SOFT SOAP differs both in composition and in the process of its manufacture, from hard soap. Instead of soda being used for the alkaline, base potash is employed. The following is given by Dr Ure as the process:—
"A portion of the oil being poured into the pan, and heated to nearly the boiling point of water, a certain quantity of the weaker lye is introduced, the fire being kept up so as to bring the mixture to a boiling state. Then some more oil and lye are added alternately, until the whole quantity of oil destined for the pan is introduced. The ebullition is kept up in the gentlest manner possible, and some strong lye is occasionally added, till the workman judges the saponification to be perfect. The boiling becomes progressively less tumultuous, the frothy mass subsides, the paste grows transparent, and it gradually
thickens. The operation is considered to be finished when the paste ceases to affect the tongue with an acrid pungency, when all milkiness and opacity disappear, and when a little of the soap placed to cool upon a glass plate assumes the proper consistency."
The peculiar granular appearance of the soft soap used in this country, and which makes it so much resemble the pulp of ripe figs, is produced by the addition of small quantities of tallow, which are disseminated through the mass, and form the white specks. From its appearance when complete, this operation is technically called figging. The oils generally used are the fish, whale, and seal oils, but on the continent various seed-oils, especially those from hemp-seed, linseed, colza-seed, and poppy-seed. The continental soap-makers give the soft soap a green colour, which is sometimes produced by the addition of indigo.
Soft soap is much used in cleansing woollen fabrics, for which its superior solubility and great detergent power specially fit it. A very coarse kind is used by farriers under the name of black soap. There are a few varieties of soft soap used for toilet purposes, the principal of which is Naples soap, used chiefly for shaving. It is said to be made only from olive-oil and potash; but all imitations of it differ from the true Italian manufacture. It is much prized in consequence of its softening power upon the hair.
The MEDICATED SOAPS have lately acquired some importance in pharmacy, particularly on the continent. The Castile soap, previously mentioned, is generally used as the base of these preparations. The most valuable of all medicated soaps is the Chlorinated, the Savon Antisyphilitique of French pharmacy. It is made by working together one part of chloride of lime with eleven of Castile soap, using spirit of wine scented with oil of verbenas to effect the incorporation. The mass is then fashioned into little flat cakes, and folded carefully in tinfoil or gutta-percha paper. It is powerfully detergent, and is very effective in removing stains, and is known to be of remarkable efficacy in preventing the effects of contagion, if the hands or clothes are washed with it. The other medicated soaps are antimonial, croton, guaiacum, iodine, mercurial, tar, turpentine, sulphuretted vitriol, &c., the formulæ for which are in the pharmacopœias.
Arsenical soap is of considerable importance to the naturalist, being an effectual preservative of the skins of animals, particularly of birds, and those most liable to the attacks of moths. It is composed of carbonate of potash, twelve parts; of white arsenic, common white soap, and air-slaked lime, each four parts; and powdered camphor, one part, with enough of water to make it into a paste.
The rationale of the process of saponification was first explained by Chevreul, who showed that in the combination new substances capable of forming salts and possessing true acid properties are generated out of the elements of the fat, under the influence of the alkaline base. Common fat saponified consists of a mixture of stearic, margaric, and oleic acids, each combined with the base, and the peculiar neutral liquid substance called glycerine, which resembles colourless syrup, and is miscible with water. Glycerine is obtained from other sources than soap, and for commercial purposes is generally procured by refining the sweet liquor of the stearine-makers; it is now extensively used chiefly in pharmacy for external applications. When pure it is colourless, odourless, sweet to the taste, and of a syrupy consistency; it feels soft like oil, but has no greasiness, and it does not evaporate at ordinary temperatures; hence its value to the surgeons for keeping inflamed parts moist.
The importance of this branch of manufacture is very considerable, whether it be viewed with respect to its sanitary effects upon the human race, or in its bearing upon other important manufactures. In no country is it used
to the same extent as in Great Britain; and, as a consequence, the skill of our chemists has been specially directed to its improved and economical production with so much success that, now the excise restrictions have left the soap-maker unfettered, we are enabled to produce all the really useful kinds, not only much cheaper, but also better, than the manufacturers of other countries; while in the ornamental varieties we beat our neighbours in cheapness, and are rapidly approaching them in elegance of production. The rapidity with which this branch of industry has developed in this country is truly marvellous. In the first year of the present century the consumption of soap was 52,947,037 lb., but in 1850 it had reached the enormous quantity of 197,632,280 lb. This increase during the half century, viewed in relation to the increase in population, is quite as remarkable. In 1801 the quantity gave 484 lb. to each person, while that in 1850 gave 971 lb. It must not, however, be assumed from these facts that the personal use of soap had doubled, as a very great proportion of the increased consumption has been due to the extension of our manufactures in which soap is used, and to the origination of new branches of industry in which it is required.
The quantity of soap at present made in Great Britain cannot be ascertained with certainty, as the duty is now removed, and we have no excise returns; but the quantity is annually increasing to a great extent. Our exports alone amounted last year (1858) to 12,500 tons, the greatest portion of which was sent to our colonies. The States of South and Central America also received large quantities; the rest found its way to Austria, Italy, Sardinia, Turkey, Java, China, and Western Africa. (T. C. A.)