﻿4 BULLETIN 1147, TJ. S. DEPARTMENT OF AGRICULTURE. 



All samples of commercial arsenic acid are likely to contain traces 

 of arsenious oxid and nitric acid. Arsenic acid solutions containing 

 from 56 to 66 per cent of arsenic oxid have a specific gravity of from 

 1.8 to 2. Solid arsenic acid containing from 75 to 80 per cent of 

 arsenic oxid has recently been placed on the market. 



BASES USED IN PREPARING ARSENICALS. 



The oxids of lead, zinc, calcium, and magnesium are the bases 

 most used in manufacturing arsenicals. Litharge is the commercial 

 lead oxid and lime the commercial calcium oxid. Zinc oxid (ZnO) 

 and lead oxid (PbO), ordinarily employed in the manufacture of zinc 

 arsenite and lead arsenate, are more expensive than calcium oxid 

 (CaO) (in the form of lime) and magnesium oxid (MgO) used in manu- 

 facturing calcium arsenate and magnesium arsenate. Table 2 gives 

 the results of the analyses of the five bases and the copper oxid 

 (CuO) and barium hydroxid (Ba(OH),) which were used in this 

 investigation. 



Table 2. — Composition of bases in arsenicals. 



Sample 

 No. 



Material analyzed. 



Moisture. 





Carbon 



Oxid. 



dioxid 





(CO s ). 



Per cent. 



Per cent. 



84.00 (CaO) 



9.02 



99.13 (PbO) 



Trace. 



97.88 (PbO) 



1.64 



lCO.OO(ZnO) 



.00 



77.16 (MgO) 



21.89 



98.75 (CuO) 



.10 



66.73 (BaO) 



14.91 



Undeter- 

 mined 



material, 

 by dif- 

 ference. 



Lime (laboratory) 



Lead oxid (laboratory) 



Lead oxid (commercial) 



Zinc oxid (commercial) 



Magnesium oxid (laboratory;. 



Copper oxid (laboratory) 



Barium hydroxid (laboratory) 



Per cent. 

 6.54 

 .00 

 .02 

 .17 

 .99 

 .00 

 14.58 



Per cent. 



0.44 



.87 



.46 



1.15 

 3.78 



ACID LEAD ARSENATES. 



F. C. Moulton, chemist for the Massachusetts gypsy moth com- 

 mittee, is credited with the discovery in 1892 of the insecticidal 

 properties of lead arsenate. The use of arsenate of lead as an in- 

 secticide, first recommended in October, 1893 (21), has greatly 

 increased during the past few years. Thirty-one United States 

 patents for its production have been issued. 



The principal lead arsenate is acid lead arsenate (PbHAsO^), an 

 acid salt, so-called because of the presence of hydrogen (H) in its 

 molecule. It has the following theoretical composition, As ? 5 

 (33.13 per cent), PbO (64.29 per cent), and water of constitution 

 (2.58 per cent). 



In the early procedure for preparing acid lead arsenate, solutions of 

 lead acetate or of lead nitrate were precipitated by sodium hydrogen 

 arsenate (Na^HAsOJ. The tendency is to produce acid lead arsenate 

 when lead nitrate is used and the more basic form when the acetate 

 is used. McDonnell and Smith (27) obtained acid lead arsenate of 



f>ractically theoretical composition by precipitating lead nitrate or 

 ead acetate by an excess of monopotassium arsenate. A method 

 frequently employed in manufacturing this arsenate is to mix arsenic 

 acid (H 3 As0 4 ) and litharge (PbO) in the presence of a small amount 

 of nitric acid. Other processes, however, are used. The fact that 

 acid lead arsenate is a comparatively stable compound and is but 



