8 THE YOUNG 
with gum or similar matter, they some- 
times crystalize in very curious forms. 
Fig. 2, sliows a form sometimes talven by 
sulphate of copper, under such circum- 
stances. The reader will observe the 
curious spiral form assumed by the crys- 
tals, and it will be well to compare them 
with crystals formed by a pure solution of 
the same salt. 
Mixtures of different salts also give rise 
to curious combinations of crystalline 
forms. Thus a mixture of sulphate of 
copper and sulphate of magnesia crys- 
tallizes in a manner that is both curious 
and beautiful. 
Of all the crystallizations which can 
be readily produced, however, none equal 
in brilliancy and beauty that of pure 
silver. But to be seen in perfection the 
crystals mast be watched during the pro- 
cess of formation ; when mounted, even 
in their best condition, they fall far short 
of the appearance which they present 
w^hile growing. The method which w^e 
have found to give the ])est results is to 
place a drop of solution of nitrate of silver 
on a slide, and bring in contact with it a 
small mass of the amalgam used for ordin- 
ary mirrors. The droi) of liquid should 
be well spread out and ^he glass should 
be black. If black or dark colored glass 
cannot be procured, a piece of black 
paper may be pasted on the under side of 
an ordinary slide. As soon as the amal- 
gam has been brought in contact with the 
solution of silver, decomposition takes 
place, nitrate of tin and mercury formed, 
and pure silver is thrown down. This pure 
silver instantly forms, with the other sub- 
stances present, a minute voltaic battery 
and the rest of the silver is deposited 
in beautiful crystals just as copper is 
deposited on one of the poles of the 
Daniel's battery. These crystals shoot 
across the field with considerable rapidity, 
and they are seen to grow in exquisite 
fern-like masses, of which our engraving 
gives a faint representation. While fresh, 
their surfaces are clear and brilliant, and 
if well illuminated by means of the bulls- 
eye condenser, or any similar method of 
condensing light on them, they are almost 
dazzling. An objective and eye-piece of 
low power should be used, a magnifying 
SCIENTIST. 
power of thirty diameters being suf- 
ficient. 
We prefer the amalgam of tin and mer- 
cur3^ to all other agents for throwing down 
the silver, because it does not interfere 
with the beautiful white color of the crys- 
tals, as do copper and most other metals. 
When a greenish hue is desired, however, 
Fif?. 3. CEYSTALS OF SILVEK. 
copper or brass may be used. When the 
solution becomes weak, the crystals form 
in slender, needle-like stems; when the 
solution is strong, the silver is deposited 
in frond-like masses. By varying the 
strength of the solution during the pro- 
cess of crystallization, ihe most beautiful 
effects may be produced . 
Home-made Telescopes and Micro- 
scopes.— XIL 
ON THE OBSERVATIONS REQUISITE FOR COR- 
RECTING OBJECT-GLASSES. 
FOE this purpose, a particle of mercury 
is placed upon a slip of black glass. 
A piece of watch-spring, or the thin handle 
of a spatula, is held up at its end by the 
fore-finger of the left hand, and slapped 
down on the mercury, which is thus 
beaten into powder, in the form of numer- 
ous minute globules. Of these, a larger 
size is selected for correction of color, and ' 
a minute one for ascertaining the errors 
of figure and centering, and state of the ' 
oblique pencils. 
The globule must be illuminated by i 
direct candle or lamp light, and not by j 
daylight, as the latter will not allow per- { 
