6 REAGENTS. 



c. c. of H,S0 4 . Much heat is generated by the action of the acid 

 and the operation should be performed in a beaker or earthen dish, 

 since the heat would probably crack a bottle should an attempt be 

 made to make the mixture in one. This cleaning mixture will after 

 a time remove balsam and sealing agents from glass, but it is not 

 so rapid in its action as the nitro-sulphuric acid mixture, nor is it 

 so disagreeable to handle, and may therefore be better adapted for 

 the use of the general student. 



Collodion. 



This is best prepared by dissolving pure gun cotton (pyroxylin) 

 in a mixture of equal parts of pure ether and 95 per cent, alcohol. 

 A 2 per cent, and 5 per cent, solution will be needed. These can 

 be made by dissolving 2 and 5 grams respectively of gun cotton in 

 mixtures of 100 c. c., equal parts of pure ether and alcohol. The 

 solutions should be kept in tightly stoppered bottles to prevent 

 evaporation of ether and consequent thickening of the collodion. 

 More satisfactory results will be secured by using gun cotton in the 

 preparation of collodion than by employing ordinary commercial 

 collodion or celloidin. 



Ether. 



Ether is used with equal parts of alcohol in the preparation of 

 collodion. Ether vapor is useful for sealing collodion sections to 

 the slide and is often a valuable agent as a solvent for oils, fats, and 

 resins. 



Glycerin. 



Glycerin is quite an important substance in microscopic man- 

 ipulation. It is used largely as a mounting medium and preserva- 

 tive. It evaporates slowly but absorbs water readily from the air. 

 Mounts in it should therefore be sealed with a water tight cement 

 shortly after preparation. Sections mounted in glycerin, unless 

 stained with a very permanent stain, are liable to become transpar- 

 ent and of but little use. Glycerin with gelatin is used to make 

 glycerin-jelly, a very convenient mounting medium for a large 

 variety of plant tissues. The tissue to be preserved in the jelly 

 can be mounted directly without dehydrating in alcohol, but in 

 most cases it should be first hardened to prevent shrinking. 



