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Some Facts About Lead Arsenate 



(This article was prepared by L. G. Gennnell of the Agricultural Insecti- 

 cide and Fungicide Association.) The real values which lie behind many of the 

 agricultural chemicals we commonly use are often lost sight of, because of the 

 present day necessity to get the job done quickly in order to take advantage of 

 particularly fine weather or to make the best possible use of the farm labor 

 available to us. Vfiiether it be a spraying or dusting operation, little thought 

 is given to the time spent in research or to the eflort that has been put into 

 the production of many common corrimercial chemicals to insure the ultimate con- 

 suTiier the highest value at the lowest cost consistent with high quality. Many 

 such products used on the farm have thus come to be taken for granted; and 

 little serious consideration given to their past history or to their value in 

 terms of better and more abundant crops. The case of Lead Arsenate aptly il- 

 lustrates this. Up until our recent emergency. Lead Arsenate, of which 

 59,000,000 to 60,000,000 pounds is used annually in this country, has been 

 very easy to obtain and has, therefore, been used in our spraying or dusting 

 programs without much regard for the raw materials -which go to make it up, 

 or for the amount that was used in our pest control programs. Now that agri- 

 culture is in the position of competing with the war industries for the Lead 

 and Arsenic which go into the making of Lead Arsenate, some understanding of 

 the manufacturing problems which lie behind this common spray chemical may 

 enable us to properly evaluate it. 



Hist.-^ry. F. C, Moulton, of the Massachusetts Gypsy Moth Committee 

 is creditlTd wxth" the discovery in 1892 of the insecticidal properties of 

 Lead Arsenate and late in 1893 its use as an insecticide was recommended. 

 Although the early ro.atsrial resembled in many ways the chemical as we know 

 it today, it differed in many important respects. The early methods of prep- 

 aration vrere crude and expensive, the product variable, and as then sold 

 contained 40-50^ water. Although the same two forms ; acid and basic Lead 

 Arsenate, were known then as now, the former, the acid or standard type, has 

 far surpassed the basic type in importance to the fruit grower. 



In the early procedure for preparing acid Lead Arsenate (PbHAs04) 

 solutions of lead acetate or lead nitrate were precipitated by sodium arsenate 

 (Na2HAs04) and the product aold as a paste with a high water content. However, 

 with the granting of over 3D patents relating to Lead Arsenate production, the! 

 methods of manufacture have improved and today the dry powdered product now 

 offered for sale contains almost pure lead arsenate. That such a product can 

 be sold at its usual low figure is a monumental tribute to the early research 

 workers and to the agriculturists who cooperated with them in testing out the 

 product on various food crops. (To be Continued in July Issue.) 



