﻿12 BULLETIN 1147, U. S. DEPARTMENT OF AGRICULTURE. 



Table 5. — Composition of lead and calcium arsenates prepared in the laboratory. 



Sample 

 No. 



Material analyzed. 



Mois- 

 ture. 



Arsenic oxid 

 (As 2 0„). 



Lead 



oxid 



(PbO). 



Calcium 



oxid 



(CaO). 



Carbon 

 dioxid 

 (CO,). 



Water of 

 constitu- 

 tion and 



Total. 



Water- 

 soluble. 



lm pun- 

 lies, by 

 differ- 

 ence. 



17 





Per cent. 

 0.02 

 .10 

 .06 

 .03 

 .23 

 1.06 

 2.30 



Per cent. 

 33.09 

 33.25 

 23.40 

 79.63 

 69.09 

 52.05 

 42.84 



Percent. 

 0.19 

 .00 

 .27 

 Trace. 

 61.67 

 .46 

 .17 



Per cent. 

 63.80 

 63.67 

 74.66 



Per cent. 



Per cent. 



Per cent. 

 3.09 



68 



... .do 







2.98 



18 









1.S8 



45 

 46 



Calcium meta-arsenate 



Monocalcium arsenate 



Tricalcium arsenate 



do 



18.45 

 19.92 

 40.07 

 44.89 



0.00 



.10 



- .96 



5.73 



1.89 

 10.66 



42 





5.86 



69 





4.24 











Lead arsenates. — The two samples of acid lead arsenate (Nos. 

 17 and 68) contained percentages of arsenic oxid very close to the 

 theoretical (33.11). They were prepared by mixing lead nitrate 

 and arsenic acid, according to the procedure of McDonnell and Smith 

 (27) . The percentage of lead oxid in the two samples is a little lower 

 than the theoretical. Basic lead arsenate (sample 18) was prepared 

 by the action of ammonia on acid lead arsenate. There is slightly 

 more arsenic oxid and slightly less lead oxid in this sample than is 

 called for by the theoretical figures. Both the acid and basic lead 

 arsenates were made from pure lead oxid and crystallized arsenic 

 acid; consequently they are extremely pure. 



Calcium arsenates.— A. calcium meta-arsenate (Ca(As0 3 ) 2 ) (sample 

 45) was prepared according to directions obtained from C. M. Smith 

 of the insecticide and fungicide laboratory. The theoretical per- 

 centage of arsenic oxid for such a product is 80. No moisture or 

 carbon dioxid was present in the sample, as the product had been 

 ignited. Although high in arsenic oxid, the product is so insoluble 

 that its insecticidal properties would undoubtedly be low. A mono- 

 calcium arsenate (CaH 4 (As0 4 ) 2 ) (sample 46) was also prepared 

 according to Smith's directions. Its theoretical composition is as 

 follows: Arsenic oxid (71.4 per cent), calcium oxid (17.41 per 

 cent), and water of crystallization and water of constitution (11.19 

 per cent). This compound is very soluble in water and can not be 

 considered a commercial possibility as an insecticide. Two samples 

 of tricalcium arsenate were prepared. The composition of sample 

 42 approached the theoretical composition of tricalcium arsenate 

 (Ca 3 (As0 4 ) 2 .2H 2 0) as determined by JRobinson (35), 38.7 per cent of 

 calcium oxid, 53 per cent of arsenic oxid, and 9.3 per cent of mois- 

 ture and water of constitution. Sample 69 was prepared by using 

 equal weights of lime and arsenic oxid, which gave a compound with an 

 excess of lime, having slightly more than 4 equivalent parts of calcium 

 oxid to 1 part of arsenic oxid, and containing but 0.17 per cent 

 of water-soluble arsenic oxid. Calcium arsenate of this composition 

 was recommended by Haywood and Smith (18) as suitable for com- 

 mercial manufacture. 



Barium arsenate seems to have been used first by Kirkland (20) in 

 1896. The next year Kirkland and Burgess (21) tested barium arse- 

 nate against certain insects. Smith (J+8) in 1907 also used a barium 

 arsenate. Its preparation is not described by any of these investi- 



