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