﻿ARSENICALS. 



3 



used for insecticide purposes. Canada, Mexico, England, Germany, 

 France, Japan, and Portugal produce large quantities of arsenious 

 oxid. 



There are three forms of arsenious oxid : (a) The amorphous , v i fc ceou s , 

 or glassy form; (&) the ordinary crystalline (" octahedral") form; and 

 (c) the orthorhombic crystalline form. The amorphous form changes 

 spontaneously into the crystalline form on standing. The trade 

 usually recognizes two grades of arsenious oxid, the light and the 

 heavy forms, although they are the same chemically. 



The literature contains conflicting statements concerning the 

 solubility of arsenious oxid in water. Because of the slowness with 

 which arsenious oxid goes into solution, many weeks being required 

 to dissolve even a small sample of the solid, it is probable that in 

 all of the reported results equilibrium had not been reached. The 

 varying percentages of crystalline and amorphous material present 

 in the samples tested, the amorphous form being more soluble than 

 the crystalline forms, may possibly help to account for these dis- 

 crepancies. 



With the exception of Paris green, the arsenites are prepared by 

 combining arsenious oxid and the base. 



As a rule, arsenates are made by the direct action of arsenic acid 

 in solution on a metallic oxid. The arsenic acid used for this purpose 

 is manufactured from arsenious oxid by oxidation, usually by means 

 of nitric acid, but sometimes by other oxidizing agents. 



The analytical results here reported are based on the weights of 

 the original samples. The methods of analyses used were in general 

 those of the Association of Official Agricultural Chemists (l). 3 



Table 1 gives the analytical results on the six samples of arsenious 

 and arsenic oxids selected to represent the arsenical materials used 

 in the manufacture of arsenicals. 



Table 1. — Composition of arsenious oxid (As 2 3 ) and arsenic oxid (As 2 5 



facturing arsenicals. 



used in manu- 



Sample 

 No. 



Material analyzed. 



Moisture. 



Total 



arsen- 

 ious oxid 

 (As 2 3 ). 



Total 

 arsenic 



oxid 

 (As 2 5 ). 



Water- 

 soluble 

 arsen- 

 ious oxid 

 (As 2 3 ).i 



Water- 

 soluble 

 arsenic 



oxid 

 (As 2 5 ).i 



Laboratory arsenious oxid 



Commercial arsenious oxid 



do 



do 



Laboratory arsenic oxid (solid arsenic acid) . 



Commercial arsenic oxid (dissolved arsenic 



acid) 



Per cent. 

 0.20 



Per cent. 

 99.80 

 99.01 

 99.29 

 99.22 



Per cent. 



Per cent. 

 17.77 

 24. 56 

 38.00 

 30.26 



Per cent. 



77.27 

 66.10 



77.27 

 66.10 



1 Determined by the A. O. A. C. method for Paris green. 



Attention is called to the wide variation in the data obtained for 

 water-soluble arsenious oxid in the different samples of arsenious oxid. 

 This is undoubtedly due to differences in the size and structure of 

 the crystals present in the samples tested. 



Traces of arsenious oxid (0.008 per cent) and nitric acid (0.02 per 

 cent) were found in the commercial sample of arsenic acid (No. 16). 



3 Italic numbers m parentheses refer to literature cited. 



