2 MASS. EXPERIMENT STATION BULLETIN 207. 



author; the preparation and application of the sprays, and the observa- 

 tions to determine their effects, were carried out by the junior author; the 

 chemical analyses and all the chemical work involved were done by Dr. 

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

 Chemistry of the Experiment 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 on a firm chemical basis. 



Materials. 



To eliminate the possibility that injury was caused by impurities in the 

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

 the action of these appeared to be desirable, as, if injurj^ 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 Avould 

 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 supply them, but the samples received 

 proved on analj^sis to be far from pure, and nearly two years passed before 

 materials were found so nearly pure that it was believed they would be 

 satisfactory. ^ 



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

 ments analyzed as follows : — 



100.06 



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, PbHAs04 

 Neutral lead arsenate, PbaCAsO^J 

 Lead chloride, PbCh 

 Insoluble matter 



100.05 



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

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



