Apr. 29, 1918 



The Calcium Arsenates 



289 



laboratory experiments, would be more vigorous than the action of the 

 carbon dioxid of the atmosphere, a similar but much slower change would 

 probably occur. In order to ascertain whether any reaction may obtain, 

 a series of flasks, each of which contained a specific quantity of calcium 

 arsenate and 50 c. c. of distilled water was prepared. Carbon dioxid was 

 then passed through the mixture, keeping the salts in a constant state of 

 agitation. After 10 hours the supernatant liquid was boiled to expel 

 excess carbon dioxid and a determination was made for arsenic in solution. 

 The results, together with amounts of arsenate used, are given in Table IV. 



Table IV. — Effect of carbolic acid on the solubility of the arsenates 



From the above results it is plainly evident that carbonic acid has a 

 solvent action upon the calcium arsenate. Furthermore, when the excess 

 carbon dioxid was boiled off, a precipitate, consisting of a mixture of 

 calcium carbonate and a smaller amount of calcium arsenate, was 

 thrown down. The presence of calcium hydroxid, however, diminished 

 the solvent action appreciably. 



REACTION BETWEEN THE CALCIUM ARSENATES AND LIME-SULPHUR 



SOLUTION 



Combination sprays are of great economic importance, since time, 

 labor, and money are thereby saved. The tendency for chemical reaction 

 that destroys or greatly diminishes the efficiency of both spray materials 

 often results, and consequently prevents their use in this manner. The 

 combination of lead hydrogen arsenate and lime-sulphur exemplifies 

 this difficulty, as shown by Robinson and Tartar.^ The concentration 

 of the lime-sulphur is reduced; arsenic is found in solution; lead sulphid 

 is precipitated out, thus utilizing part of the lead arsenate; and severe 

 burning of foliage may occur, depending upon weather conditions. 



When pure tricalcium arsenate was added to dilute lime-sulphur, no 

 reaction appeared to occur. Sanders ^ in field experiments reports 



> Robinson, R. H., and Tartar, H. V. The arsenates of lead. Greg. Agr. Exp. Sta. Bui. 128, 

 33 p., 2 fig. 1915. 



' Sanders, G. E. the effect of certain combinations of spraying materials on the set of 

 APPLES. In Proc. Ent. Soc. Nova Scotia, 1916, p. 17-31. 1917. 



41815°— 18 3 



