8 BULLETIN 1147, U. S. DEPARTMENT OF AGRICULTURE. 
The analytical results on nine samples of calcium arsenate aro 
recorded in Table 3. Samples 6, 24, and 34 were not strictly com- 
mercial products, but were made by the manufacturers as an experi- 
ment. Sample 24 contains a higher percentage of arsenic than the 
strictly commercial samples. Samples 6, 24, and 34 have a lower 
lime content than the six commercial samples analyzed, and it is 
probable that a portion of their arsenate is in the form of dicalcium 
arsenate. The somewhat large amount of carbon dioxid found in 
all of the samples of calcium arsenate comes from the lime, which 
is always carbonated to a certain extent. The water of the calcium 
arsenates varies more than that of the lead arsenates. Analyses of 
samples 56 and 57 showed, respectively, 11.75 per cent and 12.35 
per cent loss on ignition, 0.35 and 0.5 per cent of ferric* oxid and 
aluminum oxid, 0.51 per cent and 0.74 per cent of magnesium 
oxid, and 0.62 per cent and 0.51 per cent of sodium oxid. Sample 
56 contained 0.35 per cent of antimony oxid. 
Lovett {23) in 1918 reported a high water-soluble arsenic content 
in samples of commercial calcium arsenate. Since then the amount 
of water-soluble arsenic in commercial calcium arsenate has been 
reduced, as shown in Table 3. Lovett {24) in 1920 published graphs 
showing the chemical features of calcium arsenate, apparently based 
on the percentages of lime or on the ratio of lime to arsenic oxid 
in the calcium arsenates. No consideration seems to have been 
given to the percentages of total and water-soluble arsenic oxid 
which are the generally recognized criteria for judging the quality of 
calcium arsenates chemically. 
Robinson {35), who tested the solubility of calcium arsenates 
in water containing lime, reported that the lime prevents the arsenic 
oxid from becoming soluble. He also studied the action of carbon 
dioxid on calcium arsenates and found that carbonic acid has a 
solvent action upon the calcium arsenates. Patten and O'Meara 
{30) made a series of tests on the amount of soluble arsenic oxid 
obtained from calcium arsenate in water containing carbon dioxid 
and in water free from carbon dioxid. From their results, which 
showed a great increase of soluble arsenic oxid when carbon dioxid 
was present, they concluded that the burning of foliage, when 
calcium arsenate is applied, is due to the arsenic made soluble by 
the carbon dioxid of the air. 
The commercial calcium arsenates contain approximately one- 
third more lime than is required by tricalcium arsenate. They con- 
tain a higher percentage of total arsenic oxid than the lead arsenates, 
but they should be manufactured more cheaply per unit of arsenic 
oxid because of the low cost of the base (CaO). 
Coad and Cassidy {10) have recommended that calcium arsenate 
for dusting cotton should contain not less than 40 per cent of arsenic 
oxid and not more than 0.75 per cent of water-soluble arsenic oxid, 
and that it should occupy a volume of from 80 to 100 cubic inches a 
pound. 
PARIS GREEN. 
Paris green, originally used as a paint pigment, is said to have first 
served as an insecticide in the western United States. It is a com- 
pound of arsenic, acetic acid, and copper, known as aceto-arsenite of 
copper. The theoretical composition of Paris green is copper oxid 
