MINERALS. 
337 
Observation lias shown that , every substance in crystallizing has a 
tendency to assume a peculiar figure. Common suit crystallizes in cubes, 
Epsom suits in six-sided prisms, Alum in octahedrons, Sugar-candy in 
oblique four-sided prisms with wedge-shaped summits. But the cry- 
stalline form in any crystalliz&ble material is liable to be altered by 
circumstances affecting the crystallizing process; and hence the geome- 
trical forms which the same identical substances present, often bear no 
such resemblance to each other as would seem to indicate their rela- 
tion. There are, nevertheless, a certain number of figures peculiar to 
every crystal! izable body, and the crystals of that substance assume 
one or other of these forms, and no other. Common suit, for example, 
"hen it has assumed its true crystalline shape, presents itself in tire 
form of cubes ; it is also met with in octahedrons, dodecahedrons, or 
sonic figure appertaining to these solids. Sugar-canity usually crystal- 
lites in obi ique four-sided prisms, and it likewise occurs in cubes and in 
six-sided prisms with wedge-shaped summits variously modified. Alum 
crystallizes in octahedrons, but it also occurs in cubes. 
3 hi l,od of obtaining Crystals . — The method ol effecting the crystal- 
lization of such bodies as require a previous state of solution, and 
among which the class of Salts holds a distinguished rank, consists of 
beating the solution so as to dissipate gradually part of the water by 
evaporation. It is thus that chemists proceed tor obtaining crystals of 
sulphate of potash, muriate of potash, &c. 
The figure of crystals has very little regularity if the water he eva- 
porated too hastily, as by boiling; but by keeping the saline solution 
in a gentle heat, very beautiful and very regular crystals are obtained 
in a longer or shorter space of time; and there is scarcely any salt 
which may not be made to assume a very distinct form by this process 
i f it be skilfully conducted. — Accum. 
Crystals of Camphor . — Camphor dissolves readily in spirits of wine. 
To obtain the crystals it is only necessary to place one drop on a piece 
°f glass; the glass should be held over a candle a few seconds to ac- 
celerate the evaporation of the spirit, and then placed in the micro- 
SCo pe, when the configuration may be seen. 
Crystals of Silver . — This forms a very beautiful and interesting 
object. In one drop of nitrate of silver put a small piece of very 
fine brass wire ; this must be immediately placed in the microscope, 
an d the crystals will extend gradually till the whole quantity of fluid is 
evaporated. 
Miner/tls of all kinds frequently exhibit very' curious objects. Sand 
a bo should bo collected and examined, as itis subject to great variety : 
— m fact, a very good knowledge might he gained of Mineralogy from 
s uia!l specimens, which may be obtained at very reasonable pi ices, and 
which occupy but little room. 
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