2o6 Journal of Agricultural Research voi. x, no. 4 



series of experiments to ascertain the burning tendencies of calcium 

 arsenate upon foliage. 



Two types of calcium arsenate were used: the calcium arsenate 

 (CaH. AsO^) described above and calcium ammonium arsenate, obtained 

 by treating the former calcium arsenate with 2 per cent ammonium 

 hydroxid, washing the resulting salt free of ammonia and drying at 1 10° C. 



The analysis of the salt thus obtained is as follows : 



Per cent. 



Calcium oxid (CaO), total 37- 03 



Arsenic pentoxid (AsjOg), total 52. 02 



These two spray materials were tested out upon the foliage of young 

 apple trees in the Oregon Experiment Station orchard. The trees were 

 thoroughly and uniformly covered with the spray solutions. The sus- 

 pension qualities of both materials were very poor, and they appeared 

 on the foliage as coarse granules. 



The different strengths of the spray as used were as follows : 



No. I. Calcium hydrogen arsenate (2 : 50), or 4.8 gm. in 1,000 c. c. of water. 

 No. 2. Calcium hydrogen arsenate (i : 50), or 2.4 gm. in 1,000 c. c. of water. 

 No. 3. Calcium hydrogen arsenate (1:100), or r.2 gm. in 1,000 c. c. of 



water. 

 No. 4. Calcium ammonium arsenate (2:50), or 4.8 gm. in 1,000 c. c. of 



water. 

 No. 5. Calcium ammonium arsenate (1:100), or 1.2 gm. in 1,000 c. c. of 



water. 



The application was made on June 22, 1916. Showers were frequent 

 the following two days, but, on examination of the foliage, material as 

 coarse and granular as when applied was still evident. There was no 

 indication of bum at this time. Frequent showers continued, and on 

 June 28 the following effect was noted : 



No. I. Bum on leaves general, though scattered; spots of fair size. 



No. 2. Bum on leaves general, though scattered; spots small. 



No. 3. Bum slight, scattered; spots small. 



No. 4. About same as No. 2. 



No. 5. Bum about as general as No. 4; spots very small. 



From this date on the bum spread slowly but steadily, and occasional 

 showers continued. An examination on July 2 showed the bum to be 

 spreading and in all cases was too severe for practical use. 



From these preliminary tests and under the climatic conditions noted, 

 calcium arsenates can not, at present, be recommended as a safe spray 

 material. 



SUMMARY 



(i) Lead hydrogen arsenate has a higher killing efficiency at a given 

 dilution than either calcium or basic lead arsenate. 



(2) It requires a longer period of time to kill the nearly mature cater- 

 pillars than the small forms. 



