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JOURNAL OF ECONOMIC ENTOMOLOGY 



[Vol. 12 



this difficulty is worthy of especial consideration. As shown by Tartar 

 and Robinson' and later by McDonnell and Smith^ and also by G. E. 

 Smith,^ there are two lead arsenates, namely, lead hydrogen or acid 

 arsenate, and basic or neutral lead arsenate, that are easily prepared. 

 Both of these are manufactured commercially and sold on the market 

 chiefly for spraying purposes. Since perhaps more than 95 per cent of 

 the lead arsenate sold is the lead hydrogen arsenate, this is the type 

 generally used in combination sprays. When combined with hme sulfur 

 it was observed that the residue from the mixture of the lead hydrogen 

 arsenate was much darker than that obtained with the neutral arsenate, 

 indicating greater decomposition. Consequently a study was made of 

 the changes that occurred when lime sulfur, diluted to summer spraying 

 strength, was mixed with lead hydrogen arsenate and with Ijasic lead 

 arsenate. 



Lime sulfur having a specific gravity of 1.259 was diluted at the rate of 

 1 gallon to 30 gallons of water. To each of several 1000 cc. portions of 

 this dilute lime sulfur solution, 4.8 grams of the different arsenates men- 

 tioned were added. The mixture was agitated occasionally during 14 

 hours, allowed to settle, and the clear Hme sulfur siphoned off from the 

 lead arsenate residue. The residue was then transferred to a filter, 

 washed thoroughly with cold water and dried at 60 degrees C. The 

 following table shows the important changes that occurred in the hme 

 suKur, diluted for summer sprajdng, and mixed with lead hydrogen and 

 basic arsenate. 



Table I. 



Composition of Lime Sulfur Before and After Addition of Hydrogen and Basic 

 Lead Arsenate 



The above results indicate that there is considerable reaction be- 

 tween hme sulfur and lead hydrogen arsenate while the basic lead 

 arsenate caused only a slight change in the lime suKur. Calculated 

 from the original amount of lead hydrogen arsenate used, over 5 per 



1 Tartar, H. V., and Robinson, R. H. The Arsenates of Lead, Journal of American 

 Chem. Society, Vol. 36, Sept., 1914. 



2 McDonnell, C. C, and Smith, C. M. The Arsenates of Lead, Journal of Amer- 

 ican Chem. Society, Vol. 38, Oct., 1916. 



3 Smith, G. E. Lead Arsenates, Journal of American Chem. Society, Vol. 38, Oct., 

 1916. 



