Apr. 29, 1918 



The Calcium Arsenates 



291 



materials, it might be advisable to have it present in order to prevent 

 danger of a foliage bum due to severe atmospheric conditions. This 

 would be especially true of the less stable calcium hydrogen arsenate. 

 This precaution, however, must be verified by field experiments. 



Since the above conclusions were obtained on pure samples, the ex- 

 periment was repeated with commercial products in order to ascertain 

 the practicability of their use. A solution of commercial lime-sulphur 

 having a specific gravity of 1.227, or 26.7° Baume, was diluted in the 

 same proportion as indicated in the previous experiment. A commercial 

 calcium arsenate was used that had the following composition: 



Calcium oxid total . . 39.20 per cent. 



Arsenic pentoxid total. . 48.90 per cent. 



Calcium carbonate total . . 1.14 per cent. 



From this analysis we infer that the sample consisted of over 60 per 

 cent of tricalcium arsenate and the remainder calcium hydrogen arsenate 

 and calcium carbonate. 



Treatment was similar to that of the last experiment, and the com- 

 position of the lime-sulphur solution is given in Table VI. 



Table VI. — Reaction between commercial calcium arsenate and lime-sulphur 



Here again, we observe that no apparent chemical action has occurred. 

 No arsenic was found in solution, and the total calcium oxid and sulphur 

 content remained the same. It is obvious that a commercial sample com- 

 posed of both calcium hydrogen arsenate and tricalcium arsenate and 

 possibly other impurities may be combined with commercial lime- 

 sulphur with the same degree of safety as the pure laboratory products. 



The use of dry substitutes for lime-sulphur is rapidly becoming preva- 

 lent; hence, a study of their combination with calcium arsenate would be 

 beneficial. Consequently 0.5 gm. of a commercial "dry lime-sulphur" 

 and the same quantity of a so-called "soluble sulphur" which is com- 

 posed chiefly of the sulphids of sodium or potassium were used. Each 

 was introduced into 200-c. c. graduated flasks, together with i gm. of 

 commercial calcium arsenate, and each mixture was then made up to 

 mark with water. After shaking occasionally during two days the 

 mixture in both flasks was allowed to settle and was analyzed for arsenic 

 in solution, as reported in Table VII. 



