dissolving it. The yellow varnish is soluble also in alkaline leys, and it may even be separated by long-continued boiling of the silk. When the varnish is thus carried off, the silk is found to have lost about a fourth of its original weight.
47. Two methods are in practice for bleaching silk; the first, in which it is ungummed or deprived of the natural varnish; the second, in which this is retained, in order to give them that fineness which is required for gauzes, blonds, &c.
48. In the first process, the silk is to undergo a scouring, similar to what we have described, as necessary for depriving wool of the natural oil. For this purpose, a quantity of water is put into a boiler over a fire, and for every hundred pounds of silk to be scoured, thirty pounds of very fine soap are dissolved. The solution is generally boiled, but before the silk is put into it, the heat must be lowered to about 90 degrees of Fahrenheit, and at this temperature it must be kept during the process. The silks are to be hung in the liquor upon rods or frames, and left till the gum is sufficiently destroyed, care being taken to alter their position now and then, so that every part may be exposed to the action of the bath. When perfectly ungummed, they are flexible and of a dull whiteness; in this state they are to be wrung with the pin to clear them of the soapy water, then well thaken, and put into coarse linen bags, in parcels of from twenty to thirty pounds each.
49. These bags are now to be steeped in a fresh bath, or, as the workmen speak, are to be baked. The bath is prepared in a manner and proportion much as before, except that the quantity of soap may be somewhat diminished, as the heat is to be increased; for the silk is now to be boiled for two or three hours, taking care to keep the bags from sticking to the bottom of the boiler, by frequently stirring them with a stick.
50. For silk that is intended to be dyed, the former steeping in the lukewarm bath is unnecessary, and the present boiling only is employed, using a greater quantity of soap in proportion to the fineness of the colour. Thus for the ordinary colours, the proportion above laid down, or even less, will suffice, but for the saffronum colours, and the poppy and cherry red, even 50 pounds are sometimes employed to the 100 pounds of silk.
51. After boiling, the silk is wrung as before, and then washed thoroughly in a stream of water; they are then examined, and if it appears that they are not sufficiently or not uniformly scoured, they must be submitted to a fresh bath.
52. The white silk usually sold has a bluish shade. This is given it by a bath impregnated with litmus, or indigo. This is prepared by dissolving a pound and a half of fine soap in about ninety gallons of water, in which a small quantity of litmus or indigo has been diffused. The bath is heated to about 90 degrees, and the silk is passed through it over rods or reels till it have acquired the requisite shade. Being taken out, it is wrung and dried.
53. From these processes, the silk acquires a tolerably clear white, but the highest degree is given to it by the action of the sulphurous acid, either in the state of vapours, as is usually practised, or by immersing it in the liquid acid, according to the method of M. O'Reilly.
54. From what has been said above of the action of various substances on silk, it will easily be conceived, that during scouring it must suffer considerably in its quality. To avoid this, a method has been lately proposed of carrying off the varnish by the aid of steam under an increased pressure. As this has been more extensively employed in the bleaching of cottons, we shall delay giving a detailed account of the process till a future part of this article. The following is the method proposed by O'Reilly.
55. "Take a solution of caustic soda, so weak that it indicates at most but a quarter of a degree of the areometer for salts, and fill with it the boiler of the apparatus for steam bleaching. Charge the frames with the skeins of raw silk, and place them in the apparatus till it be filled, then close the door and cause the solution to boil; continue the ebullition for twelve hours; slacken the fire and open the door of the apparatus. The heat of the vapour, which is always above 100 degrees (c), will be sufficient to ungum and scour the silk. Wash the skeins in warm water; wring them with the pin; and place them a second time on the frames of the apparatus to undergo another boiling. Then wash them in a considerable quantity of water, and if you desire the greatest degree of whiteness, rinse them in water slightly impregnated with soap, to give them a little softness.
56. "The last degree of whiteness is obtained by passing the skeins through the sulphurous acid, using the method and apparatus which I have recommended for bleaching wool; and which here supercedes sulphuring. The incalculable advantage of that method over others, consists principally in the possibility of employing the operations in succession, without running the risk of injuring the quality of the silk by too strong leys."*
57. Such are the most approved methods of bleaching silk when deprived of the yellow gum; but when this is not required, the bleaching is to be performed by some substance which has the property of whitening the silk and its varnish without dissolving the gum. Of this description is alcohol, and two French authors have proposed a method of bleaching silk by means of this and muriatic acid. It was first proposed by M. Rigaud in 1778, and is thus shortly described by Pajot de Charmes.
58. "The silk intended to be bleached, is put into a glass vessel containing a mixture of spirit of wine and muriatic
* O'Reilly Effat.
(c) About 250 degrees of Fahrenheit. Chap. II. BLEACHING.
Animal muriatic acid, in the proportion of a pound of the former substances, mer to half an ounce of the latter, and in quantity sufficient to float the silk. The veifel is then clofed with wet parchment, and exposed for 12 hours to the fun, or otherwise it may be left 24 hours in the shade, at a temperature of between 16° and 20° Reamur. The silk is then taken out and preflled, and again macerated for the fame time, and under the fame circumstances, in fresh acidulated spirit of wine, in another similar veifel, clofed as before. The silk is then taken out, preflled, and washed for four or five minutes in pure spirit of wine. In the next place, it is kept for 24 hours in the fun, or 36 in the shade, in a third veifel, containing pure spirit of wine, which is to be renewed at intervals; after which, the silk is to be taken out, preflled or washed two or three times in clear water, which is to be changed at each washing. Lastly, the silk is to be exposed to dry upon a frame, so contrived as to stretch it with considerable force, and prevent its curling up as it dries.*
59. In 1795 M. Baumé proposed an improvement of this method, with the means of recovering the alcohol, which we shall give in the words of Mr Nicholson in his Journal.
60. "Berthollet, in his Elemens de l'Art de la Teinture, published in the year 1791, after describing the usual methods of depriving silk of its reinous or gummy matter*, proceeds to remark, that, in the manufacture of blonds and gauzes, the natural elasticity and diffusibility of this article are required to be preserved: whence it has become a desideratum to render the yellow silk of Europe white like that of China, without depriving it of its gum. He adds, that M. Baumé has solved this interesting problem, but had kept his process a secret; but from the facts he had possessed the means of obtaining, it appeared liable to accidents, and that the chief difficulty consisted in giving an uniform white colour when large quantities were operated upon. He also mentions a difficulty in dressing the whitened silk so as to prevent its curling, and observes that it ought certainly to be kept constantly stretched during the drying. It is besides requisite that the spirit of wine should be recovered after the process, which would else be rendered too expensive. This author does not say whether the white Chinese silk is subject to the same inconvenience of curling when dyed, which, it may be remarked, is a property of no consequence where the material is to be applied in the manufacture of white goods. The motives which led M. Baumé to communicate his process to the world, originally retained by him as a lucrative secret, do not appear. Whether the mistakes of those who carried it into effect in the large way might have led him to vindicate the reality of his discovery by publication; or whether the commercial advantages derived from superiority of quality and cheapness in this article over the Chinese silk in the market of France, might in the end have proved of less value than the scientific reputation to be derived from its disclosure; are circumstances which will, no doubt, have their proper weight with such manufacturers as may be induced gradually to adopt this process.
Vol. III. Part II.
61. "The silk of Naukin is perfectly white, silvery, Animal brilliant, and possesses all the elasticity of raw silk. Our Substances. author affirms, that the value of this article imported into Europe amounts to upwards of twenty millions of livres (about 830,000l. sterling), of which France consumes about four or five millions in gauzes, blonds, ribbands, &c. This was formerly supposed to be produced of a white colour from the worm. The late M. Truchine, intendant of commerce, procured the eggs of silk-worms from China, and cultivated them. The produce consisted of yellow cocoons, and others of the most perfect whiteness. The latter afforded silk equal in this respect to those of Naukin. But M. Baumé affirms, that most of the Naukin silk is bleached by art, and, as he thinks, by a process similar to his own.
62. "As it is impossible to wind off a large quantity of silk in the short time previous to that of the insects eating their way through the mass, it is usual, in the first place, to deprive them of life. This is commonly done by exposing the cocoons, properly wrapped up, for two hours to the heat of about 158 degrees of Fahrenheit in an oven; after which they are kept for a certain time in a mass to preserve their heat, and effectually destroy such of the insects as might have escaped the power of the oven. The effect of this process is, that the silk is hardened, and is more difficult to wind off than before. Hence the produce of silk is left by one-ninth part in quantity, and inferior in quality to what might have been obtained by winding off without this previous baking. M. Baumé, not only from these views, but likewise because the silk which has not been baked proves susceptible of a greater lustre, was induced to destroy the chrysalis by spirit of wine. For this purpose he disposes them in a wooden box in a stratum fix inches deep: upon each square foot half a chopin, or somewhat more, of spirit of wine is to be sprinkled with a small watering-pot made for that purpose. This quantity answers sufficiently near to our half-pint. The liquid is to be equally distributed, but it is not necessary that all the cocoons should be wetted. They are then to be mixed by hand. In the next place another stratum is to be formed over the first, nearly of the same depth, which is to be sprinkled and treated as before. By this method of proceeding, the box becomes filled, and must then be covered and left for 24 hours, during which time they become spontaneously heated to about 100 degrees, and the vapour of the spirit of wine exerts itself with wonderful activity. Five hundred French pounds (d) of the cocoons require 10 French pints, which is nearly the same number of English quarts. After this treatment they must be spread out to dry, which happens in a short time, and is absolutely necessary previous to winding off.
63. "When the operator proposes in this manner to extinguish various parcels of cocoons belonging to different individuals, each parcel may be tied up loosely in a canvas bag, and wetted on the outside previous to closing the box.
64. "The spirit of wine to be used in this operation, ought to be of the strength of 34 degrees of Baumé's hydrometer at the temperature of 55 degrees. It is of
(d) The Paris pound is to the English avoirdupois pound as 756 to 700. These quantities are not reduced, because the operation requires no great precision. Animal substances has been kept in vessels of glass, of tinned copper, or of pure tin. Leaden vessels are absolutely to be rejected; wooden vessels tinge the spirit, which gives the silk a degree of colour of considerable solidity, and very inimical to the bleaching process.
65. "With regard to the advantages of this method of extinction, in preference to that of the oven, the author remarks, that the cost of labour and fuel added to the loss of silk, and the probability of injury from too much or too little heat, constitute a sum of disadvantage much greater than the cost of the spirit of wine. It is besides a considerable advantage, that the spirit of wine renders more distinguishable such cocoons as have perished previous to the application of the spirit. These afford a much worse silk, and must be picked out.
66. "The silk is wound off upon a reel, while the cocoons are kept immersed in water almost boiling. Upon this part of the process M. Baumé remarks, 1st, That the dead cocoons must be separated. These are known by the brown or black spots on their surface. 2. That well water, which on account of its clearness is almost universally used in the silk manufactories, mostly contains nitre, and is extremely prejudicial to the bleaching process. The presence of nitrous acid gives a yellow colour, which resists bleaching and even scouring; he therefore recommends river water. 3. In some countries a small quantity of alum is used. Neither this nor any other saline substance is of the least advantage to the colour, beauty, or quality of the silk.
67. "At the four places of contact of the silk upon the reel, all the threads stick together. It is absolutely necessary that this should be remedied. The method consists in soaking the silk in a sufficient quantity of warm water, at about 90 degrees, for about two hours; after which the threads are to be separated by opening the hanks upon a pin, and lightly rubbing the parts which cohere. When the silk is dry, it is to be loofely folded in its original form, and is ready for bleaching.
68. "The silk while wet is soft, and part of its gummy matter is in such a state, that its threads would readily adhere, if wrung while warm for the purpose of clearing it of the water. After such improper treatment there would be no other remedy than to soak it again in warm water.
69. "The apparatus for bleaching the silk consists of a stone-ware vessel, nearly of a conical form, capable of holding about 12 gallons, having a large opening at the one end, and a smaller of about an inch diameter at the other end. Common pottery cannot be used in this operation, because it is soon rendered unserviceable by the action of the marine acid, and the stone-ware itself is not very durable. This vessel must be carefully examined, to ascertain that it does not leak in the slightest degree; after which the inside is to be rubbed with a pumice-stone, to clear it of asperities which might break the threads. A cover of the same material is to be fitted on by grinding; and the smaller aperture, which in the use is the lowest, is to be closed with a good cork, in the middle of which is thrust a small glass tube about a quarter of an inch in diameter; this is likewise stopped with a cork, excepting at the time when it is required to draw off the liquid contents of the jar. A small perforated false bottom is placed within the vessel, to prevent this tube from being obstructed.
70. "This jar, or as many of them as the purposes of the manufactory may require, is supported by a wooden frame or table, at such a height that a caulk may be conveniently placed beneath to receive what may flow from the glass tube in the several periods of the operation.
71. "Six pounds of yellow raw silk are to be depoled in the earthen pot; upon this is to be poured a mixture, previously made, of 48 pounds (e) of spirit of wine at 30 degrees, with 12 ounces of very pure marine acid, absolutely exempt from all presence of nitrous acid, and of the strength of 14 or 15 degrees of Baumé's hydrometer. The pot is then to be covered, and the whole left in digestion till the following day, or until the liquor, which at first assumes a fine green colour, shall begin to assume that of a dusky brown (feuille morte).
72. "The acidulated spirit is then to be drawn off. To prevent evaporation, M. Baumé thrusts a cork in the bung-hole of the receiving caulk, in which is a sliding glass tube. The use of this tube is completely to surround the small tube proceeding from the earthen vessel. When the whole of the fluid is thus almost entirely drawn off, clean spirit of wine is poured upon the silk, and drawn off repeatedly until it passes colourless. The silk is then suffered to drain without stirring it. In this state it is ready for a second infusion.
73. "Forty-eight pounds of spirit of wine acidulated with 12 ounces of marine acid is now to be poured on the silk, and the whole suffered to remain for 24 hours or longer, until the silk becomes perfectly white. The time required for this second infusion is commonly longer than for the first: it sometimes amounts to two, three, or even fix days, according to circumstances, particularly the temperature and the nature of the silk. Silk which has been in the oven is in general more difficult to bleach.
74. "When the silk has thus obtained its utmost degree of whiteness, the acidulated spirit is to be drawn off into a separate vessel. This fluid is but slightly coloured, and may be used again in the first infusion of other yellow silk, with addition of fix ounces more of marine acid. The receiving vessel is to be removed, and another clean vessel substituted in its place. The silk is then sprinkled with clean spirit, and occasionally pressed down with the hand. As soon as the spirit of wine comes off absolutely colourless, a third infusion is to be made, by pouring upon the silk 48 pounds of the pure spirit without acid, which is to remain till the following day: it is then to be drawn off;
(e) The pound is nearly a pint, and is divided into 16 ounces. 75. "After the silk has been left to drain, and affords no more spirit, it still retains its own weight of that fluid. This is recovered by the very simple process of sprinkling the silk with a small quantity of very clear river water at a time. While the water applies itself and sublides along the silk, it drives the spirit of wine before it, so that the first portions which flow from the tube are scarcely diminished in strength. The addition of water is to be continued until nothing but mere water comes off below.
76. "In this situation the silk is found to be well bleached, but still retains a portion of marine acid sufficient to render it harsh to the touch, and after a time brittle. It must be washed off with water. The best method is to put the silk loosely into a coarse woollen bag, which is to be secured closely in another cloth like a small bed or pillow, then placed in a basket and left in a running stream for five or six hours; but where the convenience of a stream is wanting, the earthen pot containing the silk is to be covered with a cloth, and water pumped through it for five or six hours, or until that which issues from the lower aperture gives no red colour to the tincture of tourniol. At this period the lower opening is to be closed and the vessel filled with water, which must be changed once or twice in 24 hours.
77. "The time required for washing was occasionally abridged by passing spirit of wine, or river water impregnated with a small portion of alkali, through the silk. The natural salt thus produced is, in fact, less adherent to the silk than the acid itself, but nevertheless requires to be washed off with a very large quantity of water.
78. "In these, as in every other process relating to the silk, great care must be taken to ascertain that the water made use of contains no nitrous acid, which would infallibly occasion imperfection of colour, or spots in the article. After this treatment the silk is ready for drying and lustering; previous to the description of which, the author makes several remarks to the following purport:
79. "Though the mineral acids are the most powerful and destructive of all saline substances, yet they may be applied to silk, when diluted with spirit of wine in very considerable doses. In trials, made to ascertain the maximum, two ounces of marine acid were added to one pound of spirit of wine, without altering the silk. Two drachms of marine acid cause a very perceptible alteration in one pound of silk. I suppose he means pure acid, or perhaps diluted with water; for the passage as it stands is obscure. Numerous experiments have shown that the marine acid is preferable to any other. The proportions admit of much latitude, though he prefers the dose herein before described.
80. "Spirit of wine which has been mixed with nitrous acid, cannot be used in bleaching, even though afterwards rectified upon the alkali, because it still retains a portion of nitrous gas.
81. "Pure spirit of wine without acid extracts a fine yellow colour from silk, which does not separate for years, even though exposed to the sun's light. Yellow silk exposed to the sun loses its colour in a short time. The acidulated spirit which has been used in the infusion of silk, is changed by exposure to the sun, but not in such a manner as to be rendered fit for use a second time.
82. "In order to obtain a beautiful colour, it is essential that the silk should be immersed in a large quantity of the fluid, especially at the first infusion. Without this management it would become necessary to make three infusions in the acidulated spirit. When the first infusion is well managed, the silk will have lost all its yellow colour, and become considerably white, at the same time that the liquor will have begun to change colour a little. As long as it continues of a fine green, it is certain that it has not exhausted its whole action upon the silk.
83. "The duration of this first infusion may be longer or shorter, without inconvenience, according to the temperature. When the temperature is at 20 degrees of Reaumur, which answers to 77 of Fahrenheit, the first infusion is often made in 10 or 12 hours. In small experiments the heat of the atmosphere may be supplied by the water-bath; in which case, all the infusions are easily made in the course of a day.
84. "When the first infusion is finished and the liquor drawn off, the silk appears greenish: the subsequent washings in spirit of wine clear it of the liquor it retained. This sprinkling should be made with the watering-pot, otherwise the quantity poured will be greater, and the management more wasteful.
85. "The cocoons may be bleached in this way, but the inconveniences are too great to render this process desirable.
86. "Pieces of gauze and entire garments of silk have been successfully bleached in this way.
87. "The finest natural white silks are rendered infinitely whiter by this process. Spirit of wine alone has the property of depriving yellow silk of its colour, which it brings to the state of the naturally white silk. In this state the silk is disposed to acquire a greater degree of brightness by a single infusion in the acidulated spirit. This process has its advantages over the other, to which it is also inferior in certain respects; concerning neither of which the author has entered into any detail.
88. "The colouring matter was found to be a resin perfectly animalized, affording by distillation the same products as other animal matters, and the concrete volatile alkali.
89. "Silk whitened by scouring may be dried freely in the air without affecting its lustre. This is not the case with the silk bleached in the gum: if it be left at liberty to dry in the air, it resembles white flax without any lustre. The beauty of this silk consists in its shining brilliancy; to secure which, it must be dried in a state of tension. M. Baumé has contrived a simple machine for this purpose. It consists of a strong square frame of wood standing upright upon feet: the upper horizontal bar is fix feet long, and has fix iron pins driven through it at equal distances, so as to project on each side for the purpose of receiving twelve bobbins. The lower horizontal bar is moveable up and down in a mortice by means of a screw at each end: it is furnished with fix holes, adapted to receive as many pins Animal to correspond with those above. The skeins of silk substances are to be dressed and arranged upon wooden pins, as they are taken out of the pack from washing. As soon as there are twelve together, they are to be wrung with a staff; after which the skeins are to be hung one by one upon as many bobbins put upon the upper pins of the square frame. Another bobbin with tails is to be inserted in the lower loop of the skein, and fastened to the corresponding pin of the lower bar, by means of a strap and hook, which need not be described to such as are slightly acquainted with mechanical objects. When the machine is thus supplied with skeins on both sides, the lower bar of the frame is to be pressed down by the screws until the silk is moderately stretched. When it is dry, the screws are to be equally slackened, the skeins taken off, and folded with a slight twift, that they may not become entangled.
90. "After this description of the whole of his process, the author proceeds to make certain general remarks on the white China silk. He observes, that in his process the silks acquire the perfect whiteness without much handling, and consequently that there is little cause for them to become entangled. Accordingly the loss in unwinding is found to be no greater than when they are unwound in the yellow state; that is to say, from a drachm to a drachm and a half in the pound. This saving is of the greatest importance in the price of the silk.
91. "The silk of Nankin, which he supposes to be bleached by some process of the same nature, is probably handled much more. The loss is nearly twelve per cent. when it comes to be opened, and not unfrequently even 25 per cent.: a loss which cannot in any respect arise from the package. The quality of the Nankin silk differs much in the package; the external part being always of the best quality, and that which is packed within is of such an inferior quality as sometimes not to exceed half the value. On examining this silk, it not only exhibited unequivocal marks of alkali, but its imperfections were also of the same kind as those which had occurred to M. Baumé during the progressive improvement of his own manipulations. The best China silk was neither improved nor injured by the process of Baumé; whence he concludes that they are not naturally white, but have undergone a process similar to his.
92. "The result of the whole is, that the yellow silks of Europe may be bleached to equal or greater perfection than those of Nankin; and that these may be even greatly exceeded by winding the naturally white silk apart from the other, and bleaching it by itself.
93. "To complete the description of M. Baumé's process for bleaching silk, nothing more remains, than to shew in what manner he recovers the ardent spirit, and ensures the purity of the acid made use of. These circumstances are of essential importance to the art; for the process would be much too expensive if the spirit were lost, and it could not be made to succeed at all if the acid were impure.
94. "The alcohol which has been used in bleaching silk, is acid, and loaded with colouring matter. In this state it cannot be again used. There are two methods of distilling it; which have their respective advantages and inconveniences. By the first, the acid is lost; which is saturated with potash, in order that the distillation may be afterwards performed in a copper alembic. The second is performed by distilling with glass retorts, or an alembic of silver. In either of these vessels, which are not acted upon by the marine acid, the distillation may be performed, and the greater part of the acid recovered. The inventor most generally practised the saturation of the acid from reasons of convenience; but recommends the use of a silver alembic, as being most economical upon the whole, in a manufactory.
95. "A solution of potash is to be poured into the acid spirit, and stirred about to promote the saturation. Carbonic acid is disengaged with strong effervescence from the alkali, and the point of saturation is known by the usual test, that the fluid does not redden the tincture of tourniol. The distillation is then to be made in the copper alembic, and the alcohol reserved in proper vessels, as mentioned in the beginning of this memoir.
96. "If too much alkali should have been added, the liquor remaining in the alembic may be used in another saturation. The alkali in this process being an expensive article, M. Baumé endeavoured to supply its place by chalk, quick-lime, and lime which had been flaked by exposure to the air. But he found that the action of the spirit upon the calcareous earth, or perhaps the absence of water, prevented the acid from uniting with that substance. The union does not take place to perfect saturation in less than five or six weeks, even when the alcohol is diluted with upwards of 50 times its bulk of water.
97. "In the second process for distilling without alkali, the acid spirit is distributed into a great number of glass retorts, placed in the sand-bath, on the gallery of a furnace. The first product is scarcely acid; but what follows is more and more so, and must be kept in vessels of glass or stone-ware, which become embarrassing on account of their number. The fluid which remains in the retorts has the colour of beer slightly turbid, and contains the greatest part of the marine acid. It must be poured into one or more retorts, and concentrated by heat gradually applied. The first liquor which comes over is slightly red, turbid, and scarcely acid. This is to be thrown away, and the receivers changed. The succeeding product is the colourless marine acid, of an aromatic smell resembling the buds of poplar. The resin of the silk remains in the retort decomposed by the acid. The marine acid thus obtained is weaker than it originally was: which is in fact of little consequence, as it is pure, and may be safely used, either by increasing the dose proportional to its diminished strength, or by concentrating it, if required, in the usual way.
98. "If this distillation be made in a silver alembic, instead of retorts of glass, and a capital and warm of pure tin be annexed, the alcohol will be obtained fo slightly acid as scarcely to redden the tincture of tourniol; but it is sufficiently acid to receive injury if preserved in a copper vessel.
99. "If a cucurbit of silver be prepared, of the capacity of three or four quarts, with a glass head, the residues of the first distillation may be treated in this vessel in the same manner as has been directed for glass retorts. M. Baumé affirms that he has practised all these these operations with glass retorts and a small silver alembic, with the most perfect success; but that he made use of potash to saturate the marine acid, because he had not a silver vessel of sufficient capacity. From the danger of distilling large quantities of ardent spirit in glass vessels, he is of opinion that no motives of economy are sufficient to justify the risk attending this method. In the use of tin, it is necessary to be careful that it contains no adulteration of lead, because the vapours of marine acid have sufficient power to alter this last metal very considerably.
100. "Upon the first intimation of this new process in France, manufactories were immediately established, to the number of twenty or more, without the concurrence of M. Baumé, by persons who consequently were not aware of the apparently minute but very important circumstances necessary to ensure its success. In particular, the inventor states that the marine acid of commerce is unfit for this purpose.
101. "This acid was formerly prepared with the marine salt of the saltpetre manufacturers; and even when it is made with good salt, the decomposition is effected with a small quantity of vitriolic acid which contains nitrous acid. Marine acid mixed with a small quantity of nitrous acid does not prevent the silk from being beautifully whitened: it even accelerates the process considerably, and in the most satisfactory manner. But the alcohol, every time it is used and rectified, becomes charged with the acid and gas of nitre, which assume the characters of the nitrous anodyne liquor. In this state, neither distillations nor repeated rectifications from alkali are sufficient to separate the nitrous matter from the alcohol. Then it is that the success of the operator vanishes, with a degree of rapidity equal to the advances which encouraged his hopes at the commencement. The same disappointments befel M. Baumé at the beginning of his labours; to prevent which, he directs the preparation of the vitriolic and marine acids to the following effect.
102. "The vitriolic acid of commerce is obtained by burning sulphur in chambers of lead, with the addition of saltpetre, either crude or of the second crystallization, and a small portion of flax. This acid is concentrated and rectified in France, at the place of its fabrication, to 66° of Baumé's hydrometer, or specific gravity in the usual form 1.848. It contains sulphur, lead, vitriolated tartar, Glauber's salt, alum, selenite, and particularly the nitrous and marine acid.
103. "To purify it, 100 pounds of this vitriolic acid is to be mixed in a large bason of copper with the same quantity of river water, and stirred with a wooden spatula. The mixture instantly becomes heated to the boiling-water point, and a great quantity of red vapour is disengaged, which has the smell of aqua regia, and arises from the nitrous and marine acids. When this mixture is made, it is proper to immerse the bason to a suitable depth in a large vessel of water, to hasten the cooling. As soon as it is sufficiently cooled it is to be drawn off into bottles, and left to become clear during several days. Great part of the sulphur falls down. The author obtained from four to fix drachms.
104. "A gallery must be provided, on which two rows of iron pots of eleven or twelve inches in diameter are to be properly placed for separate sand baths, as M. Baumé always practised in the sublimation of animal sal ammoniac. By this means the retorts are isolated, and if one breaks, the acid cannot diffuse itself and break the others in its vicinity. An empty retort is then to be placed in each pot, and covered with sand. In this way they are much more convenient to arrange, and are attended with no risk.
105. "The acid is in the next place to be decanted and conveyed into the retorts by a syphon funnel, and the rectification proceeded upon until it becomes perfectly white. Towards the end of the operation a small quantity of sulphur sublimes in the neck of the retort. Instead of receivers, a small glass cup is placed beneath the aperture of each retort, in order to facilitate the diffusion of the nitrous and marine acids.
106. "When the acid in the retorts is sufficiently cooled, it is poured a second time into the copper bason, and mixed with 100 pounds of river water, as at first, and again concentrated in the retorts till it becomes perfectly clear. Sulphur has been afforded in some instances by the second rectification. The liquor which diffils is received in the cups as before, and the acid in the retorts is then sufficiently pure: that is to say, it is purified from all volatile matter. The lead and neutral salt still remain combined with the acid, but fortunately they can in no respect injure the purity of the marine acid.
107. "This concentrated acid exhibits 68 degrees by the hydrometer, or specific gravity 1.896. It still contains a portion of gas, but so small in quantity as not to injure the purity of the marine acid, to which it only gives the property of crystallizing when the temperature of the air is near the freezing point.
108. "During the rectification of this acid, what first comes over is mere water, and must be thrown away; but that which succeeds is the aqueous acid. If this be set apart, and concentrated, a considerable quantity of vitriolic acid is obtained of the greatest purity. As it has been carried over in distillation, it contains no foreign matter.
109. "The author attempted, but in vain, to dissipate the nitrous acid from the acid of vitriol by ebullition in an open vessel without concentration. The experiment was made with 50 pounds of common vitriolic acid and 60 of river water. This was kept boiling in the copper bason for four days, water being added from time to time to supply the loss by evaporation. The copper bason, by weighing before and after the operation, had lost by solution no more than ten drachms of copper. The acid was blue, but became white as usual during the rectification in the retorts. From this experiment, as the author observes, it is seen not only that the nitrous acid cannot be dissipated by simple ebullition without concentration, but that the action of the vitriolic acid upon copper is extremely slight.
110. "The marine acid is to be disengaged from common salt by the application of this vitriolic acid in the usual manner. But as M. Baumé's experience led him to various simple manipulations and remarks of importance, and more especially as he considers the description of this process as part of the new art of bleaching silk, he has annexed it to his memoir.
111. "The vitriolic acid obtained by the foregoing process being too concentrated, must be diluted in the copper bason as before with river water. It is convenient to add 18 ounces of water to each pound of the acid, because the marine acid is not wanted in a state of high concentration. This mixture ought to give 35 or 36 degrees by Baumé's hydrometer; which last answers to a specific gravity of 1.333. When it is cold it may be preserved in bottles for use.
112. "In the next place, four pounds of marine salt dried, because in that state it pours best, is to be put into a retort of the capacity of five or fix French pints, or English quarts. This may be done by means of a paper funnel, or a long-necked funnel of glass, which must enter the body of the retort in order that the neck may remain clean. A number of these must be disposed on a gallery in two opposite rows, with the necks properly enclosed and enveloped in sand as usual.
113. "A bottle or gauge being provided of such a size as by previous experiment is known to hold four pounds of the vitriolic acid before mentioned; this quantity of the acid must be measured into each of the retorts by means of a curved funnel, the tube of which may pass into the body, to prevent the acid being spilled in the neck. If nevertheless a few drops should fall, no inconvenience will follow, as this pure acid is not detrimental to the bleaching process.
114. "The supports for the receivers are then to be placed, and the receivers applied, each being pierced with a small hole. The junctures are to be made good with pasted paper, and the distillation begun. A gradual heat is to be applied until the fluid boils gently. The marine acid which first rises is volatile and expansible (f), and requires the small holes of the receiver to be occasionally opened; but after one-fourth part of the time of distillation the acid comes over freely, and the vapours cease to be elastic.
115. "The distillation lasts two days: but it is practicable to avoid sitting up the intermediate night. The fire must be so managed that the contents of the retort may be very liquid in the evening: if it begins to thicken, there is reason to apprehend that it may be too hard the next day; in which case the heat will dilate the concrete matter before it liquefies, and break the containing vessel.
116. "Towards the close of the distillation the matter swells up considerably. When this happens, it is proper to empty the receivers, and raise the retorts, that more sand may flow in beneath them. When the matter is dry, and nothing more comes over, the operation is finished.
117. "Each retort affords five pounds of marine acid, of the strength of 14 or 15 degrees; specific gravity 1.114. When the retorts are half cooled, one pound of hot river water is to be poured into each, and the distillation being resumed affords 24 ounces of the same marine acid from each retort."
PART II. BLEACHING OF VEGETABLE SUBSTANCES.
118. THE composition of vegetable substances differs materially from that of animal bodies in the proportions of the three principles which are common to both, namely, oxygen, hydrogen, and carbon; and in wanting for the most part azote, which in the latter acts so conspicuous a part. The proportion of sulphur and phosphorus is also exceedingly small in vegetables.
119. As in animals, the substances derived from vegetable nature are formed by a peculiar process of secretion, from the nourishment which plants draw from the bosom of the earth, which after being absorbed by the roots, undergoes, in passing through the vessels of the plant, new modifications, and enters into new combinations.
120. By spontaneous decomposition the principles of vegetables, as of other organized matter, are separated and enter into new states. The hydrogen combines with part of the oxygen to form water, while the rest of this latter element, uniting with the carbon, generates carbonic acid.
121. These changes are the natural effect of exposure to moisture, heat, and atmospheric air, and upon the effect of these agents the chief dependence has been till lately placed in the processes for discharging the colour of vegetable substances. As the gradual improvement of the art of bleaching forms a pleasing object of contemplation both to the scientific manufacturer and the philosophic chemist, we shall, after saying something of the nature and previous preparation of the substances employed, endeavour to trace the steps which have led to the present improved state of bleaching, as it is in the linen and cotton manufactures that this is more peculiarly apparent.
122. The vegetable materials employed for clothing are usually distinguished into two kinds, linen and cotton, the former being derived from hemp and flax, the latter from the down of the cotton plant.
123. Of all the materials employed for clothing, wool seems to have been the most ancient; and indeed it was a natural and an easy step, from the skins of beasts, to the use of the detached hair. Silk seems to have been next in point of antiquity, and in a short time the fibres of hemp and flax were had recourse to for the same purposes. It is probable that the fibres of hemp were first applied to the service of man as cordage or sails, or to make tents for sheltering the inhabitant of the desert, or the soldier in the camp, as their coarseness and superior strength would point them out
(f) It might be of advantage, even in the large way, to adapt a simple pneumatic apparatus to condense the marine acid air in water, as is usual in philosophical processes. Part II.
Vegetable substances as better fitted to these uses, and less adapted to the purposes of clothing than the finer and more delicate fibres of flax.
124. The use of flax appears to have originated in Egypt, and its introduction is attributed to Isis.
125. Cotton has probably been employed among the Asiatics for a very long time; in Europe it was the latest of all the materials of which clothing is manufactured.
126. On examining the stalks of hemp and flax when they are pulled, we shall find them composed of four distinct substances; a delicate bark, a green juice or sap, the fibres which are to be employed in the manufacture, matted or twisted together, and within these the wood of the plant. As the fibres are thus enveloped in useless matter, the first object is to separate them, to peel off the bark, wash away the sap, and strip the fibres from the wood. The two first of these are effected by water and fermentation. The plants tied in bundles are placed in water, and proper methods taken to prevent their being carried away, if it be a stream, which is frequently the case (c). In a short time a fermentation begins to take place, which acts both on the bark, which it loosens, and on the sap, which it decomposes. It is necessary to be attentive not to let the fermentation proceed too far, as we thereby run the risk of injuring the texture of the fibres. As soon then, as, on examining the plants, by rubbing them between the hands, it be found that the wood breaks easily, while the plants are still green, they must be removed from the water and spread out upon the grats to dry.
In this operation, which is called watering the flax or hemp, it is necessary to employ soft water; as it is found that in hard water the fibres are much more readily injured. To account for this, it must be remembered that these waters owe their hardness to their containing a quantity of an earthy salt *; and these salts are found to promote the process of putrefaction, particularly the sulphate of lime or gypsum, which is the most abundant of these salts contained in hard waters.
127. The process of watering destroys the sap of the plants by effecting its decomposition. This sap is found to be composed chiefly of water, and what modern chemists have called extractive: by fermentation this extractive is separated into carbon, hydrogen, and oxygen. It is probable also that the water of the sap, as well as that in which the plants are steeped, is decomposed. These principles uniting again in different proportions form carbonated hydrogen, which is the cause of the offensive odour, and carbonic acid, which is found to proceed from the plants. The exposure to the air which they undergo, after steeping, contributes to the speedier escape of these principles.
After the drying the plants appear of a grayish white colour, which is called by workmen a flaxen gray.
128. One of the greatest advantages which modern chemistry has conferred on the manufacturer, is the vegetable enabling him to do the same work more completely in substances, a shorter time than by the usual processes. Of this the present state of bleaching affords innumerable proofs. Even this process of watering may be greatly improved and considerably hastened. Several days are required before the fermentation is carried to a sufficient length, and with every attention, there is a chance of injuring the material. But it is found that this process may be performed by means of a weak alkaline ley without this danger.
129. The method recommended, is to convey the steam of water impregnated with caustic soda, in the manner which will be described hereafter for the bleaching of cotton and linen, through the plants of hemp and flax contained in a chamber of twenty or thirty feet square. The expense is trifling, as the ley need not be stronger than what was recommended for ungueming and bleaching silk.
130. When the watering is completed, the plants are to be kiln-dried. There now remains only the woody part inclosed in the fibres: to separate these is the object of the processes of beating and heckling. This is either performed by mallets and a sort of wooden anvils, and in this way hemp is beaten in houses of correction; or in mills erected for this purpose. In either way the wood is broken so as to allow of its being more easily detached from the fibres by heckling.
131. This refuse should not be thrown away, as it may be without much difficulty converted into paper.
132. The fibres are now ready for spinning and weaving, operations which it belongs not to this article to describe: we shall therefore take up the cloth as it proceeds from the hands of the weaver, when it comes properly under the direction of the bleacher.
133. The pieces of hempen and flaxen cloth, as they come from the loom, are covered with a dry coating of paste made of flour and water, which is called the dressing. This paste is applied to the threads of the weaver, to render the stretching of them more easy; and its removal is the first object in every method of bleaching.
134. For this purpose, all that is necessary is to steep the pieces in water for about forty-eight hours. Some manufacturers boil the pieces in the water, but this is improper, as the paste is not soluble in that fluid, even at the boiling temperature, but must undergo a decomposition by fermentation. To effect this the water should be of a temperature from 65° to 75° Fahrenheit; the fermentation then proceeds gradually, and the cloth sustains no injury. After remaining for a sufficient time, the pieces are taken out, and well rinsed in running water, either by treading with the feet or passing them under a fluted cylinder of wood.
135. By this operation the cloth is not only freed from the paste, but it acquires a degree of whiteness, and becomes of a lighter gray than before it was subjected to the water; for by the fermentation the texture
* See Mineral waters, Chemistry Index.
(c) It is very usual in Scotland to keep flax in burns or rivulets, as these are commonly found most convenient, but as the smell of the purifying plants is intolerably offensive, and even unhealthy, and as the process is found to destroy any fish that may inhabit the stream, the practice ought to be discouraged, and in some countries is forbidden by the laws. Vegetable ture of the pieces is loosened, the threads swell, and substances part of the colouring matter is decomposed.
136. The gray substance, which it is the principal business of the bleacher to remove, is of a resinous nature; and as the theory of the processes which we are presently to describe depends on an intimate knowledge of its properties, we shall be somewhat particular respecting it.
137. Kirwan, to whom chemistry in all its departments is so highly indebted, has submitted this matter to a set of ingenious experiments.
He procured from the bleach grounds a quantity of what the workmen called dead ley, which is the alkaline ley in which cloth has been steeped, and is consequently charged in abundance with the colouring matter. He found this liquor to be turbid, of a bluish red colour, having a peculiar taste, and a strong odour. It possessed neither alkaline nor acid properties.
138. To five pints of this liquor he added two ounces of weak muriatic acid, or spirit of salt; no effervescence was produced, but a considerable quantity of greenish matter fell to the bottom, and the liquor above remained of a reddish amber colour.
139. He next day, by means of a syphon, decanted off the supernatant liquor from the green precipitate, upon which he poured two pints of distilled water, stirred them well together, and allowed the matter again to subside: he then decanted off the water, and added a like quantity of fresh. This water still exhibited strong marks of acidity, and was of a reddish colour. He could not believe that after the addition of so much water, this acidity could arise from the muriatic acid which he had employed, as this was scarcely more than sufficient to saturate the alkali, which the liquor had originally held in composition. He concluded therefore that the liquor had contained a peculiar acid, which from its weaker affinity with the alkali, had been separated from it by the muriatic acid. He set apart two pints of this for farther experiments.
140. After successive washings of the precipitate, till it no longer appeared to retain any acid, he threw it on a filter: after being dried for some time, it became a tenacious mass of a greenish colour.
141. A very small portion of it was thrown into 60 times its weight of boiling water, but not a particle appeared to be dissolved. The remainder was dried in a sand-bath, after which it was brittle, of a glossy black without, and internally of a dull green: it weighed about an ounce and a half.
142. From eight pints more of the dead ley, he obtained a larger quantity of this green matter, on which he made the following experiments:
1. A portion of it was digested with rectified alcohol; a reddish tincture was produced, and a considerable part of the matter was dissolved; but on the addition of distilled water, the solution became milky, and a white precipitate gradually subsided. The black mass obtained in the former experiment, gave the same results.
2. These two matters were digested for a long time in linseed oil and essential oil of turpentine, but were not dissolved in either.
3. The black matter thrown on red-hot coals, burned with a yellow flame, and emitted a black smoke, leaving behind a coaly matter.
4. The green matter exposed to the action of sulphuric, muriatic, and nitric acids, gave a brown tinge to vegetable substances, the two former, and a green to the latter.
143. It is pretty evident from these experiments, that the extractive matter of the fibres of flax, which is obtained from them by the action of alkalies, is a resin of a peculiar nature, differing from pure resins in its being insoluble in essential oils, and in this respect having some resemblance to lacs.
144. Kirwan thought it necessary to try the action of alkalies on this matter. Eight grains were digested in a saturated solution of crystallized soda, at the temperature of 60° Fahrenheit, which was immediately tinged of a deep brown colour. Two measures of this solution of soda, weighing each 265 grains, did not entirely dissolve the matter, but two measures of a solution of potash dissolved the whole.
A measure of caustic soda of the specific gravity 1.053, dissolved nearly the whole, leaving a small quantity of a white substance.
A measure of caustic potash of the specific gravity 1.039 dissolved the whole.
A measure of an alkaline sulphuret or liver of sulphur, of the specific gravity 1.170, also dissolved the whole.
A measure of ammonia dissolved a small portion of it.
145. These experiments were sufficient to satisfy Mr Kirwan, but, for the purposes of the manufacturer, he judged it proper to repeat them with the ordinary alkaline substances employed in bleaching, and with soap.
He therefore dissolved an ounce of the soda of commerce, and as much Dantzic potash, each in fix ounces of distilled water; he added eight grains to an ounce measure of each solution, and allowed them to digest together in a temperature of 180° Fahrenheit for three hours and a half. At the end of this period it was found that more was dissolved in the potash than in the soda, and an ounce of this latter was required to complete the solution, whereas this was effected by the addition of half an ounce of the Dantzic potash liquor; thus shewing the superiority of the potash over soda.
An ounce of white soap was dissolved in eighteen ounces of distilled water; the solution remained turbid, and could be rendered transparent only by bringing it to the boiling heat, an operation which he found extremely difficult; for when the fluid was near boiling, it was thrown out to a distance of more than three feet from the matras. After completing the solution, he found that three ounces of it were required to dissolve eight grains of the colouring matter.
146. In forming an accurate idea of the comparative effect of these solutions, it must be observed, that an ounce of the soda of commerce contains only 114 grains of pure soda, and consequently, supposing the solution to have been made as above, in fix ounces of water, each ounce will contain 19 grains of soda, while an ounce of the solution of Dantzic potash contains fifty grains.
147. He tried the effect of lime on the colouring matter, on which it produced the effect; three ounces of water saturated with lime were employed, which contain at most three grains of that earth.
148. Having been so full on the nature and previous preparation of flax and hemp, it remains only to say something Vegetable something on cotton before we proceed to the bleaching substances, of these substances.
149. Cotton is a filamentous substance or down, which is found surrounding the seeds of the cotton plant.
This substance, as it is first obtained from the plant, is covered with a brownish coloured matter, by which it is rendered dirty and opaque. This matter is of a greasy nature, in which it resembles the oil contained in wool, as is evident from the flownfs with which raw cotton imbibes water, and the avidity with which it attracts it after having been scoured. Scouring, by removing this greasy matter, also renders it clear and transparent.
150. There is considerable variety in the quality of cottons, arising from their different kinds, the climate in which they were produced, and the degree of culture which they received. They are sometimes of a yellow colour, sometimes white, but most commonly their colour is a dirty yellow.
151. The bleaching of cotton does not call for those preparatory operations which we have described as necessary for hemp and flax. It is first to be scoured by steeping it in a slight alkaline solution, or, what is better, by exposing it to the vapour bath in the manner which we shall soon direct. After this operation, the cotton is to be placed in baskets in the stream of a river or other running water, so as to be well rinsed.
152. After the immersion of cotton in an alkaline ley, there is always left, however completely it be rinsed, a small quantity of an earthy sediment. This may be removed by the cautious use of acids. We know that cotton bears the action of acids much better than either hemp or flax, and that it may remain exposed to them for some time without injury. Advantage has been taken of so fortunate a discovery, and it is found, that by keeping the cotton for a short time pressed down in a very weak solution of sulphuric acid and subsequent thorough washing, to remove all the acid, this earthy sediment may be completely removed.
153. The methods which have been employed or recommended for the bleaching of hemp, flax, and cotton, may be reduced to five, viz.
1st, By the action of the atmospheric air, assisted by alkalies and soaps.
2d, By the action of water only.
3d, By the action of the oxygenated muriatic acid, or dephlogisticated marine acid of Scheele; and this method may be resolved into four; according as the acid is employed in its simple state of combination with water, or in combination with other matters.
a, By the action of oxy-muriatic acid alone.
b, By the action of oxy-muriatic acid combined with potash.
c, By the action of oxy-muriatic acid combined with lime or other earths.
d, By the action of oxy-muriatic acid combined with sulphuret of lime.
4th, By the action of diluted sulphuric acid.
5th, By the action of steam impregnated with caustic alkali, or by employing this alternately with the oxymuriatic. Of these we shall treat in the above order.
I. Of Bleaching by the Action of Atmospheric Air.
154. This is the method which was commonly adopted till within these twenty years, and is still retained in some old manufactories. After steeping the cloth, as has been related (134.), to remove the weaver's dressing, the pieces are dried in the field, and then submitted to the operation of bucking.
For this purpose a ley is prepared by dissolving a quantity of potashes in soft water, and boiling it for about half an hour, when it is allowed to settle, and forms what is called the mother ley. For bucking, this mother ley is weakened by the addition of 16 or 18 times its bulk of water; and to this is generally added a quantity of soap, or, for the sake of economy, a few gallons of ley which has already been employed for the first buckings. This liquor, which has been called the bucking ley, is now heated to about 100 degrees, and poured on the pieces sorted according to their quality. After pressing the cloth well down in the ley, it is drawn off, heated a little higher, and again poured upon the cloth. This operation is repeated at intervals, allowing the ley to remain longer each succeeding time, and moderately increasing the heat to the bucking temperature, for five or fix hours. Then the cloth is left steeping for three or four hours, when it is taken out, well rinsed, and carried to the field.
155. Here it is spread out upon the grats and secured by pins; water is sprinkled on it so as not to allow it to become dry for some hours. After it has lain about half a day the watering is less frequent, and at night it is left to the full action of the air and dews. On the succeeding days it is watered three or four times a-day if the weather be dry, and thus it remains on the field till the air seem to have less effect in whitening. It is then brought back to the coppers, and bucked again with a ley somewhat stronger than the last, rinsed, and again spread out on the field. It is thus alternately bucked and watered 10 or 15 times according to the weather, making the bucking stronger and stronger till about the middle, and then weaker and weaker till the last, after which it undergoes the process of scouring or steeping in some acid liquor.
156. The acid which has been usually employed in the process of souring is generated by the fermentation of bran and water; or, where the bleachfield was in the neighbourhood of a dairy, four whey was used for this purpose. It has been found that a very weak solution of sulphuric acid is more convenient and not more injurious than these, and this is now generally employed. The cloths are steeped in the souring for five or six days, if it be formed of milk or bran, or a less time where the sulphuric acid is used, and they are then given to the washers to be rubbed with soap, which is more particularly necessary to the selvages, as these resist the action of the air and alkalies longer than the rest of the cloth.
157. After being well soaped, the cloth is again bucked in a strong ley, rinsed, and again watered and exposed to the air, and all these processes are repeated in succession till it has acquired the requisite degree of whiteness. It must be observed that the strength of the acid liquors is diminished at each succeeding immersion. 158. The theory of these operations was, till lately, very little underflooded, but it admits of an easy explanation by the principles of modern chemistry. It has been proved, as will be shewn in chemistry, that the air of the atmosphere consists principally of two airs or gases, oxygen gas or vital air, and azotic gas, in the proportion of about .23 of the former to .77 of the latter. The only active principle in most of the operations of art and nature appears to be the oxygen, and this uniting with various inflammable bodies produces acids. Now the colouring matter of cloth is a compound inflammable matter or resin, composed chiefly of carbon (the base of charcoal), and hydrogen (the base of hydrogenous gas or inflammable air). As has been shewn, this is partly soluble in alkalies; hence the use of the alkaline leys in bucking is to dissolve as much as possible of the colouring matter; but, as the action of the alkali extends only to the surface of the cloth, it is soon over. The subsequent exposure to the air promotes the union of the carbon and hydrogen with the oxygen of the atmosphere, producing carbolic acid gas, or fixed air, and water.
When it was the fashion to denominate every combination of oxygen with an inflammable substance, combustion, this was considered as a species of burning*.
159. The great objection to this method of bleaching is its tediousness, two or three months being requisite to give the cloth the necessary whiteness. The simplicity of it, and the little apparatus it requires, recommend it however on some occasions, and accordingly it is employed by those country people who make their own cloth, particularly in Scotland.
The bucking of coarse cloths is expedited by boiling them in the ley, but this is seldom required for the finer kinds.
II. Bleaching by Water only.
160. We have observed (135.), that during the process of steeping, the cloth acquires some degree of whiteness; and it was long ago remarked, that the pulp from which paper is formed, while acted on by the stampers, was rendered whiter than before; it is found too, when the stalks of hemp and flax remain too long in the water in which they are steeped, they become considerably whiter, while, however, their texture is much injured. A manufacturer of Amiens, M. Brasie, conceived that, by cautious management, he might turn these facts to account, and bleach by means of water alone, which would be certainly one of the most economical methods. He allowed the hemp (for to this his experiments seem to have been confined) to remain steeping till the bark was pretty much destroyed by the fermentation. He then drew it through the teeth of a heckle or comb, which easily tore away the half putrid bark, permitting the fibres to pass uninjured between the teeth. During this process the hemp was perpetually immersed in water, by which means the green bark was much more easily separated, and the fibres acquired a much greater degree of brilliancy. Indeed, the whiteness produced in this way is truly surprising, and it is much to be regretted, that this cannot be obtained without injuring the quality of the cloth, which is prepared from the hemp thus treated. By this operation, however, the hemp does not acquire so pure a white as to render unnecessary the other processes, but vegetable substances, by it these would be greatly shortened.
161. As it is a matter of the greatest consequence to the bleacher, to be perfectly acquainted with the nature of the substances which he employs, as well as the most economical and convenient methods of procuring or purifying them, we shall take an opportunity, in the course of this article, of treating these subjects pretty fully. There is no material which has been more extensively employed in bleaching than potash or potashes.
162. If a pile of wood, or a heap of land-plants tolerably dry, be kindled and burned in the open air till the whole is consumed, there remains a considerable quantity of ashes, which on being boiled in water, impart to this fluid a strong saline taste, and give it the property of tingling syrup of violets, or any blue vegetable infusion, of a green colour. It was long ago known, that this liquor thus impregnated, possessed the valuable property of facilitating the removal of dirt and grease from cloth or linen, and with these views it has been employed from time immemorial; and is still used for this purpose by the country people. At length it was discovered, that by driving off the water by evaporation, the useful part of the liquor might be obtained in the form of a whitish solid substance, which being thus rendered capable of being carried to any distance, or kept in a dry place to any length of time, was much more convenient than the liquor itself. It is said that the Germans were the first who procured this salt in the solid state from the ashes of wood, and as it was prepared by boiling in iron pots, it received the name of potash or potashe.
163. Potashes have long been a considerable and lucrative article of commerce, and a great quantity is annually imported into the British empire, for the purposes of several manufactures, but particularly for the process of bleaching. The greatest quantity is brought from Russia and America, and of these the American is considered as the best. Good potashes should be very soluble in water, and should leave a small quantity of sediment, and they should have the property of easily deliquescing or becoming moist when freely exposed to the air. But as the sale of potashes is extremely extensive and beneficial, it has been found convenient to the vendor to increase their bulk by the addition of some other substance which he can procure at a cheaper rate; it is therefore of much importance that the manufacturer should be able to detect this imposition, which he will not find a difficult matter.
164. The ashes of most plants, besides the alkaline salt, which is more properly called potashe, and of which we shall speak presently, contain a compound salt, formed of this potas united to sulphuric acid, called sulphat of potas. This salt is an injurious addition to the potas, as it possesses no detergent properties, and is very little soluble in water, one part requiring 16 of water at an ordinary temperature to dissolve it. This salt is sometimes added to the potas by the merchant or the manufacturer to increase its bulk, and as it is a very cheap article in comparison with potas, the adulteration turns out very profitable.
"During a mineralogical excursion through England," says Mr Higgins, "in the summer and autumn of the year Part II.
B L E A C H I N G.
Vegetable year 1785, the different manufactures which fell in my Substances way were not passed over. Upon inquiring of the distillers of aquafortis (nitrous acid) how they disposed of the large residuum left in the still, which is sulphat of potash, and which is of little or no use in the arts, they informed me it was bought up by the Irish merchants.
"Sulphat of potash, when ground down, cannot readily be distinguished as to its external appearance, from pearl-ash, and being so much cheaper than the latter, is well calculated for the above fraudulent purpose.
"By no means do I intimate that this is a common practice, as from experience I know the contrary.
"However, to pass it over in silence would be unpardonable, when it is considered that the bleacher is at the expense of an article of no use whatever in bleaching, and that, by the adulteration, the proportion best known by experience to answer his purpose, is varied; by which means his process, although not altogether frustrated, must be materially retarded."
165. The difficult solubility of sulphat of potash renders it easy to separate it from the pure alkaline salt. Higgins gives the following method.
"Three pounds of pearl-ash, and two quarts (a Scotch pint) of water, should boil together for a few minutes, then be removed from the fire and suffered to stand for twenty-four hours, when the clear liquor is to be decanted off. Half a pint more of cold water is to be poured upon the dregs, and this again drawn off when clear. The insoluble salt is afterwards to be well dried and weighed, which being a foreign salt, will give pretty nearly the quantity of impurities in the potash.
"I would recommend the above mode of analysis to the bleachers before they purchase or use this potash."
166. Though the potash in the state in which it is sold answers sufficiently well for many purposes, it is not, however, pure potash, but is a compound salt formed of this united to carbonic acid, or fixed air, and it is called by modern chemists carbonat of potash. It is necessary for some processes to have it in the pure and caustic state, in which it acts much more powerfully. The carbonic acid is carried off by means of lime, for which it has a greater affinity than for potash. For this purpose a quantity of quicklime fresh burnt is to be flaked with soft water in a wooden or iron pot, and afterwards the potash is to be added dissolved in water, after being purified in the manner above directed. They must stand together well covered from the air for some hours, frequently shaking the vessel, and then the fluid may be drawn off clear for use. This is commonly called soap-leys, as it is used in the manufacture of soft soap; it is called caustic alkali, from the violent action which it exerts on animal and vegetable matters, which it corrodes or burns very speedily; whereas the action of carbonat of potash is much less violent, and this is therefore distinguished by the name of mild alkali. The use of the caustic ley requires great caution, but when sufficiently diluted it is perfectly safe.
167. It is proper to remark here, for the sake of manufacturers who are not scientific chemists, that the lime is of no farther use here than taking the carbonic acid from the potash, by uniting with which it is converted into chalk or carbonat of lime. The effect which the lime has in rendering the alkali caustic, was long known to manufacturers, and they were led to suppose that it entered as an ingredient into the soap-ley, and was itself useful as a detergent substance. This capital error led some into the employment of quicklime in bleaching without any addition, by which means the texture of the cloth was greatly injured.
168. As potash is the alkali which has been most employed in bleaching, we have mentioned it first; there is, however, another of still greater consequence in most manufactures, and which deserves our particular attention, from its being employed in the method of bleaching by steam, to be described hereafter. This is called soda or mineral alkali.
When sea-weed or wrack, and several plants which grow on the sea-coasts, particularly several species of falfola and falcicornia, are burned, the ashes form an impure alkaline mass of a different nature from that produced by the burning of land plants. What is obtained on our coasts from the sea-weed is called kelp, and that which is brought from the continent, especially from Spain, is called barilla, or barilla. The latter is the purer of the two, and is generally employed in the manufacture of soap. When these masses are reduced to powder, boiled in water, and the liquor filtered, sufficiently evaporated and set by to cool, a quantity of large beautiful crystals are obtained, which are carbonsal of soda, or salts of soda.
169. The soda, as contained in barilla, is in a much more caustic state, or less of it is combined with carbonic acid, than potash in the raw state; neither of these alkalies will crystallize in the caustic state, but by standing for some time freely exposed to the atmosphere, they imbibe from it carbonic acid gas, and are then capable of crystallization. It is therefore necessary to allow the solution obtained from barilla or kelp to stand thus exposed for about a week. It must then be evaporated to a proper degree, determined by experience or by the areometer for salts, and set by to crystallize. To make sure of obtaining crystals, which it is not always easy to procure, it would be better to evaporate to dryness, then dissolve the dry mass in the least possible quantity of boiling water, and, on cooling, crystals will be formed.
170. Soda, as existing in barilla and kelp, is sometimes contaminated by the mixture of muriat of soda, or common salt, from which it may be freed by careful evaporation. Carbonat of soda is less soluble in cold than in hot water, while the solubility of muriat of soda is much the same in both. After obtaining the first crop of crystals, therefore, which will be pure carbonat of soda, the remainder of the solution must be gently evaporated to about one half, when part of the muriat will separate and remain at the bottom of the vessel: the hot liquor is now to be poured off from it and set by to cool; when a fresh crop of crystals will be obtained, and thus the remainder is to be successively treated till all the soda is procured, and all the salt separated.
171. For most purposes of the manufacturer, soda is required in its caustic state, and for this purpose, the carbonic acid is removed by means of quick-lime. But as barilla contains most of it in a state sufficiently caustic for the ordinary purposes of the bleacher, he is seldom at the pains of purifying it. The usual way is to tie up a quantity of powdered barilla in a thick canvas bag, which Vegetable is suspended in the copper in which the cloth is boiled. Substances. A sufficient quantity of the soda is thus dissolved in the water, and imbibed by the cloth, while the insoluble dregs remain behind in the canvas bag. For the finer cloths, however, and for the purposes of bleaching with vapour impregnated with caustic soda, it would be much better to obtain the soda in its purest form.
172. Soap is an article of the utmost importance to the bleacher, and which we are naturally led to consider after speaking of potash and soda.
These alkalies readily combine with vegetable oils and animal fat, and on this property is founded the manufacture of the detergent substances denominated soaps. There is a difference sufficiently marked between the soap produced by the union of fatty matters with soda, and that formed from their union with potash. The former combination produces a hard, the latter a soft soap. The invention of this valuable substance is attributed by Pliny to the Gauls. The original composition of soap seems to have been much the same in all ages, but the first attempts to make it appear to have been extremely rude. The ancients formed their soap of goats fat mixed with the ashes of beech. Various improvements have been successively and gradually introduced into the manufacture, in proportion as accident, the parent of the most important discoveries, pointed out their necessity.
173. In France two kinds of soap are manufactured; hard, formed of soda, combined with olive-oil, and soft, composed of potash and vegetable oils, of inferior quality.
In Hungary and some parts of Germany, soap is made of tallow and barilla. A hard soap is prepared in Russia of bad salt butter, but it is held in little estimation, as the rancidity of the butter, and the quantity of cheesy matter which it contains, contribute to render it of a very inferior quality. We are informed by Weiglib that they also form a very hard soap of yellow and white bees wax, which has a very agreeable smell of almonds.
174. In Britain, where vegetable oils are by no means plentiful, and are consequently expensive, they manufacture this soap entirely with animal fat, employing either tallow, fish oil, kitchen grease, or stale butter. There are four kinds of soap manufactured here. 1. A hard white soap formed of soda of Alicant, and of Varech, combined with tallow. 2. A marbled soap, made of soda, tallow, and kitchen grease: the marbling is produced, not by a metallic oxide, as is the case in France, but by mixing a little ley towards the end of the boiling with the whole matter, drawing off the surplus to prevent the marbled part from setting, and then quickly conveying the soap into the frames to cool suddenly; this is at least the way in which the red marbled soap is made with us, but the mottled appearance in the blue marbled wash-balls is said to be occasioned by indigo*. 3. A hard yellow soap composed of soda, tallow, and rosin, which last seems to be added to make the soap cheaper, as it certainly does not increase its detergent property; and indeed it is said that the use of rosin is very injurious both to the arms and hands of the washers who employ this soap, vegetable which it irritates exceedingly, and to the linen washed substances, with it, to which it gives a yellow colour. 4. A soft soap, formed of whale or other fish oil combined with potash.
175. Attempts were long made to discover substances, which might supply the place of these fatty matters, in the manufacture of soap. It was reserved for Chaptal to point out the road to this valuable end, by introducing his soap formed of wool, and thus converting scraps of cloth and pieces of old woollen garments, into an excellent soap. He has been followed in Britain by Sir John Dalrymple, who conceived, that by a process similar to Chaptal's he might form a soap of the mucular parts of the fat fish. Some successful experiments completely proved the justice of the idea (H).
III. Of Bleaching by the Oxygenated Muriatic Acid.
176. The muriatic acid (see Chemistry), or spirit of salt, is not proved to contain oxygen, to which most other acids appear to owe their acidity. It is, however, capable of combining with this principle, by the addition of which it acquires new and very extraordinary properties. It will take oxygen from most of the metallic oxides or calces, as red lead, or, what is more commonly employed, the black oxide of manganese. If the muriatic acid be digested for some time, over either of these oxides, it acquires a most penetrating and suffocating odour, and instead of reddening a blue vegetable infusion, it banishes the colour altogether. It is this latter property of destroying colours, which renders the oxygenated muriatic acid of such importance in bleaching.
For the discovery of this acid, we are indebted to the immortal Scheele of Sweden, who was also acquainted with its property of discharging vegetable colours. The true application of this property, however, to the purposes of bleaching we owe to M. Berthollet, of whose paper in the annals of chemistry, (Annales de Chimie,) we shall present a brief abstract, as this was the foundation of all those improvements which have been lately made in the art, and of which we are presently to speak.
177. The oxygenated muriatic acid is obtained in the form of an air or gas, and was procured by Scheele in the following manner. He put a quantity of black oxide of manganese reduced to powder, into a glass retort, and poured on it some muriatic acid. To the retort he fixed a receiver, capable of holding twelve ounces; but containing only two drachms of water. On placing the retort in a sand bath, so that any acid which came over unchanged might fall back, and applying heat, the receiver was soon filled with a yellow-coloured gas. Having filled one receiver, he applied others successively, till no more gas was extracted, or till he had obtained sufficient for his experiments.
178. The experiments made by Scheele to ascertain the nature and property of this acid were few and simple; he suspended several substances in the necks of the receivers, and observed the following facts.
* Monthly Mag. for July 1803. For a full account of the manufacture of this soap, vide Annales des Arts et Manufactures, par O'Reilly. Part II.
Vegetable Substances. 1. The corks which closed the mouths of the vessels which contained the gas, were rendered yellow, as if they had been corroded by nitric acid (aquafortis). 2. Paper tinged blue, with infusion of litmus or tournefol, was rendered nearly white. 3. The red, blue, and yellow parts of flowers, as well as the green leaves of vegetables, were by the action of the gas rendered pale and colourless. 4. When these changes were produced by the action of water, by which this gas had been absorbed, the water was changed into very weak common muriatic acid. 5. Neither acids nor alkalies were capable of restoring the original colours thus changed.
179. Berthollet repeated and confirmed these experiments of Scheele's, and explained the theory of the changes produced by the action of this new substance. "I have shewn," says he, "that one portion of the common muriatic acid employed in the preparation diffuses the oxyd of manganese, and displace a part of the oxygen, or basis of vital air, which was, in that substance, combined with the metal in larger proportion than is necessary for enabling it to be dissolved in acids. This superabundant and now disengaged oxygen being in a non-elastic form, or, as Priestley calls it, in a nascent state, and being thereby greatly disposed to enter into new combination, unites itself to the other portion of the muriatic acid, and, in consequence of this union, the oxygenated muriatic acid gas is produced."
Having examined and explained the experiments of Scheele, Berthollet goes on to make others of his own.
180. His first object was to examine the degree of solubility of the gas in water, which he suspected to be greater than Scheele had supposed.
181. "He soon perceived, if a body with a recurved tube be filled with this water, impregnated with the dephlogisticated or oxygenated muriatic acid, and the outer extremity of the tube be immersed under a receiver filled with water; if, in this situation, the fluid be exposed to the light of the sun, bubbles are soon disengaged, which pass into the receiver, and are found to consist of pure or vital air. When the bubbles have ceased to be disengaged, the liquor is found to have lost its characteristic smell, colour, and all its distinctive properties; and is found to consist of mere water, containing a proportion of common muriatic acid. This simple experiment, M. Berthollet observes, ought to be sufficient to afford a conviction, that the oxygenated muriatic acid is really nothing but a combination of the muriatic acid with basis of vital air, or oxygen, which is found so abundantly in the black oxyd or calx of manganese, that nothing more is necessary than to urge this oxyd by a strong heat, in order to obtain a large quantity. Manganese, thus treated, is no longer proper to form the oxygenated muriatic acid; because it is deprived of that portion of oxygen which is required to combine with part of the muriatic acid.
182. "He remarks, that light possesses the property of disengaging the oxygen which was combined with the muriatic acid, by restoring that elasticity of which it was partly deprived; a restoration not to be effected by mere heat: he concludes therefore that the light combines with the oxygen, and that the elastic state of vital air is owing to this combination: which air, Vegetable by loosing a second time its elasticity in the process of combustion, that is to say, by a rapid combination with some other body, again suffers the principle of light to escape, at the same time that much heat is disengaged; the relation of which last substance with light is still an object for future discovery.
183. "If vegetable colours be plunged in the oxygenated muriatic acid, they disappear more or less speedily, and more or less perfectly. When the substance under examination possesses a mixture of different colouring parts, some disappear more readily, and leave only those which more effectually resist the power of this agent, but have nevertheless suffered a considerable alteration. The yellow colouring matters usually resist the most strongly, but at length they all disappear; and when the oxygenated muriatic acid has exerted its whole action, it is found to be reduced to the state of ordinary muriatic acid. Hence it follows, that the colouring matters have deprived it of the oxygen, or vital air; and have, by this combination, acquired new properties, at the same time that they have lost that of producing colours. This ingenious chemist declines entering, in his present memoir, into the properties of these oxygenated substances; and proceeds to observe, that the oxygenated muriatic acid owes its property of destroying colours to the oxygen, which not only is combined abundantly with it, but likewise adheres with very little force, and readily passes into a state of combination with such substances as have a certain degree of affinity with it. The habitues of such a variety of colouring matters as exist in nature, with the oxygen, with light, with alkalies, and with other chemical agents, cannot but form a highly interesting, and almost entirely unexplored, part of natural philosophy.
184. "After having observed the action which the oxygenated muriatic acid exercises in general upon colouring matter, he concluded that it might produce the same effect upon those substances which colour thread and linen, and which the art of bleaching proposes to destroy. Without confining himself to describe the process as now practised, he enters into a concise detail of the imperfect essays he made at first, a detail which will be by no means without its utility to such as are desirous of carrying the process into execution.
185. "He at first used a very concentrated liquor, which he renewed when exhausted, until the thread or cloth appeared sufficiently white; but, in this way, he soon perceived that their texture was considerably weakened, and that they were even entirely deprived of their solidity. He therefore slightly diluted the liquor, and succeeded in bleaching his cloth, without altering it; but it soon became yellow by keeping, and more especially when it was heated, or subjected to the action of an alkaline lixivium. He directed his reflections, therefore, to the circumstances of the usual process of bleaching, which he endeavoured to imitate; because he had adopted the opinion, that the oxygenated muriatic acid ought to act in the same manner as the exposure of cloth upon bleach-grounds; which exposure alone is not sufficient for the purpose, but appears merely to dispose the colouring matter to solution in the alkali of lixiviums. He examined the dew which is precipitated from the atmosphere, and like- Vegetable wise that which is afforded by the nocturnal transpiration of plants; and observed that both the one and the other were saturated with oxygen to such a degree, as to destroy the colour of paper weakly tinged with tournesol; and he remarks that the ancient prejudices respecting May dew, which is the season wherein the transpiration of plants is abundant, might probably depend on some observation of this nature.
186. "He therefore employed, alternately, the lixiviums, and the action of the oxygenated muriatic acid; by which means he obtained a permanent white. And as it is the practice, in the ordinary way of bleaching, to pass the cloth through four milk, or vitriolic acid, diluted with a large quantity of water, he made the trial likewise of passing his cloths through a very diluted solution of vitriolic acid, and observed that the white was much brighter.
187. "As soon as he had made use of the intermediate lixiviums, he found that it was not necessary to use a concentrated liquor, or to leave the cloth long in the fluid at each immersion. By this observation he avoided two inconveniences, which might have rendered the process impracticable in the large way: the first is, the suffocating smell of the fluid, which would be very inconvenient, and even highly dangerous to be respired for a long time, and which has discouraged several operators from pursuing their attempts in this way: the second is, the danger of weakening the cloth. At this period of his experiments he likewise gave up the idea of mixing alkali with the oxygenated muriatic acid, as he had before done in most of his experiments*.
188. "This was the state of the experiments of this excellent chemist when he repeated them in the presence of the celebrated Mr Watt. A single glance, he observes, is sufficient to a philosopher whose abilities had been so long exercised upon the arts. Mr Watt soon afterwards wrote to him from England, that in his first operation he had bleached 500 pieces of cloth on the premises of Mr Grigor, who has large bleach-grounds at Glasgow, and continues to use this new process.
189. "In the mean time M. Bonjour, who had assisted M. Berthollet in his experiments, and who to a large share of sagacity has added a very extensive knowledge in chemistry, entered into an agreement with Mr Constant of Valenciennes to form an establishment in that town. This project was opposed by the prejudices and interest of the bleachers, who were apprehensive of the competition of a new method. Mr Constant could not even procure a piece of ground in the town of Valenciennes; but the Count de Beaulange favoured this enterprise, and gave up a piece of ground which possessed every advantage; but, being at a certain distance from Valenciennes, would have the disadvantage of distance, if any manufactory should be established at Valenciennes itself. M. Bonjour had given up the well-grounded hopes which his knowledge and talents gave him reason to expect at Paris: and had in return found, in the enterprise to which he had devoted his attention, nothing but those disgusting circumstances which usually accompany new processes in the arts. He addressed himself to the Bureau de Commerce, not to reward his services, but to request that he might be defended from the disadvantages and obstacles which prejudice and an opposition of interest had created in Valenciennes, by granting to him a certain space of two leagues round Valenciennes and Cambrai, in which he alone might, during a certain number of years, exercise this new art; without constraining in any respect those who might choose to adhere to the ancient processes, or attempt new processes, in which no use should be made of the oxygenated muriatic acid. He offered to instruct in his manufactory, in all the details of his process, all such as might be desirous of using it, and might obtain the function of the ministrv. It is probable that, if his request had been granted, the establishment at Valenciennes might have produced a greater degree of confidence in those who had undertaken to make the necessary advances. It is probable, continues M. Berthollet, that they might have shortened their trials, instead of establishing the process at Courtray, as they have done; many artists might probably have been formed under the direction of M. Bonjour; and a great number of establishments might have been formed in the French provinces, by avoiding those fruitless trials which tend to throw discredit upon an useful art.
190. "As soon as M. Berthollet had reason to hope that the process might be executed in the large way, he endeavoured to diminish the price of the liquor, by decomposing the marine salt in the very operation which served to form it. His first trials were unsuccessful; but Mr Welter, a young ingenious chemist, to whom M. Berthollet had entrusted the management of the process, observed that it might be of advantage to dilute the vitriolic acid; and the operation then succeeded in the most satisfactory manner. He immediately wrote to M. Bonjour and Mr Watt, the latter of whom informed him that he had made this change from the first: and the operation was long afterwards described by M. Chaptal in a memoir forwarded by him to the Academy of Sciences. Mr Watt had likewise made use of a certain cask or butt, of a construction which M. Berthollet was not acquainted with; but, before this apparatus was mentioned, Mr Welter had constructed one, which is not only very proper to prepare the oxygenated muriatic acid, but very well calculated for several other chemical operations.
191. "The intention of this apparatus is to multiply the surfaces of contact between the gas and the water, as it is evident that the combination can take place only at their surfaces. That part of the gas which did not enter into combination in the lower space, where it is first conveyed, passes into a second cavity or space, which is above the tube intended to give it vent. The vessel which is intermediate between the pneumatic cask and the distillatory matraf, is designed to retain that part of the muriatic acid which is not oxygenated: a small quantity of water is put into this vessel, a glass tube being plunged therein, the height of which exceeds that of the column of water the gas must overcome in the cask. The gas which passes out of the matraf compresses the water in the intermediate vessel with a force equal to that opposed to its engagement; so that the water rises in the tube of safety, and forms a column equal to the weight of the water which Vegetable which presses on the tube through which the gas enters the cafs. But if, during the operation, a sudden cooling or rapid abforption of gas should take place, the water defcends again in the tube, the air of the atmosphere enters, and prevents a vacuum from being formed within, which would have been attended with a reformation of the liquor, and consequently break the distilling vessel by the sudden cooling.
192. "If the oxide or calx of manganese be of a good kind, in small crystals, and contain very little foreign matter, the proportions which M. Berthollet found best calculated for distillation, are the following:
193. "Six ounces of pulverized calx of manganese, one pound of pulverized sea salt, twelve ounces of concentrated vitriolic acid, and from eight to twelve ounces of water. If the calx of manganese contain foreign earth or metallic substances, the quantity must be augmented in proportion to its impurity. It will be known, after the operation, whether a sufficient quantity has been employed; because a small quantity ought to remain undecomposed, and of its original black colour: from this observation, the quantity proper to be used in the following operations may be ascertained.
194. "When the calx of manganese is found to contain calcareous spar, as may be known by its effervescing upon the contact of a small quantity of vitriolic acid, it is proper to wash it before the operation with diluted vitriolic acid, to separate the calcareous part, which might be troublesome on account of the effervescence it produces: the calx must be dried after this washing.
195. "M. Berthollet is of opinion, from his trials, that when the calx of manganese contains much phlogifticated air, it is scarcely proper to form the oxygenated muriatic acid: M. Fourcroy, however, affirms, that the phlogifticated air escapes in distillation from manganese by a degree of heat less than ignition, but that ignition is necessary to deprive it of its vital air. It might perhaps be found advantageous to make use of this information to purify such manganese as contains phlogifticated air, by distilling off this last aerial substance by a moderate heat before it is applied to the purpose of oxygenating the marine acid.
196. "A greater or less quantity of water must be added, not only according to the degree of the concentration of the sulphuric acid, but likewise according to the quantity of matter subjected to distillation. If this quantity be considerable, the acid must be more diluted than if it be small. It might be more advantageous to make use of an acid which had not been concentrated; because the operation of concentrating it adds to its price, and it is obliged to be again diluted with water. But M. Berthollet observes, that this saving can only take place when the manufactory of the vitriolic acid is near at hand; for in those situations where this acid is to be brought from a considerable distance, the expense of carriage of a greater quantity of fluid might exceed that of concentrating it.
197. "When the materials are prepared, the calx of manganese must be carefully mixed with the sea salt, and the mixture introduced into the distillatory vessel, placed on a sand bath: the vitriolic acid must then be diluted, and suffered to cool; after which it is to be poured on the mixture, and the tube of communication between the matrads and the intermediate vessel quickly fitted in. A particular attention to the luting is required in this operation. M. Chaptal takes notice, that when the vapour is perceived to escape by the smell, it is sometimes difficult to ascertain the imperfect place; but that if a feather dipped in volatile alkali be passed on such occasions over the lutes, it will shew the faulty place, by the white cloud of ammonia formed in consequence of the combination of marine acid with the volatile alkali.
198. "The size of the vessels ought to be such, that the matrads should be about one-third empty; and that, for the quantity here laid down, the cafs should contain 100 pints of water, with an empty space of the bulk of about ten pints; because, when the gas comes to occupy the cavities designed to receive it, the water will require a space into which it may ascend.
199. "Before the operation is begun, the pneumatic cafs must be filled. The mixture being made, the gas, which soon begins to be disengaged, first drives the atmospheric air out of the apparatus. As soon as it is apprehended that the atmospheric air has passed into the cavities, it is emptied out by means of a recurved tube, successively introduced beneath each; and in order to drive the water out which has entered into the tube, M. Berthollet recommends blowing strongly into it. The operation is suffered to go on without the application of heat, until it is perceived that the bubbles are more slowly emitted: at this period, a slight degree of heat is applied. It must not be strongly urged at the beginning; but by a gradual increase it is at last to be carried to ebullition, towards the end of the operation. It may be known when the operation is near its termination, by the tube of communication and intermediate vessel becoming hot.
200. "When the gas is no longer disengaged but in small quantities, the fire is to be put out, and a sufficient time must be suffered to elapse until the matrads is nearly cold. The tube of communication may then be removed, and hot water poured in to keep the matter in solution, that it may be more easily taken out: this residue is to be poured into a large vessel, intended to preserve it for a use to be presently mentioned. The operation lasts longer in proportion to the quantity of matter. With the before-mentioned quantity, it ought to last five or six hours. It is proper not to be too much in haste, because a larger quantity of gas is by that means obtained. One single person may inspect and manage several of these apparatus, and the quantities may be much larger.
201. "The intermediate vessel gradually becomes filled with a fluid, which consists of pure but weak muriatic acid: several operations may, however, be made without taking it out; but when it is apprehended that there is not a sufficient space left empty, this acid is taken out by means of a syphon: and, when its quantity is considerable enough, it may be substituted instead of the mixture of sulphuric acid and muriate of soda, in a similar operation, if it be not wanted for another use. In order that the quantity of common muriatic acid which passes out of the matrads, may be inconsiderable, it is expedient that the first tube should make a right angle, or even a more obtuse angle, with the body of the matrads. During the operation, it is necessary to stir Vegetable stir the water, from time to time, by means of the agitator, in the apparatus, to favour the absorption of the gas by the water. When this is completed, the liquor is sufficiently strong to be used in bleaching. A smaller proportion of water may be put into the cask, and the fluid may afterwards be properly diluted.
202. "In this state of concentration, though the liquor retains a considerably strong smell, yet it cannot prove noxious, or even very inconvenient, to those who use it. It is nevertheless proper to conduct it into the vessels in which the cloths are arranged, by wooden channels, fitted to the opening at the lower part of the cask. It is proper to draw off the liquor from the cask as soon as it is prepared, because it acts upon the wood, and not only becomes by that means weaker, but likewise hampers the destruction of the cask: but when it is conveyed into a vessel in which cloths are properly placed, these speedily weaken it to such a degree that it does not perceptibly act upon the wood.
203. "The cloths are to be prepared by leaving them 24 hours in water, or still better in the old lixivium, to extract the dressing; after which they must be once or twice well washed in alkaline lixiviums, because all that part which can be extracted by the lixiviums would have neutralized a portion of the liquor, which requires to be carefully used. After this the cloth must be carefully washed, and disposed upon sticks in such a manner that it may be impregnated with the liquor poured on it, without any part being compressed. The framing of the sticks, as well as the cask and vessel intended to contain the cloths, ought to be constructed without iron; because this metal becomes calcined by the oxygenated muriatic acid, and would produce iron moulds, not to be taken out but by means of salt of forret.
204. "The first immersion must be longer than the following ones; it may last three hours: after which, the cloth is to be taken out, lixiviated anew, and then put into a shallow vessel, in order that new liquor may be poured on it. It is sufficient that this immersion, and the following, should continue for the space of half an hour. The cloth is taken out, and cleared of the liquor by pressure; then lixiviated, and subjected to new immersions. The same liquor may be used until it is exhausted; and when it is found to be much weakened, a proportion of the liquor which has not been used may be added.
205. "When the cloth appears white, excepting at the selvages, and a few threads darker than the rest, it must be impregnated with black soap and strongly rubbed; after which it is to be lixiviated for the last time, and immersed once more in the liquor.
206. "The number of lixiviations and immersions which are necessary cannot be determined, because it varies according to the nature of the cloth: the limits of this number, however, are between four and eight for linen and hempen cloths. M. Berthollet expresses his inability to point out the best method of making the alkaline lixiviums; this useful art being still a matter of mere practice, and variously performed in different places. It appeared advantageous to him to render the alkali caustic, by mixing one-third of lime; but in this case care must be taken that the lixivium be strained through a cloth, in order that the calcareous earth may not mix itself with the linen, as its particles might corrode or wear it by their hardness. By this management the lixivium being rendered more active, does not require to large a quantity of alkali; and nevertheless, if the quantity of alkali be not too considerable, it produces no damage to the cloth, notwithstanding the contrary prejudice, which is very general. He has likewise remarked that it was of no advantage, and even prejudicial, that the lixiviations should be of long duration; but it is necessary that the fluid be very hot, and of considerable strength, otherwise the cloths bleached by the aerated marine acid would become coloured and ruddy when submitted to new lixiviations. This accident took place in the trials already mentioned. Cottons are much more easily and speedily bleached than linens: two lixiviums, or at most three, with the same number of immersions in the liquid, are sufficient; and as they are so much the more readily bleached, it is advantageous, when linen, hemp, and cotton, are to be bleached, to reserve the liquors for the latter, which have been already weakened by exerting their action on the former. Such liquors are so exhausted as scarcely to act upon hemp or linen, will do very well for cotton.
207. "After the last immersion in the liquor, the cloth must be plunged in four milk, or water acidulated with vitriolic acid. The true proportion is not well ascertained; but our author thinks, from his experiments, that one part of the acid by weight, with fifty parts of water, may be employed successfully, and without danger. The cloths are to be kept about half an hour in this fluid, warmed; after which, they must be strongly pressed, or wrung, and immediately plunged in common water: for, if they were suffered to dry by evaporation, the vitriolic acid, becoming concentrated, would attack them. When the cloths are well washed, nothing more is necessary than to dry and prepare them in the usual manner.
208. "It is an obvious precaution, that this acid water be not too strong, as it would of course injure the texture of the stuffs.
209. "Fig. 5, Pl. XCI. exhibits the apparatus for preparing the liquid intended to be used in this new method of bleaching. ABC is a furnace; C is the matrass, or distillatory vessel; GHI the tube of communication with K, the intermediate vessel; L the tube of safety; M a tube communicating with the tub N, the section of which tub is exhibited in fig. 6, while the lower orifice of this tube is seen at y. In the tub N are fixed three inverted vessels, open beneath, as represented in fig. 7, and intended to contain the aeriform marine acid. PPP are agitators for the purpose of stirring the water by the rotation of the upright post OQ. The effect of this apparatus may be easily understood, by considering that the aeriform dephlogisticated marine acid, issuing from the tube y, passes into the vessel X, until it has excluded the water it may contain: after which the surplus issues through the tube Z, and runs into the second vessel; which, becoming also filled, affords its surplus to the third or uppermost vessel. Hence it follows, that three surfaces of the water are exposed to an atmosphere of dephlogisticated marine acid; and these surfaces must of course be changed by the rotation of the agitators. In this manner the water becomes impregnated, and may be drawn off at P. It is of consequence to ascertain its relative Vegetable relative strength, in order that the experiments may at all times be equally successful. M. de Croifille makes use of a solution of indigo in the vitriolic acid; for which purpose he takes one part of finely-pulverized indigo, with eight parts of concentrated vitriolic acid. This mixture is kept in a matrafs for several hours on the water bath; and, when the solution is complete, it is diluted with a thousand parts of water. In order to ascertain the force of the oxygenated muriatic acid, one measure of this solution is put into a graduated tube of glass, and the liquor or impregnated water is added, until the colour of the indigo is completely destroyed. In this way it is ascertained, by means of the graduations, how many measures of any liquor, whose goodness has been ascertained by direct experiments upon linen or cotton, are necessary to destroy the colour of one measure of the solution of indigo; and this number will serve to ascertain the respective force of all the liquors which are required to be compared together. Mr Watt makes use of a solution of cochineal for the same purpose.
210. "In the sixth volume of the Annals of Chemistry, M. Berthollet has published some additions to the foregoing Memoir, which, on account of its extensive utility, I have scarcely at all shortened. They are the following:—Mr Welter finds that it is advantageous to terminate the process, by exposing the thread or cloth for three or four days in the field; during which they must be occasionally watered, and afterwards washed with pure water. He considers this exposition as indispensable. But M. Berthollet observes, that other persons have bleached to the perfect satisfaction of artists without it; though he admits that it may happen, in the large way, that certain pieces may not turn out perfectly white after the last operation, in consequence of some of their parts having suffered casual prejudice; and he thinks that, although a continuance of the operation would remove these imperfections, it might, in such cases, prove more advantageous to remove them by exposure on the grass; very little loss of time, and no considerable extent of premises, being required for this purpose.
211. "M. de Croifille has excluded the use of wood in every part of his apparatus; and has applied the process not only to bleaching, but to the discharging of colours in dyed cottons or linens.
212. "M. Berthollet further observes, that the precaution of plunging the cottons in pure water, after they have been taken out of the acidulated water, is not sufficient; but it is necessary to plunge them into a weak caustic lixivium, moderately heated, and keep them there for a short time.
213. "When the liquor is suffered to run immediately into troughs, care must be taken to mix it well with the agitator; because otherwise the most saturated liquor, which occupies the lower part of the vessel, running first, would exert too strong an action; or if half or three quarters of the liquor be drawn off, and mixed with the proper quantity of water, according to the precautions before established, the rest of the fluid may be used together with the water for the succeeding operation: lastly, he observes that this process, simple as it is, can scarcely be carried into execution, without, in the first instances, being directed by a person to whom the operations of chemistry are familiar.
He observes that a diminution, or even an equality of Vegetable the expences, relative to the ordinary process, is not to be hoped for, excepting for the bleaching of fine cloths, unless the operator possesses a good process to extract the soda from the residue of the distillation; and without this condition the bleaching of coarser cloths ought not to be undertaken, excepting in those cases wherein the advantages arising from the speed of the operation, the facility of performing it in all places and at all times, and the diminution of the stock or capital, are sufficient to compensate for the excess of the price. These observations are perhaps applicable to linens, and not cottons. It is not possible, he continues to observe, to lay down principles applicable to every particular case; but he advises those who may undertake this object, to begin by trials, and by means of those trials to form calculations, without any allowance on the favourable side. On the other hand, he advises the operator not to suffer himself to be imposed on by those losses which arise for want of being familiarized with the operations; as there is no great expense incurred by making trials for a time, by which this advantage is derived, that the operator renders himself more expert for carrying more extensive processes into effect **."
214. Such is the method of procedure recommended by M. Berthollet, which was soon found liable to many inconveniencies; and various amendments and alterations have been suggested, the principal of which we shall relate. Pajot de Charmes was one of the first improvers of the new method. He states the following objections to Berthollet's process.
1. He thinks the furnaces recommended by Berthollet not well adapted to the purpose, as they are difficult to procure and expensive; as they will only contain each one matraf; as they are not calculated to shew the progress of the process, are too speedily heated, and consequently endanger the lutes; and lastly, as they will not always guard against abortion, notwithstanding the tube of safety in the intermediate vessel. The furnace which he would have employed in place of these is thus constructed:
215. The furnace is supported upon a frame-work of wood, between which and the hearth tiles are disposed in a bed of clay. The furnace itself is built of brick, which he recommends to be lined with platter of Paris. It ought always to be double, and is divided by a partition in the middle. In the upper part at the front are two cavities intended to admit the vessels used in the distilling; they may be either round or square; and, as the latter is most convenient to the builder, they should perhaps be always square, provided with a ledge, and rounded at bottom. The combustible matter, which may be charcoal, is burned in a sort of chaffer, or in a portable grate, which is introduced by an opening in the side of the furnace: and this opening may be closed during the process by a door of plate-iron so as to prevent the too free access of air. From behind the distilling vessels and charcoal grate proceeds a funnel through which the vapour, and heat of the fuel is conveyed into a cavity with raised edges, over which is placed an oblong vessel of sheet iron, intended to be kept filled with muriat of soda, which may dry during the process. At each extremity of this cavity is a hole which may be opened or closed as required, so as to Vegetable admit a greater or less quantity of air. Below the substances drying place, in the sides of the empty space at the back of the furnace, are places where boxes of sheet iron, containing the requisite proportion of manganese and salt, ready mixed, are kept for the purpose of keeping the materials dry.
In each of the square spaces is placed a capsule, which may be made either to contain sand or water, in which the distilling vessels are to be inserted. These capsules rest with their rims upon the edges of the cavities, and are supported below by a small bar. The furnaces, according to the directions of De Charmes, are made so as to be portable, an advantage which may perhaps, in most manufactories, be dispensed with.
216. 2. De Charmes next objects to the curved tube as being liable to be broken; and thus expose the workmen to the noxious gas, of which the accident will also cause a considerable loss. Berthollet's method of applying the tube is also objectionable from the destructible nature of the cork stoppers, and the difficulty of preserving the flability of the latter.
He proposes, instead of the matrads, tube, and intermediate vessel, to substitute tubulated retorts, furnished with curved necks of glass or lead; the beak of which is fitted by luting to a leaden support in the form of a funnel; and to that is adapted the end of a leaden tube which passes into the pneumatic tube, and has its lower extremity bent to a right angle, serving instead of the glass tube used by Berthollet.
217. 3. Berthollet's pneumatic tub was not provided with a cover close enough to prevent the escape of the gas; and his inverted vessels appear to De Charmes to be improper, from the difficulty there is of constructing their sides and borders so as to concentrate the gas in the best and most complete manner.
His pneumatic tub is conical, and divided into three parts by two false bottoms, which are made to rest on hoops or sliders within the tub, and kept firm by means of pins.
218. The distilling vessels employed by De Charmes are not high enough to prevent a portion of the sulphuric acid from passing over without combination; and they are besides too dear for ordinary use. In Ireland they employ leaden alembics of a sufficient height, and capable of containing 40 gallons of liquor, which is a capacity amply sufficient for allowing the swelling of the materials. These alembics are conical, have a broad bottom, which is supported in a vessel of water to regulate the heat; the neck is so long as to allow any sulphuric acid, which may rise, to fall back again, and the cover of it is perforated in two places; one of the perforations serving for the passage of a rod of iron with prongs entering within the alembic, but so covered with lead as to prevent the action of the sulphuric acid, and the handle passes through a leathern collar to prevent the escape of gas, the whole being intended for stirring the materials; the other hole intended to admit a leaden funnel curved like an S, to prevent the reaction of the gas on the diluted sulphuric acid which is to be introduced through it.
219. It is of the greatest importance to prevent the escape of the gas, as well to prevent danger to the workmen as loss to the manufacturer. "C. Widmer, at Jouy, has arranged his apparatus in such a manner as to lose the least gas possible during the condensation: he receives the gas under a capsule inverted at the vegetable bottom of the apparatus; above these are two tours de substances goutiere also inverted, then another capsule above these; then two more tours de goutiere, and then another capsule, which terminates the apparatus. The disposition of his tub is such, that he places around in his laboratory several distilling apparatuses, which are going at the same time.
"Apparatuses constructed on similar principles are also in use at Glasgow and Manchester. Bourboulon-de-Bonneuil has likewise invented an apparatus, consisting of several matrads, ranged as in an aquafortis manufactory, the tubes of which are conveyed into a chamber containing concentrating tubs. His apparatus for the bleaching of paper is very ingenious, and deserves to be described. In the last place, others have arranged five or six large casks, like Wolfe's apparatus, in such a manner as to make each cask perform the functions of a tubulated flask."*
220. Before we proceed to describe the most approved method of immersing the cloths in the oxygenated liquor, it will be proper to treat particularly of the materials employed in preparing this liquor, the mode of preparing them for the process, and the method of adjusting the apparatus and conducting the distillation.
221. The selection and preparation of the materials is of the greatest importance, as on them will depend in a very great measure the success of the operation.
The materials are either the muriatic acid and black oxide of manganese, or this latter and sulphuric acid and murat of soda, which are usually employed as being cheaper. There are, however, advantages in using the muriatic acid ready prepared, where the bleach-field is in the neighbourhood of such a manufactory, as the danger of breaking the vessels (where glass is employed) from the incrustation of the residuary salt is much less in this case.
222. The crystallized ore of manganese is to be preferred, such as appears to be composed of splendid needles slightly adhering to each other; this variety is generally purer, and much more easily reduced to powder, and a smaller quantity of it is sufficient. It must be reduced to a very fine powder, a short time before it is wanted, as if kept long in the state of powder, it is said to be injured.
223. The gray murat of soda is employed in France as being cheaper than the white, but probably the present regulations of the salt duties in this country are such as preclude the manufacturer from employing it in this state†. The salt is to be dried on an iron plate in that part of the furnace described in 205, and then rubbed to a fine powder, and passed through a Charmes sieve; this is necessary, to mix it more intimately with the manganese, and to enable the sulphuric acid to act more uniformly and completely on it.
224. In order to be more certain as to the proportion of the ingredients, the sulphuric acid should be procured in its concentrated state, and acid of the same specific gravity should always be employed. Before using, it is to be lowered with its weight of water, and it is proper to observe, that in making the mixture, the water should not be added to the acid, but the acid be poured in a gentle stream into the water, pouring it down the sides of the glass vessel in which the mixture
*Philosoph. Mag. vol. x. p. 258. Part II.
Vegetable ture is made, adding the acid by portions at intervals, Substances, and turning the head aside to avoid any drops which may fly up from the effervescence produced, which, however, is much less in this way than when the mixture is made in any other way. As a heat greater than that of boiling water is generated, it is better that the vessels have the form of jugs with spouts and handles, that the mixture may be more easily poured into the distilling vessels.
225. The proportions in which the ingredients are employed, are variously adjusted by different manufacturers. De Charmes recommends the following:
Oxide of manganese crystallized, twenty ounces. Muriat of soda, four pounds. Sulphuric acid (at 60° of Masfy's aerometer), 44 ozs. Water, three pounds and a quarter *.
Mr Rupp of Manchester recommends the following, as affording him the strongest liquor.
Manganese, three parts. Muriat of soda, eight parts. Sulphuric acid, fix parts. Water, twelve parts †.
Mr Higgins uses the proportions as under:
Manganese, sixty pounds. Muriat of soda, sixty pounds. Sulphuric acid, fifty pounds. Water, about thirty pounds ‡.
In Germany, and in France at present, the proportions are nearly as follows:
Manganese, twenty parts. Muriat, sixty-four parts. Acid, forty-four parts. Water, fifty-four parts §.
226. It would conduce much to the economy of this method of bleaching, if the manufactory of sulphuric acid could be carried on under the same roof with the bleaching process, or if some method could be devised to prepare this acid, without employing the nitrat of potas (faltpetre). The latter has been attempted by De Charmes, and as his experiment may afford a hint to manufacturers, we shall copy it.
"The present is certainly the place to speak of the attempt I have made, to procure the sulphuric acid without the intermediate of nitre, and to describe the apparatus I made use of for that purpose. It consisted of a pitcher or pot of stone-ware, perforated at the bottom, the neck of which communicated with two small two-necked glass bodies connected together, and each half filled with water. Under each of these glass vessels was lighted charcoal, to keep the water in a state of evaporation, and under the earthen pot there was likewise fire to heat and inflame the sulphur, which was put into the pot through the opening opposite the neck. This opening, which draws in the external air for the combustion of the sulphur, was closed with a stopper, perforated like the nozzle of a garden-pot.
"The sulphur, thus inflamed, soon filled the vacant part of the glass vessels with its whitish cloudy vapour. Vegetable This vapour, meeting that of the water, combined with Substances, it, and fell in acidulous drops on the lower water, over which the vapour of the sulphur circulating for a time, does also probably combine with it to a certain point. Another proof that this condensed water did combine with the vapour of the sulphur is, that the same vapour received in drops beyond the second glass vessel by means of a recurved adopter, came out in the acid state, reddening the tincture of turmouf, and effervescing with alkalies when concentrated. I have twice repeated this experiment with success, and with scarcely any inconvenience.
"I likewise attempted to burn sulphur and heat water, in two separate vessels communicating with a third. The two vapours combining together in the receiving vessel, likewise produced by their condensation a fluid, which afforded the same indications of acidity as that of the former experiment.
"When sulphur was burned in an earthen vessel, and its vapour communicated into an earthen jar, in which water almost boiling was poured, the results were the fame.
"It is probable that if these experiments were repeated more at large, with a suitable apparatus, a longer series of glass vessels, and proper furnaces, the success would be more complete. I intend at some future time to resume this process, and shall hasten to communicate my success to the public, if success should attend my endeavours (1) *.
227. The disposal of the apparatus for the distillation of the success of this operation will depend on the goodness of the lute, it is proper to make a few remarks on this subject. The following is recommended by De Charmes (or rather M. Baumé) as a fat lute. Take any quantity of good gray or blue clay, or, what answers extremely well, fullers earth. Let it be dried in thin cakes in an oven after the bread is baked, then pounded or sifted; a certain quantity of this clay is to be mixed with a sufficient quantity of boiled linseed-oil, in an iron or bell-metal mortar, in which they must be well beaten together for a long time, so as to form a tenacious stiff paste of a uniform consistence, and perfectly free from lumps. A considerable quantity of lute is usually made at once; and, far from losing any of its tenacity by being kept, it is asserted that lute which has been made a twelvemonth, provided that it has been preserved in a cool damp place, as a cellar, and in a covered vessel, is more pliant and better than when first made. If too dry and hard, it may be easily rendered of a due consistence by being warmed and worked with the fingers, or beaten in a warm mortar.
The lute which has been used in one distillation must not be thrown away, as, with proper management, it may serve again, and is even better than before. It must be carefully freed from the burnt and hard parts, however, as these would render it crumbly.
228. "When the quantity to be mixed, or kneaded
(1) Chaptal made a great number of experiments in the large way, for the purpose of discovering the means of acidifying sulphur, without the expense of nitre; but upon the whole they were unsuccessful. Vegetable up again, is very small, the trouble of beating it in Substances, the mortar may be avoided, because the operation is performed very well, by kneading the matter with the hands. For this purpose, a portion of the lute already kneaded in the mortar, and soaked with oil, may be taken and rolled in the vessel containing the pounded and sifted earth; the portion of earth which adheres may then be worked in; and, by a repetition of this manipulation, the mals will speedily become enlarged, and must be strongly compressed, rolled out, and doubled again, until it is found that it possesses the requisite softness and tenacity, and does not crack when doubled.
"If it should happen that the lute should become too soft by excess of oil, and clay is not at hand to correct this fault, the mals will soon acquire firmness by exposing it to the open air upon parchment, or upon a plate. It must not be laid upon paper, because it is very difficult to separate this material entirely; and if any particles should remain, there would be reason to fear that, when incorporated in the mixture, they would either prevent the perfect adhesion of the lute, or would allow the passage through that kind of void or pore, which the fragments of paper would form. It is, moreover, to be remarked, that this lute cannot be too smooth and uniform. It ought not to afford any perception of inequality when it is handled, or kneaded, nor indicate the presence of foreign substances, such as sand, straw, earthy particles, &c. which are capable of preventing the intimate connexion of its parts.
"I strongly insist on the perfection of this lute, because it is the soul of distillation.
229. "Boiled linseed oil is thus made: two pounds of common linseed oil being put into a saucepan, or proper vessel, of copper, iron, or pottery, add three ounces of red litharge, finely powdered and sifted; after stirring the whole well together, place the vessel on the fire, heating it gradually, until the litharge is completely dissolved. It is necessary to stir the mixture very frequently with a wooden spatula, until the whole solution, which at first acquires a brick-dust colour, is completed; it is then to be removed from the fire, and, when cold, transferred into a stone or earthen vessel, and kept well corked. This is the boiled linseed oil above directed to be used in making the fat lute.
"When this oil, which is blackish after boiling, is well made, it congeals in the vessel as soon as it is cold. When it is required to be poured out, it may be rendered fluid by bringing it near the fire. To save the trouble of heating it, it may be poured, as soon as made, into a plate or shallow vessel, or left in the vessel used for boiling it. It is seldom necessary to heat it for the mere purpose of mixture; the quantities required for this purpose may be taken up with the fingers, or in any other manner.
"It is proper to observe, that the vessel in which the oil is boiled must be sufficiently high, to afford a space for the swelling of the fluid; for, as soon as the heat begins to act, it will rise and overflow the vessel, if particular attention be not paid to it. As soon as this process begins, the vessel must instantly be taken off the fire, and the mixture strongly agitated by plunging the spatula in it, at the same time blowing strongly at its surface with the mouth; by which means the ebullition will be checked. After this event has happened two or three times, it may with certainty be concluded, that the oil will be sufficiently confluent to form a good fat lute. By cooling, it immediately congeals, as has been remarked, to the consistence of plaster, of a black colour, inclining to brown.
230. "The lute made of linseed oil cake is thus made:
"The cake is first to be broken and pounded in an iron or bell-metal mortar, and afterwards sifted through a filken sieve: starch is then to be boiled up, to the consistence of size or glue; a small piece of this, being powdered with the flour of the oil-cake, is to be worked in a plate, or with the hands; more of the flour may then be added, and the kneading continued until the mals is absolutely without any lump, or inequality, and its consistence has become nearly the same as that of the fat lute; after which it is to be kept in a plate, or covered wooden bowl, in the cellar, for use. The same care must be taken with this, as with the fat lute, not to wrap it in paper, but in parchment, if thought necessary.
"This lute dries and hardens much on its outer surface, which remains uninjured at the place where it is applied; but it is decomposed more speedily than the fat lute, on account of its peculiar property to become hard and shrink with a strong heat. In this state, in consequence of the action of acids, it assumes a yellow colour, and is then good for nothing: it must be renewed.
"A very good lute is likewise made with equal parts of the flour of almonds, of linseed, and of starch, kneaded together. It must be understood, that the latter is to be boiled to the consistence of starch.
"To these different lutes we may add that which is composed of lime and white of egg, which has the property of acquiring a considerable degree of hardness.
"Among all these lutes, that to which I have constantly given the preference, and is always kept in sight in the present work, is the fat lute. The lute of white of egg and lime, retained by a cloth and a bandage, may be advantageously used as a covering to the fat lute.
"The fat lutes adhere very much to the hands, during the kneading or working; but it is not difficult to wash off the remains after the operation: nothing more is necessary, than to use warm water and soap, or soap leys, after having previously wiped off the greater part with blotting paper."
*Nicholson's De Charmes.
231. As the directions given by De Charmes for disposing the apparatus will, with a few modifications, apply to every case, it will be proper to give them without abridgment.
"Our distillation may be performed either in a retort, or a tubulated body or bottle. There can be no difficulty in properly placing these vessels. The junction of the neck or tube, communicating with the pneumatic vessel, is the only object which requires particular care. The manner of joining these two parts, by means of lute alone, will be explained below.
"As the use of the retort requires more attention with regard to its form, and the application of the additional part, the following details will be of use to prevent accidents.
232. "When the retorts are new, and have not be- Vegetable fore been luted to any additional part, it is advisable either to rub a small quantity of warmed wax on the parts where the lute is to be applied, that is to say, the neck of the retort, as well as the correspondent part of the additional piece, or to suffer a small quantity of starch or paste to dry upon those parts; without this precaution the lute could not be easily applied; it would slide and roll upon the glass instead of adhering.
"Care must afterwards be taken to fix round the neck of the retort a mass of lute, somewhat greater than is supposed to be necessary to fill the additional part to the place where it is to be fixed, in order that by the forcing of that piece upon the neck of the retort, the lute may extend and apply itself more intimately. The same attention must also be paid to the mass of lute, which is required to secure the beak of the additional piece in its connection with the pneumatic apparatus. These observations are of more importance, in order that the two pieces may, by this compression, be made to operate as if they formed one entire vessel.
"To apply these lutes with ease and convenience, the retort is to be held in one hand, in such a manner as that its belly or lower part may not touch or rest upon anything whatever, because the slightest blow upon this very thin part will break it.
"Before the lutes are applied, care must be taken to introduce the neck of the retort into the additional piece, and mark with lute or wax upon the additional piece the place where the extremity of the retort touches it internally; and, in like manner, on the retort itself, the place where the extremity of the additional piece touches its neck. By means of these marks it is easy to estimate the thickness of the masses of lute, by placing the two vessels near each other in the respective positions they ought to have been fixed. Lastly, they are united together by sliding the recurved additional piece upon the neck of the retort, which is to be held firmly by its neck, resting the hand on the surrounding part, if the retort is small; or holding it by the recurved part, if it be large, or the additional piece should be too long and heavy. The greatest attention must be paid not to turn the parts round, during this operation, more than is absolutely necessary to bring them together; and if this can be done without any turning at all, it will be still better, as the lute will hold more effectually. The neck of the retort must be entered into the additional piece as far as it is capable of compressing the lute, or nearly to the marks made upon the pieces before they were put together. In this situation the lute, which forms a mass round the edge of the additional piece, must be raised so as to cover both surfaces, after having first pressed it as firmly as possible into the joint; smoothing it upon the two pieces, so as to prevent the smallest opening or crack. It is advisable after all to spread a thin coating of the boiled linseed oil over the lute, which not only renders it smoother and more perfect, but by the density it acquires from evaporation it forms a kind of varnish or pellicle, which supports the lute, and prevents the fissures which might be formed during the actual operation. Whenever in the course of the work the lute should appear too dry, it must be supplied with a thin coating of oil.
"While the lute is thus spread and applied on the external part of the additional piece and the neck of the retort, the compound apparatus is to be held by the Vegetable additional piece only, and the retort left to be supported substances, ed, untouched in the air, by its insertion at the neck only.
"Instead of luting the additional piece to the retort, simply at the extremity of the neck of this last, and at the place where the wider part of that piece touches the retort, we might apply the lute upon the whole surface comprehended between those parts. But I have found that it is sufficient if these two parts be made secure. A retort luted in this manner forms one single and entire body with its additional neck; and with very little care and attention, the lute will seldom or ever have occasion to be renewed before one or two months service.
233. "The tube on which the recurved additional piece rests during the distillation, and through which the gas is introduced into the pneumatic tube, is, as I have remarked, entirely of lead. If it be not cast, it ought to be carefully joined with strong folder; and for fear this last should fail, it will be prudent to cover it with a coating of yellow wax, pitch, or melted pitch.
"That part of the tube, (if foldered as before mentioned) which passes under the lower false bottom, ought to be carefully bended with a round corner, before it is coated with the wax or pitch; and in the bending it is safer to cause the foldered part to lie within the angle. It is likewise proper to stop the mouth of the tube with paper, or a cork, during the time of waxing or tarring, in order to prevent any introduction of those substances into its cavity, taking care to withdraw this temporary stopper before the apparatus is applied to actual use. It is not absolutely necessary to coat any other part of the tube, but that which is to be placed within the pneumatic apparatus, because it is easy to stop any other part, out of which the gas might issue, with soft wax or lute.
"The extremity of this tube, in which the recurved neck of the additional piece is to be inserted, must have the form of a small funnel, not only for the purpose of affording the most convenient support, and the more ready adaption to the various sizes of those necks, but also because it more readily supports the only kind of lute which in this work we suppose to be used. This lute is never deranged, if care be taken to press it against the internal surfaces of this small funnel, and of the glass or lead of the additional piece, so as to unite them as much as possible, it being always understood that the lute is good, and suffices the properties before described in treating of that substance.
234. "I have remarked, that the use of the retort with its additional neck might be dispensed with, by simply using a body or bottle with a neck (even a wine bottle may be used in case of necessity, provided its bottom be either very thin, or very gradually heated). In the orifice of the neck of these vessels, is to be adapted a tube of lead, properly bended, and of a due size. This method is in fact very advantageous and economical; but care must be taken to join the tube, if it be of sheet-lead, particularly in the parts below the bottle which are liable to become heated, a short time before the end of the distillation; to join it I say, without folder, by fusing the two edges together. For in process of time the folder, though ever so strong, yet. Vegetable yet because it contains tin, is liable to excessive corrosion by the oxygenated muratic acid, which, notwithstanding its heat, is not found to attack lead in any perceptible degree.
"But it may, perhaps, be more convenient to cast such a tube at one heat, as well as the additional piece in the apparatus, with the retort; unless, indeed, it should be practicable to have it made of stone-ware or porcelain, the latter of which is the least permeable to the gas. Or we might, with more advantage, make use of a thick tube of common glass, which might be easily bended in a charcoal fire, and might be adapted to the tubulated bottle, as well as the leaden tube. But the danger of its breaking, and the difficulty of procuring others in case of need, together with the expense, have led me to reject this, as well as the tubes of pottery or porcelain.
"In order that the tube adapted to the neck of the bottle may accurately fit, and prevent all escape of the oxygenated muratic acid, it is defended by lute in such a manner, that it shall not be thrust into the neck of the bottle, without extruding a portion of that substance; and a border of luting must then be applied round the place of junction, which will effectually prevent the escape of any vapour which might issue through the first luting. Lastly, the whole surface of this external luting is to be smeared with boiled linseed oil; after which the distillatory apparatus may be considered as perfectly secure.
"If a tube of glass be used, it may be so adapted by grinding with emery as to fit the neck of the glass body, and require no luting. The same might be done with a tube of porcelain, if the material were sufficiently fine.
235. "With regard to the other neck which I have recommended, as well in the bottle as in the retort, it serves not only to introduce the materials when the leaden tube is previously luted in, but likewise to admit the external air, if by chance an absorption should be perceived to take place; that is to say, if the water, by diminution of the heat, which leaves a kind of vacuum, should rise from the pneumatic apparatus into the body: though even in this case there would be no reason to fear its breaking, notwithstanding its being considerably heated, as at the end of the operation. I have expressly made the trial several times, and always without any accident. The fluid becomes gradually heated in its passage along the sides of the tube or neck of the distilling apparatus, before it enters and mixes with the matter in the body itself; and again, if the tubulated bottle and tube be made use of, the water rising through the latter, and falling in the middle of that contained in the vessel, cannot directly touch the sides before it becomes mixed. But, at all events, if the smallest absorption be feared, it will be sufficient to raise the stopper, and return it to its place the instant after the introduction of the atmospheric air. Instead of a glass stopper, a cork may be used, which must be carefully luted round the neck, if there be any reason to think that the vapour should find its way through, in consequence of the neck being perfectly round.
236. "With regard to the pneumatic vessel, the following is the method of placing and fixing the false bottoms:
"A common wooden hoop is plained flat on the side which is to bear the false bottom, and fixed within the cask with pegs which do not pass quite through the staves. The false bottom, secured together by two dove-tails is placed upon this hoop, and fixed there by similar pegs, which penetrate part of the bottom itself, and by that means prevent it from either rising or turning. The cavities between the false bottom and the sides are then to be closed round with caulkers stuff (brai fisc), or melted pitch. It must be remembered, that the vertical axis with its crois-arms is to be placed beneath each false bottom. The arms are fixed in a mortice by means of two pins, which prevent them from vibrating or getting loose. The leaden pipe in which the extremity of the additional neck is to be inserted, is not to be put into its place till the first false bottom is immovably fixed. A notch is supposed to have been cut in this bottom to admit the tube; and when it is duly placed, the vacant space is to be made good, first with tow and then with melted pitch.
"Instead of the wooden hoop, which affords a solid support for the false bottom, it may answer the purpose very well, if cleats or blocks of wood, three inches thick, be pinned on, at different parts of the circumference; or, which is still better, if the trouble be taken to fit the false bottom so well, that it may bear firmly upon the inclination of the staves, which naturally oppose its descent. This method would certainly be the quickest, and is not very difficult to be done.
"When the false bottom is thus fixed, it must be retained in its place by pins placed at certain distances, and afterwards made tight by caulking.
"In order that the tube may not be exposed to vary in its position, a mark must be made on the edge of the funnel which terminates one of its extremities, by which it is easy to ascertain the position of the bended part below, and place the fame in the most favourable situation. It will be convenient to fix the pipe in this proper situation, by means of two pegs, which must be drawn out previous to the last fixing of the false bottoms.
237. "When the first or lowest false bottom is secured in its place, the second arm of the agitator is to be fastened to the axis, and the other false bottom is to be placed and made fast in the same manner as the first.
"It is particularly necessary to place these two partitions in such a manner, as that the holes of communication may not be in the same vertical line, but as far as possible from each other; that is to say, diametrically opposite. This disposition is necessary in order that the gas may have time to concentrate in one part, before it escapes to the other. For the same reason, it is proper to direct the lower opening of the leaden tube to that extremity of the diameter which is opposite the pipe of communication from the first to the second bottom, in case one distilling vessel only is used. If two or more communicate with each pneumatic apparatus, the openings of the tubes must be respectively disposed at equal distances, as far as possible from each other, and from the opening in the false bottom next above them.
"If instead of false bottoms the preference should Vegetable be given to inverted tubs (cuvettes), the following method may be used to make the rims or sides, and to fix them immovably.
"The rim may be made in two ways; either by short staves, fixed with wooden hoops as usual, scarfed or hooked together at their two extremities, or else, by simply fixing a broad wooden rim, like that of a sieve, round the bottom of this inverted vessel, by means of small wooden pins with heads.
"Both these methods are good. The second has the advantage of taking less room and being cheaper. If this method be used, the point of the pins must be made a little thicker than the item, in order that they may be less disposed to draw out of the holes bored in the bottom. With regard to the joining of the two ends of this kind of broad hoop, it may be effected very firmly by sewing them together with a flat strip of oifer, as is done in the better sort of chip boxes, or it may be very well managed by means of two pins with heads, which may be driven through the overlapping part, and secured at the other side by driving a small wedge into the tail of each pin. With regard to the empty spaces or openings which may be between the rim and its bottom, they must be stopped with glaziers putty (mastic du vitrier), which may be smoothed with oil. This putty is of excellent service when the muriatic acid is used without potsals; but it is soon destroyed if potsals be put into the pneumatic vessel. In this case the internal part of the places of junction must be pitched or caulked, as has been already shewn.
"The method of making these inverted vessels with staves and hoops, has the advantage of being close, and not requiring any particular caulking.
238. "Lastly, Instead of these inverted vessels, the operation may be performed merely by flat boards without rims, provided, however, that the upper board be some inches broader on every side than the lower, in order that the bubbles of gas may be forced in their ascent to strike each board in succession, and remain for a short time in contact with it. The essential circumstance in this arrangement will be to keep the upper part of the vessel well closed, which is to be defended at the hole which admits the axis of the agitator by a central tube to retain the gas; and the partial escape which might take place between that axis and the covering, must be more effectually prevented by a cloth soaked in alkaline leys. This method, besides its convenience, requires less care in fixing, but it renders it necessary to work the agitator more frequently, in order to hasten the absorption of the gas in the water. I have determined to relate all the methods which I have successfully practised, in order that those who may undertake any work of this nature, may determine for themselves, not only with regard to general motives of preference, but likewise the facility with which their own situation or circumstances may enable them to carry the same into execution.
239. "The next object is to fix these inverted vessels in the pneumatic apparatus. This is a very simple operation, and consists merely in fixing pieces of wood or brackets, three inches in length, under each of the two bars which connect the pieces of the bottoms of the inverted vessels together. The bracket pieces are fastened to the side of the vessel with oak pegs, and the cross-bars which rest upon them are secured by pins of the same material driven above them and on each side, in such a manner that the central perforation is in its true place, and the whole is incapable of being removed or disturbed.
"In this operation, as I have already recommended with regard to the false bottoms, it is advisable to place the revolving axis in its proper situation, in order to ascertain that it is not likely to be impeded in its action. It is best, indeed, to avoid fixing either the two inverted vessels or the two false bottoms, if these be used, until the clear movement of the agitator has been ascertained; without which precaution, there might probably be occasion to displace them, either in whole, or in part, to remove the impediments which might prevent the free motion of these parts.
"From the description I have here given, it may be seen that my pneumatic vessels have only two false bottoms or inverted vessels. I think it advisable not to use more, because I have remarked that three of these vessels requiring a greater depth, the distillation became much more laborious, particularly when I made use of the intermediate apparatus. 1. The lutes did not so well resist the pressure of the vapour. 2. It was not disengaged with the same speed, and consequently the operation was more tedious. It is better, therefore, to use shallower vessels, and enlarge their dimensions in the diametral direction, as I have constantly found. The proportions which have appeared to me to be advantageous for a small common workshop, are 1 1/2 foot in height, 32 inches in diameter below, and 36 inches diameter above, all inside measure.
240. "With regard to the kind of wood for constructing the vessels, it has appeared to me to be almost a matter of indifference, I used fir, oak, and chestnut, without observing that either the one or the other was productive of any inconvenience to the quality or clearness of the liquor, unless that, at the first or second distillation, the degree of force was a little altered, by soaking into the wood. That kind of wood may, therefore, be used which can the most readily be procured. I must, however, observe, that the large casks in which oil is brought from Languedoc, which are mostly made of chestnut-tree, are very convenient when cut in two to form the pneumatic vessels. They have even an advantage over the oak and fir casks, because they are closer in the joints, better hoop'd with iron and wooden hoops, and impregnated with the oil, in consequence of which they are not subject to become dry, how long soever they may be out of use, provided they are kept in a close place; whereas the tubs of fir wood require to be almost constantly filled with water. Oak does not contract so soon as fir.
"It must also be observed that the white deal must not be used, because it transmits water like a sponge. The yellow deal is to be preferred, because it undergoes less alteration from the fluid, no doubt on account of the resin it contains. But if the use of the white deal, or any other spongy wood cannot be avoided, it will be proper to paint the vessel within and without with one or two good coatings of white lead. I have had the great satisfaction to observe, that this treatment not only prevents the water from passing through, but likewise that the oxygenated muriatic Vegetable acid does not attack this colour, or, if it does attack it, substances, a long course of time must be required for that purpose. Melted pitch or tar likewise afford a good defence for such wooden materials as have this defect. A mixture of yellow wax and resin is likewise of excellent service as a coating for the whole internal surface of the pneumatic vessel, including the inverted vessels and the agitator.
241. "Besides the false bottoms, or inverted vessels we have described, each apparatus must likewise have its cover chamfered, to fit the circumference, with apertures to admit the tubes and the central axis; together with two others, namely, one of considerable size, to receive a funnel through which water is poured as occasion requires, and the other smaller, to be opened on such occasions, in order that the air may escape. The cover being nailed, or rather fastened with wooden pins, in its place, is afterwards secured by gluing slips of paper over the line where it is applied to the vessel.
"Instead of the wooden pneumatic vessel, it might be more advantageous to use similar vessels of gritstone (gres), rolled or cast lead, or cement of loiriot (K). Manufacturers must form an estimate of the advantages to be derived from the expenses they incur. If leaden vessels be used, it will be proper to defend the soldered places with one or more coats of white lead, or putty, or resin, or pitch mixed with beeswax. I have tried these preservatives against the destruction of the solder, and found them answer very well.
242. "As it is useful to possess a knowledge of the height and quantity of water contained in the tub, there is a tube of glass fixed against its outer side, the lower end of which is bended and enters the vessel about five or fix inches from its bottom. This part, into which the tube is stuck by firm pressure, is to be previously defended by lute, which is afterwards trimmed and laid smooth upon the sides of the tube and the vessel.
"Lastly, As it is essentially necessary to ascertain, from time to time, the strength of the liquor, and to draw it off upon occasion, I have usually availed myself of a brass cock, covered with several coatings of white lead for this purpose. By means of this cock, it is easy to draw off any small quantity of the fluid at pleasure. It has likewise the advantage of readily filling the narrow-mouthed stone-ware or glass vessels, in which the liquor may be kept when there may be any to spare, or in case it is thought fit to preserve a quantity always in readiness.
"When it is required to draw off the acidulated water with speed and in abundance, it is convenient to use one or more wooden tubes or spigots, which may be opened separately, or all at once, into appropriate vessels. But it is most convenient that they should have stoppers of cork only, because those of wood, vegetable though covered with tow, are very apt to burst the substances, wooden tubes by their swelling; besides which they very seldom fit with accuracy, unless turned with extraordinary care.
243. "With regard to the intermediate vessels mentioned in the Annales de Chimie, in case the operator is determined to use them, it is proper to avoid using stoppers of cork to close the orifices, and support the tubes at the same time. For this substance being very speedily acted upon by the corrosive gas, expolos the lutes and closures to frequent derangement, as well as the tubes which pass through them. At the beginning of my operations, I supplied the place of these stoppers as follows, when the necks were of a larger diameter than the tubes. I made stoppers of glass, with flanges on the sides. These were ground with emery upon the necks themselves, and they were perforated quite through with a hole, no larger than was proper to admit the passage of a glass or leaden tube. This tube was coated with lute of sufficient thickness, that it could not pass through the hole without forming a protuberant piece, which I pressed and smoothed against the tube as well as the orifice. Or if the stoppers of cork should, nevertheless, from convenience be chosen, the necks may be covered with lute, and the stoppers forced in. In case the interval be small, the parts may be heated a little, covered with virgin-wax, and then forced into the neck, and the small vacancies which may remain may be filled up with the same wax, melted and poured out of a spoon. Instead of lute, yellow wax may also be used to fix the tube of safety; and the same operation may be performed with regard to the glass or leaden tube, which communicates from the tube to the intermediate vessel. Stoppers and tubes luted in this manner, are, in some measure, fixed for ever; for when the wax is once hardened, they are in no further danger.
244. "If the operator be so situated, that he can order the intermediate vessels of whatever form he chooses, it will be advisable to have the orifices of no greater diameter than just to suffer the tubes to pass through. No other defence will then be necessary, than that they should be covered with lute at the time of placing them, which will render them sufficiently firm. The rim, or border of these orifices, ought likewise to be large enough to support the mass of lute which it is proper to apply round the tube."* Nichol- son's De Charmes.
245. Having adjusted the several parts of the apparatus, we proceed to prepare for the distillation, by filling the pneumatic tub with water, or such fluid as it is intended should be impregnated with the gas, and introducing the materials into the distilling vessels.
The cover of the tub is first to be properly secured by pegs and slips of paper, pasted over the joinings. The tub is then (if not done before) to be filled to within
*(K) The author does not appear to speak from experience in this place. It is not probable that any manufacturer would be tempted to incur the expense of stone vessels; but it is nevertheless proper to remark, that every stone which could with facility be wrought, contains lime or clay, or both; the former of which would no doubt be speedily corroded by the liquor, on which it would also have a pernicious effect. It is not likely that clay would be more durable. So that on the whole there is no temptation to use, and many reasons to reject, the earths. Vegetable within an inch and a half of the top, with soft water. Substances. Care must be taken to leave open the orifice, by which the air may be allowed to escape on pouring in the water, as, were this close, the water would infinuate itself under the paper, and destroy the luting.
The distilling vessels are now to be placed in the capsules, or the vellies of water, and firmly secured. De Charmes directs the mixture of manganese and muriat of soda to be introduced at this time; but perhaps it would be better to have this ready done before fixing the vessels, and then nothing remains, but to add the sulphuric acid, which is best done by means of the crooked funnel. This being done, the stoppers are to be well secured, and the various jointures clofed up with lute, where this has not been done before.
246. All these steps (except the addition of the acid) should be executed the evening before the distillation; and the next morning, the acid just distilled may be added, if the leaden alembics are used, but if glass retorts or bottles be employed, it is safer to allow the acid to cool before it is poured in.
"If the acid has been poured in warm, and the muriat is very dry, and well mixed, the sulphuric acid not more diluted than has been prescribed, and the manganese of a good quality, bubbles of air will be heard to pass into the wooden vessel, through the leaden tube, at the end of two or three minutes. If the above requisites be wanting, the escape will not take place till somewhat more than a quarter of an hour. In either case it is necessary, a few infants after the pouring of the acid, to place a chafing dish with lighted charcoal beneath the vessel which holds the retort.
247. "About half an hour after the pouring of the acid, a considerable effervescence takes place, which sometimes swells the materials as high as the neck of the retort, if this last be too small for its charge. The bubbles of the froth are large, and covered with a kind of pellicle, formed by a portion of the mixture carried up during the agitation. This intumescence lasts about two hours, during which time the bubbles of oxygenated muriatic acid gas are most abundantly engaged in the water. They even succeed with such rapidity, that the intervals are not distinguishable, and an incessant noise is heard in the pneumatic vessel, which very often lasts three or four hours, according to the management of the fire, and the goodness and accurate mixture of the materials. The agitation produced by this rapid escape is commonly such, that it is scarcely necessary to move the agitator.
"The fire is not to be renewed till the expiration of two hours, even though it may have gone out in the mean time. After this, it is not to be renewed till the end of an hour and a half, and after that period, at the end of an hour, and so forth, without any perceptible increase of its intensity. It will be sufficient after these periods to keep up the fire, excepting that during the last two hours the fire must be maintained without suffering the charcoal to be almost burned away, as in the former cases, before it is renewed. The chafing dish must be raised upon bricks, to bring it nearer the retort, during the last hour. I must observe, with regard to this chafing dish, that the grate must not be too open, lest the charcoal should be too rapidly consumed. After the intumescence of the mixture has ceased, the rapid escape of bubbles does not diminish for a long time, in consequence of an effervescence which constantly proceeds. It is true that this continually diminishes, and towards the end of the distillation the bubbles which pass into the tube appear only at intervals, notwithstanding the matter in the retort may, by the gradual augmentation of the heat, be brought into the state of ebullition. The heat is such, that eight or nine hours after the commencement of the operation, the hand can scarcely be endured near the aperture, or the neck of the retort, or other distillatory vessel, though between the fourth and sixth hours the same parts are scarcely warm. The distillation of one or more retorts or bodies into a single vessel, according to the doses before mentioned, takes usually eleven or twelve hours, and even less; the time for stopping the distillation is known from the escape of the bubbles being very slow, and the noise less perceptible. This flight noise is even a mark to form a judgment of the concentration of the gas, and the degree of saturation of the water. In order to hear the bubbles, it is often necessary to apply the ear against the tub. Moreover, the adopter of the retort begins to be heated, and the lute upon its neck becomes a little softened. Another indication that the process is near its termination is had from the long vibrations of the water in the indicatory tube, placed on the outside of the tub, and likewise in the tube of safety, when an intermediate vessel is used.
248. "If a proper regard be not paid to the signs here enumerated, and the distillation be not stopped, there will not only be a loss of time and fuel, and a distillation of mere water; but the steam, when an intermediate vessel is used, will drive the water through the tube of safety, and itself immediately follow, if not instantly remedied by diminishing or removing the fire, and cooling the neck of the retort and its adopter with a wet cloth, or, which is better, by drawing the proper of the retort for an instant.
"As soon as the distillation is stopped, the impregnated fluid of the pneumatic vessel is to be drawn off into tubs or other vessels, proper to receive the goods which are previously disposed therein. If it be not convenient to use it immediately, the liquor may be left in the tub without fear of any perceptible diminution of its virtue, provided the cover and its joinings be well closed with lute and stripes of paper pasted on, and likewise that the space between the axis of the agitator and the cover be similarly secured. It may likewise be drawn off in floneware bottles well closed with corks, covered with lute at the place of their contact. In this manner the liquid may be preserved till wanted. I have kept it for several months without its goodness having been impaired.
249. "I must observe in this place, that if it be wished that the liquor at the upper part of the vessel should be equal in strength to that of the lower, without regarding the distillation (which may be uselessly prolonged for upwards of twenty-four hours, by an effect of the concentration of the gas in the bottom of the vessel, and the resistance it then opposes to its introduction, which singularly contributes to increase the heat of the retort); I have found no better method than that of drawing off the liquor, either into earthen pitchers or vessels filled with merchandise ready for immersion. I have done this after a limited Vegetable time, and repeated proofs of the good quality of the Substances fluid. At the end of eight hours distillation, I drew off one-fourth of the contents of the vessel; a second fourth two hours afterwards; a third fourth after ten hours and a half, or eleven hours; and the rest after twelve hours distillation, which formed the conclusion.
"When the liquor is entirely drawn off from the vessel, it must again be immediately filled with water, or at least to the height of five or fix inches above the return of the leaden tube, otherwise the gas, which continues to escape from the distilling vessel and then affords no resistance, might attack the pneumatic vessel itself.
250. "The fire must be taken from beneath the retort as soon as the distillation is finished, not only to prevent the effect of the gaseous vapours, which still continue flowly to escape, from acting on the sides of the tub, but likewise to dispoze the retorts or bodies to receive a quantity of warm water, which is to be poured in up to the neck. There is no reason to fear an excess of quantity, and the hotter the vessels are, the better. It is essential, however, that it be not poured in cold, for fear of breaking the glass. The adopter is then to be unlooted from the neck of the leaden tube, if the operator chooses; and in order that no vapour may escape into the workshop, a bit of lute or a cork may be applied to the beak of the adopter. The sand bath easily permits the retort to be raised and returned again to its place, as well as the application of the lute or stopper to the neck of the adopter, this last being raised with one hand while the cork is put in with the other.
"Nevertheless, as the lutes which connect the adopter with the retort are somewhat softened towards the end of the operation, it would be more prudent to leave every thing in its place, for fear of deranging those lutes. This danger is greater when the adopter is of lead, because the great length of this additional piece tends to force the luting still more on that account. If it be required to proceed immediately to a new distillation, the retort or bottle with its capsule or pan must be immediately taken from the furnace, and another substituted in its place ready prepared during the former distillation. This necessarily requires a double set of vessels.
251. "When the distilling vessel is cold, or nearly so, the whole of its contents must be shaken, by holding this vessel by the neck with one hand, and applying the other to its bottom. The stopper must then be taken out, and the vessel speedily inverted, shaking the residue to facilitate its escape. In this last situation the retort is to be held by the neck with one hand, and its side gently resting against the other. The vessels into which the water and residual matter of the retorts are poured, should rather be of stoneware, pottery, or lead, than of wood, unless these last be oil vessels, which are less subject to dry in the part above the fluid. If this circumstance be not attended to, there will be danger of losing great part of the contents.
"It is most convenient to disengage the retorts or bodies while they are still warm, which continues to be the case the next morning after distillation, in consequence of the heat of the sand bath. If they be left to cool entirely, the sulphate of soda will crystallize, and it will be necessary to dissolve in hot water such larger portions as cannot pass through the neck. But vegetable this inconvenience is not likely to happen, unless the substances quantity of water last added be too small, and the residues have been left undisturbed for several days. The same observation is applicable to that kind of incrustation which is formed by the muriat, if not properly pulverized, dried, or mixed; this cannot be separated from the bottom of the retort, but by means of hot water poured at different successive times. It is likewise essential to leave no crust or deposition of muriat, or other matter, in the vessels which are emptied, unless the same be moveable, in which case the risk is less. But if the urgency of business should then require that the same vessels be used without entirely clearing them, it will be necessary to range this residual matter on one side, where it will be less exposed to the heat, and will afford a greater degree of facility for the nitric acid to act upon it.
"In order that the vapour which exhales from the distilling vessels may not prove inconvenient, it is necessary to pour in a small quantity of alkaline lixivium in the first place, which instantly destroys the smell. This may be done immediately after the end of the distillation, and the weak alkaline solution may supply the place of the water used for diluting the residues. At the instant of pouring this lixivial water, a strong effervescence takes place; for which reason it is proper to pour it in by several successive portions, waiting a little between each time.*"
252. The oxygenated liquor prepared in this way is very effectual in bleaching the stuffs which are immersed in it; but at the same time possesses an odour so suffocating as to render its use unpleasant and even injurious to the workmen employed in the process, should any of it escape. "I have witnessed, (says O'Reilly) in an extensive manufactory near Paris, the cruel sufferings experienced by the wretched workmen, from these suffocating vapours; I have seen them rolling on the ground in the excess of agony. Frequently even severe disorders are the consequence of the first effects produced by the oxygenated liquor." De f O'Reilly Charmes gives a long account of the sufferings which Eiffai he underwent in his course of experiments with this acid. It produces symptoms completely resembling those of a violent cold, but which go off in a day or two after having desisted from the use of the liquor.
This inconvenience may be avoided in two ways: 1. By rendering the vessels for immersion so tight as to prevent the possibility of the escape of the gas. 2. By diffusing in the water some substance which has the property of so far neutralizing the acid as to correct its odour, without destroying its bleaching quality to any considerable degree.
253. Mr Rupp of Manchester contrived a tub for immersion, which is admirably adapted to answer the first purpose. Its construction is simple, and not expensive.
"It would therefore, be desirable to have an apparatus for the use of the pure oxygenated muriatic acid simply diffused in water, which is at once the cheapest and best vehicle for it. This apparatus must be simple in its construction, and obtainable at a moderate expense; it must confine the liquor in such a manner as to prevent the escape of the oxygenated muriatic acid gas, which is not only a loss of power, but also an inconvenience Part II.
Vegetable nience to the workmen and dangerous to their health; Substances, and it must, at the same time, be so contrived, that every part of the stuff which is confined in it, shall certainly and necessarily be exposed to the action of the liquor in regular succession. Having invented an apparatus capable of fulfilling all these conditions, I have the pleasure of submitting a description of it to the society, by means of the annexed drawing.
Plate XCI. "Fig. 4, is a section of the apparatus. It consists of an oblong deal cistern, ABCD, made water-tight. A rib, EE, of ash or beech wood, is firmly fixed to the middle of the bottom CD, being mortised into the ends of the cistern. This rib is provided with holes, at FF, in which two perpendicular axes are to turn. The lid, AB, has a rim, GG, which sinks and fits into the cistern. Two tubes, HH, are fixed into the lid, their centres being perpendicularly over the centres of the sockets, FF, when the lid is upon the cistern. At I, is a tube by which the liquor is introduced into the apparatus. As it is necessary that the space within the rim, GG, be air-tight, its joints to the lid, and the joints of the tubes, must be very close; and, if necessary, secured with pitch. Two perpendicular axes, KL, made of ash or beech wood, pass through the tubes, HH, and rest in the sockets, FF. A piece of strong canvas, M, is sewed very tight round the axis K, one end of it projecting from the axis. The other axis is provided with a similar piece of canvas, N, pieces of cloth rolled upon the axis L. Two plain pulleys, OO, are fixed to the axes, in order to prevent the cloth from slipping down. The shafts are turned by a moveable handle, P. Q, a moveable pulley, round which passes the cord, R. This cord, which is fastened on the opposite side of the lid (see fig. iv.), and passes over the small pulley S, produces friction by means of the weight T. By the spigot and faucet V, the liquor is let off, when exhausted.
"Fig. iv. A plan of the apparatus, with the lid taken off.
"The dimensions of this apparatus are calculated for the purpose of bleaching twelve or fifteen pieces of 4 calicoes, or any other stuffs of equal breadth and substance. When the goods are ready for bleaching, the axis, L, is placed on a frame in the horizontal position, and one of the pieces, N, being fastened to the canvas, M, by means of wooden skewers, in the manner represented in fig. 4, it is rolled upon the axis by turning it with the handle, P. This operation must be performed by two persons; the one turning the axis and the other directing the piece, which must be rolled on very tight and very even. When the first piece is on the axis, the next piece is fastened to the end of it by skewers, and wound on in the same manner as the first. The same method is pursued till all the pieces are wound upon the axis. The end of the last piece is then fastened to the canvas of the axis K. Both axes are afterwards placed into the cistern, with their ends in the sockets FF, and the lid is put on the cistern by passing the axes through the tubes HH. The handle P is put upon the empty axis, and the pulley Q upon the axis on which the cloth is rolled, and the cord R, with the weight T, is put round it and over the pulley S. The use of the friction, produced by this weight, is to make the cloth wind tight upon the other axis. But as the effect of the weight will increase as one cylinder increases and the other lessens, I recommend that three or four weights be fupended on the cord, which may be taken off gradually, as the person who works the machine may find it convenient. As the weights hang in open hooks, which are fastened to the cord, it will be little or no trouble to put them on and to remove them.
"Things being thus disposed, the bleaching liquor is to be transferred from the vessels in which it has been prepared into the apparatus, by a moveable tube passing through the tube I, and descending to the bottom of the cistern. This tube being connected with the vessels, by means of leaden or wood pipes provided with cocks, hardly any vapours will escape in the transfer. When the apparatus is filled up to the line a, the moveable tube is to be withdrawn, and the tube I closed. As the liquor rises above the edge of the rim G, and above the tubes HH, it is evident that no evaporation can take place, except where the rim does not apply closely to the sides of the box: which will, however, form a very trifling surface, if the carpenter's work be decently done. The cloth is now to be wound from the axis L upon the axis K, by turning this; and when this is accomplished, the handle P and pulley Q are to be changed, and the cloth is to be wound back upon the axis L. This operation is, of course, to be repeated as often as necessary. It is plain, that, by this process of winding the cloth from one axis upon the other, every part of it is exposed, in the most complete manner, to the action of the liquor in which it is immersed. It will be necessary to turn, at first, very briskly, not only because the liquor is then the strongest, but also because it requires a number of revolutions, when the axis is bare, to move a certain length of cloth in a given time, though this may be performed by a single revolution when the axis is filled. Experience must teach how long the goods are to be worked; nor can any rule be given respecting the quantity and strength of the liquor, in order to bleach a certain number of pieces. An intelligent workman will soon attain a sufficient knowledge of these points. It is hardly necessary to observe, that, if the liquor should retain any strength after a set of pieces are bleached with it, it may again be employed for another set.
"With a few alterations, this apparatus might be made applicable to the bleaching of yarn. If, for instance, the pulley O were removed from the end of the axis K, and fixed immediately under the tube H; if it were perforated in all directions, and tapes or strings passed through the holes, skeins of yarn might be tied to these tapes underneath the pulley, so as to hang down towards the bottom of the box. The apparatus being afterwards filled with bleaching liquor and the axis turned, the motion would cause every thread to be acted upon by the liquor. Several axes might thus be turned in the same box, and being connected with each other by pulleys, they might all be worked by one person at the same time; and as all would turn the same way and with the same speed, the skeins could not possibly entangle each other*."
254. As far as respects the confinement of the gas, this apparatus of Mr Rupp is extremely well contri- Vegetable ved, but in his method of rolling up the stuffs, there is an inconvenience which M. O'Reilly has corrected. The inconvenience arises from the axis being vertical, as when several pieces are rolled upon the same axis, some parts of them are liable to sway down, and thus render the action of the bleaching liquor unequal. He proposes to remedy this inconvenience by making the axis horizontal, and to make the passage of the stuff through the liquor more complete, he places a roller at each end of the vessel, above and below, and three others in the middle, as will be explained when we describe the apparatus.
255. Soon after the appearance of Berthollet's paper in the Annales de Chimie, it was proposed to employ the oxygenated muriatic acid, in the flate of gas applied immediately to the cloths previously moistened, and we believe that it has been so employed by some bleachers. We are, however, disposed to consider the method as highly injurious to cloth so bleached, although the danger to the workmen might be avoided, by the use of the immerging vessel above described.
256. In employing the simple oxygenated liquor, it is of consequence to possess some criterion, by which we may ascertain its comparative strength. The method contrived by M. Defcroizilles has been described in paragraph 259. Mr Rupp has improved on this, by employing the acetite of indigo, prepared by pouring acetite of lead (sugar of lead) into a solution of indigo in sulphuric acid, as long as any precipitate appeared.
257. The second means of avoiding the unpleasant effects of the suffocating gas, we have said, consist in diffusing in the water through which the gas is passed, some substance which is capable of mixing with, and correcting it.
Two substances may be employed with this view, potash and lime.
258. When potash is employed, a quarter of a pound of the common potash purified as directed in 165, is to be used for every pound of muriat of soda introduced into the distilling apparatus. This is to be diffused in the water with which the pneumatic tub is filled. It is most convenient to dissolve the potash in a small quantity of water, and add the solution to the water in the tub, but care must be taken to stir them well together with the agitator, that the potash may be equally combined with the water.
But, although this weak solution of potash certainly renders the bleaching process much less inconvenient to the workmen employed, it is yet much more expensive than the simple oxygenated liquor, and more of it is necessary to perform the same work than is required of this latter. Mr Rupp has completely proved this by a set of ingenious experiments which he made, comparing the quantity of colouring matter in the acetite of indigo, and in an infusion of cochineal, destroyed by the same quantity of the two liquors. His experiments are highly interesting, and are thus related by himself.
"Experiment I.—To half an ounce of oxygenated muriatic acid, I added a solution of indigo in acetous acid (1), drop by drop, till the oxygenated acid ceased to destroy any more colour. It destroyed the colour of 160 grains of the acetite of indigo.
"Experiment II.—A repetition of Experiment I. The colour of 165 grains of acetite of indigo was destroyed in this experiment.
"Experiment III.—A repetition of Experiments I. and II. The colour of 160 grains of the acetite was destroyed.
"Experiment IV.—To half an ounce of the oxygenated muriatic acid, were added eight drops of pure potash in a liquid state. This quantity of alkali was about sufficient to deprive the acid of its noxious odour. This mixture destroyed the colour of 150 grains of the acetite of indigo.
"Experiment V.—A repetition of Experiment IV. The colour of 145 grains of the acetite was destroyed.
"Experiment VI.—To half an ounce of the oxygenated muriatic acid, ten drops of the same alkali were added. It destroyed the colour of 125 grains of the acetite of indigo.
"Experiment VII.—A mixture of half an ounce of the oxygenated acid, and 15 drops of the alkali, destroyed the colour of 120 grains of the acetite of indigo.
"Though I had taken the precaution of avoiding the sulphuric acid, for the reason stated in the foregoing note, I was not quite satisfied with these experiments, on account of errors which might have taken place through a double affinity. I therefore made the following experiment, in which I employed a decoction of cochineal in water, instead of the acetite of indigo.
"Experiment VIII.—To half an ounce of the oxygenated muriatic acid, a decoction of cochineal was added till the acid ceased to act on its colour. It destroyed the colour of 390 grains of the decoction.
"Experiment IX.—A repetition of Experiment VIII. The colour of 385 grains of the decoction was destroyed in this experiment.
"Experiment X.—To half an ounce of the acid, fix drops of the liquid alkali were added. This mixture destroyed the colour of 315 grains of the decoction.
"Experiment XI.—Eight drops of the alkali were mixed with half an ounce of the acid. This mixture destroyed the colour of 305 grains of the decoction.
In order to shew the usefulness of this apparatus still more clearly, I request the society to attend to the following statement of the expense of a given quantity of bleaching liquor, with and without alkali, but of equal strength.
With
(l) It has been usual to estimate the strength of the oxygenated muriatic acid by a solution of indigo in sulphuric acid. This method was inadmissible in these experiments on the comparative strength of the bleaching liquor, with and without alkali; because the sulphuric acid would have decomposed the muriat of potash, and thereby produced errors. I therefore added to a solution of indigo in sulphuric acid, after it had been diluted with water, acetite of lead, till the sulphuric acid was precipitated with the lead. The indigo remained dissolved in the acetous acid. Part II.
Vegetable Substances.
With Alkali (M).
<table> <tr> <th></th> <th>L.</th> <th>s.</th> <th>d.</th> </tr> <tr> <td>80 lb. of salt, at 1 d. per lb.</td> <td>0</td> <td>10</td> <td>0</td> </tr> <tr> <td>60 lb. of oil of vitriol, at 6½d. per lb.</td> <td>1</td> <td>12</td> <td>6</td> </tr> <tr> <td>30 lb. of manganese,</td> <td>0</td> <td>2</td> <td>6</td> </tr> <tr> <td>20 lb. of pearl-ashes, at 6d. per lb.</td> <td>0</td> <td>10</td> <td>0</td> </tr> <tr> <td colspan="4">L. 2 15 0</td> </tr> </table>
But it appears, by the foregoing experiments, that the liquor loses strength by an addition of alkali. The value of this loss, which on an average amounts to 15 per cent. must be added to the expense,
<table> <tr> <th></th> <th>L.</th> <th>s.</th> <th>d.</th> </tr> <tr> <td></td> <td>0</td> <td>8</td> <td>3</td> </tr> <tr> <td colspan="4">L. 3 3 3</td> </tr> </table>
Without Alkali.
<table> <tr> <th></th> <th>L.</th> <th>s.</th> <th>d.</th> </tr> <tr> <td>80 lb. of salt,</td> <td>0</td> <td>10</td> <td>0</td> </tr> <tr> <td>60 lb. of oil of vitriol,</td> <td>1</td> <td>12</td> <td>6</td> </tr> <tr> <td>30 lb. of manganese,</td> <td>0</td> <td>2</td> <td>6</td> </tr> <tr> <td colspan="4">L. 2 5 0</td> </tr> </table>
"It appears from this calculation, that a certain quantity of the liquor, for the use of my apparatus, costs only 2l. 5s. but that the same quantity of the alkaline liquor costs 3l. 3s. 3d. which is 40 per cent. more than the other. The aggregate of so considerable a saving must form a large sum in the extensive manufactures of this country*."
*Mancheff. 259. Indeed, that the addition of potash should diminish the bleaching power of the oxygenated muriatic acid might easily be inferred, from knowing that the oxygenated muriat of potash, or rather the hyperoxygenated muriat of potash, does not in any degree possess the power of destroying vegetable colours, and consequently, the more completely the acid is saturated with the potash, the more completely is its bleaching power destroyed.
260. The method of employing lime in correcting the oxygenated acid was first used in Ireland; and some years ago, there were not less than thirty apparatus for preparing this mixture established in the northern parts of that kingdom†. It has been also employed at Glasgow; and a patent, which is now set aside, was obtained by a manufacturer there for preparing the liquor, and a solid oxymuriat of lime, which might be employed at all times, and conveyed to any distance.
The pneumatic tub should be of such a capacity as to hold 800 gallons of water; and to this is to be added eight pounds of flaked and well sifted lime, which is to be well mixed with the water by means of the agitator, both at the time of making the mixture and during the distillation.
Between the tub and the distilling vessel is placed a leaden receiver capable of holding eight gallons, which is to be two-thirds filled with water, intended to retain any common muriatic acid which may come over. Vegetable For this purpose a leaden tube, three inches diameter in the bore, proceeds from the alembic, and passes nearly to the bottom of the receiver, and another tube of the same diameter passes from the upper part of this latter to the pneumatic tub. It is known that the limed water in the tub is saturated with acid, when on drawing off a portion of the liquor and adding lime to it, the lime sinks to the bottom. The liquor is then to be drawn off and mixed with thrice its bulk of water, when it is fit for bleaching.
The oxymuriat of lime is found to be superior to the oxymuriat of potash in bleaching, and it is certainly far less expensive. Barytes (ponderous earth) and frontites might probably be used with still greater advantage, from their greater solubility in water, and could be procured at a cheaper rate.
261. Previous to immering the stuffs in any of this oxygenated liquor, they are to be steeped and fulled in the same way as in the old method, to deprive them of the weavers dressing, and the saliva of the spinners. For this purpose it is proper to employ a weak alkaline ley.
In Britain and Ireland machinery is commonly employed in the fulling process, but it is generally so constructed as to wear the cloth. O'Reilly has proposed the following machine for this purpose.
He constructs a circular platform, which revolves about a moveable axis, and is supported at the extremities of the spokes by rollers of cast iron, the circumference of the platform is indented to receive a paul or catch, which makes it recede one notch at each stroke produced by the motion of the mill-tree. To the axis of the mill-tree are fixed spokes which raise several wooden beaters, which falling on the platform loaded with cloth or thread, rinse them more completely than can be effected in any other way, water being constantly supplied from gutters which are filled by buckets attached to a water wheel.
Cotton, thread, and stuffs, more particularly require this preparation, as without it the ley cannot penetrate the substance of the cotton, because of the resinous matter with which it is impregnated.
In some manufactories a bath of soap is employed, but this is unnecessary, as all that is requisite is to form a combination of the oily matter of the cotton with an alkali in order to render it soluble in water; and afterwards to submit the colouring matter to the action which another part of the alkali may exert on it. The preparations which the stuffs must undergo previous to their immersion in the oxygenated liquors consist therefore in steeping in an alkaline ley, rinsing in water, and subsequent pressing and wringing.
262. In disposing the apparatus for the immersions, regard must be had to the objects on which we are to work. Skains of thread are to be suspended in the tub which is intended to receive them; and the stuffs are to be rolled round the rollers of the immerging tub which we have described. The method of doing this is as follows: A piece of cloth is to be fastened to one
(M) I make no mention of the expense attending the preparation of the liquor, it being the same in both cases. Vegetable of the horizontal axes which correspond to those of Mr Substances. Rupp, and is to be rolled round by means of the handle till the whole is upon the axis; to this is fastened a second piece, which is rolled on in the same manner, and thus as many pieces as required are rolled upon the axis. The end of the last piece is then made to pass over the roller h at the upper part of the extremity of the tub next to g; is carried down below the roller h at the lower part of the same extremity; is carried along the bottom of the tub under the next roller up to the roller at the upper part of the partition; passes over this to the roller at the bottom of the tub on the other side of the partition; so on below the lower roller at the other end of the tub, over the upper roller of the same end, from which it passes to the other horizontal axis, and is there secured.
When the pieces are thus fastened, the immersing tub is filled with the liquor intended to be used from the pneumatic tub; and this, if it be the oxymuriat of lime, may be done by a funnel, but if it be the simple oxygenated liquor it is best done by a stop-cock passing from the pneumatic tub into the immersing vessel: when this is filled, the handle of the axis to which the last end of the cloth is fastened is turned till the whole of the cloth is unrolled from the first axis round the second, and then again the handle of the first is turned to reverse the situation of the cloth. Thus the cloth is made to pass to and fro through the liquor till the strength of this is exhausted.
263. This is discovered by drawing off a little of it, and adding to it a portion of the acetite of indigo; if the colour of this is not diminished, the liquor has lost its bleaching power, and the cloth may be removed, and the water, if the simple oxygenated liquor was employed, may be used for a new impregnation.
264. After the stuffs or thread have been removed, they must be well rinsed and again subjected to an alkaline ley. The lixiviations and immersions are repeated as often as is requisite till the bleaching is completed.
The number of lixiviations and immersions differs according to the articles. Cotton cloth requires only two operations of each; cotton-thread three; fine flax will require four; and articles of hemp five or six alternations.
265. "As it is of essential consequence to be aware of certain events, or facts, by which the progress of the bleaching may be ascertained, I shall here point out the gradations of colour, which the pieces assume after each immersion in the oxygenated muriatic acid without smell, made according to the proportions here described. The first immersion gives the thread, or piece-goods, a reddish colour, slightly inclining to yellow; the second, a colour inclining to ruddy yellow; the third, a whitish yellow; the fourth, a white, slightly inclining to a ruddy tinge; and by the fifth and sixth, the white becomes clearer and clearer. These are very nearly the shades which are assumed by coarse goods, for the fine goods frequently pass to the second or third gradation by one single immersion.
"When the liquor is strongly concentrated in potash, such as that which is denoted in the Annals of Chemistry by the name of javoelle, the goods immediately, and without previous lixiviation, assume the third colour; but I have observed, that it is difficult to bleach them further without using the sulphuric acid, to remove the lees with which they are loaded. It must, moreover, be remarked, that in order to obtain this tone of colour, it is sufficient that the lixivium be diluted with water, so as to mark two or three degrees only on the aerometer, instead of eighteen or twenty, which it may mark after it is prepared by distillation.
"There are some who do not approve the colour which the thread acquires after the first immersion; but it may immediately be reduced by steeping the goods in cold or hot lees. The latter produces its effect more speedily; and after subsequent rinsing and drying, the goods retain a gray white colour, more or less deep according to the shade it has received. Many vendors prefer this gray, or reduced colour, on account of its preferable sale in certain markets.
"With regard to the bright and perfect white, there are very few persons in the provinces who care for it, or appear to give it an exclusive preference. Two reasons may be given for this: first, because a prejudice is unfortunately established against the speed with which the new invented method of bleaching operates: and secondly, the consumer is constantly persuaded, whether the bleaching may have been performed in this manner or in the field, that when the goods have attained an extreme degree of whiteness, they cannot be so durable as such as are left white. It is thought to be rotten, or burnt; and this opinion leads to a preference in favour of such linens, and even cottons, which preserve after bleaching a solid shade of gray, or duncefs in the white.
"From a prejudice of the same kind, it is, that in many countries, the women, particularly the peasants, prefer their linen, whether for clothing or household use, simply cleared without bleaching. The orders of proprietors, or purchasers, must therefore be attended to, and the number of immersions and lixiviations regulated accordingly.
"It may be considered as a rule, that when the goods no longer communicate a perceptible colour to new lees, they are entirely finifhed, and consequently, that every subsequent lixiviation, or immersion, will be attended with absolute loss, unless the immersion is necessary to clear off the last lees, on the supposition that simple rinsing in a large quantity of water may not be sufficient.
"I must, nevertheless, remark, that thread bleached by the oxygenated muriatic acid, may be used by the sempitres with much more speed and briskness than thread of the same quality bleached in the field; it is less brittle, and, on that account, is better for the weft, as well as the warp. It likewise may be struck much more effectually home to its place in weaving, and does not afterwards move. I received this valuable observation from impartial and unprejudiced manufacturers, for whom I bleached thread according to this method for making handkerchiefs*."
266. The theory of these operations is simply this: The oxygenated liquor supplies to the cloth the place of the oxygen of the atmospheric air, and this in greater abundance, and in a state which renders its action on the cloth more expeditious and more complete. By the union of the oxygen with the carbon of the colouring matter of the cloth, carbonic acid is formed, to produce and carry off which is the object of the several processes which we have described. It is car-
* Nicholson's De Charmet. Part II.
Vegetable ried off by the subsequent lixiviations, in which the substances, alkali answers two purposes; part of it combining with the carbonic acid forms carbonate of potash, while another portion acts on the remaining colouring matter, and dissolving part of it prepares it for another immersion in the oxygenated liquors.
267. The expense of potash soon suggested to scientific bleachers the importance of endeavouring to discover a substitute for it which might render their processes more economical. Kirwan with his usual ingenuity, discovered, that saline sulphures would answer the purpose, and Mr Higgins has lately much improved on this discovery by bringing into use the sulphuret of lime, which he has fully proved may be employed as a substitute for potash with the greatest advantage. His account of his views, and of the method of preparing and using this substance are too interesting not to find a place in this article.
268. "Since I had the honour of being appointed chemist to the Linen Board, which is now more than three years, I have allotted a considerable portion of my time and attention to the investigation of the principles of that science, applicable to the art in which I am thus more particularly interested. It appeared, that until potash could be dispensed with, we must forever remain in the power of foreign nations as to our staple commodity; observing also, that all the late improvements in bleaching were exclusively confined to the one object, that of imparting oxygen to the cloth, in a safe and expeditious manner, but that there had been no effort made to supercede the necessity of potash, by far the most expensive and uncertain article employed by the bleacher, and for which he is entirely dependent upon foreign markets; I directed my attention chiefly to discover a substitute for potash; which, provided it should be of Irish production, though it might be equally expensive, I conceived would be of the utmost national importance. Impressed with these ideas, I undertook a series of experiments with that view.
269. "To enumerate the many disappointments and failures I experienced during my investigation, would be endless, and an unnecessary intrusion upon my reader. Knowing, from an important observation of Mr Kirwan, that saline hepar, or the combination of an alkali with sulphur, might, from its detergent properties, be advantageously employed in bleaching, as a substitute for mere alkali, by an obvious analogy I was led to expect a similar effect from calcareous hepar, or, more properly speaking, sulphuret of lime, being a combination of lime and sulphur.
270. "In these expectations I was not disappointed, but at that time (about three years since) I contented myself (rather through necessity, for large cities are very unfavourable to experiments on bleaching by exposure to the atmosphere), with pointing it out to some of the principal bleachers from the north then in the town, earnestly recommending it to them to give vegetable it a fair trial with and without potash. Since that time, substances, alkaline salts having become progressively dearer, and in consequence of a late proposal of substituting lime for potash, in condensing the oxyurinated gas, I was instigated to resume the subject, and make further and more varied trials. The result of which has been, that the use of the sulphuret of lime may be most advantageously combined with that of the oxyurinated lime, and that thus cloth may be perfectly whitened without the use of a particle of alkali. This then alone would seem to give it a decided preference over the methods at present in use, while at the same time it possesses peculiar advantages, and is exempt from the principal objections to which other substitutes are liable: for 1st, Quicklime and sulphur, the materials of which the calcareous hepar consists, are both articles of trivial expense, especially as the latter enters but sparingly into the composition; 2dly, Their combination is effected in the safest and most expeditious manner possible, and perfectly level with the capacity of the meanest workman; 3dly, As the manner of its application is, by steeping the cloth in it cold, the saving of fuel is a matter of great magnitude; and, lastly, There is no danger to be apprehended in the use of it, from the unskilfulness or negligence of the workman, as it appears to be incapable of injuring the texture of the cloth.
271. "The sulphuret of lime is prepared in the following manner: Sulphur, or brimstone in fine powder, four pounds; lime well flaked and sifted, 20 pounds; water, 16 gallons: these are all to be well mixed and boiled for about half an hour in an iron vessel, stirring them briskly from time to time. Soon after the agitation of boiling is over, the solution of the sulphuret of lime clears, and may be drawn off free from the insoluble matter, which is considerable, and which rests upon the bottom of the boiler (N). The liquor in this state, is pretty nearly of the colour of small beer, but not quite so transparent.
"Sixteen gallons of fresh water are afterwards to be poured upon the insoluble dregs in the boiler, in order to separate the whole of the sulphuret from them. When this clears (being previously well agitated) it is also to be drawn off and mixed with the first liquor; to these again, 33 gallons more of water may be added, which will reduce the liquor to a proper standard for steeping the cloth.
"Here we have, (an allowance being made for evaporation, and for the quantity retained in the dregs) 60 gallons of liquor from four pounds of brimstone.
272. "Although sulphur by itself is not in any sensible degree soluble in water, and lime but very sparingly so, water dissolving but about \( \frac{1}{5} \)th part of its weight of lime; yet the sulphuret of lime is highly soluble (o).
(N) Although lime is one of the constituent principles of the sulphuret, yet being so intimately united to the sulphur, it has no longer the property of lime; upon the same principle that sulphuric acid in sulphat of potash, has not the property of that acid.
(o) When the above proportion of lime and sulphur is boiled with only 12 gallons of water, the sulphuret partly crystallized upon cooling, and when once crystallized, it is not easy of solution.. 273. "When the linen is freed from the weavers dressing, in the manner already described, it is to be steeped in the solution of sulphuret of lime (prepared as above) for about twelve or eighteen hours, then taken out and very well washed; when dry, it is to be steeped in the oxymuriate of lime for twelve or fourteen hours, and then washed and dried. This process is to be repeated six times, that is, fix alternate immersions in each liquor, which I found sufficient to whiten the linen.
"When I submitted the linen to fix boilings in potash, and to fix immersions in the oxygenated liquor, it was not better bleached than the above.
"The three first boilings in potash, it is true, produced a somewhat better effect than as many steeps in the sulphuret; but towards the conclusion, that is, when the linen was bleached, the smallest difference was not observable as to colour. The linen bleached with the potash was thinner, or more impoverished than that treated with sulphuret, and the latter flood the test of boiling with soap much better than the former, although it did acquire a slight yellowish tinge, which I should suppose a week's, or at most, a fortnight's grafts, as they term it, would remove.
274. "I contrasted the effects of hot and cold sulphuret in various temperatures, and although the difference appeared in favour of the hot liquor, yet it was so trifling as not to deserve consideration, or the expenditure of the smallest quantity of fuel.
275. "When I steeped the linen in the sulphuret first, and afterwards boiled it in potash, and then immersed it once in the oxygenated liquor, a better effect was produced than from two previous boilings in potash, or from two steeps in the sulphuret; so that the two substances seem to co-operate with each other.
"Indeed, from what I have seen, two successive steeps in fresh sulphuret, previous to the immersion in the oxygenated liquor, seemed to afford very little better effect than a single one, which is not the case with respect to potash.
276. "It was observable, that the cloth was invariably thicker or more swelled coming out of the sulphuret, than after being boiled in potash, and remained so even when washed and dried.
"It appears to me, that the sulphuret opens the fibres of the linen more speedily and better than the latter, by softening and swelling, rather than dissolving, the resinous or colouring matter. This accounts for the better effect of potash upon the linen when previously steeped in the sulphuret, than when used by itself.
277. "Probably those bleachers who do not at present find it convenient to use the oxygenated liquor, but continue to bleach by exposure to air, may derive some advantage from this, by using the sulphuret and potash conjointly or alternately.
"Mr. John Duffy, of Ball's bridge (who from his knowledge of chemistry is very well acquainted with the principles of bleaching), was kind enough to repeat the above experiments, and his report to me corresponded with my own observations.
278. "It is almost impossible to ascertain to the ful extent, more especially by small experiments in an elaboratory, the many advantages any substance not hitherto used in bleaching, will afford by varying the mode of application.
"The experimenter does a great deal by discovering the efficacy, proving the practicability, and ascertaining the safest and most economical method of directly using it, and also the best proportion of it. Before he can arrive at any one of these, many a round of changes are necessary; indeed a greater number than any man who is not used to experiments can be aware of. But I should hope that the bleacher need not hesitate to use it in the state in which I present it to him, more especially as he runs no risk of injuring the cloth with it. If he can make more of it hereafter, I shall feel happy upon the occasion; no discovery was ever brought to perfection at once.
"How gradually, and yet how progressively, the steam engine, from its first invention by the marquis of Worcester, was brought to its present degree of perfection! Undoubtedly, it was just so with respect to alkalies, the substances now used by the bleachers; it must have taken a considerable time after their first application in bleaching, before they could be made the most of.
279. "I will now conclude by pointing out the advantage likely to accrue from the use of the sulphuret, to the nation, and also the saving to the individual.
280. "Hence it seems, that the quantity of foreign alkalies imported into the kingdom every year, amounts to 265,968 pounds; and that the quantity used in bleaching alone, amounts to about 215,307 pounds annually.
"The average price of brimstone for the last three years, is about 25l. a-ton, which is at the rate nearly of 2 1/2d. a-pound; four pounds of brimstone, and twenty pounds of lime, as already observed, will produce 60 gallons of liquor. In this country twenty pounds of lime may be valued at about 4d. so that the bleacher may have the 60 gallons at the expence of 1s. 1d.
281. "By what I could learn from different bleachers, the common allowance of alkali for 60 gallons of water is fix pounds of barilla or four pounds of potash at the very least, and most bleachers use more than this. The price of four pounds of potash at the rate of 65l. a-ton, is about 2s. 4d. which is 2d. more than double the price of the sulphuret; but as the brimstone must be ground, an allowance should be made for it; and being easy of pulverization, a farthing per pound is an ample consideration for the expence attending it.
282. "The saving of fuel only remains now to be taken into consideration; and as this cannot be calculated with any degree of accuracy, I shall content myself by particularizing facts. In the first place, but 16 gallons of liquid are to be boiled in preparing 60 gallons of the sulphuret, while the whole 60 gallons must be boiled when the alkali is used; hence it might appear that two-thirds of the fuel are saved in the quantity of liquor, but it is not quite so much, suppose we estimate it at one half, which is rather under-rating it. Let us add to this the time necessary to boil the different liquors; the sulphuret requires but about half an hour, and the alkaline lixivium at the very least seven hours, to boil the linen in it, which is in the proportion of one to fourteen.
283. "The saving altogether to the bleacher from this Part II.
Vegetable this statement, is obviously very considerable; and as Substances the Wicklow copper mines are sufficient to supply the whole kingdom, or indeed two such kingdoms, with abundance of sulphur, let the consumption be ever so great, the entire of the alkali, or 215,307 pounds, must be annually saved to the nation.
"But suppose two-thirds only of the quantity of alkali generally consumed in bleaching were dispensed with by the use of the sulphuret (which is a supposition not warranted by my experiments) still the saving to the nation, and to the individual, must evidently be great indeed*."
Effay.
284. The goods which have been bleached in the methods above described, require to undergo what are called dressings, to give them a clear and bright white. This is particularly necessary for the finer piece goods, sewing thread, stockings, gloves, and all cotton articles.
After the last immersion, the goods are to be pressed or wrung, and then immersed in a bath of water, holding in solution about a hundredth part of its weight of sulphuric acid. The acidulous bath may be employed cold, but it is better to heat it so moderately, that the hand may be borne in it. The best way to make the mixture of sulphuric acid and water, is to invert the bottle containing the acid in the water, when the acid by its greater specific gravity quits the bottle, and by agitation for a considerable time combines with the water.
It is usual to leave the goods for some days in the bath, but it is safer to allow them to remain only a few hours, and to renew the bath till they are sufficiently white. Too many articles must not be crowded together, nor too much pressed, that the acid may exert its action equally.
After removing the goods from the acid bath, they must be wrung, and washed repeatedly in fair water till they no longer retain any marks of acidity.
285. It is customary to give to linen cloth a bluish shade: this is produced by dispersing through the water in which it was last rinsed, a little indigo or Prussian blue; or it may be given by a solution of white or mottled soap, in which the cloth is washed, while it still retains a little acid.
286. As accidents are apt to occur during these processes, it is proper to inform the artist how these may be remedied.
287. "Accidents in the distillation.—The principal accident which is capable of interrupting the distillation, is when the lutes of the adopter suffer the gas to escape. The most speedy remedy, in this case, to prevent the exhalation of the acid, which cannot be retained but with difficulty, seldom for any length of time, and then very imperfectly, in consequence of its great expansion; the shortest method, I lay, at least if the distillation be not near its conclusion, is to remove the fire immediately from beneath the capsule of the retort, and to suffer this last to cool for a certain time, by raising it a little in its sand bath. If it be not possible to take it out of the furnace, together with its capsule, on account of the heat, or its sticking too fast, the adopter must be united from the funnel of the leaden tube, and the aperture of this tube closed with a cork, or lute, to prevent the gas of the pneumatic vessel from evaporating; after which the retort must be raised, and placed gently upon a bag of straw, or on coarse cloths Vegetable folded together; and then holding the retort by its Substances neck, near the flexure, the adopter must be entirely unluted, by twisting it round and drawing it off. The orifice of the neck of the retort is then to be closed with a cork stopper, but not so closely but that a very small portion of gas may be suffered to escape, for fear of an explosion. The stopper of the neck may, for greater safety, be slightly raised. This precaution is necessary, on account of the great expansion of the muriatic acid gas. The old lute must then be taken off, as well from the adopter as the retort, and the places to which they were applied must be well cleaned, in order to receive fresh lute, after having carefully wiped off the moisture with a cloth or a sponge. If the lute which comes off be full good, it may be kneaded again, adding, if required, a small quantity of boiled oil, or it may be mixed with new lute, if it be burned or decomposed. This decomposition in the fat lute may be known by the white or reddish colour which it acquires, and the facility with which it breaks, on account of its having lost the gluten which afforded it that toughness and tenacity, on which its goodness chiefly depends.
288. "With regard to the lute of linseed cake, it must, in almost every case, be totally renewed, particularly when internally applied, because the heat hardens it too much to admit of its being kneaded again, with any moderate degree of facility; the decomposition of this lute is known by the yellow colour it acquires, and the contraction it undergoes from the effect of the heat. The lutes being kneaded to a proper consistence, and duly placed according to the direction laid down in (232.) the adopter is to be fixed, previously removing the stopper from the mouth of the retort, and placing another in that of the small end of the adopter, to prevent any inconvenience from the vapour which might issue out during the time of fixing it. This vapour is likewise condensed within the adopter, in consequence of its coldness. The retort is then to be placed, as before, on the furnace, the adopter uncorked, and its beak luted into the tube of lead; after which, the fire is to be replaced beneath the capsule, and distillation very speedily recommences, and proceeds as usual. The operation is a work of some delicacy; it requires to be performed with speed, and great care must be taken while placing the lutes and the adopter in their proper situations, to stand always in such a position, that the current of the external air may drive the vapour from the operator himself.
289. "If the accident here described should take place towards the end of the distillation, as it may sometimes happen, in consequence of the strong heat which, at that time, may soften the lutes, it will be sufficient if the fire be taken from beneath the capsule. The distillation soon ceases when this is done, particularly if care be taken to condense the gas, by the prudent application of wet cloths on the neck of the retort, as well as of the adopter.
290. "This inconvenience would not take place, if the workmen in those glass-houses which are principally employed in the fabrication of chemical vessels, could make retorts with necks recurved in the form of the adopter. These kind of vessels may be assiduously supplied by making use of a tube of lead, so formed as Vegetable to serve instead of the adopter, as I have already ob- Substances, served, with regard to the tubulated bottles or bodies (p). If, by accident, the lute which is adapted should fail, or suffer the gas to pass through, it may easily be stopped, by applying a new lute to the place of junction. Instead of the leaden tube, we may substitute, with still greater convenience (the danger of breaking excepted), a tube of glass, of which the end nearest the bottle, or tubulated body, should be ground with emery. By these means there would be no application of lute, and consequently no danger to be feared with regard to the filtration of the gas, the escape of which is easily perceived by the smell which diffuses itself through the workshop, and is more particularly perceived when the nose is applied near the vessels, or the lute. But as this last method of discovering the place where the lute has failed may be attended with the most serious consequences, if the greatest precaution be not used, it is more prudent to apply an open bottle of ammonia near the suspected place; at the instant that it is presented, a white fume is formed, which immediately points out the defective spot. The bottle must be presented above the current of air, which takes place near the lute, or in the workshop. If this precaution be not attended to, the operator might be induced to re- move good lute, instead of one which was really de- fective.
291. "On the other hand, if in the course of the di- stillation, and for want of keeping up the heat, the fluid in the pneumatic vessel should be absorbed and rise into the distilling apparatus, it is necessary the instant it is perceived to withdraw for a moment the stopper out of the neck of the retort, where, as I have already had occasion to observe, the absorption instantly ceases. Ne- vertheless, if, for want of being observed in time, the water should rise so far as partly to fill the retort or bo- dy (for it never entirely fills it), the distillation will be stopped, from the coldness of the water, and its too great quantity. The shortest remedy is to draw out the excess of water, which is thus introduced into the distil- ling vessel, by the assistance of a glass pump, or syphon, and afterwards to heat the same vessel, first returning the water into the pneumatic vessel, if thought expedient: but if the distillation be properly attended to, this accident can never happen.
292. "Accidents in the lixiviations and immersions. I place the accidents arising from these two operations in the same class, because they can scarcely take place, but by the joint operation of both.
"Any article which is badly cleared of the lixivium, and afterwards immersed in the oxygenated muri- atic acid, becomes almost immediately of a nankeen co- lour, particularly in the folds, either in spots where cer- tain parts have not been sufficiently rinsed, or else the colour is general, if the whole has not been well rin- sed.
"The same accident happens if foot has fallen on the linen or thread. The difference is simply in the colour, which approaches more to brown. The colours are capable of becoming more and more deep if the mismanagement be not remedied as soon as perceived, ve- getable and that before the goods are subjected to other im- mersions in the alkaline lees, or of the oxygenated muriatic acid. The same accident is to be expected, if the goods, though white at the time of their immer- sion, are suffered to remain too long in the bleaching liquor. This does not fail to happen, particularly if the articles which are suffered to remain even in a weak solu- tion, are kept in that state the whole night. The next day they are found to be yellow, or charged with lixivium.
293. "The only method of remedying these acci- dents consists in the use of water, slightly acidulated with sulphuric acid, no matter whether cold or hot, but the hot solution operates more speedily. The spotted or tinged goods are to be soaked in this water for a few minutes, or a quarter of an hour, accordingly as the col- our may be more or less deep, in consequence of a se- ries of lixiviations or immersions, more or less repeated. In this situation the offensive colour is seen almost im- mediately to disappear.
294. "Instead of making a sulphuric solution ex- pressly for that purpose, that which has served for the dressing may answer very well: neither of these need be stronger than has been there directed, unless the goods be considerably charged with colour, and there be a great quantity to immerse at once. The acidu- lated water is tried by the aerometer, and if, in conse- quence of having been used, it should not be suffici- ently strong, it may be restored by adding the requi- site quantity of acid for that purpose. It is necessary, when any new acid is poured in, to mix it well with the water before any goods are immersed therein.
"It must, in this place, be observed, that though the thread and piece-goods may become charged with a fo- reign colour, in consequence of the accidents here pointed out, both these articles are frequently very well bleached at the under surface. It is even a proof that the muriatic acid has operated effectually, in causing the lixivium to produce such an effect: but these accidents are difficult to be observed on objects simply cleared, or in the crude state. In the latter case, a permanency of the original colour may alone shew the necessity of using the sulphuric acid, particularly when the lees and the muriatic acid which have been used are not at all exhausted.
295. "Accidents attending the preparation or dressing. When the piece-goods are immersed in a solution of soap, after having been taken out of the sulphuric acid, while they are still too strongly acidulated, or instead of rinsing them they be immediately conveyed from the acid into the solution of soap; this last solution is subject to curdle, or become immediately decomposed; whence the operator has the mortification to observe the whole surface of the goods covered with an infinite number of small spots of oil, in the form of clots, of a yellowish colour, and very tenacious, particularly on stockings or cotton goods, because they incorporate as it were with the nap or texture of the goods: they dif- appear
(p) This last method appears to be preferable to every other; because it requires only a slight attention to the lute, and can never produce those dangers which arise from the use of retorts. Part II.
Vegetable appear in consequence of much washing or rinsing. I Substances must particularly mention an accident which may happen to any one, namely, that of placing by mistake stockings or other bleached objects, which have received their first treatment in the solution of soap, upon articles which have been exposed to the vapour of sulphur. I have placed stockings upon gauze, which had been whitened by sulphur, and found, that after they had remained in this situation for the course of a night, they became entirely of a brown red at the place of contact. They appeared as if burnt or marked with a hot iron. This colour, which, no doubt, was produced by the combination of the volatile sulphuric acid, with the alkali of the soap, with which the stockings were still impregnated to a certain degree, immediately disappeared upon expelling them, first, to the action of a bath of the odorant oxygenated muriatic acid, and afterwards to another of water, slightly acidulated with the sulphuric acid.
296. "Every salt with excess of acid, such as the salt of forrel, removes the ruddy spots here mentioned with equal ease. It is true, that this salt cannot with convenience be used, on account of its dearness; but the residue of the distilling vessels, that is to say, the water which holds in solution the residue of the distillation of the oxygenated muriatic acid, is very serviceable in this process, and may be advantageously used either hot or cold, to remove those very tenacious spots, which are not at all capable of being removed by soap or alkaline leys.
297. "When the spots of oxide of iron, commonly distinguished by the name of ironmould, are small, they may easily be taken out with the salt of forrel in powder, laid upon the spot itself, which is afterwards to be moistened with a small quantity of water; or the part which is spotted may be steeped in a solution of the same salt. It soon becomes fainter, and at length disappears, after which the place must be very well rinsed. The sulphuric acid may be usefully applied instead of the salt of forrel, as Berthollet seems to affirm in his memoir; and I have proved with success, that, though the spots may penetrate quite through the cloth, and be very broad, yet if they be soaked in a bath of sulphuric acid, either warm or cold, when the goods are taken out of the bath of muriatic acid, the effect will be that the spots insensibly disappear. If the goods be of clothe texture, the operation of the acid is slower (Q).
298. "With regard to the spots of rust which are frequently seen on thread or cotton stockings, they are produced by the needles of the engine, and commonly disappear during the dressing, that is to say, in the bath of sulphuric acid. The same observation is true of the spots of rust which sometimes appear on the piece-goods, in consequence of their having been in contact with iron. In general, the older any iron-mould may be, the more tenacious it is, and the more difficult to be effaced; but every spot may be made to disappear in time.
299. "It frequently happens that piece-goods are spotted with tar, during their carriage by water, in Vegetable boats, where they are liable to be placed upon the pitchy parts of the vellies, or in contact with tarred ropes. These spots may be soon taken out, by rubbing them with oil of olive, which dissolves the tar; or still better, by holding the part in spirit of wine, if this process should be thought more convenient. The latter method operates by the complete solution of the tar.
300. "With regard to spots of wine, cyder, or any kind of fruit, they may be effaced by dropping a few drops of the oxygenated muriatic acid upon them, which causes them almost instantly to disappear. But there are certain fruits, such as plums, of which the spots are more difficult to efface; they requiring one or two lixiviations. Those that are gray, or reddish, at first, assume a fine yellow colour in the muriatic acid, which does not disappear during a subsequent lixiviation, but requires a second immersion in the bleaching liquor.
301. "I must not omit a second very simple and economical method to take out every kind of spot occasioned by fruits, such as strawberries, gooseberries, &c. It consists in cauuing the spotted part to imbibe water, and afterwards to burn one or two common brimstone matches over the place: the sulphurous gas which is discharged soon causes the spot to disappear.
302. "There is a kind of indelible spot which is produced from red ochre and the charcoal black, with which the weavers mark the turns of the beam, in order to ascertain the length of the chain of piece-goods. This kind of mark, which is impressed on the goods at equal distances, is so far from being effaced, that it seems, in some measure, to receive strength from the oxygenated muriatic acid, notwithstanding the intermediate action of the leys."
Use of the Oxygenated Muriatic Acid in discharging the colours of dyed or printed goods.
303. There are several processes allied to bleaching, which depend on the agency of the oxygenated muriatic acid, and of which we shall therefore treat before proceeding to describe the remaining bleaching processes. These are the discharging of dyed or printed colours; the bleaching of paper; the cleaning of books, maps, and prints; and the bleaching of wax.
304. White silk and wool, on being steeped in oxygenated muriatic acid, acquire a yellow colour; hence this acid is of no use in bleaching these animal substances. It readily discharges the simple colours with which silk has been dyed, such as, indigo blue, gray, lilac and crimson, and gray, orange, green, Saxon blue, apple green, fawn colour, brown, lemon, and dipped blue, with which wool has been dyed. It leaves the goods, however, of the same yellow cast as it imparts to white wool and silk; but this yellow colour is readily altered to a clear white, by immersion in the sulphurous acid, as described in the bleaching of these substances.
Silk dyed with some compound colours, as violets, greens, browns, blacks, acquires the same yellow colour,
(2) The salt of forrel is sold in London, in small bottles, by the perfumers and apothecaries, under the name of Salt of Lemon. The sulphuric acid, as prescribed above, must of course be diluted. Vegetable lour, but not so speedily, two immersions being usually Substances, found necessary to discharge the colours completely.
In the brown violet and puce colours, which are composed of blue and red, the blue commonly first disappears, and by a subsequent immersion the red is discharged. The same happens with the yellow, which forms a part of the composition of green and orange, the blue of the former and the red of the latter remaining. In blacks which are composed of brown laid upon a blue or a root colour, the brown first vanishes.
When more than one immersion is required, it is proper to use a bath of sulphuric acid between them; and this is particularly necessary where iron has entered into any of the colours.
These effects of the oxygenated muriatic acid serve to explain the action of the air in discharging the less permanent colours of woollen and silken goods, and in giving to white clothes a yellow colour. It is evidently oxygen which is in both cases the active principle, but its action is more speedy in the acid than in the atmosphere, from the facility with which the former is decomposed.
305. The colours employed in dyeing or printing cottons or linens are of two kinds; chemical, or, as they are sometimes called, false colours, and fast or true colours. The former disappear in a very short time upon one immersion in the acid, except one description of yellow, which contains in its composition sulphate of copper (blue vitriol), sulphate of iron (green vitriol or copperas), and acetite of lead (fugar of lead). Goods which have been dyed with this colour must first be well scourd with soap, which so far separates or decomposes the colour, that a subsequent immersion will readily discharge it, whereas, without this previous scouring, the acid would have completely fixed the colour.
Several of the fast colours, as the blues, yellows, and blacks, require a lixiviation before immersion; and two or sometimes three, immersions, with intermediate baths of sulphuric acid, are necessary completely to remove them. Most other fast colours yield to a single immersion. A peculiar exception to this is the Adrianople red, which never becomes entirely white, however numerous the lixiviations, immersions, and acid baths employed.
306. "There is another thing, no less worthy of remark, with regard to the black colour, which forms the outline or border of designs, namely, that if the muslin, or cleared fine piece, upon which the different flowers were designed which have been discharged, be folded together in several folds, or placed upon a dark-coloured ground, the effaced outline becomes visible according to the exposure of the piece under a certain obliquity of the light, exhibiting the appearance of a slight trace. The kind of outline which, under these circumstances, becomes visible, cannot be compared to any thing better than the embroidery of muslins placed on a coloured ground. This trace seen at a certain distance has the same effect, and even when closely observed, it is impossible to determine what it is, because it is not visible, except under a certain reflection of the light; nevertheless the whole piece appears white, and of a very superior quality. I have remarked, that this effect does not take place excepting with vegetable regard to the old prints of flowered designs of the true Substances, India calicoes imported from that part of the globe. For in the printed goods of our manufactures, such as those of Paris, Joly, St Denis, and Beauvais, all the traces of the designs completely disappeared, to my great surprize. It must, therefore, necessarily be admitted, that the difference in these results depends on the qualities of the mordants, which are more or less oily, or the manner of striking the blocks in the act of printing.
"If this effect were produced by the mordant with the outlines of the designs in the pieces of printed goods, it might, perhaps, be of advantage to take the same method of obtaining a substitute, instead of the rich expensive embroideries with which the fine muslins of India and Switzerland are covered. These designs likewise do not appear in their full effect, but when they are placed upon a transparent stuff of a deep colour, which exhibits all the outline. This method of producing so rich an effect would be extremely simple, singularly permanent, and highly economical. I think, however, that I may add, that, after many trials, I have at last succeeded in discharging this mordant, sometimes by a bath of sulphuric acid, rather stronger than usual, and at other times by soaping the goods before and after the bath. This management is very essential to be known, in order that the operator may not be exposed to the mortification of seeing the same designs return again by the second action of the madder applied to the same bleached piece in a subsequent printing process. To obviate every accident of this kind, it will be proper to inform the owner which of the methods have been used to bleach their goods, and in case the new method may have been used, it would then be prudent to pass them previously through a good bath of sulphuric acid*."
307. Colours laid in oil, which do not contain madder, must be first heated in an alkaline ley, and then scoured with soap.
Bleaching of Paper.
308. The bleaching of paper has been rendered considerably more expeditious by the use of the oxygenated muriatic acid. The following processes are given by De Charmes, as extracted from different French memoirs.
Bleaching of old printed Papers, to be worked up again.
309. "1. Boil your printed papers for an instant in solution of soda rendered caustic by potash. The soda of varech is good.
"2. Steep them in soap-water, and then wash them, after which the material may be decomposed, or reduced to a pulp, by the machinery of the paper mill. The washing with soap may be omitted without any great inconvenience.
Bleaching of old written Papers, to be worked up again.
310. "Steep your papers in a cold solution of sulphuric acid in water, after which wash them before they are taken to the mill. If the acidulated water be heated, it will be so much the more effectual." Part II.
Vegetable Bleaching of printed Papers without destroying the texture of the Leaves.
311. "1. Steep the leaves in a caustic solution of soda, either hot or cold. 2. And in a solution of soap. 3. Arrange the sheets alternately between cloths, in the same manner as the paper-makers dispose thin sheets of paper when delivered from the form. 4. Subject the leaves to the press, and they will become whiter, unless they were originally loaded with size and printers ink. If the leaves should not be entirely white by this first operation, repeat the process a second, and if necessary, a third time. The bleached leaves, when dried and pressed, may be used again for the same purposes as before.
Bleaching of old written Papers without destroying the texture of the Leaves.
312. "1. Steep the paper in water acidulated with sulphuric acid, either hot or cold. 2. And in the solution of oxygenated muriatic acid. These papers, when pressed and dried, will be fit for use as before.
The method of bleaching Rags of the natural brown colour for the Manufactory of white Paper.
313. "1. Let the rags be opened or separated from each other, after previous soaking or maceration for a longer or a shorter time, according to their texture and quantity. 2. Give a lixiviation in caustic vegetable or mineral alkali. 3. Pass them through the oxygenated muriatic acid, more or less concentrated with alkali. 4. Let the mass be then worked for a sufficient time in the apparatus of the paper-mill, and it may be advantageously substituted instead of that which is afforded by white rags.
"The white colour will be still better, if, after the maceration, the rags be opened, and subjected, as usual, to the action of the mill; after which the paste itself must be subjected to one lixiviation, one immersion, and a bath of sulphuric acid. The mass being then well washed and pressed out, may be thrown into a trough to be manufactured.
Method of bleaching Rags, of all Colours whatever, in order to make white Paper.
314. "1. Let the rags be opened, as before. 2. Steep them in the oxygenated muriatic acid. 3. If, as it commonly happens, the colour is discharged by this first immersion, let these bleached and decomposed rags be immersed in water acidulated with sulphuric acid. 4. Complete the disorganization by the mallets or cylinders of the mill, after having previously well washed them.
"If the colour should not be sufficiently discharged by the first immersion in the oxygenated muriatic acid, which is very seldom the case, give them another alkaline lixiviation, and after that a second immersion in the oxygenated muriatic acid; after which steep them in water acidulated with sulphuric acid, either hot or cold, the latter of which is the most active and effectual; and, lastly, let them be subjected to the action of the mallets or cylinders.
"Red and blue colours are most tenacious. With regard to black, it will be sufficient if they be steeped after opening their texture, 1. In a diluted solution of sulphuric acid; and, 2. In a solution of the oxygenated muriatic acid. If the operator could know that Vegetable these rags had been dyed in the raw state, a still more brilliant white might be obtained by following the second method described in the preceding article. But it very seldom happens that coloured rags have not been bleached before they were dyed. The manipulations may be performed with sufficient speed to bleach at least three thousand pounds weight in the course of the day, without appropriating any extraordinary edifice or workshop to this purpose*."
315. But by far the best method of bleaching paper, is by applying the gas to it while in the state of paste; the method of doing which, with the steps which led to it, are thus related in a Memoir of C. Loyfel, in the Ann. de Chimie, as translated by Mr Nicholson, in his valuable Journal, from which we have extracted it.
316. "The process of bleaching the paste of the paper-maker, even when produced from the most common rags, will communicate to it the quality of the best sort. By these means our paper manufactories may supply our wants in fine white paper, and even obtain the preference in foreign markets. The result of this operation would be, that a greater number of workmen would find employment, and the advantages of this increase of industry would be of still greater national value, than even the foreign export which might be expected.
"The success of bleaching the paste of paper by the method of Citizen Berthollet is no longer problematical. The application which has been made to the paper used in making assignats, has placed this question beyond all doubt as to its solution.
317. "It was at the commencement of the year 2, that the committee of assignats and monies of the national convention, of which I was a member, resolved to employ this method, together with that of stereotype, which had been adopted, to oppose new obstacles to the practice of forgery.
"We particularly consulted Citizens Berthollet, Fourcroy, and Guyton on this enterprise. Their approbation of the project, and the information they afforded us, soon gave us the power of realizing it. We were also assisted with the knowledge of Citizens Welter, Athenas, Alban, Carfy, Marchais and Ribaucour, who with great zeal communicated their processes, and permitted us to inspect their several manufactories.
318. "Our first processes were executed precisely according to the method of Citizen Berthollet. The rag was subjected in succession to different leys, to baths of the bleaching liquor and sulphuric acid pointed out in his memoir. Berthollet had shown, and we were also convinced by our own experience, that the gas is less confined in the simple fluid, prepared without addition of fixed alkali, than it is in that which contains potash or soda; and that it is consequently more disposed to separate and enter into new combinations. We therefore at first made use of this simple liquor; but the workmen soon exhibited a strong repugnance to its use on account of the fumes it emits, which are extremely inconvenient, even when chalk is diffused in the liquor. This inconvenience forced us to abandon it, though with regret. This sacrifice was so much the more considerable, as it occasioned a loss of time, and considerable increase of expense. We decided that Vegetable we would receive the gas in a solution of potash; but substances, as the doses in which this alkali may be used have limits of great extent, we endeavoured to keep as near as possible to that preparation which is sufficient to prevent the spontaneous disengagement of the gas, and by that means cause the liquor to lose the odour we were desirous of avoiding. This dose was 5 kilograms of potash to 100 litres of water, (11 pounds avoirdupois, to 21 1/2 ale gallons).
319. "The rags bleached in this manner became of the most brilliant white. Nevertheless, a part of this perfection disappeared, when the rag was converted into paste, and that paste into paper. It was easy to discover the cause; namely, that the interior parts of the thread in the rag were less exposed to the action of the liquor than those at the surface. This motive determined us to abandon the bleaching of the rags, and to operate upon the paste itself.
320. "We were here opposed by new obstacles. When the rag is converted into a paste proper to be worked, its coherence is such that it settles, and no longer permits the leys and baths of the bleaching liquor to penetrate through all its parts, in consequence of which property the paper was found to have veins and different shades of colour. We remedied this inconvenience, by taking the matter in a mean state between the rag and the paste proper to be converted into sheets of paper. We succeeded in this respect by destroying the texture of the rag under the first cylinder so as to separate its fibres, an operation which usually lasted two hours for a pile of 50 kilograms. Thus it was, that by successively avoiding the extremes of too much and too little mechanical connexion, we advanced towards our object.
321. "The apparatus which Citizen Welter imagined, and of which Citizen Berthollet has given a description in the first volume of the Journal of Arts and Manufactures, is applicable to all the methods which can be employed to procure the different kinds of bleaching liquor, whether the water of the receiver contains fixed alkali or not; whether the muriatic acid be used on the oxyd of manganese, or the gas be obtained by sulphuric acid, upon the mixture of oxyd of manganese and muriate of soda. This apparatus is particularly preferable to all others in the case where the water of the receiver contains no alkali, because the absorption of the gas is favoured by its being brought into contact with the water at a great number of surfaces. But as we had determined to use a solution of potash, we were able to make some modifications of this apparatus.
322. "One thousand litres of water are placed in the receiver, holding in solution fifty kilograms of white purified and calcined potash.
"When the disengagement of gas is effected by the muriatic acid, the materials are used in the following doses:
Oxyd of manganese 24 kilograms Muriatic acid at 20 degrees of density according to the aerometer of Baume, 68 — 92
which makes for each of the eight distilling vessels 11 1/2 kilograms of materials.
323. "The operation is begun by charging the receiver with 1000 litres of alkaline water, after which the aperture 8 is closed with its flopper well luted. Each matra is then placed in its sand-bed; and pul. XCII. verized manganese is introduced. The muriatic acid is poured upon the manganese, and the floppers into which the tubes of communication pass, are duly placed. The juncture is luted with paper soaked in starch. And the lute is left to dry from fix to twelve hours, after which the fire is lighted in the furnaces.
324. "The process of distillation lasts from ten to twelve hours. When it is finished the tubes are unluted, the fire extinguished, and the matrasses suffered to cool in their sand beds, till the temperature of these beds has descended to 60 or 70 degrees, (centigrade) at which period, water of the same heat is poured into the matrasses. The water dilutes the residue of the distillation, which mixture is to be poured out, and the vessels suffered to cool in baskets containing straw. If the precaution of introducing hot water in this manner upon the residue were not taken, it would become so solid when the operation is performed with sulphuric acid, in the manner we are about to describe, that it could not be extracted without much trouble and danger of breaking the vessels.
325. "If the disengagement of the gas be made by sulphuric acid, the following doses are used:
<table> <tr> <th>Oxyd of manganese</th> <th>25 kilograms</th> </tr> <tr> <th>Muriate of soda</th> <th>70</th> </tr> <tr> <th>Sulphuric acid at 50 degrees of density</th> <th>25</th> </tr> <tr> <th>Total</th> <th>120</th> </tr> </table>
"The acid is to be diluted with an equal bulk of water, or 16 litres, which will reduce its density to 31 degrees.
"The eighth part of this for each matra amounts to 1 1/4 kilograms.
326. "The oxyd of manganese and muriate of soda being pulverized are mixed together. The matra is to be charged and the operation conducted as before described. This method is the most economical, because the sulphuric acid is cheaper than the muriatic, and also because it is practicable to obtain from the residue of the distillation, the soda of the muriate which is converted into sulphate of soda; that salt being decomposable by well-known processes.
"In order to measure the force of these liquors, or their bleaching power, we made use of the solution of indigo prescribed by Citizen Defcroizilles.
"One part by measure of the bleaching liquid prepared as before mentioned, will usually destroy the blue colour of nine parts of proof solution of indigo; it was of the same strength as that of Javel, prepared by Citizen Alban.
Choice and Preparation of the Rags.
327. "The strength or tenacity of paper depends upon the staple or fibre of the material from which it is made. Rags of new cloth and cordage compose a paper more tough than old rags, and the first of these materials presents a great variety on account of the quality of the hemp or flax of which they are formed. Part II.
Vegetable Rags of fine new cloth, whether raw or bleached by the Substances. oxygenated muriatic acid, stand in the first rank, after which cordage and old rags may be classed.
328. "Paper intended for bills of exchange, or other commercial and legal instruments, ought to be tough, in order that it may not be easily torn when thin. For this paper the materials of the first class must be entirely, or in large proportion, employed. The price which the consumers are disposed to pay for this article, is sufficient to indemnify the manufacturer for his care and industry, as this kind of paper is sold in France for 5 or 6 francs the kilogram.
329. "The other papers also require to be more or less tough, according to their thinness, and the use to which they are applied, but a clear white colour is sought in paper of every description. The first operation to which the rags are subjected is sorting, in order that each branch of the manufacture may have its appropriate material, after which they are cut with shears into pieces of about one decimeter, or three or four inches square.
330. "I will suppose that the object of the manufacturer, is to obtain paper of a beautiful white. If it is intended to be thin, fo that, for example, a ream of the size denominated rajin should weigh only four or five kilograms, that is to say, about one-third of the weight of common paper of the same form; the manufacturer makes choice either of new rags already of a fine white, or of unbleached rags.
"In the case of the white rags, it is sufficient to pass them under the first cylinder, then to give them a bath of the bleaching liquor, and afterwards a bath of sulphuric acid, as we shall proceed to direct; after which they are passed under the finishing cylinder for seven or eight hours, and, lastly, conveyed to the working trough to be made into sheets of paper.
331. "Rags, which have never been bleached, may be treated by either of the following processes: that is to say, the first, which preserves the utmost degree of toughness to the paper, but is likewise the most expensive, consists in decomposing the rag, and afterwards applying the method of Citizen Berthollet for bleaching piece goods; namely, subjecting it to three or four lixiviations, and afterwards alternately to lixiviations, baths of the bleaching liquor, and baths of sulphuric acid. The weight of the raw unbleached material is diminished from 50 to 45 per cent. in these operations.
332. "This method was the first which we used for the affignat paper; but we soon perceived that we might omit most of the lixiviations and baths of the bleaching fluid, and still preserve as much toughness as the paper required. Nothing further was necessary for this purpose than to suffer the rag to undergo a degree of fermentation more or less advanced, by leaving it to rot. In this operation the colouring matter undergoes a slow combustion, and passes to a kind of sapaneous state, and is carried off by the water, by washing the rags in the vessel of the first cylinder.
"One single lixiviation, two baths of the bleaching liquor, and one of sulphuric acid, are then sufficient to bleach completely the raw rags or cordage. This is the second method. We were not at that time acquainted with the economical process of Citizen Chapal in the operations of lixiviation. This will, no doubt, be used; but the effect of rotting, carefully conducted, will always be found very advantageous.
333. "Lastly, If the rags be neither perfectly white, nor raw and unbleached, but in a medium state, they are left to rot for a shorter time, for example, 12 or 14 days, and are taken up when the heat of the fermentation raises the thermometer to 30° or 35°, after which the process is to be conducted as before mentioned.
Composition of a bath of the bleaching liquor, for a pile of decomposed rags, weighing 50 kilograms.
334. "For each heap of rags, a certain number, for example, eight or nine, wooden tubs are disposed in a line, capable of containing in the whole 600 litres of water: 450 litres of pure water are poured in, and 90 litres of bleaching liquor are added in equal portions to each of the vessels, after which the 50 kilograms of decomposed rags are disposed in equal portions in each tub. The stuff is left for about 12 hours in this bath, agitating it from time to time, after which it is to be completely washed in clean water, and put into a bath of sulphuric acid, composed of water 200 litres, and acid at 50 degrees 3 kilograms, which bath will then have the strength of about four degrees of the aerometer of Baumé.
"The immersion in the bath must continue for three quarters of an hour or an hour, after which the materials must be well washed in clear water, and carried to the mill to be manufactured.
335. "If the action of the baths of bleaching liquor be not exhausted by the immersion of the decomposed rags (which may be ascertained by the solution of indigo), it may be applied to other materials of the same kind.
336. "Such was the state in which we left this new art in the year 3. Since that time Citizen Welter, to whom chemistry and the arts are indebted for a number of ingenious processes, has simplified that of preparing the bleaching liquor. He has found, for example, that instead of the three vessels of the receiver, it is sufficient to employ two even for the simple liquor that contains no fixed alkali.
"It was before seen that we were obliged to employ an alkaline solution in the receiver, to prevent that odour which the simple liquor emits when paper stuff is agitated in the baths. The use of alkali answered our purpose very well in this respect; but this expenditure, besides weakening the bleaching liquor, nearly doubled our expense. Though this difference in the price was of little consequence with regard to the object we then had in view, it is not so with regard to the common operation upon paper intended for sale. Every means of economy must then be used. Now Citizen Welter found that it is easy to obviate the inconvenience of the same liquor in the operation. His method consists in no longer agitating the goods or material in an open bath, but to close it exactly by means of a cover; and he agitates it by means of cros pieces attached to a handle turned on the outside.
337. "A rough estimate of the price of the simple bleaching liquor prepared by the sulphuric acid, this being the most economical process.
"The receiver is supposed to contain 1000 litres of water. 25 kilograms of oxide of manganese cost at most 70 kilograms of muriate of soda 25 kilograms of sulphuric acid, at 50 c. Three days work principal men Three days do. assistant or labourer Fuel, about Wear and tear Our apparatus cost 622 francs, and the carriage and fixing increased our expense to 1000 francs, the interest of which, at 10 per cent. is 100 francs; and if the work be repeated so many times in the year, the interest per operation will be
Fr. cent.
15 0 7 0 37 50 9 0 4 50 3 0 6 0
Fr. 83 0
"Hence the litre of bleaching liquor will cost nearly 9 cents in round numbers (R)."
338. "Estimate of the increase of expense occasioned in the operation upon a pile of 50 kilograms of the patte of paper, supposing one bath of the bleaching liquor and one of sulphuric acid, which is most commonly the case.
Ninety litres of the bleaching liquor at nine cents 8 fr. 10 c. Three kilograms of sulphuric acid, at 1 fr. 50 c. 4 50 Workmanship 0 50
Total, 13 20
Which gives for each kilogram of paper an expence of 5,262 francs, or about 27 cents. Now the common paper in the market usually sells for about 1 fr. 30 c. or 1 fr. 40 c. the kilogram, and with the simple augmentation of 27 cents for the operations of bleaching, it obtains the preference beyond that which is sold for three, four, or even five francs, which can only be obtained in a limited quantity, on account of the selection of rags. The foregoing methods must therefore produce a great diminution in the price of fine paper. They are more particularly advantageous when applied to the manufacture of thin paper, because the expenses of bleaching are always proportioned to the weight of the material, and consequently are least upon thin paper."
Of Whitening and Cleaning Prints, Maps, Books, and other Articles of Paper.
339. The oxygenated muriatic acid was first applied to this purpose by Citizen Chaptal, and the method has been employed with the greatest success by Citizens Vialard and Heudier.
The acid in the state of gas might be used for this purpose, but it is safer and equally efficacious to employ it in the liquid form.
340. "Simple immersion in oxygenated muriatic acid, vegetable letting the article remain in it a longer or shorter space substances of time, according to the strength of the liquid, will be sufficient to whiten an engraving. If it be required to whiten the paper of a bound book, as it is necessary that all the leaves should be moistened by the acid, care must be taken to open the book well, and to make the boards rest on the edge of the vessel, in such a manner that the paper alone be dipped in the liquid: the leaves must be separated from each other, in order that they be equally moistened on both sides.
"The liquor assumes a yellow tint, and the paper becomes white in the same proportion. At the end of two or three hours the book may be taken from the acid liquor and plunged into pure water, with the same care and precaution as recommended in regard to the acid liquor, that the water may exactly touch the two surfaces of each leaf. The water must be renewed every hour, to extract the acid remaining in the paper, and to dissipate the disagreeable smell.
341. 'By following this process, there is some danger that the pages will not be all equally whitened, either because the leaves have not been sufficiently separated, or because the liquid has had more action on the front margins than on those near the binding. On this account the practice followed by book-binders, when they wish to whiten printed paper, is to be preferred. They destroy the binding entirely, that they may give to each leaf an equal and perfect immersion; and this is the second process recommended by M. Chaptal.
"They begin (says he) by unsewing the book and separating it into leaves, which they place in cases formed in a leaden tub, with very thin slips of wood or glass, so that the leaves when laid flat are separated from each other by intervals scarcely sensible. The acid is then poured in, making it fall on the sides of the tub, in order that the leaves may not be deranged by its motion. When the workman judges, by the whiteness of the paper, that it has been sufficiently acted upon by the acid, it is drawn off by a cock at the bottom of the tub, and its place is supplied by clear fresh water, which weakens and carries off the remains of the acid, as well as its strong smell. The leaves are then to be dried, and, after being pressed, may be again bound up.
"The leaves may be placed also vertically in the tub; and this position seems to possess some advantage, as they will then be less liable to be torn. With this view I constructed a wooden frame, which I adjusted to the proper height, according to the size of the leaves which I wished to whiten. This frame supported very thin slips of wood, leaving only the space of half a line between them. I placed two leaves in each of these intervals, and kept them fixed in their place by two small wooden wedges, which I pushed in between the slips. When the paper was whitened I lifted up the frame with the leaves, and plunged them into cold water to remove the remains of the acid, as well as the smell. This process I prefer to the other."
(R) As the price of all these several items in France must materially differ from the same in England, it was thought unnecessary to reduce the numbers. Vegetable. 342. "By this operation books are not only cleaned, but the paper acquires a degree of whiteness superior to what it possessed when first made. The use of this acid is attended also with the valuable advantage of destroying ink spots. This liquor has no action upon spots of oil, or animal grease; but it has been long known, that a weak solution of potash will effectually remove stains of that kind.
343. "When I had to repair prints so torn that they exhibited only scraps pasted upon other paper, I was afraid of losing these fragments in the liquid, because the paste became dissolved. In such cases I enclosed the prints in a cylindrical glass vessel, which I inverted on the water in which I had put the mixture proper for extricating the oxygenated muriatic acid gas. This vapour, by filling the whole inside of the jar, acted upon the print; extracted the grease as well as ink spots; and the fragments remained pasted to the paper."
344. Vialard and Heudier have by this process restored several of the most valuable books of the French national library, and we believe they were the first who carried Chaptal's process into actual execution.
It is necessary, that we may fully succeed in this process, to be very precise in the quantity of the acid employed, and to use considerable address in the management of it, otherwise we shall injure the paper, and render the books incapable of being bound again. But with caution and a little experience, the method is perfectly safe and easy.
345. As it is convenient to be able to prepare the acid employed for this purpose in the most simple and economical way, we may recommend the following:
"To oxygenate the muriatic acid, nothing is necessary but to dilute it, and mix it in a very strong glass-veevel with manganese, in such a manner, that the mixture may not occupy the whole content of the glass. Air bubbles are formed on the surface of the liquor; the empty space becomes filled with a greenish vapour; and, at the end of some hours, the acid may be farther diluted with water and then used. It has an acid taste, because the whole is not saturated with oxygen; but it possesses all the virtues of the oxygenated muriatic acid. This process may be followed when there is not time to set up an apparatus for distilling, in order to procure the oxygenated acid."
346. It has been said, that the acid is not capable of removing spots of grease from books and prints. A method of doing this was lately published by M. Defchamps junior, and is as follows:
"After having gently warmed the paper stained with grease, wax, oil, or any fat body whatever, take out as much as possible of it, by means of blotting-paper. Then dip a small brush in the essential oil of well rectified spirit of turpentine, heated almost to ebullition (for when cold it acts only very weakly), and draw it gently over both sides of the paper, which must be carefully kept warm. This operation must be repeated as many times as the quantity of the fat body imbibed by the paper, or the thickness of the paper, may render necessary. When the greatly substance is entirely removed, recourse may be had to the following method to restore the paper to its former whiteness, which is not completely restored by the first process. Dip another brush in highly rectified spirit of wine, and draw it, in like manner, substances, over the place which was stained, and particularly round the edges, to remove the border, that would still present a stain. By employing these means, with proper caution, the spot will totally disappear; the paper will resume its original whiteness; and if the process has been employed on a part written on with common ink, or printed with printer's ink, it will experience no alteration.
Of Bleaching Yellow Wax.
347. Before the discovery of oxymuriatic acid and its application to bleaching, this was effected by exposing the yellow wax, formed into thin cakes, to the free action of the air, sun, and dews. The acid, however, as being far more expedient, is to be preferred.
In the bleaching of wax, it is proper to employ the simple acid, and its action would be the most effectual if used in the gaseous form. For this purpose, a pneumatic tub, with a cover secured in the manner recommended by Rupp, is the most proper. This should be filled with water, and the wax shred very fine must be introduced, and the gas made to pass through the water, while the agitator is kept in constant motion. In the course of an hour or two the wax will be bleached, may be separated from the water, melted and formed into cakes.
On applying the Residuums to profit.
348. Before we conclude our account of the various bleaching processes in which the oxygenated muriatic acid is concerned, it will be proper to inquire how far the materials employed in procuring this acid may be turned to account after the distillation.
The substances which remain in the distilling articles are a portion of undecomposed oxide of manganese, some sulphat of manganese, and a large quantity of sulphat of soda, (Glauber's salt).
The whole mixture may be employed with advantage as a glazing to coarse earthen-ware. This glazing has a dark colour, something like that of bronze, which it receives from the manganese; it is attended with this advantage, that it is perfectly safe, and is therefore much superior to any glazing, where lead enters as a part of the composition.
349. But the object of most importance is to decompose the sulphat of soda, in order to obtain the alkali. There are several methods of effecting this, but perhaps the two following are the best.
350. The first is that contrived by M. M. Malherbe and Athenas. The first object in this process, is to reduce the sulphat to the state of an alkaline sulphuret (liver of sulphur).
"Malherbe and Athenas have succeeded in this by employing iron as the intermediate substance: they mixed one part of charcoal dust with nine parts of the sulphat of soda, and exposed the mixture to the heat of a reverberating furnace: when the sulphuret entered into combustion, they added from three to five parts of old iron rendered as small as possible; and the whole being fused together, they obtained a black paste, composed of iron, soda, sulphat of iron, &c. This mixture was lixiviated, and filtered through a basket filled Vegetable with lime: it was then evaporated to dryness, and the substances residuum was calcined in a reverberating furnace.
When soda of a superior quality is required, the washing and calcination must be repeated.
"Dize and Le Blanc decomposed the sulphat of soda, by means of the carbonate of lime, in order to neutralize the alkali, by saturating it, at a very high temperature, with carbonic acid. Their process consists in taking two parts of sulphat of soda, dried to deprive it of its water of crystallization, two parts of well ground chalk (carbonate of lime), and one part of charcoal powder, mixing them well in a modified mortar, and then bringing the mixture to a white heat in a reverberating furnace: when the matter is fused, it is stirred till the sulphur is consumed, and the ebullition and the jet of the flame produced by the hydrogen gas have ceased to appear. It is then taken from the furnace, and it may be lixiviated to obtain the soda very pure. In whatever manner the sulphat is decomposed, this object merits the greatest attention at bleachfields on account of the considerable degree of economy which results from the different manipulations. The ley of the oxygenated muriatic acid will be obtained at little or no expense by bleachers, when they seriously set about extracting the soda from the sulphat formed during the distillation.
Bleaching by Sulphuric Acid.
351. From the effects produced by sulphuric acid in the processes of bleaching, in which it has been seen to act a material part, a proposal was lately made to employ it solely for this purpose, but we believe the project has never been carried into execution. It is certain, that a very weak bath containing one part of acid to five hundred of water* may be employed with the greatest safety; and when cloth remains immersed in it for a considerable time, it acquires a high degree of whiteness.
Of Bleaching by Steam.
352. The various processes which we have described, form nearly a complete abridgment of the history of bleaching; we have endeavoured to follow as closely as possible the progress of human genius, and to show how the rapid advances of modern chemistry have contributed to the improvement of this interesting art.
353. We are now to describe a new method, for which we are indebted to C. Chaptal. This ingenious and learned man, published some time since a memoir on the method of bleaching with steam, a process which we received from the Levant soon after the introduction of the art of dyeing Adrianople red, and which has been ever since employed in the interior of France, under the name of Blanchiment à la fumée. At the time when the disinterested Chaptal published an account of this method, it was a secret, the knowledge of which was confined to a few manufacturers. They only employed it in bleaching cotton in the states of wool and thread, in imitation of the eastern nations; vegetable but Chaptal, with his usual ingenuity, perceived the possibility of extending the process to the bleaching of thread of flax and hemp, and he invited the affluence of artists for the purpose of effecting this desirable end.
354. This appeal of Chaptal, induced many manufacturers as well in France as in other countries to make trial of this new method; and it was tried nearly at the same time at Paris and in Ireland. The apparatus constructed by C. Bawens, proprietor of the manufactory of cotton thread and stuffs at Bons Hommes near Pally, gave surprising results. He could bleach from two to three thousand ells of cotton in a day, with such facility, and at so moderate an expense, as proved the new method to be incomparably better than any before employed. The first trial was made on 1500 ells of cloth intended for printing; after the operation, it exhibited no variegation of surface, no shades, but one uniform complete whiteness. His apparatus resembles perfectly what has been described by C. Chaptal, and answers extremely well for bleaching cotton, both in the wool and when spun into thread. There have been several improvements lately made on it, which render it much more advantageous and of more extensive utility; but it will be proper, before examining these, to describe the apparatus recommended by Chaptal, which we shall do in his own words.
355. "At the distance of about sixteen inches above the grate of a common furnace, supplied with pit-coal, is fixed a copper boiler of a round form, 18 inches deep and four feet broad. The edges of this copper turned back, are made to rest on the side-walls of the brick-work of the furnace; they are about seven inches broad. The rest of the furnace is built of hewn stone, and forms an oval boiler six feet in height, and five feet in breadth at the centre: the upper part of this boiler has a round hole eighteen inches in diameter, which may be shut by a moveable piece of strong stone, or a copper lid adapted to it. Upon the edge of the copper boiler which forms the bottom of this kind of Papin's digester, is placed a grating made of wooden bars, so close together, that the cotton placed on them cannot fall through, and sufficiently strong to bear the weight of about 1600 pounds."
356. In the apparatus of C. Bawens, the mode of heating employed in Count Rumford's furnaces was used to reduce the quantity of fuel consumed, and thus render the process more economical. The heat of the chimney also served to heat the bath of weak sulphuric acid.
In other countries an apparatus has been employed, which possesses the advantage of winding up the stuffs within the copper, which resembles that of a steam engine with its tubes, safety valves, and collars of leather; but it has this inconvenience, that the stuff must be introduced at the top (s).
357. C. O'Reilly, to whom Chaptal had communicated
(s) The following passage translated by Nicholson from the Journal de Physique, is worthy of notice.
"A new method of bleaching has just been tried at Balynah, and has completely succeeded. The principle of the process appears to have been published by a French chemist, Chaptal, who is much respected by our manufacturers. I speak of the art of discolouring piece-goods in a digester, by caustic alkaline ley. Though our Part II.
Vegetable ed his ideas, soon conceived methods of improving the substances apparatus, and of applying it to various purposes suited to the different articles.
The first apparatus which he proposed to be executed at Jouy, represented an arched chamber of hewn stone, six feet eight inches long, by three feet ten inches broad; and three feet and a half high above the level of the wooden grate. (See Plate XII. fig. 8.). At one of the extremities is a door three feet long and two high, which is closed by a plate of cast iron, in which a hole is made for the introduction of a conical valve which is kept in its situation by a screw and a spring made as powerful as possible. The object of this valve was to guard against an explosion which might take place from the sudden expansion of the steam, which there is some cause to dread. The door was moveable, and fastened by ten bars and as many screws, which prevents against the rabbit, (which is covered with tow or wet leather) so as to prevent any of the steam from escaping this way. The door should be made with two iron handles, that it may be removed with the more ease.
The copper which forms the bottom of this apparatus, and in which the caustic alkaline solution is boiled, is 18 inches deep, and its other dimensions are less by four inches than those of the chamber. This gives room for the edges of the copper, and for a wooden grate on which the men may walk and conduct the operations. In the middle of the chamber are fixed two reels, on which from eighteen to twenty pieces of cloth are rolled. The axes of these reels pass through collars of leather, which prevent the escape of the steam; they have handles on the outside to roll and unroll the pieces, and there is a regulator communicating with the inside of the copper, to point out the height of the liquor, and shew how far it is exhausted. It is heated after Count Rumford's plan.
358. Another apparatus was constructed at Troyes for the purpose of bleaching hosiery. As these goods cannot be rolled up; and as the action of the vapour might be lessened were they heaped together, O'Reilly contrived frames of wood covered with cloth, and placed at the distance of four inches, one above another. Upon these frames the goods were spread in such a manner that the vapour rising from the copper might penetrate to every part, destroy the colouring matter, and thus complete the bleaching.
359. From some farther observations he was led to propose a roller placed in such a way, that the cloth rolled on it might on occasion be drawn through the liquor in the copper, to moisten it now and then, and thus increase the action of the liquor*.
360. After this account of O'Reilly's apparatus, of which a more particular description will be given presently, we come to the actual method of bleaching by steam. The following are the directions given by Chaptal.
361. "The cotton, disposed in handfuls, must first be impregnated with a slight solution of soda rendered caustic by lime. This operation is performed in a wooden or stone trough, in which the cotton is trod down by means of the feet covered with wooden shoes. When the alkaline liquor has uniformly penetrated the cotton, it is put into the boiler, and piled up on the wooden grate before mentioned; the redundant liquor runs through the bars into the copper boiler, and forms
first attempts did not perfectly succeed, we were not discouraged. The linen was exposed to the action of vapour in the apparatus, but it was not equally affected, as it appeared to be blotched in several places; we were, therefore, obliged to construct an apparatus, in order to unroll and separate the goods, and to expose the greatest surface possible to the action of the vapour. Suppose the boiler of a steam engine, in the form of an elongated ellipsis, provided with a safety valve, two tubes with cocks, to shew the consumption of the liquor, and a mercurial gage, to ascertain the strength of the steam. This boiler is bedded in masonry, or brick work, that it may resist the excessive pressure which necessarily takes place. In the interior part of the apparatus are fix reels, three at each end, alternating with each other, in order that the action of the steam may be more equable upon the goods. These reels are slowly and uniformly carried round by simple tooth and pinion work of wood, and the first motion is given to an axis which passes out of the boiler through a stuffing box, which prevents the escape of vapour. At the top is an opening of about fifteen inches diameter, with a rim or flanch, on which the cover is fitted, and firmly secured by screws. Between the two metallic faces are placed strips of soaked leather, to prevent the vapour from escaping. When the cover is taken off, the workmen can enter the boiler, to dispose the goods upon the rollers, each of which contains about fifteen or twenty pieces, making in the whole about forty-five or sixty. The raw material, namely, cunnamara kelp, is an article of inconsiderable expense, or else the soda extracted from sea salt, in which there remains indeed a small portion indecomposed, but which we procure at a very reasonable price. It is rendered caustic by the addition of some good lime, which is made from our limestone of Parre. With these a ley is formed, which is equal to fourteen degrees of our hydrometer. In this lixivium the piece goods are boiled, and then conveyed to the digester, on the bottom of which the ley stands to about five inches in depth. The workman stands upon a perforated stage, which prevents him from stepping into the ley while he is arranging the pieces: after which, having placed them on the rollers, the apparatus is closed, the fire lighted, and the operation begins. As soon as ebullition takes place, the handle on the outside is incessantly turned, and as soon as the roller at one end is filled, the handle is shifted to the other roller, and the turning performed in the contrary direction. In this manner the operation is continued till the whole of the contents is bleached. From this description you may easily understand how this operation is performed; I shall, however, take the first opportunity of sending you a plan and description of the apparatus, if you wish for further information. You are at liberty to make whatever use you please of this account: the expense of bleaching is not more than one farthing per yard, including coals, workmen's wages, &c. as well as interest for the capital employed in the apparatus." Vegetable a stratum of liquid, which permits the mass to be heated without any danger of burning either the cotton or the metal. To form the alkaline ley, Alicante soda equal to a tenth of the weight of the cotton subjected to the operation is employed, and in a boiler such as that the dimensions of which I have given, about 800 pounds of cotton may be put at one time. The ley is generally of two degrees by the aerometer. As soon as the cotton is introduced into it, and arranged in the boiler, the upper aperture is shut with its usual covering, scarcely any opening being left, that the steam developed by the fire may assume a much more considerable degree of heat, and react with force on the cotton. When every thing is arranged, the fire in the furnace is kindled, and the ley is maintained in a state of slight ebullition during 36 hours. The apparatus is then suffered to cool, and the cotton being taken out is carefully washed; after which it is exposed on the grats for two or three days, extending it on poles in the day time, and spreading it out on the grats during the night. The cotton will then have acquired a high degree of whiteness; and if any portions of it be still found coloured, they must be put into the boiler for a second operation, or be left on the grats some days longer. These shades in bleaching cotton arise, in particular, from all the parts of the cotton in the first operation not having been completely and uniformly impregnated with the ley. They may be owing also to the cotton, when arranged in the boiler, having been too much accumulated on certain points. When it is judged that the ley has been exhausted by ebullition, the boiler is opened, and the dried cotton is moistened with a new quantity of the solution of soda: without this precaution it would be in danger of being burnt. It may be easily conceived, by an estimate of the matters and time employed in this operation, with how much saving of expense it is attended: cotton is bleached by this method in all the manufactories of the south of France, where it is used, at the low rate of two sols per pound."
362. Cloth may be bleached in the same way, but requires first to be freed from the weavers dressing, &c. as formerly directed.
363. While the goods are steeping so as to be perfectly impregnated with the alkaline ley, the copper is to be filled to the height of a foot with ley of the same strength. This may be done by means of a curved leaden funnel, but as the door is sufficiently large, the ley may be thrown in with buckets.
A workman then enters the chamber, and fixes one end of a piece of cloth by means of packthread to one of the arms of the farthest reel A (fig. 9. Plate XCII.) while another workman without turns the handle till the whole piece is wound on; the end of another piece is then fastened to the first, and so on till 18 or 20 pieces are wound round the first reel. The remaining extremity of the last piece is then passed over the roller B, near the arch of the chamber; from thence it is carried below the two rollers C, D, in the copper EE; is again carried to the arch, and made to pass over the roller F, and is lastly fastened to an arm of the other reel G. The workman then ascertains the height of the liquor in the copper by the regulator, and then shuts the cock, and closes up the door by rags and the proper screws, so as to prevent all escape of steam. The fire is then kindled, and the liquor made to boil. The vegetable workman then begins to wind off the pieces, commencing with the reel to which the last end was tacked, till this has received the whole charge; he then lowers the cranks of the lower rollers, so as to plunge the goods into the boiling ley, and immediately begins to reel off with dispatch; again raises the rollers, and reels the pieces back without pausing through the ley.
At the end of two hours, more or less according to the fineness of the pieces, the alkali carried up by the heat will completely have penetrated the fibres of the cloth, which are swelled by the extraordinary heat of the steam.
The fire is now extinguished, and as soon as all is sufficiently cool, the door is opened, and they prepare for immerging the stuffs in the oxygenated muriatic acid, after they are first well rinsed in fair water.
364. For immersion the tub described in 262. is employed, and the pieces are fastened and reeled in the manner there described, till the liquor on examination is found pretty much exhausted. The pieces are then taken out separately, well rinsed in a stream of water, and exposed on the grats for three or four days. They are then passed through a bath of very weak sulphuric acid, and will then have acquired a high degree of whiteness.
If linen or hempen cloth should retain a slight yellow cast, which will sometimes happen, the steaming must be repeated; and they must be exposed again for a day or two on the grats.
365. Hosiery and threads are bleached in the same way, but they are to be placed on frames at such a distance from each other that they may be easily penetrated by the steam; but as these articles cannot, like the cloths, be made to pass through the ley in the copper, the process is to be stopped at the end of two hours, and then the upper frame is completely wet with ley, which oozes through, and thus moistens all the lower frames. The boiling is again commenced, and continued for four hours. For the immersion, the apparatus of Rupp with the vertical reels is the best possible, and the goods are to be hung on the upper end of the reel. After immersion, they are rinsed, exposed on the grats, and passed through the acid bath as other articles.
366. Chaptal has lately applied this method to a very important object, the scouring and whitening of foul linen.
"I have no doubt," says he, "but that linen garments may be bleached to advantage by the same process; but as it was necessary to bring these notions to the test of experiment, I invited Citizen Bawens to allow me to make the experiment on a large scale with his apparatus. Accordingly, on the 27th Pluviose, in the year 9, I had 200 pair of sheets from the hospital of the Hotel Dieu at Paris, chosen among those that were most soiled, and taken to the manufactury of Citizen Bawens.
"Three experiments were made upon these sheets.
"Experiment 1. One hundred and thirty sheets were impregnated with a caustic alkaline ley, containing one hundredth part of soda. They were kept for six hours in the engine of steam; after which they were impregnated again, in order to be placed again six hours in the same machine.
"The same process was repeated a third time; after which they were carefully rinsed, and no spots of wine, Part II.
Vegetable wine, grease, blood, or animal ejection, was to be seen. Substances. One quarter of a pound of soap was used in rinsing these cloths.
"All the assistants were convinced that the ordinary processes would not have given either so perfect a white, nor so agreeable a lixivial smell.
"The texture was in no respect altered.
"Experiment 2. The alkaline ley contained only six parts of soda, but five pounds of soap were also added. The cloths were treated in the same manner, and the results appeared more advantageous. They were easily washed out.
"Experiment 3. To the bath of the second experiment a sufficient quantity of new ley was added. One hundred and forty sheets were treated like the preceding, and the result was the same.
"It must be observed that the water of the Seine, in which these sheets were rinsed, was at that time very yellow.
"This experiment appeared to me to offer several results worth the attention of the Institute.
"In the first place the process is economical. Two hundred pair of sheets, which were bleaching by three successive operations, demanded an expenditure, according to the account furnished by Citizen Bawens, which is in the proportion of 7 to 10, compared with that commonly made in the hospitals. This expense may be reduced to less than one-third, if a suitable place and apparatus were appropriated to this use.
"2. Two days at most are required to complete the operation. This economy of time is incalculably beneficial.
"3. The linen is neither changed nor torn, as it passes through the hands only once, and it is of no use to beat it.
"4. The extreme heat to which the linen is exposed in the apparatus, causes its texture to be penetrated by the alkaline fluid to such a degree, that the substances with which it is impregnated cannot be masked from its action; so that the putrid exhalations, and other substances attached to its texture, are necessarily destroyed or changed in their nature.
"This effect must be more particularly seen with regard to its value, by physicians, who are aware with what facility the seeds of various disorders are perpetuated in hospitals, and how insufficient the greater number of processes used in washing linen have proved to destroy them."
367. It only remains that we should give a brief explanation of the manner in which the steam, thus confined, acts in bleaching the goods.
It has appeared from the former parts of this article, that the bleaching of vegetable substances depends on the united influence of moisture, light, and oxygen; and the mode in which these act, as also the action which alkalies exert on the colouring matter of cloth, has been explained. This action of the alkali is materially assisted by the increased temperature of this vapour bath, by which the fibres of the cloth, &c. are swelled and opened; and thus the caustic alkali carried up with the steam, greedily feizes on and destroys the colouring matter; or, should some part of it escape, a second steaming, after immersion and exposure to the air, never fails to discharge it. The increased temperature, independently of swelling and opening the texture of the cloth, seems also to render the alkali more active than it can be in the ordinary leys, in which the substances, temperature never exceeds 162° Fahrenheit; for one degree of the aerometer is always a sufficient strength, and very seldom more than half a degree is required.
By passing the goods through a single bath of oxygenated muriatic acid, or oxymuriat of lime, a combination takes place between the oxygen of the liquor and the carbon produced by the destruction of the extracto-refinous matter by the alkali, and carbonic acid is formed, and this is dissipated by the subsequent exposure to the atmosphere.
368. We cannot however agree with O'Reilly*, that *Effai sur le steam itself possesses no bleaching power, as we are le Blanch. convinced from the common process of cooking green vegetables in steam, by which, as is well known, they lose their green colour, that this is not the case.
369. It has been supposed that the vapour arising from a boiling solution of caustic alkali would not itself be caustic, or produce the same effects as the solution; a supposition which was founded on the concentration of salts by evaporation; but we are by no means to infer, from what takes place in the open air, where the moisture is constantly absorbed as it rises, that the same will happen in a close apparatus, where the temperature is considerably increased; and, in fact, that alkali is capable of being raised by steam is fully proved by suspending paper tinged blue over a boiling solution of potash, when the blue will soon be converted into a green.
We shall conclude this article with M. Chaptal's observations on the art of scouring different kinds of stuffs.
"This art supposes, 1st, a knowledge of the different substances capable of staining any kind of cloth; 2d, of the substances to which recourse must be had in order to make those deposited on the stuff to disappear; 3d, a knowledge of the effects produced on colours by those re-agents which it may be necessary to employ to destroy stains; 4th, a knowledge of the manner in which the cloth is affected by those re-agents; 5th, of the art of restoring a colour changed or faded.—Of those bodies which occasion spots on different kinds of cloth, some are easily distinguished by their appearance, such as greasy substances; but others have more complex effects, such as acids, alkalies, perspired matter, fruits, urine, &c. Acids reddish black, fawn, violet and puce-colour, and every shade communicated with orchilla-weed, iron, arrtingents, and every blue except indigo and Prussian blue. They render the yellows paler, except that of annatto, which they change into orange.
"Alkalies change to violet the reds produced by Brazil wood, logwood, and cochineal. They render the greens on woollen cloth yellowish, make yellow brownish, and change the yellow produced by annatto to aurora. Perspired matter produces the same effects as alkalies.
370. "When the spots are produced by simple bodies on stuffs, it is easy to remove them by the means already known. Greasy substances are removed by alkalies, soaps, the yolk of eggs, fat earths; oxyds of iron, by the nitric and oxalic acids; acids by alkalies, and reciprocally. Stains of fruit on white stuffs may be removed by the sulphurous acid, and still better by the oxygenated Vegetable-oxygenated muriatic acid. But when the spots are of substances, a complex kind, it will be necessary to employ several means in succession. Thus, to destroy the stain of coom from carriage-wheels, after the greafe has been diffolved the oxide of iron may be removed by the oxalic acid.
371. "As colours are often changed by re-agents, it will be necessary, in order to restore them, that the scourer should possess a thorough knowledge of the art of dyeing, and how to modify the means according to circumstances. This becomes the more difficult when it is necessary to reproduce a colour similar to that of the rest of the stuff, to apply that colour only in one place, and often to restore the mordant by which it was fixed, and which has been destroyed, or even the first tint which gave the colour its intensity. It may be readily conceived that the means to be employed must depend on the nature of the colour, and the ingredients by which it was produced; for it is known that the same colour may be obtained from very different bodies. Thus, after an alkali has been employed to destroy an acid spot on browns, violets, blues, poppies, &c. the yellow spot which remains may be made to disappear by a solution of tin; a solution of sulphat of iron restores the colour to brown stuffs which have been galled; acids restore to their former splendour yellows which have been rendered dusky or brown by alkalies; blacks produced by logwood become red by acids; alkalies change these red spots to yellow, and a little of the astringent principle makes them again become black. A solution of one part of indigo in four parts of sulphuric acid, diluted with a sufficient quantity of water, may be employed with success to revive the blue colour of cotton or wool which has been changed. Scarlet may be revived by means of cochineal and a solution of the muriat of tin, &c.
"The choice of re-agents is not a matter of indifference. Vegetable acids are preferable; the sulphurous acid, however, may be employed for stains occasioned by fruit: it does not change the blue of silk nor colours produced by astringents: it does not degrade the yellow of cotton. Ammonia succeeds better than fixed alkalies in removing spots produced by acids. It is employed in vapour; its action is speedy, and seldom alters the colour.
372. "The means of removing greasy spots are well known. This effect is produced by alkalies, fullers earth, volatile oils diffolved in alcohol, a heat proper for volatilizing greafe, &c. Spots occasioned by ink, rust, or iron-mould of any kind, and all those produced by the yellow oxide of iron, are removed by the oxalic acid: the colour may be restored by alkalies, or a solution of the muriat of tin. These spots may be removed also by the oxygenated muriatic acid, when they are on white stuffs or paper.
"The action of alkalies, and that of perspired matter, are the same: their spots may be effaced by acids, or even by a weak solution of the muriat of tin. When these spots arise from several unknown causes, in order to destroy them recourse must be had to poly-chrest compositions. The following may be considered as one of the most efficacious. Dissolve white soap in alcohol, and mix this solution with the yolks of from four to fix eggs: add gradually essence of turpentine; and incorporate with the whole some fullers earth, in such a manner as to form balls of a suitable consistence. Sublimate the spot; and, having rubbed it with these balls, the spot will be removed by washing the stuff. All spots, except iron-mould and ink, may be removed in this manner.
"Washing destroys the lustre, and leaves a tarnished place disagreeable to the eye; but the lustre may be restored by drawing over the washed place, and in the direction of the pile, a brush moistened in water impregnated with a little gum. You may then apply a sheet of paper, or a piece of cloth, and a considerable weight, under which the cloth must be left to dry."
Description of Apparatus.
Plate XCI.
Fig. 1, 2. O'Reilly's Apparatus for preparing SULPHURIC ACID.
Fig. 1. Elevation of the APPARATUS.
A, The furnace which is made capable of containing three distilling vessels. a, A curved funnel for introducing the sulphuric acid. b, A tube passing from the matras to an intermediate leaden vessel B intended to condense the sulphuric acid which comes over undecomposed, and having five necks, three of which receive tubes similar to b, and from the fourth passes the tube d. c, A tube of safety. d, A tube passing from the intermediate vessel to the first of the tall Wolfe's vessels C intended to condense the sulphuric acid. D, The second of the Wolfe's vessels, with tubes to connect it with the first and third.
Each of these vessels has a leaden cock to empty the acid liquor into the immersing tubs.
Fig. 2. Plan of the above VESSELS.
Fig. 3. A vertical Section of RUPP'S IMMERSING TUB, as improved by O'Reilly.
a, b, The tub. c, d, The cover perfectly air-tight. e, The partition dividing the tub into two parts. f, A funnel filled with a plug. g, g, The wooden reels on which the stuffs are rolled. h, h, h, h, h, h, h, Seven rollers, over and under which the stuffs pass, so as to expose a large surface to the bleaching liquor. i, A leaden cock to draw off the liquor.
Fig. 4. Rupp's Original Apparatus, as described in 253.
Fig. 5, 6, 7. The Original Apparatus for distilling the OXYGENATED MURIATIC ACID GAS, described in 209.
Plate XCII.
Fig. 8. The Apparatus employed for this purpose in IRELAND.
a, The ash-hole. b, The place for the fire. c, A c, A door by which fuel is introduced. d, Door of the ash, with a register to regulate the draught of air. e, A boiler of cast iron filled with hot water, in which is placed the alembic. f, A three-footed iron stand to support gg, A leaden alembic. h, A glass or leaden curved funnel for introducing the sulphuric acid. i, A leaden cover firmly fixed by luting to the neck of the alembic, and pierced with three holes for the transmission of the funnel, the handle of an agitator, and a condensing tube. k, The agitator formed of iron covered with lead. l, A leaden tube three inches in diameter for conducting the gas into m, An intermediate vessel of lead for condensing the acid which may pass over from the alembic unconsumed. The tube l descends through the first opening m 1, nearly to the bottom of the vessel, which is two-thirds filled with water; the oxygenated muriatic acid traverses the water, and passes out at the top through the leaden tube n into o, o, the pneumatic tub, made of wood fitted with a cover r, which is perfectly air-tight, and through which passes an agitator p, with three leaves for mixing the gas with the water. q, q, q, Three shelves in the tub, which by retarding the ascent of the bubbles of gas, facilitate its union with the water. s, A stop-cock for letting off the liquor.
Fig. 9. A Vertical Section of O'Reilly's Apparatus for bleaching by Steam. E, E, E, The boiler. A, G, The two reels. B, F, The upper rollers. C, D, The lower moveable rollers. H, The regulator. I, A stopcock. K, The door of the chamber.
Fig. 10. The Apparatus, with Frames for Bleaching Thread and Hosiery.
Fig. 11. Plan of Loysel's Apparatus for Bleaching Paper. 1, 1, 1, &c. Eight furnaces, having a chimney of sheet iron common to each pair of furnaces. 2, 2, 2, &c. Eight vessels of cast iron, containing fand. 3, 3, 3, &c. Eight matrasses, balloons, or bottles of stone-ware, compact, and well baked, intended to contain the materials which afford the gas. Each matras must be filled only to one-third of its capacity at most. Bodies of glass of little thickness may also be used for this purpose. 4, 4, 4, &c. Tubes of glass to conduct the gas into the receiver. Or these tubes may be made of lead. 5. The receiver. It is composed, 1, of an internal vessel, covered with plates of lead well soldered together, and provided near its bottom with a cock 6, to draw off the liquor when prepared. 2. Another vessel, 7, likewise covered with plates of lead within and without. This second tub is inverted in the first, to contain the gas in proportion as it is disengaged, and to keep in contact with the water of the receiver that portion of gas which had not time to be diffused in passing through that fluid. There is a hole, 8, in the upper part of this second vessel. It serves to suffer the common air to escape when water is first poured into this receiver, and it is afterwards closed with a stopper of lead or cork, covered with paper soaked in starch, and fastened to the cork by a piece of cloth or bladder, before the operation begin.
Fig. 12. Vertical section of the apparatus. Fig. 13. Elevation of the apparatus.
The disposition of the furnaces about the receiver, and the circular form of the receiving vessels, was rendered necessary by the local circumstances of the laboratory in which our operations were carried on. In other circumstances square vessels might be employed, and all the furnaces might be ranged in a right line under a common chimney.
INDEX.
A ACCIDENTS occurring in bleaching, modes of remedying, N° 287, 292, 295 Acid, muriatic, employed for bleaching silk, 71 best mode of preparing, 111 et seq. nitric, improper in any process to which silk is subjected, 78 oxymuriatic, discovered by Scheele, 176 first applied to bleaching by Berthollet, ib. effects of, on vegetable colours, 178, 183
Acid, oxymuriatic, modes of preparing, N° 177, 245, 345 of no use in bleaching animal substances, 304 sulphurous, wherein it differs from sulphuric, 30 mode of procuring, 32 et seq. sulphuric, mode of purifying, 103 Air, atmospheric, composition of, 138 Alcohol, effects of, on yellow silk, 87 retained by silk in bleaching; mode of recovering, 75 employed in bleaching silk; modes of recovering, 94, et seq.
Alkalies, effect of, on the colouring-matter of cloth, N° 144 capable of being raised in vapour, 359 Alum of no use in the bleaching of silk, 66 Animal substances, in what they differ from vegetable, 10 employed for clothing, 12 B Bawens, his success in the application of steam to bleaching, 334 Baumé, his method of bleaching silk, 62 et seq. his lutes, 228 Berthollet, Berthollet, his mode of bleaching, No 185 et seq.
Bleaching, origin of, uncertain, probably of later date than dyeing, ib. extent of, 6 theory of, 158, 266 by atmospheric air, 154 by water, 160 by oxymuriatic acid, 203, et seq. by sulphuric acid, 351 by steam, 355, et seq. liquor, strength of, mode of ascertaining, 256, 263
Bonjour, his attempt to introduce Berthollet's method of bleaching, 189
Books, and prints, mode of cleansing and whitening, 339, 346
Bucking, what, 154
Chaptal, his soap of wool, apparatus for bleaching by steam, 355 method of cleaning books and prints, 340 of scouring linen, 366 observations on scouring various stuffs, 369 Cloth, steeping of, 134 colouring matter of, 135 Kirwan's experiments on, 137 et seq.
Cocons of silk, ill effects of baking, best method of preparing by alcohol, ib.
Colours assumed by goods during the processes of bleaching, 265 of printed and dyed goods, 304 method of discharging, chemical and fast, 325
Cotton, its nature, more easily bleached than other substances, 151 bears the action of acids better than hemp or flax, 152
Dalrymple's fish-soap, 175 De Charmes, his improvements on Berthollet's method, 214 et seq. his furnace, 215 mode of obtaining sulphuric acid, 226 Ce Croizille, his mode of determining the strength of bleaching liquor, 209 Dressing, weavers, 133
E Earth, a new, for scouring, account of, No 23
F Flax, beating of, 130 effect of watering, 127 frit used in Egypt, 123 nature of, 126 method of preparing, 126, 129
G Glazing for coarse pottery, 348
H Higgins, his account of the mode of bleaching with sulphuret of lime, 171 Hyperoxymuriat of potash possesses no bleaching power, 259
K Kirwan, his experiments on the colouring matter of cloth, 137, et seq.
L Lime, injurious to cloth, 167 Lutes, mode of preparing, 228, et seq. applying, 232
M Manganese, mode of purifying, 194, et seq. May-dew, effects of, ascribed to oxygen, 185
O O'Reilly, his mode of preparing sulphurous acid, 30, et seq. method of bleaching wool, 36 apparatus for rinsing cloths, 261 for bleaching by steam, 375, et seq. method of bleaching by steam, 363 Oxymuriat of lime, use of, in bleaching, 260
P Paper, method of bleaching, 318, et seq. method of renewing, 309, et seq.
Potash, nature of, 162 how purified, 165 added to oxymuriatic acid, corrects its odour, but diminishes its power, 258
R Residuums, of the distillation of oxymuriatic acid, uses of, 348 Rigaud, his method of bleaching filk, 58 Rupp's immerging tub, 253 experiments on adding potash to oxygenated liquor, 258 improvement on Defcroizille's proof liquor, 255
S Scouring, ancient mode of, 5 Silk, baking of, 39 nature of, what, 44 colouring matter of, nature of, 88 effect of reagents on, 46 BLEACHING
PLATE XCI.
Fig. 1. Fig. 2. Fig. 3. Fig. 4. Fig. 5. Fig. 6. Fig. 7.
Engr. by W. & D. Lizars Edin.
PLATE XCII.
Fig. 8. Fig. 9. Fig. 10. Fig. 11. Fig. 12. Fig. 13.
Engraved by W.C.D. Lizars Edin'