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 5 ). 
Lead 
oxid 
(PbO). 
Calcium 
oxid 
(CaO). 
lip 
116 
Water of 
constitu- 
tion and 
Total Water- 
rotaK soluble. 
impuri- 
ties, by 
differ- 
ence. 
17 
Percent. 
0.02 
.10 
.06 
.03 
.23 
1.06 
2.30 
Per cenLl Percent. 
33.09 n. 10 
Percent. 
63.80 
63.67 
74.66 
Percent. 
Per cent. 
Percent. 
3.09 
68 
do 
Basic lead arsenate 
33.25 
23.40 
79.63 
69.09 
52.05 
.00 
.27 
Trace. 
61.67 
.46 
2.98 
18 
1.88 
45 
Calcium meta-arsenate 
Monocalcium arsenate 
18.45 
19.92 
40.07 
44.89 
0.00 
.10 
.96 
5.73 
1.89 
46 
10.66 
42 
5.86 
69 
do 
42.84 -17 
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 (AsOJ 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 Kobinson (35), 38.7 per cent of 
calcium oxid, 53 per cent of arsenic oxid, and 9.3 per cent of mois- 
ture and water 01 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 (48) in 1907 also used a barium 
arsenate. Its preparation is not described by any of these investi- 
