﻿ARSENICAJLS. 5 



slightly soluble in water, offers an explanation as to why it burns 

 foliage only very slightly when properly applied. McDonnell and 

 Graham (26) found that long-continued exposure to constantly 

 changing water brings about decomposition, both lead and arsenic 

 being dissolved, the arsenic, however, at a relatively greater rate, 

 leaving the residue more basic than the original acid lead arsenate. 

 According to McDonnell and Smith (27), the specific gravity of acid 

 lead arsenate crystals is 6.05. 



The chemical data on 10 samples of powdered lead arsenates and 

 on 9 samples of paste lead arsenate, the latter being dried in the 

 laboratory before analysis, are reported in Table 3. Of the powdered 

 arsenate samples 1 apparently was a basic lead arsenate and 9 were 

 acid lead arsenates. Of the paste lead arsenate samples, 1 appar- 

 ently was a basic lead arsenate and 8 were acid lead arsenates. These 

 samples, which were obtained from various manufacturers in this 

 country, include most of the leading brands. The results of the 

 analyses, therefore, are representative of the composition of the 

 commercial lead arsenates on the market in 1916. 



Table 3. — Composition of powdered and paste commercial lead and calcium arsenates. 



Sample 

 No. 



Material analyzed. 



Mois- 

 ture. 



Arsenic oxid 

 (As 2 6 ). 



Oxid. 



Carbon 

 dioxid 

 (CO,). 



Water of 

 constitu- 



Total. 



Water- 

 soluble. 



impuri- 

 ties by 

 differ- 

 ence.' 



1 

 2 



Powdered acid lead arsenate 



do 



Percent. 



0.32 



1.43 



.21 



.17 



.30 



.14 



.20 



2.06 



.45 



.35 



.10 



.12 



.19 



.11 



.11 



.11 



.22 



.12 



.11 



.28 



1.58 



1.33 



.31 



9.56 



7.71 



11.30 



.99 



6.07 



Percent. 

 30.86 

 31.55 

 32.29 

 32.00 

 31.24 

 32.47 

 32. 93 

 32.76 

 31.59 

 24.80 

 31.95 

 32.30 

 30.38 

 32.07 

 33.17 

 32.51 

 33.09 

 32.98 

 23.00 

 43.35 

 43.35 

 49.40 

 41.82 

 38.16 

 39.19 

 40.49 

 47.83 

 45.37 



Percent. 



0.31 

 .24 

 .32 

 .30 

 .38 

 .45 

 .67 

 .45 

 .22 

 .43 

 .34 

 .42 

 .53 

 .11 

 .22 

 .22 

 .67 



1.73 

 .50 

 .70 

 .38 



2.74 

 .22 



1.92 

 .55 

 .08 

 .25 



2.32 



Per cent. 

 64.88 (PbO) 

 62.95 (PbO) 

 64.23 (PbO) 

 63.42 (PbO) 

 64.35 (PbO) 

 64.29 (PbO) 

 63.92 (PbO) 

 63.70 (PbO) 



63.00 (PbO) 

 72.23 (PbO) 

 64.57 (PbO) 

 64.50 (PbO) 

 65.21 (PbO) 



65.01 (PbO) 

 63.82 (PbO) 

 64.67 (PbO) 

 63.41 (PbO) 

 63.13 (PbO) 

 73.99 (PbO) 

 38. S6 (CaO) 

 44.08 (CaO) 

 40.57 (CaO) 

 42.61 (CaO) 

 37.38 (CaO) 

 42.79 (CaO) 

 44.03 (CaO) 

 46.16 (CaO) 

 41.48 (CaO) 



Percent. 



0.54 



.15 



Percent. 

 3.40 

 3.92 



13 



do 



3.27 



14 



do 





4.41 



35 



do 





4.11 



38 



do 





3.10 



39 



do 





2.95 



40 



do 





1.48 



70 



do 





4.96 



28 



Powdered basic lead arsenate 



Paste acid lead arsenate, dried.. 

 do 





2.62 



3 



4 



Trace. 



3.38 

 3.08 



29 



do 





4.22 



43 



do 





2.81 



44 



do 





2.90 



47 



do 





2.71 



48 



do 





3.28 



49 



do 





3.77 



21 



Paste basic lead arsenate, dried. 

 Paste calcium arsenate, dried.. 



Powdered calcium arsenate 



do 





2.90 



6 



7 

 24 



2.74 

 1.S3 

 .98 

 1.64 

 4.34 

 4.04 

 1.05 

 1.70 

 2.43 



14.77 

 9.16 

 7.72 



32 



do 



13.62 



34 



do 



10.56 



56 



do 



6.27 



57 



do 



3.13 



58 



do 



3.32 



59 



do 



4.65 









The results in Table 3 show that in most cases the chemical com- 

 position of the commercial samples of acid lead arsenates closely 

 approaches the theoretical composition. The manufacture of lead 

 arsenate has become standardized to such an extent that different 

 batches, or "runs, " of the product vary but little from the theoretical 

 figures. Acid lead arsenates are sold in both dry and paste form, the 

 paste containing usually from 45 to 50 per cent of water. 



