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 decantation 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 As 2 5 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 1 (80 per cent CaO) pounds. . 6 



Sodium arsenate, 2 fused (dry powdered) 62 per cent As 2 5 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, As 2 5 20. 37 



Total arsenious oxid, As^ 21 



Calcium oxid, CaO 18. 95 



Carbon dioxid, C0 2 18 



Undetermined, mainly sodium hydrate 13. 39 



Total 100. 00 



Soluble arsenic oxid, As^ 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 AsOi. Asj0 5 =61.86 per cent: As 2 3 = 1.42 per cent. 



