48 LEAD ARSENATE. 



While the total amount of dissolved salts occurring in this water 

 is small, it will be noticed that the sodium chlorid content is rela- 

 tively high, and to this the solvent action which this water exerts: 

 on lead arsenate is no doubt largely due. It would appear from 

 these results that if certain salts commonly occurring in waters are 

 present in more than very small amounts they will exert a solvent 

 action on the lead arsenate. 



CONCLUSIONS. 



Referring again to the fact that no injury resulted in 1907 from 

 the lead arsenate, while in 1908 severe damage followed the use of 

 the same water and chemicals, this may be explained by the differ- 

 ence between the two seasons with respect to climatic conditions. 

 In 1907 every application was followed by cool, cloudy weather and 

 rain within forty-eight hours. In 1908 the first two applications 

 were followed by cool days and light rains soon thereafter, but the 

 last application, which caused practically all of the injury, was 

 followed by five clear, hot days and no rain. The dews at night 

 would be sufficient to moisten the material, and when hot sunshine 

 followed the conditions would be just right to dissolve the maximum 

 amount of arsenic, and therefore cause the maximum injury. The 

 salts (sodium chlorid and sodium carbonate and no doubt others 

 which have not been tried), which cause the lead arsenate to be 

 broken up, are readily soluble in water, and if their application were 

 followed by rain they would be washed out, and therefore no injury 

 should result. 



Headden, a in a publication which has recently been issued, calls 

 attention to the danger that may result from using water containing 

 certain salts. He says : "It has often been asked at meetings of these 

 orchardists whether it was a safe practice to use -their surface alkali 

 water in applying the lead arsenate and I have stated thai it was 

 not a good practice, for one could easily conceive of conditions under 

 which the whole of the lead arsenate could be converted into sul- 

 phate of lead and sodic arsenate be formed in solution. This state- 

 ment never seemed to be an acceptable one. I have in this case 

 not depended upon any chemical laws, however evident their ade- 

 quacy might be, but took well-washed lead arsenate, a sample which 

 we found by rigid test to be free from soluble arsenic, suspended 

 1 gram of it in 2,000 times its weight of water and added 2 grams of 

 Glauber's salt, allowed it to stand three days, filtered off a portion 

 of it, concentrated by evaporation, and tested it for arsenic. I found 



a Colorado Agr. Exper. Sta., 1908, Bui. 131, p. 22. 



