4 MASS. EXPERIMENT STATION BULLETIN 207. 



not cause any injurious effect on foliage. Rather more than half of the 

 whole consisted of arsenates of lead, but the neutral salt formed a much 

 greater part of the total than was the case with the pure material. About 

 the same amount of water was present as in the pure substance. Or, 

 the total amount of arsenate in the two did not differ greatly, but there 

 was more than three times as much of the neutral arsenate in the com- 

 mercial salt as in the pure one, the acid arsenate being correspondingly 

 decreased. Any marked difference in the results following spraying by 

 these materials, then, might possibly be explained by this difference in 

 composition. In fact, the results did not differ greatly. 



This paste, mixed with water as described for the pure paste, gave .09 

 per cent of arsenic pentoxide as entering solution in twenty-four hours. 

 Tliis, though more than with the pure paste, is also far below the amount 

 permitted by the Federal law. Complete settling after mixing with water 

 required only thirty-four minutes, showing that this commercial material 

 was rather poor in this regard as compared with the pure paste. 



Commercial Acid Lead Arsenate Powder. — The appearance on the mar- 

 ket during the progress of these experiments of lead arsenate in powder 

 form led to the addition of this material to the list of substances to be in- 

 vestigated. Samples from a brand on sale were obtained, analyzed and 

 tested like the others. The analysis gave: — 



99.90 



From this the original composition of the powder was probably sub- 

 stantially as follows : — 



Water, H2O 



Water in combination and occluded . 

 Acid lead arsenate, PbHAs04 

 Neutral lead arsenate, Pb3(As04)2 

 Iron and aluminum as ferric arsenate 

 Insoluble matter . . . . 



Per Cent. 



.45 



.68 



89.93 



7.28 



1.16 



.38 



99.88 



This material as used for spraying, therefore, contained a little more than 

 1 per cent of water, about 90 per cent of acid lead arsenate, rather more 

 than 7 per cent of neutral lead arsenate, and about 1^ per cent of im- 

 purities, none of them of a nature or present in sufficient amount to be 

 liable to cause any injury. 



The amount of arsenic pentoxide which had entered into solution after 

 twenty-four hours of treatment was .16 per cent, which, though more than 

 with either of the other materials already considered, was still far below 



