(From crystal).

Crystallization. The parts of all bodies which take the solid state are disposed to arrange themselves in such a manner, as to produce some regular geometrical figure in the solid. This property is called crystallization, and the regularly figured bodies we crystals. In this process the integrant parts of a solid body, separated from each other by the intervention of a fluid, exert the mutual attraction of to coalesce and produce a solid mass.-when the particles of a body are only separated by caloric, and the substance is retained in the liquid state by its means, all that is necessary for its crystallization is, to remove a part of the caloric; in other words, to cool it. If this refrigeration be slow, and the body be at the same time left at rest, its particles assume a regular arrangement; and crystallization, properly so called, takes place: but if the refrigeration is rapid, or if the liquor be agitated at the moment of its passage to the concrete state, the crystallization is irregular and confused. The same phenomena occur in watery solutions, or rather in those made partly in water, and partly by caloric. So long as there remains a sufficiency of water and caloric to separate the particles of the body beyond the sphere of their mutual attraction, the salt remains in a fluid state; but when the necessary quantity of either is deficient, and the attraction of the particle each other becomes superior to the power which separates them, the salt recovers its concrete form, and the crystals produced arc more regular in proportion as the evaporation has been slower, and more tranquilly performed.

To dispose a substance to crystallization, it is neces-sary, in the first place, to reduce it to the most com-plete state of division. This may be effected cither by solution, or by an operation merely mechanical. Solution may be effected either by the means of water or fire. The solution of salts is generally performed by means of the first; that of metals of the second. In order that the form of a crystal may be regular, three circumstances are required; time,a sufficient space, and repose. Sometimes the assistance of light is apparently requisite, though in general injurious to the regular formation of crystal. Time brings the integral parts by insensible gradation nearer each other, and without any sudden shock; so that they unite according to their constant laws, and form a regular crystal. Space, or sufficient room, is likewise a condition necessary for obtaining regular crystallization. If nature be restrained in her operations, the product of her labour will exhibit symptoms of constraint. A state of repose in the fluid is likewise necessary to obtain very regular forms: uninterrupted agitation opposes all syrnmetrical ar-rangement; and in this case the crystallization obtained will be confused and indeterminate.

This term, however, is most commonly applied to bodies of the saline kind; but not till lately applied to the freezing of water, or to the consolidation of metals after they have been melted. In every change, however, from a fluid to a solid state, we can perceive traces of this operation, if we, perhaps, except the fat oils. Though this is accounted one of the processes of chemistry, it is truly a process of nature, and maybe discovered in all her operations. All the deliquescent are excluded from this operation, and the volatile ones never assume this form, unless their vapours arc con-lined. Some of the neutral kind, particularly those of which certain metallic bodies are the basis, are as capable of crystallization, if a sufficient quantity of water be added, or any substance with which the v 3 U 2 affinity. Different salts also require different quantities of water to dissolve them; so that if a mixture of two salts be dissolved in one fluid, they will begin to separate at different times of the evaporation: upon this foundation salts are freed not only from their impurities, but also from one another; that which is least soluble shooting first.

The manner of crystallizing salts is, to make a saturated solution of them in boiling water; for hot water dissolves a larger quantity of many salts than it can suspend when cold. The solution must be then put into a proper vessel, and stand still in a cool place till the crystals are formed, which sometimes require several days. When crystals are formed, the remaining solution must be poured off, and what the crystals retain drained from them, by means of bibulous paper, then dried. There is a certain portion of the menstruum, which, though it contains salts, never permits them to crystallize. This arises from a viscidity or oiliness in the fluid, which prevents the mutual attraction of the saline particles; and in the salt works it is called oil of salt. Chemists style it the mother water; sometimes the mothers.

The cause of crystallization seems to depend on the attraction and repulsion with which the different portions of the molecule are endowed. Attraction alone will not explain the phenomena; and, indeed, with the assistance of its antagonising power, they are very obscure. The crystals are apparently formed with some momentum, and they are seen in their shootingto strike the glass forcibly. Vauquelin saw a thin glass broken by this means. Whatever be the variety of crystals, the primordial forms are few. Their forms have been explained with great precision by Haiiy; and they appear so constant and regular, that they become the best criterion often for distinguishing the species of natural bodies. See Crystalli.

If salts are dissolved in too much water, the superfluous fluid must be evaporated slowly until the salts show a disposition to concrete, even from the hot water, by forming a pellicle on the surface. If large, and the most perfect crystals are required, the solution must be removed from the fire before the pellicle appears; otherwise the sudden crystallization will diminish their perfection. In this case the evaporation must be continued until some drops of the liquor, falling on a cold glazed plate, discover crystalline filaments: the vessel must then be removed from the fire into a less warm, but not cold place, covered with a cloth, and left till crystals are formed. If the salt be pure, no more is necessary; but if not, filtration will be required, previous to the solution being left for the separation of its contents.

In crystallizing large quantities, sticks are placed, and sometimes threads, across in the vessels, on which the salts form, and are taken out in a more perfect figure than when they adhere in thicker concretions to the sides and bottoms of the vessels. Sudden cooling, or shaking of the vessel, will prevent the salts from being properly and regularly formed; and care should be taken that the substance of the vessels are such as not to endanger corrosion.

The figures of salts cannot be destroyed; for if they are comminuted ever so small, yet, upon re-crystallization, they form themselves again into their proper shape.

Salts entangle, in the interstices of their crystals, a portion of water, called the water of crystallization; which occasions the efflorescence of salts in the air, and their effervescence on the application of heat: and on this their crystalline form seems much to depend. Nitre contains about one twentieth-of its weight of water; alum one sixth; sea salt one fourth; borax, green vitriol, and the bitter purging salts, from one third to one half.

Rectified spirit of wine dissolves some salts, assists the crystallization of others, and is necessary for separating any oily matters from them. See Menstruum and Solution.

See Chaptal; Fourcroy; Lavoisier's Elements of Chemistry; the Encyclopedia Britannica; Boerhaave's Chemistry; Dictionary of Chemistry; Neumann's Chemical Works; Haiiy Traite de Mineralogie; and Rome llsle's Crystallographie.