2 BULLETIN 750, U. S. DEPARTMENT OF AGRICULTURE. 
PREPARATION Ol CALCIUM ARSENATE. 
The Bureau of Entomology of this Department has carried out 
experiments with "homemade" calcium arsenate prepared by slaking 
burned lime with a solution of sodium arsenate. Others 1 have 
recommended calcium arsenate prepared by The action of soluble 
lime salts on sodium arsenate. In all such eases soluble by- 
products are formed. Since these may influence the action of the 
spray if not removed, they should be washed and filtered out if a 
; grade of commercial calcium arsenate is desired. 
From the chemical standpoint, the simplest means of producing 
calcium arsenate is the direct union of calcium liydroxid and 
iirseiik acid. As the only by-product of this reaction is svater. 
nitration of the material is the only treatment that should be re- 
quired. Thus eliminating the washing necessary with most products. 
The following experiments were made with the idea of determining 
the proportions and procedure necessary to obtain a product hav- 
ing the properties desired for spraying purposes 1 . The arsenic acid 
used was commercial 75 per cent acid. Its density was found to 
be l.SS. corresponding to 61 per cent As 2 : . or 75 per cent arsenic 
acid. H 3 As0 4 . The lime was a good grade of commercial lime of 
the following composition : 
Pei 
L. -ss on ignition 5.07 
Calcium oxid. CaO 93.36 
Magnesium oxid. MgO 69 
Silicon dioxid. SiCh 54 
Oxids of iron and aluminum. ItO : 68 
100 . 34 
In the absence of other drawbacks, the must desirable method of 
uniting lime and arsenic acid is to have both ingredients in solu- 
tion before they are mixed. This necessitates the use of lime water 
which contains only about 1 gram of CaO per liter, and of a quan- 
tity of water so large that it probably would be prohibitive in com- 
mercial practice. Xevertheless. a few experiments were made to 
discover the nature of the product so formed. 
: Oregon Agr. Exp. Sta. Bui. 131. 
: Tlie desirable features of a good arsenical spray material may be enumerated here. 
It should not contain an excessive amount of soluble arsenic, which would cause 
injury to foliage: it should be very finely divided in order that it may be dis- 
tributed well over the foliage: it should be light when in the to permit 
of ready application by dusting: it should suspend well in wate .rait of 
even distribution when applied in the form of a spray: and wii tf n sprayed and 
subsequently dried it should stick well to the foliage. 
