10 BULLETIN 750, U. S. DEPARTMENT OF AGRICULTURE. 



1 . Use a good grade of lime, 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 3y 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 5 used. This 

 gives a product with a molecular ratio slightly over 4, which is 

 necessary if the soluble As.>0 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. 



0. 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 86 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 water of crystallization, together with 

 excess of other calcium compounds, such as calcium hydroxid and 

 calcium carbonated The product, therefore, should not be designated 

 simply "'Calcium Arsenate," but by some such designation as, "Cal- 

 cium Arsenate Containing other Calcium Compouuds." 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 <if 1910', relative to the statement of active and inert in- 

 gredients arid total ami water-soluble arsenic! 

 Ai tire ingredient : 



Tricalcium arsenate % 



Inert ingredients % 



Total arsenic < as metallic i % 



A.reenie in waters-soluble forms (<ds metallic) % 



O 



