290 



Journal of Agricultural Research 



Vol. XIII. No. s 



more favorable results obtained with the calcium-arsenate-lime-sulphur 

 combination spray than with lead-arsenate-lime-sulphur. Hence, a 

 study of the chemical reaction, if any, was initiated. Pure lime-sulphur 

 was prepared in the laboratory from crystallized sulphur and calcium 

 oxid, the latter being obtained by igniting calcium carbonate. The 

 lime-sulphur produced had a specific gravity of 1.242, or 28.2° Baume, 

 and was diluted to average field spraying strength. Both of the calcium 

 arsenates were prepared in the laboratory in pure form. Into each of 

 several flasks i gm. of tricalcium arsenate, i gm. of calcium hydrogen 

 arsenate, or i gm. of calcium hydrogen arsenate -f-0.5 gm. of calcium oxid 

 was introduced, and 200 c. c. of the diluted lime-sulphur were added. 

 A control flask containing 200 c. c. of the diluted lime-sulphur only was 

 also prepared. The flasks were then shaken at intervals during two days, 

 after which the salts were allowed to settle and determinations were 

 made for total sulphur, calcium oxid, and arsenic pentoxid in the super- 

 natant lime-sulphur solution. Table V records the results, expressed in 

 grams contained in 200 c. c. 



Tabi^E V. — Reaction between lime-sulphur and the calcium arsenates 



Constituent. 



ContTol. 



Lime- 

 sulphur 

 and 

 tricaldtun 

 arsenate. 



Lime- 

 sulphur 



and 

 calcium 

 hydrogen 

 arsenate. 



Lime- 

 sulphur 



and 



calcium 



hydrogen 



arsenate 



+ calcium 



oxid. 



Sulphur total . 



Calcium oxid total . 



Arsenic pentoxid total . 



Gm. 

 I. 8400 



Gm. 



I. 8450 



None. 



Gm. 

 I. 8490 

 .8820 

 None. 



Gm.. 

 I. 8420 

 I. 1090 

 None. 



The above results proved favorable beyond expectation. There 

 appears to be no chemical change whatsoever in the lime-sulphur solu- 

 tion, all constituents remaining constant and agreeing with results given 

 for the control solution. Barring the possibility of chemical reaction 

 after spraying, we have in the calcium arsenate an ideal spray material 

 to be used in combination with lime-sulphur. The efficiency of the latter 

 is not reduced and the calcium arsenate remains unchanged. 



Attention is further brought to the analysis of the liquid in the flask 

 containing calcium hydrogen arsenate H- calcium oxid. As with calcium 

 hydrogen arsenate and tricalcium arsenate, no arsenic was found in the 

 lime-sulphur solution, and the sulphur content remained constant. The 

 amount of calcium oxid, however, exceeds that obtained in the other 

 flasks. This increase of the calcium oxid is equivalent to the solubility 

 of calcium hydroxid in pure water at the temperature under observation. 

 Since the addition of lime in no way reacts with either of the other spray 



