1912.] 



PUBLIC DOCUMENT — No. 31. 



187 



Experimental Results. 



The terms '' instantaneous " and " slow process •' are used to 

 designate Paris greens of different physical structure. AVhile 

 this classification may not be in strict conformity with some 

 writers it apjxmrs, nevertheless, the most desirable for the pur- 

 pose intended. 



Instantaneous green is the result of a quick boiling process as 

 previously shown. The ultimate reaction is illustrated by the 

 following equation : — 



3 AsoOa + 4 Cu ( C2H3O2 ) 2H2O 



= Cu(C2n.:02)2 • 3 Cu(As02)2 + () ('2lll02 + 1120. 



If the process could be carried out with the ingredients in the 

 proportion given there would be very little waste. In practice, 

 however, instead of 1 part by weight of arsenous acid to 1.34: 

 parts of coj)])er acetate, an equal amount appears necessary to 

 insure the desired change. This is probably due to the weak 

 acid projierties of the arsenic. 



Slow process green is generally formed less rapidly and at a. 

 lower temperature than the instantaneous. From what could 

 be learned the slow process seems to be the one employed by 

 most of the large manufacturers. Blue vitriol is used as the 

 source of copper, and sodium arsenite (ISTaAsOo) in place of 

 ai'senous oxide, on account of its gTeater solubility and the ne- 

 cessity for a base to neutralize the sulfuric acid. Sodium arse- 

 nite is easily prepared i)v adding a thin paste of arsenous oxide 

 in slight excess to a boiling solution of caustic soda or of a 

 carbonate. Na2C03 + AS2O3 = 2 NaAs02 + CO2. 



The soda and arsenic readily combine with volatilization of 

 carbonic acid. As commercial salts were often employed in our 

 work the analyses of two are given : — 



