38 



of lead is formed as a curdy white precipitate. The following 

 table adapted from Smith * shows the necessary amounts of the 

 ingredients where acetate of lead is used : — 



Using nitrate of lead the following amounts of ingredients are 

 necessary : — 



The use of 50 per cent arsenate of soda is not recommended 

 when the 65 per cent can be purchased at a fair price, since the 

 former product is generally adulterated with common salt. Where 

 large quantities of arsenate of lead are to be prepared it will be 

 advisable to buy as high grade commercial arsenate of soda as 

 possible, and to have a chemist determine the amount of acetate or 

 nitrate of lead required for use with it. 



The quantity of arsenate of lead to be used as a standard charge 

 for the spraying tank having been decided upon, the ingredients 

 necessary to make this quantity are determined. It will be de- 

 sirable to make two ballasts, equal in weight respectively to that 

 of the arsenate of soda and the acetate or nitrate of lead, in ea<5h 

 case plus the weight of the scoop on the balance scales used. 

 These ballasts may be made of glass jars filled with shot and by 

 their use the ingredients may be accurately weighed, when they 

 should be placed in stout paper bags, each package of arsenate of 

 soda being tied inside of the corresponding package of the lead 



* For an excellent and comprehensive treatise on the preparation of arsenate of 

 lead, see article by F. J. Smith in Report, Gypsy Moth Committee, January, 

 1898, pp. 57-69. 



