134
THE ART OF PROJECTING.
Starch,
Tartaric Acid
Urea,
Human hair,
Petals of flowers, as of the
Geranium,
Scales of Fishes.
Fig. ioi represents
the appearance of
starch grains of the
potato, as seen in
common light with
the microscope, and
Fig. io2, the same seen by polarized light.
The following method of preparing double salts for
examination with polarized light is given by Mr. Davies
in the “ Quarterly Journal of Microscopic Science ” v—
“ To a nearly saturated solution of sulphate of cop¬
per and sulphate of magnesia add a drop on the glass
slide, and dry quickly. To effect this, heat the slide so
as to fuse the salts in its water of crystallization, and
there remains an amorphous film on the hot glass.
Put the slide aside and allow it to cool slowly. It will
gradually absorb a certain amount of moisture from
the air, and begin to throw out crystals. If now
placed in the microscope, numerous points will be seen
to start out here and there. The starting-points may
be produced at pleasure by touching a film with a
fine needle point so as to admit of a slight amount of
moisture being absorbed by the mass of the salt.”
A slide of salicine crystals makes a splendid object
for such projection, and should be in every collection.
Make a saturated solution of the crystals in distilled
water, and place a drop carefully upon a slide that has
been carefully cleaned. Evaporate over a lamp until
it is dried to an amorphous mass. Upon cooling, a