326 REAGENTS AND PROCESSES 



Potassium Alcohol. — Used for bleaching sections. It may be 

 prepared by mixing a concentrated aqueous solution of potas- 

 sium hydrate with 90 per cent, alcohol until a sediment is formed. 

 This is allowed to stand for twenty-four hours with frequent 

 violent shaking, and then the clear liquid is poured off and is 

 diluted for use with 2 or 3 parts of water. 



Potassium Hydrate. — ^For general use, dissolve 5 gm. of 

 potassium hydrate in 95 c.c. of distilled water. This is used as 

 a clearing agent for sections and small organisms. The process 

 of clearing may require from several hours to several days. After 

 clearing, the potash should be washed out in plenty of water, 

 and then the preparation may be neutralized with acetic acid. 

 This will tend to make the objects more opaque, and if too much 

 is added, the objects may be cleared again by caustic potash or 

 ammonia. A dilute solution of caustic potash, as above, may 

 be used for the maceration of cork, while delicate tissues in gen- 

 eral may be macerated by boiling for a few minutes in a 50 per 

 cent, solution of potassium hydrate in water; the tissues should 

 then be washed in water and teased out on a slide in a drop of 

 water. 



Ruthenium Red. — An aqueous solution is an excellent stain 

 for pectic substances and for gums and slimes which have been 

 derived from these. Ruthenium red is not soluble in alcohol, 

 clove oil, or glycerine, and, therefore, preparations stained by it 

 may be dehydrated and mounted in glycerine or balsam. 



Safranin. — A saturated solution of safranin in alcohol should 

 be made, and this should be diluted with an equal bulk of water, 

 or with an equal bulk of a saturated aqueous solution of saf- 

 ranin. This is an excellent general stain, and gives good differ- 

 entiating effects when used singly. It is one of the few stains 

 which are particularly adapted to the staining of pectic com- 

 pounds. It also gives beautiful results in staining the cell- 

 contents of Spirogyra and other algae. The algae, after fixing 

 in a fixative containing chromic acid, should lie in the alcoholic 

 solution diluted with an equal bulk of water for twelve or twenty- 

 four hours. They should be transferred to 50 per cent, alcohol. 



