180 



CHEMICAL TECHNIQUES 



will become apparent since the acid that seeped into them during 

 the cleaning will cause the indicator to turn yellow. The complete 

 stirring equipment is available from A. H. Thomas Co. and E. 

 Petersen. 



istiH_3> -=C_M} 



nT 



1 



(qM§) 



100 



98 



96 



Fig. 64. Microtitration arrangement 



for use with magnetic "flea" stirrer. 



From Linderstr0m-Lang and Holier (1940) 



Heatley, Berenblum, and Chain (1939) employed steel ball bear- 

 ings, ^/i6 in. in diameter, given several coats of Bakelite varnish No. 

 V-5209/2. Each coat was polymerized by stoving before applying the 

 next, and then the balls were given a layer of paraffin by heating 

 them to 100° in a paraffin bath. After excess paraffin was removed 

 by rolling the bearings on hot filter paper, they were rolled in the 

 clean, dry palm of the hand with some well-washed kaolin to enable 

 them to be wetted by aqueous solutions. Of course these balls should 

 not be used with liquids that might attack the coating. 



E. HEATING DEVICES 



A simple micro muffle furnace was described by Kirk and Bentley 

 ( 1936) which, when employed with the proper rheostat, can be 

 used for temperatures up to 1000°. The furnace is made by winding 

 Chromel A resistance wire around a porcelain cup (2 in. inside di- 



