DRYING THE PREPARATIONS. 287 



Before being finally finished, every slide should be examined 

 under that power most suited to show its characteristics, and 

 if it is defective in any way it should be discarded and washed 

 off the slip. 



The final washing of an object treated with water or 

 any aqueous fluid should be made with distilled water 

 ordinary water leaves more or less residue, which interferes 

 with the brilliancy of the preparation. 



Drying the Specimens. The moisture can be abstracted 

 from many substances by contact with a fluid such as 

 alcohol in a small corked tube, but in many instances this 

 is not admissible, so that a desiccator becomes necessary. 

 The form used by the author is shown at Fig. 238. It 

 consists of a mahogany base- 

 board, in which a circular groove 

 is turned to admit the bell-jar 

 standing over it. This groove 

 is filled with mercury, which 

 acts as a lute and cuts off all 

 connection with the outer air. 



Under the bell-jar, and standing FlG 23 & 



upon the base-board, is a vessel 



containing concentrated sulphuric acid, one of the most 



powerful absorbers of water we have. A shelf is fixed 



over the acid, upon which are laid the slides requiring 



desiccation. 



Unless the operator is careful and has a safe place to 

 keep the desiccator, he had better choose another pattern, 

 as concentrated sulphuric acid is a fluid not to be 

 spilled with impunity, and quicksilver is an extremely 

 awkward metal to pick up from the floor upon which it may 

 have been dropped accidentally. The sulphuric acid may 

 be replaced by fused chloride of calcium, carbonate of 

 potash, or even by quicklime broken in pieces the size of 



