1912. 



PUBLIC DOCUMENT — No. 31, 



197 



of sodium chloride than to tako chances on possible hydrolysis 

 and decomposition of the arsenite, an action readily inferred 

 from the behavior of Paris green under similar conditions. 

 The above method of preparation was employed in all subse- 

 quent work unless otherwise noted. ]\[inor changes were at- 

 tempted in some instances from which no apparent benefit was 

 derived. 



As previously stated there was considerable uncertainty as 

 to the composition of the lime precipitate. To ascertain 

 whether the resulting product was a definite compound and, 

 if so, its composition, salts were produced fi'om an excess of 

 sodium arsenite into calcium chloride and vice versa, observing 

 the usual precautions as to dilution, precipitation of calcium 

 hydroxide, oxidation of the arsenic, etc. Incomplete analyses 

 of a few laboratory samples are given. 



Calcium Arsenite produced in the Laboratory {Per Cent.). 



The small samples were of uniform composition, indicating 

 a definite compound of about 77 per cent, arsenic content. 

 This amount of arsenic exceeds the requirements of the ortho 

 and pyro salts, and substantially conforms to that of the meta 

 compound with a theoretical content of 77.92 per cent. The 

 following equation illustrates the reaction that must have 



occurred 



CaCb -H 2NaAs02 = Ca(As02)2 + 2 NaCl. 



Attention has been calltd on pages 180, 181 and 182 to 5 

 samples of lime arsenite supplied by several firms for the inves- 

 tigation. Manufacturer C was furnished directions deduced 

 from experimental work in the station laboratory. A and B 

 evidently employed a different method. 



