Bauhaus-Universität Weimar

The Art of Projecting. A Manual of Experimentation in Physics, Chemistry, and Natural History with the Porte Lumière and Magic Lantern
Dolbear, A. E.
Tartaric Acid 
Human hair, 
Petals of flowers, as of the 
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


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