lil 




32 THE NORTHERN MICROSCOPIST. 
answering admirably. When fusion has taken place, it is necessary to 
spread the fused mass with a hot needle over the desired surface, 
keeping the slide still heated until this is done. As the slide cools 
the crystals will be formed. I have been informed that for these 
slides castor oil is the best mounting medium, but have in- 
variably mounted them in pure Canada balsam, and I think with. 
good effect. 
This process of fusion will be found to be of great advantage in 
many other cases ; but fusion of the second kind mentioned may 
also in the case of Santonine be chosen with good results, as the: 
process of fusion under the cover glass renders the film of extreme 
tenuity, and in this case produces a slide of wavy crystals ex- 
tremely beautiful under a spot lens, and also very permanent. 
Of another mode of producing interesting Micro-crystallizations, 
that of Sublimation, I can only indicate broadly the methods to. 
be employed, as I have not experimented much in this direction ; 
but it is a process which must not be passed over, yielding as it 
does good results in the case of Benzoic Acid, Anthracene, 
Anthraquinone, Iodine, Naphthaline, and many others. 
To obtain results by this process, it is really only necessary to 
place a little of the material in a small box,—a match box for in- 
stance, and cutting a hole in the lid of the size required, placing a 
slide with its well-cleaned surface downward over the hole. If this 
is placed in a warm place the material will sublime and condense 
again on the glass above. Of course, should great heat be re- 
quired in the process, it will be necessary to use something better 
than the box described ; and the material to be sublimed may be 
placed in a test tube, and the test tube being held by a clamp at 
the proper distance above a spirit lamp, the slide may rest with its 
central portion over the mouth of the tube, and will thus receive: 
the sublimation. 
Of the crystallization of fatty acids, which would of itself afford 
ample occupation for anyone wanting a subject, I can say nothing, 
now. 
And of the combination of two or more salts, which is a subject 
requiring, and which will reward any amount of investigation, I can. 
only outline the matter by saying that fine slides Aave been pro- 
duced of various salts of Copper and Magnesia, Copper and 
Ammonium, Copper and Potassium, Chromium and _ Potass,. 
Chromium and Ammonium, and many others, and of which pro- 
cess of combination the Platino-cyanides are fine illustrations. 
Some crystals possess a power known as Dichroism, or the 
presentation to the observer of two colours according to the direc- 
tion of the light, and which is said to depend upon the absorption. 
of some of the rays of light in the passage through the crystal.. 
This power is possessed by Acetate of Copper, Chloride of 

