10 BULLETIN 750, U. S. DEPARTMENT OF AGRICULTURE. 
1 . Use a good grade of linie, containing a high percentage of CaO. 
2. Slake the lime to as smooth a paste as possible, for upon this 
depends the smoothness of the final product, as well as the readi- 
ness with which the lime and acid react. . Use from 3 to Zy 2 
times as much water, by weight, as lime, and have it, preferably, 
warm. Let stand for a while, then thoroughly mix, after which add 
twice as much hot water as used for slaking, and mix again. 
3. The lime and arsenic should be in such proportion that the 
weight of actual CaO used will equal that of the As 2 3 used. This 
gives a product with a molecular ratio slightly over 4, which is 
necessary if the soluble As 2 5 is to be kept down to desirable limits. 
4. Add the acid at room temperature to the lime as quickly as 
possible, and stir well until the liquid becomes alkaline to phenol- 
phthalein. 
5. Filter to as dry a state as possible, do not wash, and if a dry 
product is desired dry directly in any suitable manner. 
6. Crush in a suitable disintegrator, or grind if necessary. 
To produce 100 pounds of a commercial grade of calcium arsenate 
by this process will require 45 pounds of CaO (approximately 50 
pounds of a high-grade lime) to be slaked with 18 gallons of water, 
the addition of 36 gallons more of water, and then 45 gallons of a 
solution containing 1 pound of As 2 5 per gallon. Slight departure 
from the figures given for water will probably have little effect. 
LABELING THE PRODUCT. 
A product prepared in accordance with the procedure outlined 
is, of course, not pure calcium arsenate, but consists of tricalcium 
arsenate, probably with some Avater of crystallization, together with 
excess of other calcium compounds, such as calcium hydroxid ana 
calcium carbonate. The product, therefore, should not be designated 
simply "Calcium Arsenate," but by some such designation as. "Cal- 
cium Arsenate Containing other Calcium Compounds." In labeling 
such a product, the following is suggested by the Insecticide and 
Fungicide Board of this Department as the simplest form of state- 
ment which will fulfill the requirements of section 8 of the Insecti- 
cide Act of 1910, relative to the statement of active and inert in- 
gredients and total and water-soluble arsenic. 
Active ingredient : 
Tricalcium arsenate % 
Inert ingredients % 
Total arsenic (as metallic) % 
Arsenic in water-soluble forms (as metallic) % 
O 
