92 MASS. EXPERIMENT STATION BULLETIN 210. 



The original composition of this material was probably substantially 

 as follows : • — ■ 



Per Cent. 



Water, H2O 79.03 



Calcium ortho arsenate, Ca3(As04)2 . . . . . . . .06 



Calcium metarsenite, Ca(As02) 2 . . . . . . . .20.34 



Magnesium metarsenite, Mg (As02)2 ....... .30 



Sodium arsenite, NaAs02 . . . . . . . . . . 13 



Sodium chloride, NaCl ......... .05 



Organic matter, etc. . . . . . . . . . . .08 



Insoluble matter . . . . . . . . . . .01 



100.00 



The arsenic in this material, also, proved so soluble on standing in 

 water as to make it unsafe for application to foliage. It was tested both 

 in water alone and with the addition of various percentages of milk of 

 lime. With both samples, enough was taken to give the standard amount 

 of arsenic, so that the treatments should be comparable with those made 

 with the lead arsenates and lime arsenates. 



Experimental Work. 



The materials described above were sprayed upon the apple, cherry, 

 peach, pear, plum and elm, under the same conditions as given in Bulletin 

 No. 207, and the results obtained follow. 



Pure Acid Calcium Arsenate with 1 Per Cent Milk of Lime. — The 

 apple, sprayed with this material in clear weather, shows injury above 

 the safety line (Fig. 1, AB), from high temperature with low humidity 

 to low temperature with high humidity. The line for the greater part 

 of its course runs lower than the safety line for lead arsenates, though at 

 the high humidity end the reverse is true to a slight degree. As the gen- 

 eral safety line for the apple is much below most of those given in clear 

 weather, the difference is more marked by com.paring any of the clear 

 weather lead arsenate safety lines in Bulletin No. 207 with Fig. 1, than 

 when the general one is used. The evidence is that pure acid calcium 

 arsenate with 1 per cent milk of lime cannot be used on the apple at as 

 high temperatures and humidities as the lead arsenates in clear weather. 

 This is true, also, for cloudy weather, though the difference is not so great. 



On the pear, clear- weather tests gave six cases of injury above the 

 safety line (Fig. 2, AB) , which runs considerably higher than in the case 

 of the apple. In the cloudy weather tests (Fig. 2, CD), as was the case 

 with the lead arsenates, the pear is evidently much more resistant to 

 spray injury than the apple. 



In the case of the cherry (Fig. 3), the leaves are more liixhXa to injury 

 than the apple, but less so than the plum. The cloudy weather safety 

 lines for the cherry and plum (Figs. 3 and 4, CD) are verj^ nearly the same, 

 however. With the plum, temperature seems to play an important part, 

 injury beginning in clear weather at quite a low point, while high humidity 

 seems to be less dangerous (Fig. 4, AB). 



