1901] MICROSCOPICAL JOURNAL. . 193 
a drop with the pipette in the centre of a 3 by 1 inch slip; 
slope the slide to make the liquid spread in a film, then 
absorb the superfluous moisture from the side of the slip 
with blotting paper. Now hold the slide wet side up over 
the flame of a Bunsen or spirit lamp, at such a distance 
that the liquid just steams. Continue this until you see 
a thin film of the salt form at the edges, then withdraw, 
allow to cool, and examine under the microscope. If sat- 
isfactory, the crystals can then be permanently mounted 
by depositing a drop of the cold xylol balsam over the film 
and covering with a clean cover-glass. 
When the salt is insoluble in water, any suitable sol- 
vent such as alcohol, chloroform, etc., may be employed ; 
in this case, of course, evaporation will take place rapid- 
ly without the aid of heat. Crystals formed from such 
solutions will probably require a different mounting me- 
dium, such as castor oil, or one in which they are not sol- 
uble. A method recommended by Dr. Lankester is to dis- 
solve a little gelatin or gum acacia in distilled water and 
to add to this a few drops of a saturated aqueous solution 
of the salt. A drop of the warm mixture is then depos- 
ited on a slip, superfluous moisture drained. off, and the 
slide is put on one side to cool. With some salts—copper 
sulphate, iron sulphate, etc.—remarkably beautiful crys- 
talline forms make their appearance, frequently in the 
form of flowers and fern-like branches. Epsom salts, 
chlorate of potash, bichromate of potash, and, in fact, 
any salt soluble in water will lend itself for preparation 
by the above process. 
The second principal method is by fusion. Its applica- 
tion is necessarily more restricted than the foregoing, but 
by its means some very effective slides may be prepared. 
The process is equally simple, but the results attained will 
not be so uniformly successful. A good substance to ex- 
periment with is salicine. Place a small quantity on the 
centre of a thin slip and heat it over a flame until it just 
