DEHYDRA TING A GENTS. 3 1 3 



the weakest reagent. When used in concentrated solu- 

 tion, animal substances, especially of an albuminoid nature, 

 are entirely dissolved, while when used in a weaker form 

 many organs are separated in such a way as to be readily 

 obtained. Upon vegetable substances the alkalies act 

 somewhat similarly, the leaf the esparto grass (Macrochloa 

 tenacissimd) and the straw of cereals, and even blocks of 

 pine wood, are all softened and disintegrated by boiling in 

 a solution of caustic soda containing 50 grains to the 

 ounce of water. Dilute nitric acid (one part of acid to ten 

 of water) may also be used as a softening agent in certain 

 cases, and, it may be added, should be used in glass or 

 porcelain vessels, as metals are rapidly dissolved by this 

 acid. This remark applies also, though in a lesser degree, 

 to acetic acid. 



Dehydrating and Hardening Agents. D ehy drating agents 

 for use with the desiccator (Fig. 238) are not put in con- 

 tact with the preparation ; but placed below in a separate 

 compartment underneath a bell-jar, as shown in the figure. 

 Anhydrous phosphoric acid is perhaps the most powerful 

 absorbent we have, and next to this in usefulness is con- 

 centrated oil of vitriol. 



Fluids, however, are not so handy as solids, and there, 

 fore for general work fused chloride of calcium, quick-lime, 

 or carbonate of potash, are more generally used. 



When, however, a substance requires to be dried or 

 dehydrated without losing its fresh or moist appearance, 

 it must be brought in contact with a water-absorber, such 

 as alcohol. Absolute alcohol is an excellent fluid for this 

 purpose, and is not equalled by any other reagent ; methy- 

 lated spirit is often used in its place, and for many 

 purposes will suit admirably. 



It must not be forgotten that alcohol has a more or less 

 solvent action upon most of the gums used for micro- 



