PRACTICAL MICROSCOPY. 



a solvent action upon many of the varnishes used for 

 microscopical purposes, and therefore great caution should 

 be exercised in this respect. 



Solvents. Under this heading come many reagents of 

 diverse character : we have alkalis, acids, and neutral com- 

 pounds, all of which have their special applications. Amongst 

 the first class are solutions of potash, soda, and ammonia, 

 having a great affinity for most animal substances. Grease 

 unites with any of these, producing a soap which easily 

 dissolves in water. The alkalis in their solid state should 

 be handled with caution, owing to their corrosive nature ; 

 they are chiefly used in solution to dissolve out the internal 

 organs of insects, and to prepare the leaves of mosses for 

 exhaustive scientific examination. 



The acids, sulphuric, nitric, hydrochloric, and acetic, 

 have each their uses ; for dissolving metals, oxides, car- 

 bonates, phosphates, and other salts, they are necessary. 

 They have no action upon silica, but upon animal and 

 vegetable fibres the action is very decided. 



By far the most important solvents we have to consider 

 are ether, alcohol, benzol, glycerine, oil of cloves, oil of caje- 

 put, and last, and not least, water. Ether is not very 

 soluble in water, it dissolves in about fourteen parts at the 

 ordinary temperature of the air ; it carries into solution 

 many organic compounds, as the volatile oils, resins, fats, 

 alcohols, tannic acid, which are but sparingly soluble in 

 alcohol, while it is without action upon many substances 

 easily dissolved by that reagent. It is miscible in all pro- 

 portions with alcohol, bisulphide of carbon, and naphtha. 



Alcohol is probably the most used fluid in microscopy ; 

 it is miscible in all proportions with wood-spirit, chloro- 

 form, acetic acid, and naphtha, and is a good solvent for 

 most resinous substances. Attention should be paid to 

 the strength of the alcohol ; alcohol absolute is expensive, 



