68 THE GYPSY MOTH APPENDIX. 



been obtained by the method adopted during the season of 

 1897. The amounts of lead oxide and arsenic pentoxide in 

 the commercial salts having been determined the necessary 

 quantities of acetate of lead and arsenate of soda were lixed. 

 The work of weighing the salts was carried on rapidly by the 

 aid of ballasts, on balance scales. The acetate of lead was 

 placed in a strong paper bag which was sufficiently large to 

 hold the smaller bag of arsenate of soda, and the whole made 

 into a single package and tied with stout twine. A printed 

 label giving directions for the preparation of arsenate of lead 

 was attached to each package. When needed for spraying 

 the salts were dissolved separately by suspending each in a 

 small basket in a wooden* tub or keg of water. When the 

 solutions thus obtained are poured into the spraying tank 

 partially filled with water, arsenate of lead is thrown down 

 as a fine white precipitate. Acetate of lead dissolves in water 

 at about the rate of 1 pound to 1 gallon ; arsenate of soda dis- 

 solves readily at the rate of 1 pound to 3 quarts of water. 

 Both these salts dissolve easily in smaller quantities of hot 

 water, and where the latter is available it should be used in 

 preference to cold water. In either case great care must be 

 taken to avoid spilling the solutions before precipitation. 



It should be recognized that the arseuate of lead commonly 

 sold in the market is a mixture and not a compound, and in 

 reality contains but about 50 per cent, of actual arsenate of 

 lead. In making recommendations concerning the use of this 

 insecticide, care must be taken to indicate whether the arsen- 

 ate of lead or arsenate of lead mixture is to be used. Table 

 No. 6 o-ives the amounts of ' white granulated acetate lead" 



O 



and " 65 per cent, arsenate soda" necessary to make known 

 quantities of arsenate of lead. In this case the acetate of lead 

 contains 60 per cent. PbO, and the arseuate of soda 45 per 

 cent. As L ,O 5 and 3 per cent, chlorine. 



* Metallic pails should never be used. 



