﻿16 BULLETIN 1147, U. S. DEPARTMENT OF AGRICULTURE. 



The data given in Table 6 (series 2) show that no detectable changes 

 took place when calcium arsenate and lime-sulphur were mixed. 

 The small amount of arsenic found in the filtrates was the water- 

 soluble arsenic originally present in the calcium arsenate and 

 amounted to 0.2 per cent of the total arsenic oxid in the calcium 

 arsenate,. 



In brief, it is evident that chemical changes take place when acid 

 lead arsenate and lime-sulphur are mixed. This mixture is therefore 

 incompatible chemically. When calcium arsenate is mixed with 

 lime-sulphur no soluble arsenic is formed in the case of high-grade 

 products. Therefore this arsenate, when mixed with lime-sulphur, 

 would seem to be a satisfactory insecticide. Field experience, how- 

 ever, shows that it often injures the foliage sprayed. 



Such a mixture is chemically compatible and has been recommended 

 by Quaintance and Siegler {32), Sanders (40), and others, who, how- 

 ever, do not claim that it is always free from burning properties. 



No experiments with basic lead arsenate and lime-sulphur were 

 performed. Bradley (5), in 1909, used basic lead arsenate in com- 

 bination with lime-sulphur, and found 0.28 and 0.43 per cent of 

 soluble arsenic. He considered that there was no danger of the 

 formation of excessive amounts of soluble arsenic in such mixtures. 

 Bradley and Tartar (6), who used both acid and basic lead arsenates 

 in combination with lime-sulphur, found eight times more soluble 

 arsenic with acid lead arsenate than with basic lead arsenate. Both 

 forms of lead arsenate were more soluble in saline water than in pure 

 water. Alkaline carbonates exerted a decomposing action, especially 

 on acid lead arsenate. 



ARSENATES AND BORDEAUX MIXTURE. 



Fields and Elliott (15) stated that very little soluble arsenic is 

 present when Bordeaux mixture is combined with lead arsenate. 

 They found in both the acid and the basic lead arsenates only from 

 1 to 3 parts of soluble arsenic per million. 



Since combinations of arsenicals with Bordeaux mixture are fre- 

 quently made, it was considered important to determine whether or 

 not chemical changes take place in these combinations. Tests were 

 therefore conducted in which 4-3.67-50 Bordeaux mixture was pre- 

 pared, dried, and passed through a 100-mesh sieve. Four-gram sam- 

 ples of the dry Bordeaux were placed in each of a series of 300 cubic 

 centimeter flasks and to each flask were added portions of one of the 

 four arsenicals in the following amounts: 0.8 gram of acid lead arse- 

 nate (sample 39); 0.667 gram of calcium arsenate (sample 57); 0.69 

 gram of sodium arsenate (sample 25) ; and 0.47 gram of Paris green 

 (sample 64). Mixtures of the various arsenicals alone and of Bor- 

 deaux alone in distilled water were prepared and tested under the 

 same conditions as the mixtures of the arsenicals and Bordeaux. The 

 flasks were agitated at a temperature of 35° C. for periods of 1 hour, 

 1 day, and 3 days. The mixtures were filtered immediately and the 

 filtrates were tested for copper by the colorimetric test with potas- 

 sium ferrocyanid (12) and for lead by the lead sulphid color test as 

 used by W. D. Lynch, of the insecticide and fungicide laboratory. 

 The analytical data are given in Table 7. 



No copper was found in any of the filtrates. The filtrates from the 

 acid lead arsenate Bordeaux mixtures contained the following per- 



