30 BULLETIN 278, U. S. DEPARTMENT OF AGRICULTURE. 
not be obtained on the market to advantage. In view of this fact 
arsenate of calcium may be prepared at home by combining fused 
(dry powdered) sodium arsenate with lime. The by-product is largely 
sodium hydroxid, most of which may be decanted. It is possible 
that decant ation will not be necessary when the arsenate of calcium 
is to be applied to foliage that is not too tender. The formula for 
making is herewith given : 
Stone lime (90 per cent CaO) pounds. . 55 
Sodium arsenate, fused (dry powdered) 65 per cent AS2O5 do 100 
Water gallons. . 26 
Place the stone lime in a wooden container and add a small amount of water, just 
enough to start slaking. When slaking is well under way pour in the sodium arsenate, 
which should first have been dissolved in hot water. Keep stirring until the lime 
has thoroughly slaked. Sufficient water should be added from time to time to prevent 
burning. 
The resulting arsenate of calcium should contain about 18 per cent 
of arsenic oxid. In making this compound it will of course be neces- 
sary to know approximately the calcium oxid and arsenic oxid con- 
tent of the materials employed and to vary the formula accordingly. 
Arsenate of calcium was prepared at the laboratory in the propor- 
tions as given below: 
Stone lime x (80 per cent CaO) pounds. . 6 
Sodium arsenate, 2 fused (dry powdered) 62 per cent AS2O5 do 10 
Water gallons. . 2 
The above was analyzed by the Bureau of Chemistry, United States 
Department of Agriculture, as follows: 
Per cent. 
Moisture 46. 90 
Total arsenic oxid, A^Os 20. 37 
Total arsenious oxid, AS2O3 21 
Calcium oxid, CaO 18. 95 
Carbon dioxid, C0 2 18 
Undetermined, mainly sodium hydrate , 13. 39 
Total 100. 00 
Soluble arsenic oxid, As 2 5 04 
Experiment XVII. 
FIELD TESTS OF POWDERED ARSENATE OF LEAD VERSUS PASTE ARSENATE OF LEAD 
AGAINST THE CODLING MOTH, 1914. 
Since the advent of the powdered form of arsenate of lead the 
question has naturally arisen as to whether this newer form of the 
arsenical is as effective as the older or paste form. The powdered 
arsenate of lead has been on the market for several years and is now 
being recommended by several manufacturers, who claim for it 
1 This lime was not well burned, since it contained considerable calcium carbonate. 
2 Sodium arsenate, fused (dry powdered) Na»H AsO*. As 2 5 =61.86 per cent: As«0 3 = 1.42 per cent. 
