12 MICRO-CHEMICAL REAGENTS. 



in alum water. Sometimes the process has to be 

 repeated several times before the desired effect is 

 obtained. After washing in distilled water, prep- 

 arations made in this way can be kept for a long 

 time in glycerine, which clears them still more. 



Russow's alcoholic potash is used for the same 

 purpose as the aqueous solution, 'and in most cases 

 is preferable, since the presence of alcohol pre- 

 vents the excessive swelling of the cell-wall, that/ 

 often occurs when the Hanstein process is em- 

 ployed. With this reagent acetic acid may be 

 used for neutralization, and the preparations keep 

 well in glycerine. Starch swells and is destroyed 

 in potash, which is therefore useful for clearing up 

 tissues, like the albumen of seeds, that contain 

 much starch. 



The aqueous solution of potash, causing swelling 

 of the cell-wall, often facilitates the study of its 

 striation and stratification ; this is especially the 

 case in collenchyma. 



A warm solution of potash, being a solvent for 

 the so-called intercellular substance, is sometimes 

 employed for isolating cells by maceration. 



Potash is useful as a test for suberin. 1 When 

 thin sections of corky tissue are well boiled in this 

 reagent the suberin is extracted from the cell- 

 wall, appearing as yellow drops, that soon run 

 together. 



1 Hohnel: Kork u. verkorkte Gewebe. Sitzber. wien. Akad., 1877, 

 Abth. I., p. 1 6. 



