Tur Microscope. 63 
glass. Carefully loosen the cover-glass so that water can pass in, and 
hen lay the slide flat in a dish of soft water until the glycerin has 
thoroughly diffused with the water. Carefully remove the cover- 
glass (under water) and float the specimen off by aid of a camel’s 
hair brush. You can remount such specimens in glycerin or any 
other medium that is suitable. 
H. M. Wuetptey, St. Louis, Mo. 
PrrrspurG, Pa., December 13th, 1888. 
Dear Sir :—Through kindness of my friend, Dr. Frank Slocum, 
I enclose the following description of Guanidine Carbonate, which I 
exhibited at the late meeting of the I. C. M.S. 
Guanidine is a monoacid polyamine (CH ° N*), was discovered 
by Strecker in 1861, being produced by the action of hydrochloric acid 
‘and chlorate of potash on guanine. There have been several methods 
devised since then to produce this substance artificially, but none 
have proved practical until Prof. Volhard, early in the’70s, produced 
it by simply heating sulphocyanide of ammonium in retort to 180°— 
190° centigrade for 20 hours, dissolving the residue in water, adding 
potassium carbonate, evaporating to dryness, dissolving in alcohol 
and crystalizing therefrom; this gives pure guanidine carbonate 
[(CH® N*)?-H?CO*]. The free base, guanidine, will, as shown in 
the process of its formation, decompose potassium carbonate, is the 
strongest known organic base, absorbs moisture and CO” from the 
air with as great avidity as caustic potash. Its main interest from a 
scientific point of view, is its strong basic properties. The numerous 
salts and compounds which can be produced from it, and especially 
the fact that it adds one more link of vantage to the production of 
uric acid artificially, the accomplishing of which will be a great step 
forward in the branch of medicinal chemistry, as well as a great 
discovery. 
Truly yours, W. J. PRENTICE. 
9. Does carmine. used in staining wood sections, require a 
fixative, and if so, what? 
10. For mounting stained sections of wood, which is the pre- 
ferable medium, balsam or glycerine jelly ? | 
As, Balt 
11. Why is carbolic acid used in mounting insects, and what 
are the objections to its use? 
12. Where can I find instructions for mounting insects without 
pressure ? D. 
13. Please mention some of the most important tests, and state 
the objectives for which they are tests ? S. BuG: 
