2 MASS. EXPERIMENT STATION BULLETIN 207. 



author; the pro])ai'ation and appheation of the sprays, and the obsen'a- 

 tions to determine their effec^ts, were carried out by the junior author; the 

 chemical analyses and all the cheirjral work involved were done by Di-. 

 E. B. Holland and his assistants of the Department of Plant and Animal 

 Chemistry of the I^xporiment Station, and to him and to those who worked 

 with him the authors desire to express their appreciation of the efforts 

 made to establish this work (ni a firm chemical basis. 



Materl^ls. 



To eliminate the possibility that injury was caused })y impurities in tlie 

 spraA' materials, pure arsenates were first sought. A definite knowledge of 

 the action of these appeared to be desirable, as, if injun,' resulted from their 

 use, it seemed probable that the factors causing it would be indicated, 

 uncomplicated by the presence of injurious impurities, uncombined ar- 

 senic or too loosely combined arsenic. In fact, such knowledge would 

 provide a basis or standard with which to compare results obtained from 

 the use of commercial materials. Accordingly, the attempt was made to 

 obtain pure acid lead arsenate and pure neutral lead arsenate. 



To get these seemed at first to be almost impossible. A number of 

 manufacturers were willing to su])ply them, but the samples received 

 proved on analysis to be far from pure, and nearly two years passed before 

 materials were found so nearly pure that it was belieA'ed they would be 

 satisfactoiy. ^ 



Pure Acid Lead Arsenate Paste. — The material used in these experi- 

 ments analyzed as follows: — 



Per Cent. 



Water, H2O 46.99 



Water in combination and ocrlusion . . .1.33 



Lead oxide. PbO 34.58 



Arsenic pentoxide, A^^>05 . .17.11 



Chlorine, CI 04 



Insoluble matter . . . . .01 



100. or. 



The probable original composition of the paste, reconstructed from this 

 analysis, was substantially as follows: — 



Per Cent. 



Water, H2O 46.99 



Water occluded . . . 09 



Acid lead arsenate, PbHAsOi .47.87 



Neutral load arsenate, PbsCAsOi)-.- 4.93 



Lead chloride, PbCl-. 16 



Insoluble matter . . . . .01 



100.05 



' See Holland and Reed: The Chemistry of Arsenical Insecticides, Twenty-fourth Annual Re- 

 port, M.18S. Agr. Exp. Station, Part I, pp. 180-182, 1912, for a fuller discussion. 



