in general, signifies the natural formation of any substance into a regular figure, resembling that of natural crystal. Hence the prairies of crystallized ores, crystallized salts, &c., and even the basaltic rocks are now generally reckoned to be effects of this operation. See BASALTES, and VOLCANO. The term, however, is most commonly applied to bodies of the saline kind, and their separation in regular figures from the water, or other fluid in which they were dissolved, is called their crystallization*. The word crystallization is never applied to the freezing of water, or to the consolidation of metals after they have been melted; though it might certainly be applied with as much justice to these substances as to any others; for all of them concrete into a certain regular form, from which they never deviate, unless disturbed. When water freezes slowly, it always forms regular crystals of ice, which are constantly of the same form. They are long, needle-like masses, flattened on one side, and joined together in such a manner, that the smaller are inserted into the sides of the greater; and thus these compound crystals have the appearance of feathers, or branches of trees with leaves. The most remarkable circumstance attending this crystallization is, that the angle formed by the insertion of the smaller pieces into the larger is either 60°, or 120° degrees. The figures assumed by metals of different kinds have not been so exactly investigated, except in the regulus of antimony, which is observed always to take a flatted form. Experience also shows, that all kinds of earths, or other mineral matters, are capable of assuming a crystalline form, and may easily be made to do so by taking away part of the water which dissolves them.

Different salts assume different figures in crystallization, and are thus most easily distinguished from one another. The methods of reducing them into this form, for sale, are mentioned under the article CHEMISTRY, n° 74. But besides the large crystals produced in this way, each salt is capable of assuming a very different appearance of the crystalline kind, when only a single drop of the saline solution is made use of, and the crystallization viewed through a microscope. For our knowledge of this species of crystallization we are indebted to Mr Henry Baker, who was presented with a gold medal for the discovery, in the year 1744. These microscopical crystals be distinguished from the large ones by the name of configurations; but this term seems inaccurate, and the distinction may well enough be preserved by calling the large ones the common, and the small ones the microscopical crystals of the salt. His method of making these observations he gives in the following words:

"I dissolve the subject, to be examined, in no larger a quantity of rain or river water than I am certain it is sufficient to saturate. If it is a body easily

diffusible, I make use of cold water; otherwise I make the water warm, hot, or even boiling, according as I find it necessary. After it is perfectly dissolved, I let it rest for some hours, till, if overcharged, the redundant saline particles may be precipitated, and settle to the bottom, or float into crystals; by which means I am most likely to have a solution of the same strength at one time as at another; that is, a solution fully charged with as much as it can hold up, and no more; and by these precautions the configurations appear alike, how often forever tried: whereas, if the water be less saturated, the proportions at different times will be subject to more uncertainty; and if it be examined before such separation and precipitation of the redundant salts, little more will be seen than a confused mass of crystals.

"The solution being thus prepared, I take up a drop of it with a goose quill cut in fashion of a scoop, and place it on a flat slip of glass of about three quarters of an inch in width, and between three and four inches long, spreading it on the glass with the quill, in either a round or an oval figure, till it appears a quarter of an inch, or more, in diameter, and so shallow as to rise very little above the surface of the glass. When it is so displosed, I hold it as level as I can over the clear part of a fire that is not too fierce, or over the flame of a candle, at a distance proportionable to the heat it requires, (which experience only can direct), and watch it very carefully till I discover the saline particles beginning to gather and look white, or of some other colour at the extremities of the edges. Then, (having adjusted the microscope before-hand for its reception, armed with the fourth glass, which is the fittest for most of those experiments), I place it under my eye, and bring it exactly to the focus of the magnifier; and, after running over the whole drop, I fix my attention on that side where I observe any increase or pushing forwards of crystalline matter from the circumference towards the centre.

"This motion is extremely slow at the beginning, unless the drop has been overheated, but quickens as the water evaporates; and, in many kinds, towards the conclusion, produces configurations with a swiftness inconceivable, composed of an infinity of parts, which are adjusted to each other with an elegance, regularity, and order, beyond what the exactest pencil in the world, guided by the ruler and compasses, can ever equal, or the most luxurious imagination fancy.

"When this action once begins, the eye cannot be taken off, even for a moment, without losing something worth observation: for the figures alter every instant till the whole process is over; and, in many sorts, after all seems at an end, new forms arise, different entirely from any that appeared before, and which probably are owing to some small quantity of salt of another kind, which the other separates from, and leaves to act after itself has done: and in some subjects, three or four different sorts are observable, few or none of them being simple and homogeneous.

"When the configurations are fully formed, and all the water evaporated, most kinds of them are soon destroyed again by the moisture or action of the air upon them; their points and angles lose their sharpness," Crystalline florets become uneven and defaced, and moulder, as it were, away. But some few are permanent, and being inclosed between glasses, may be preserved months or even years, entertaining objects for the microscope.

"It happens oftentimes that a drop of saline solution can hardly be spread on the slip of glass, by reason of the glass's smoothness, but breaks into little globules, as it would do if the surface were greasy; this was very troublesome, till I found a way of preventing it, by rubbing the broken drop with my finger over the glass, so as to leave the surface smeared with it; on which smeared place, when dry, another drop of the solution may be spread very easily in what form one pleases.

"It likewise sometimes happens, that when a heated drop is placed properly enough for examination, the observer finds he can distinguish nothing: which is owing to saline steam that rise from the drop, cover and obscure the object-glass, and therefore must immediately be wiped away with a soft cloth or leather.

"In all examinations by the microscope of saline solutions, even though made in the day-time, I always employ the light of a candle, and advise every observer to do so likewise: for the configurations being exceedingly transparent, are rendered much more distinguishable by the brown light a candle affords, than by the more white and transparent day-light; and besides, either by moving the candle or turning the microscope, such light may be varied or directed just as the object requires."

In this manner were produced the beautiful crystallizations represented Plate LXXXVII. They are vastly different from such crystals of the same salts as are obtained by the common processes; but Mr Baker assures us they are no less constant and invariable than they, and that he has repeated the experiments a great number of times with the same success.

Fig. 1. shews the microscopical crystals of nitre or salt-petre. These shoot from the edges, with very little heart, into flatish figures of various lengths, exceedingly transparent, and with strait and parallel sides. They are shewn in their different degrees of progression at the letters a, b, c, d, e; where a represents how they first begin. After numbers of these are formed, they will often dissolve under the eye, and disappear entirely; but if one waits a little, new shoots will push out, and the process go on afresh. These first figures sometimes enlarge only without altering their shapes, and sometimes form in such sort as the drop represents; but if the heat has been too great they shoot hastily into numerous ramifications very numerous and very beautiful, but very difficult to be drawn; and which Mr Baker therefore did not attempt. There seems all the while a violent agitation in the fluid, and most commonly, towards the conclusion, a few octaedra (composed of eight triangular planes, or two quadrangular pyramids, joined base to base), make their appearance.

2. Blue vitriol produces crystals round the edges, very short at the beginning, but increasing gradually, as represented at the figures 1, 2, 3, which denote their difference of form, and the progress of their growth. These crystalline shoots are solid, regular, transparent, and reflect the light very beautifully from their polished sides and angles. As the watery part evaporates, numbers of long slender bodies like hairs are seen here and there, some lying side by side, or crossing each other as at 4, others forming star-like figures with many radiations (5, 5). This salt shoots but slowly, and therefore requires patience. At last the true crystals begin to appear commonly in the middle of the drop, and are very prettily branched, as at 6.

3. Distilled verdigris, dissolved as above directed, and immediately applied to the microscope, shews abundance of the regular figures 1, 2, 3, 4, 5, 6, 7: but if the solution is suffered to stand for a few hours, and a drop of it is then heated over the fire on a slip of glass, till it begins to concrete about the sides, and then examined, sharp-pointed, solid, figures, bifected by a line cut through the middle, from which they are cut away towards the edges begin to appear, and shooting forwards (1, 1, 1). These figures are often striated very prettily from the middle line to the edges obliquely, (2, 2); and frequently they arise in clutters; and shooting from a centre (3, 3). These figures are a long time in growing; and whilst they are doing so, several regular crystals appear forming in several parts of the drop, of the most lovely emerald colour, and reflecting the light from their sides and angles, which are most exactly disposed, and finely polished. No crystals are formed in the middle, till the water is nearly evaporated; and then they begin to form hastily, for which reason they must be carefully attended. Their common figure resembles two long croffing each other in an angle of about 60°, and shooting branches every way: each of which again protrudes other branches from one, and sometimes from both its sides; making together an appearance like four leaves of fern conjoined by their stalks (5, 5). Separate clutters of the same sharp pointed figures as those at the edges of the drop, are also formed in the middle of it (6). Sometimes also they put on another form, like the leaves of dandelion, (7). Very beautiful figures are likewise produced by a kind of combination of sharp points and branches, (8, 8). All these crystals are of a most beautiful green colour, but deeper or lighter, according to the time of their production. The deepest are constantly produced first, and the paler ones afterwards. Towards the end of the process some circular figures are formed, extremely thin, and so slightly tinged, with green lines radiating from a centre, as to be almost colourless (9, 9). When all seems in a manner over, bundles of hair-like bodies appear frequently scattered here and there throughout the drop, like those of blue vitriol already described.

4. Alum. The microscopical crystals of this salt prove more or less perfect according to the strength of the solution and the degree of heat employed in making the experiment. The solution of alum, however saturated with the salt, will not be found over-strong after standing some days; for in that time many crystals will have formed in it. This separation will often leave the remainder too weak for the purpose; but by holding the vial over, or near the fire, the crystals will again dissolve. After it has stood about half an hour, it may then be used. The drop, put on the glass, and properly heated, exhibits commonly at first a dark cloud which appears in motion somewhere near the edge, and runs pretty swiftly both to the right and left, until it is either stopped by the intervention of regular crystals, or else it proceeds both ways at once, till having surrounded the whole drop, the two ends rush together, and join into one (a, a). This cloudy part, which seems to be violently agitated while it is running round, appears on a strict examination to consist of farts, shot into long and very slender lines, much finer than the smallest hair, crossing each other at right angles. As they go along, rows of solid crystals are produced from their internal edges. These are composed of many oblique plain sides, (b, b), and which have all a tendency towards the figures of the regular crystals to be described presently. But it frequently happens, that, in some parts of the drop, many minute and circular figures are seen, rising at some little distances from the edge, which enlarging themselves continually, appear at last of a star-like form (c, c). The crystals in the middle seldom appear till the fluid seems almost wholly evaporated; when, on a sudden, many straight lines appear pushing forwards, whose sides or edges are jagged, and from which other similar straight and jagged lines shoot out at right angles with the first. These again have other small ones of the same kind shooting out likewise from themselves, and compose altogether a most beautiful and elegant configuration (D). Each of these lines increasing in breadth towards its end, appears somewhat club-headed (e, e, e). Sometimes, instead of sending branches from their sides, many of these lines rise parallel to each other, resembling a kind of palisadoes, and having numberless minute transverse lines running between them (F). But the most wonderful part of all, though not producible without an exact degree of heat and right management, is the dark ground work (G). It consists of an infinity of parallel lines, having others crossing them at right angles, and producing a variety scarcely conceivable from lines disposed in no other manner: the direction of the lines (which are equitably straight and delicate) being so frequently and differently changed, that one would think it the result of long study and contrivance. During the time this ground work is framing, certain lucid points present themselves to view most commonly on one side. These grow continually larger, with radiations from a centre, and become star-like figures as before-mentioned. Some of them send out long tails, which give them the appearance of comets: and at the end of all, a dark lineation in various directions darts frequently through, and occupies all, or most of the spaces between them, making thereby no ill representation, when viewed by candle-light, of a dark sky, illuminated with stars and comets. The regular crystals are often formed in the same drop with the others (f).

5. Borax. If a drop of solution of borax is held too long over the fire, it hardens on the lip of glass in such a manner that no crystals can appear. The best method is to give it a brisk heat for about a second, and then applying it to the microscope, the crystals will quickly form themselves as represented in the figure.

6. Salt ammoniac begins with shooting from the edges great numbers of sharp, but thick and broad spicula, from whose sides are protruded as they rise, Crystallization many others of the same shape, but very short; parallel to each other, but perpendicular to their main stem (1). These spicula arrange themselves in all directions; but for the most part obliquely to the plane from whence they rise, and many are frequently seen parallel to one another (1, 1). As they continue to push forwards, which they do without increasing much in breadth, some shoot from them the small spicula only (2); others divide in a singular manner by the splitting of the item (3); and others branch out into smaller ramifications (4). Before the middle of the drop begins to shoot, several exceedingly minute bodies may be discerned at the bottom of the fluid. These, in a little while rise to the top, and soon distinguish their shape as at (5). Their growth is very quick, and for some time pretty equal; but at last some branch gets the better of the rest, and forms the figure (6). The other branches enlarge but little after this, all the attraction seeming to be lodged in that one that first began to lengthen; and from this, more branches being protruded, and they again protruding others, the whole appears as at (8). It is not uncommon to see in the middle of the drop, some crystals, where instead of the straight stems above described, there is formed a kind of zig-zag, with spicula like those in the other figures (7).

7. Salt of Lead, or saccharum saturni. A little of this salt dissolved in hot water, which it immediately renders milky, after standing a quarter of an hour to subside, is in a fit condition for an examination by the microscope. A drop of it then applied on a slip of glass and held over the fire to put the particles in action, will be seen forming round the edge a pretty even and regular border of a clear and transparent film or gleamy substance (a a a a); which if too sudden and violent a heat be given, runs over the whole area of the drop, and hardens so on the glass as not to be got off without great difficulty. But if a moderate warmth be made use of, which likewise must not be too long continued, this border proceeds only a little way into the drop, with a kind of radiated figure composed of fine lines, or rather bundles of lines, beginning from the centres in the interior edge of the border, and spreading out at nearly equal distances from each other every way, towards the exterior (b b b b). From the same centres are produced afterwards a radiation inwards, composed of parallelograms of different lengths and breadths; from one, and sometimes both the angles of these, are frequently seen shootings so exceedingly slender, that they are perhaps the best possible representations of a mathematical line. The extremities of the parallelograms are generally cut off at right angles; but they are sometimes also seen oblique (c c c c). Centres with the-like radii issuing from them, and some of the glutinous matter for their root, are sometimes formed in the drop, entirely detached from the edges; and in these it is very frequent to find a kind of secondary radii proceeding from some of the primary ones; and others from them again to a great number of gradations, forming thereby a very pretty figure (D).

8. Salt of Tin, produces at the edges of the drop a number of octaedra, partly transparent, standing on long Crystallization, long necks, at small distances from each other, with angular florets between them (a a). At the same time, solid and regular opaque cubes will be seen forming themselves in other parts of the drop, (b b). In the middle of the same drop, and in several other parts of it very different figures will also be formed; particularly great numbers of flat, thin, transparent, hexangular bodies (c c c); some among which are thicker (e), and a few appear more solid, and with six flopping sides rising to a point, as if cut and polished (d). The figure (f) is composed of two high pyramids united at their base. Some in this kind of form are found truncated at one of their ends, and others at both. Several of the hexagonal bodies may be observed with flopping sides, forming a smooth, triangular, rising plane, whose angles point to three intermediate sides of the hexagon (g).

9. Epsom Salt, begins to shoot from the edge in jagged figures (a). From other parts differently figured crystals extend themselves towards the middle, some of which have fine lines proceeding from both sides of a main stem, in an oblique direction; those on one side shooting upwards in an angle of about 60°, and those on the other downwards in the same obliquity (c, f). Others produce jags from their sides nearly perpendicular to the main stem, thereby forming figures that resemble some species of the polypody (e); but in others the jags are shorter (d). Now and then one of the main stems continues shooting to a considerable length, without any branchings from the sides; but at last tends out two branches from its extremity (g). Sometimes a figure is produced having many fine and minute lines radiating from a centre (b). The last shootings in the middle of the drop (h) are not unlike the frame work for the flooring or roofing of a house, but with the angles oblique: and sometimes a form of another kind presents itself (i).

10. Scarborough Salt, begins to shoot from the edges: first of all in portions of quadrilateral figures, much resembling those of common salt; but two of their angles, instead of 90°, are about 120°. They shoot in great numbers round the borders of the drop, having their sides as nearly parallel to one another as the figure of the drop will allow: some proceed but a little way, others farther, before they renew the shoot (a a). In some places they appear more pointed and longer (b); and sometimes, instead of the diagonal, one of the sides is seen towards the edge, and the other shooting into the middle (c). The middle crystals (d, f) seem to be of the vitriolic kind.

11. Glauber's Salt, produces ramifications from the side of the drop, like the growth of minute plants, but extremely transparent and elegant (e). Some of them, however, begin to shoot from a centre at some distance from the edge, and protrude branches from that centre in a contrary direction (b). Sometimes they shoot from one, and sometimes from more sides of the central point in different varieties (d). Other figures are produced from different parts of the edge of the drop (a, f, e); but the most remarkable and beautiful crystallization forms last of all near the middle of the drop. It is composed of a number of lines proceeding from one another at right angles with transparent spaces and divisions running between them, appearing all together like streets, alleys, and squares, (g g). When this crystallization begins, it forms with great rapidity, affording the observer a very agreeable entertainment: but its beauty is of very short duration: in a few moments it dissolves and vanishes like melted ice, which renders the drawing of it very difficult.

12. Salt of Jesuits bark. The few shootings which this salt produces at the edge of the drop are of no regular figure (a). The whole area becomes quickly filled with great numbers of rhombi, of different sizes, extremely thin and transparent (b). Some of these enlarge greatly and acquire a considerable thickness, forming themselves into folds of many sides (c c). Near the conclusion some crystals of sea-salt are formed (d d), and likewise a few odd triangular figures (e).

13. Salt of Liquorice, begins shooting from the edge with a fort of rhombic spicula (a). Some four branched figures like those of vitriol, commonly appear, but moulder away before their ramifications are completed, leaving only their stamina behind (b b). The middle of the drop is usually overspread with great numbers of parallelograms, some exceedingly transparent, being mere planes; having sometimes one, sometimes more of the angles canted, in such a manner as to produce pentagonal, hexagonal, and other figures. Others have much thickness, and form parallelopipeds, prisms, (e). Some of the plane figures now and then protrude an irregular kind of shooting which appears very pretty (d).

14. Salt of Wormwood. The first shootings of this salt from the edges of the drop appear of a considerable thickness in proportion to their length: their sides are deeply and sharply jagged or indented, being made up of many somewhat obtuse angles, and their ends pointed with angles of the same kind (a). But other florets frequently branch out from these original ones, and they again send forth others making all together a very pretty appearance (b b). The crystals of this salt are very different from each other, consisting of squares, rhombi, parallelograms, &c. (c).

15. Salt of Tobacco. If a moderate degree of heat is given to a solution of this salt, its first shootings will be from the edges of the drop, in slender tapering figures, ending with very sharp points, but at considerable distances from one another. Along with these, are formed other crystals nearly of the same kind, but entirely detached, and farther within the drop, having the thicker ends towards the centre of the drop, and the sharp points turned towards its edge (a). When a little more heat has been given, other spicula are produced from the edge, whose ends spread on either side, and then terminate in a point: and which have all along their sides triangular pointed crystals placed alternately so as to represent a zigzag, with a line drawn through its middle (b). The regular crystals are produced in the middle of the drop, and are either hexagons or rhombi (e). When the moisture is nearly exhaled there are sometimes seen to shoot from, or rather under the spicula, upon the plane of the glass, a representation of leaves very small at their first appearance, but gradually increasing (d). A violent agitation may be discovered in the fluid by the first magnifier, during the whole process; but but especially at the beginning, and extremely minute crystals rising from the bottom.

16. Salt of Hartshorn. On the application of a very small degree of heat, salt of hartshorn floats near the edges of the drop into solid figures somewhat resembling razors or lancets, where the blade turns into the handle by a clasp (d). The crystals of this salt are produced with great velocity, and are somewhat opaque, shooting from the edges of the drop, on both sides a main stem, and with a kind of regularity, rugged branches like those of some forts of coral (a a). But sometimes, instead of these branches, sharp spiculae, some plain, and others jagged, are protruded to a considerable depth on one side only (b). As the fluid exhales, some of the branching figures generally extends to a great length, producing on one side shoots that are rugged and irregular, and, on the other, curious regular branches resembling those of some plant (c).

17. Salt of Urine, floats from the edges of the drop in long parallelograms like nitre (a a). But in other places, along the sides of the drop solid angles are formed, that seem to be the rudiments of common salt (b). Some of the parallelograms increase much in size, and spread themselves in the middle, so as to change their first figure, and become three or four times bigger than the rest: and these have a dividing line that runs through their whole length from end to end, whence issue other short lines at small distances, opposite to one another; all pointing with the same degree of obliquity towards the base (c c). Among these enlarged figures, some few float still forward and tapering towards a point, but, before they form one, twirl again, and begin as it were anew; and thus they proceed several times before their figure is quite finished (d d). The figures 1, 2, 3, 4, 5, 6, are the regular crystals of this salt when it is allowed to dissolve in the air, and no heat at all is given.

18. Rheum, or the clear liquor which distills from the nostrils when people catch cold, is strongly saturated with salt. A drop of it on a slip of glass will soon crystallize in a beautiful manner, either with, or without heat; but if heated to about the warmth of the blood, and then viewed through the microscope, many lucid points will be seen rising and increasing gradually, till their form is shown to be quadrangular, with two transparent diagonals crossing each other (d d). These diagonals float soon after far beyond the square, protruding other lines at right angles from their sides; and thus they go on to form the most elegant and beautiful crystals. When a drop of rheum is set to crystallize without any heat, instead of branched crystals over the whole area, such are formed only in the middle; but, about the edges, plant-like figures are produced shooting several stems from one point, and resembling a kind of sea-moss (E).

19. Camphire, though insoluble in water, dissolves very readily in spirit of wine. A drop of this solution spread upon a slip of glass crystallizes instantly in the beautiful manner represented in the figure.

20. Manna easily dissolves in water, and a drop of the solution is a very pretty object. Its first shootings are radiations from points at the very edge of the drop; the radiating lines seem opaque, but are very