2 BIILLETi:^- 1115, IT. s. DEPARTMENT OF AGEICULTUEE. 



safe to use calcium arsenate that had been stored for any appreciable 

 length of time. A preliminary investigation showed that in the 

 cases of the most serious burning reported, the injury was due to the 

 use of improperly made calcimn arsenate. The evidence of deteriora- 

 tion seemed sufficiently suggestive, however, to warrant an investiga- 

 tion of the matter under accurately controlled conditions. 



RESULTS OF PREVIOUS INVESTIGATIONS. 



Robinson^ showed that chemical changes occur in calcium arse- 

 nate through the action of carbon dioxid in the presence of water and 

 stated that under atmospheric conditions a similar but much slower 

 action probably would occur. As a result of bubbling carbon 

 dioxid through suspensions of dicalcium and tricalcium arsenates 

 in water, he concluded that there was an evident "solvent action 

 upon the calcium arsenates. " However, while this writer's results for 

 tricalcium arsenate were higher, those for dicalcium arsenate were 

 lower than his figures for the solubility of the same salts in pure 

 water. 



Patten and O'Meara* suggested that calcium arsenate when 

 applied to foliage would almost certainly be subject to change by 

 the carbon dioxid given off by the leaves. In pursuance of this 

 idea, they determined the amount of arsenic rendered soluble when 

 saturated carbon dioxid water was used in place of distilled water 

 in the regular method for determining water-soluble arsenic oxid in 

 calcium arsenate. The six samples used by them gave an average 

 of 0.7 per cent soluble arsenic oxid with distilled water and an aver- 

 age of 18.5 per cent soluble arsenic oxid with the carbonated water. 



The work of the previous investigators was done in connection 

 with the action of carbon dioxid on calcium arsenate when applied 

 to foliage in a thin film and subjected to the effect of moisture. Reedy 

 and Haag,^ the only workers who have considered the question of a 

 possible change in calcium arsenate during storage, state that "dur- 

 ing storage this product undergoes some change in composition which 

 results in a considerable increase in the amount of water-soluble arse- 

 nate." They thought at first that moisture and carbon dioxid from 

 the air caused this change, but state that "the use of air-tight con- 

 tainers has not been sufficient to prevent it." However, they report 

 experiments showing that exposure to laboratory air and to moist 

 carbon dioxid caused an increase in the water-soluble arsenic which 

 in the latter case was quite marked. As a result of their work, they 

 conclude that "the decomposition of tricalcium arsenate is due to 

 hydrolysis, which seems to be catalyzed by many substances that 



3 J. Agr. Research, 13 (1918): 2S8; Oregon Agr. Col. Exp. Sta. BuU. 131 (1918), p. 10. 



4 Mich. Agr. Col. Exp. Sta., Quart. Bull., Nov., 1919, p. 83. 

 6J.Ind. Eng.Chem., 13 (1921): 1038. 



