Water of crystallization

“ As light at any spot in the world-space creates a central point, the nucleus of a comet, around which more of the mass of æther is constantly accumulating till it finally coagulates into the solid condition; so does the process of crystallization evoke some particular spot, point or nucleus in the water, wherein the crystallizing forces are excited, which attract the mass that is susceptible of fixation and fashion it into a crystal. The process of crystallization is a process of fixation, and with it also is furnished the theory of crystallization. ”

“ But this law of crystallization gives to snow and ice their mechanical properties, and is connected with a multitude of adjustments of water in the solid state to its place in nature. The same law, varied in a vast number of ways in every distinct substance, builds up crystals of all kinds and crystalline rocks, and is connected with countless adaptations of different kinds of matter to mechanical and chemical uses in the arts. ”

“ UNSTRATIFIED ROCK.—A VOLCANIC BLOCK.
"Crystallization" means those particular forms or shapes in which the particles of a liquid arrange themselves, as that liquid hardens into a solid—in other words, as it freezes. Granite, iron, marble, are frozen substances, just as truly as ice is a frozen substance; for with greater heat they would all become liquid like water. When a liquid freezes, there are always crystals formed, though these are not always visible without the help of a microscope. ”

“ The reasons why no crystals appear when the evaporation is hastily performed, and carried on to dryness, are, first, that the particles of salt, being always in motion while the solution is hot, have not time to exert their mutual affinities, and to unite together as crystallization requires: Secondly, that a certain quantity of water enters into the very composition of crystals ”

“ Here again we need none of Vulcan's aid, for we all know that when once crystallization commences each little crystal will have its growth in spite of almost any resistance. Witness the growth of ice crystals in our water pipes in zero weather. In other words, the force exerted by growing crystals is known to be at least of the same order of magnitude as the crushing strength of the grown crystal. ”

“ Charcoal is pure carbon in the uncrystallized state, which the magic of crystallization has transformed into the symbol of all that is brilliant and beautiful.
Beauties of Crystallization.
Dissolve alum in hot water until no more can be dissolved in it; place in it a smooth glass rod and a stick of the same size. Next day the stick will be found covered with crystals, but the glass rod will be free from them. In this case the crystals cling to the rough surface of the stick, but have no hold upon the smooth surface of the glass rod. ”

“ In order wholly to prevent the tendency of pieces of ice to freeze together, when meeting in water with curved surfaces and without pressure, it would be necessary that , except so far as the case is modified by passive resistances to change, and by the inequality in the values of and for different directions of the axes of crystallization. ”

“ There are exceptions, however, to the general laws of expansion; some liquids have a maximum density corresponding to a certain temperature, and dilate whether that temperature be increased or diminished. For example—water expands whether it be heated above or cooled below 40°. The solidification of some liquids, and especially their crystallization, is always accompanied by an increase of bulk. Water dilates rapidly when converted into ice, and with a force sufficient to split the hardest substances. ”

“ The boy who plays with blue-stone, dissolving it in water and then recovering it again by crystallization, thus doing for fun what the freshman in a chemical laboratory does because he is directed, learns that the crystals will be large or small, few or many, according to the speed with which they form; large and few if they form slowly, small and numerous if they form rapidly. This is equally true of sugar, common salt and other crystalline substances. We see, then, that circumstances as well as substance have to be taken into account. ”

“ The impediments may restrain the accomplishment of the arrangement of the particles for a time, but the disposing power will overcome them, if the reduction of temperature go on; and when they are overcome suddenly, the crystallization will take place instantly. Hence the sudden rending of vessels, trees, mountain rocks, &c., upon the sudden congelation of water. ”

“ Although the phenomenon of crystallization does not essentially depend upon temperature, but rather upon the relative quantity of liquid that holds the substance in solution, it will be conceived that a moment will arrive when, the liquid having evaporated, the atmospheres will be close enough to each other to attract each other and become polarized and symmetrically juxtaposed, and, in a word, to crystallize. ”

“ When a lava is cooled quickly, the commingled silicates solidify in the diffused condition essentially as they were in the liquid; for there is no time for the silicate molecules of a like kind to come together, particle by particle, in regular systematic order, as required in crystallization. The essential feature of crystallization is this systematic arrangement of the molecules according to a definite plan, giving a specific crystal form, as a cube, a hexagonal prism, etc. ”

“ Now crystallization may be considered as a species of elective concretion, by which every particular substance, in passing from a fluid to a solid state, may assume a certain peculiar external shape and internal arrangement of its parts, by which it is often distinguished. But, to suppose the solid mineral structure of the earth explained, like an enigma, by the word crystallization, is to misunderstand the science by which we would explain the subject of research; and, to form a general mineral theory thus upon that term, is an attempt to generalise without a reason. ”

“ For example, let the effect a be crystallization. We compare instances in which bodies are known to assume crystalline structure, but which have no other point of agreement; and we find them to have one, and as far as we can observe, only one, antecedent in common: the deposition of a solid matter from a liquid state, either a state of fusion or of solution. We conclude, therefore, that the solidification of a substance from a liquid state is an invariable antecedent of its crystallization. ”

“ Crystalline growth may also take place in solid amorphous matter, for example, in the devitrification of glass, and the slow change in metals when subjected to alternating stresses. Beautiful crystals of many substances may be obtained in the laboratory by one or other of these methods, but the most perfectly developed and largest crystals are those of mineral substances found in nature, where crystallization has continued during long periods of time. ”

“ However the fact may be explained, it is certain that when the liquid refuses to crystallize on the admission of air, the solidification occurs directly a minute crystal of sulphate of soda, or Glauber's salt, is dropped into the vessel.
When the crystallization is accomplished, the whole mass is usually so completely solidified, that on inverting the vessel, not a drop of liquid falls out. ”

“ Crystallisation depends, as you may recollect, on the slow and regular reunion of particles dissolved in a fluid; common sea-salt is only in a state of imperfect crystallisation, because the process by which it is prepared is not favourable to the formation of regular crystals. But if you dissolve it, and afterwards evaporate the water slowly, you will obtain a regular crystallisation.
Muriat of ammonia is another combination of this acid, which we have already mentioned as the principal source from which ammonia is derived. ”

“ If he means by this to say, that a precipitation without solution would take place the sooner the more inadequate the menstruum was to dissolve the whole, the proposition may be true; - 181 - but will be of no use to explain the crystallization of minerals, (the very object he has in view,) because to crystallization, it is not a bare subsidence of particles suspended in a fluid, but it is a passage from chemical solution to non-solution, or insolubility, that is required. ”

“ Now, Miss Isaac and I have found in the course of our researches that, as the solution becomes stronger and stronger—say, by the evaporation of some of its water, it continues to be in the ordinary state of supersaturation in which it does not crystallize save by inoculation with a germ of solid alum crystal, but at last it suddenly reaches a condition in which it can crystallize spontaneously, and at this moment it is enough to stir or shake the solution, and you will at once witness the birth of thousands of tiny crystals which appear as a cloud in the liquid and begin to grow rapidly. ”

“ The principle of crystallization is in the solution; yet it requires more to set it agoing, or into action, such, e.g., as a solid surface. The deficiency in the production of a true crystal may be in the solution itself; or, I can conceive, that a very slight circumstance might alter the form of a crystal, and even give the disposition for one (crystal) to form upon another. Quickness in the progress of crystallization produces irregularity and diminution in size.’ Hunter's Essays, London, 1861, vol. ”

“ Fig. 28.—Three crystals of sodium chloride in process of formation, each in the centre of a field of crystallization.
Every crystallizable substance gives a different characteristic field of crystallization. In 1903, at the Congress of Angers, I terminated my address by these words: "The field of crystallization may serve to determine the character of a substance in solution." ”

“ Upon entering their intimate structure, it orients or groups their atoms, and separates their molecules or brings them together. From this, would it not be surprising if it did not intervene in the wonderful phenomenon of crystallization? Crystallization, in fact, depends upon cohesion, and, in the thermic theory, this force is not distinct from affinity, just as solution and dissociation are not distinct from combination. ”

“ The phenomena of crystallization are of the highest interest and beauty, for in them we see shapeless matter fashioning itself into definite and often perfect geometrical solids, as if it had been wrought by the hand of some mathematical artist. Every substance forms crystals of some one shape when the conditions are identical, and one essential condition for any crystallization is that the particles should be capable of free movement in arranging themselves, and this condition can occur only when the substance is in the state of liquid or of gas. ”

“ An example of this is sugar-candy, of which a single isolated crystal may have grown freely in a solution of sugar. Matter presenting well-defined and regular crystal forms, either as a single crystal or as a group of individual crystals, is said to be crystallized. If, on the other hand, crystallization has taken place about several centres in a confined space, the development of plane surfaces may be prevented, and a crystalline aggregate of differently orientated crystal-individuals results. ”

“ For the liquid water occupies less room than did the ice from which it was produced, owing to the well-known fact that water expands on freezing. This abnormal expansion with cooling begins at the temperature of the maximum density of water, 484° C., and proceeds steadily until the freezing point 0° is reached, when, at the moment of crystallisation, the mass suddenly increases in volume by as much as 10 per cent. ”

“ Fig. 98 gives a general diagrammatic representation of Miers’ results for a typical crystalline substance soluble in water. S is the ordinary solubility curve, which may also be termed the “curve of crystallisation by inoculation.” For as soon as the solution reaches this condition of normal saturation it is liable to be caused to commence crystallising if a germ crystal, that is, a miniature crystallite floating in the air as dust, of the substance itself or of one isomorphous with it or capable of forming parallel growths with it, fall into the solution from the air. ”

“ HOW A CRYSTAL GROWS FROM A SOLUTION. One of the most deeply interesting aspects of a crystal, especially from the point of view of the history of crystallographic investigation, concerns the mysterious process of its growth from a solution (in a solvent) of the substance composing it. The story of the elucidation, as far as it has yet been accomplished, of the nature of crystallisation from solution in water is one of the most romantic which the whole of scientific progress can furnish. Again we are struck with the parallelism between crystals and living objects. ”

“ By repeating this process, the composition of the successive crops of mixed crystals which are obtained approximates more and more to that of the pure component B, while, on the other hand, the composition of the liquid phase produced tends to that of pure A. By a systematic and methodical repetition of the process of fractional crystallization, therefore, a practically complete separation of the components can be effected; a perfect separation is theoretically impossible. ”

“ Crystallization, whether in a pure or impure solution, will proceed to only a certain extent, and will only partially remove the sucrose from the solution in one boiling, the limit of crystallization being governed by the amount and nature of impurities present. ”

“ I should not omit also to mention that bodies, in crystallising from their watery solution, always retain a small portion of water, which remains confined in the crystal in a solid form, and does not reappear unless the body loses its crystalline state. This is called the water of crystallisation. But you must observe, that whilst a body may be separated from its solution in water or caloric simply by cooling or by evaporation, an acid can be taken from a metal with which it is combined only by stronger affinities, which produce a decomposition. ”