1912. 



PUBLIC DOCUMENT — No. 31. 



191 



water. The mixture in a closed cylinder was thoroughly agi- 

 tated, and the reading, in minutes, taken with a horizontal 

 microscope, using a 1-inch eyepiece and i/^-ineh objective, when 

 movement of the particles midway of the column (6 inches 

 down) was no longer apparent. The slow process green gave a 

 reading of seventeen minutes in water and forty-eight minutes 

 in filtered lime water. As lime tends to flocculate the par- 

 ticles of Paris green, the test should be performed immediately 

 after mixing. 



Although copper aceto-arsenite is termed insoluble in water, 

 decomposition readily takes place under certain conditions ; 

 therefore, the determination of so-called " free " and " loosely 

 combined " arsenic is closely related to stability of product and 

 should be considered in that connection. 



Solubility. 



Instan- 

 taneous 

 Green. 



Slow 

 Process 

 Green. 



Manufacturer, .......... 



Water (per cent.), .......... 



Sodium acetate soluble "free arsenic" (.\very and Beans Method): - 



Cupric oxide, .......... 



Arsenic trioxide (per cent.), ....... 



Copper acetate soluble: — 



Arsenic trioxide (per cent.), ....... 



Water soluble "free and loosely combined arsenic" (Hilgard Method): 



Cupric oxide, 



Arsenic trioxide, (per cent.) 



Solids (per cent.) 



Lime water soluble: — 



Cupric oxide, 



Arsenic trioxide (per cent.), ....... 



Ammonia insoluble (per cent.) 



A 



.78 



Trace. 

 1.45 



1.09 



B 



1 46 



Trace. 

 .74 



.45 



l^either of the greens contained an excessive amount of free 

 or of free and loosely combined arsenic, judging by the stand- 

 ard, although the slow process was decidedly the better in that 

 respect. This was to be expected, as the finely divided angular 

 particles of the instantaneous green offered greater surface and 

 apparently less resistance to a solvent than the nearly perfect 



