64 THE GYPSY MOTH APPENDIX. 



mixture of the di-plumbic and tri-plunibic arsenates, their 

 relative proportions varying according to the conditions of 

 temperature and concentration at the moment of precipi- 

 tation . 



Where the acetate of lead is used approximately, the whole 

 of the arsenate of lead product consists of tri-plunibic arsen- 

 ate, as indicated by the following reaction : 



3Pb(C 2 H 3 O 2 ) 2 3H 2 O4-2Na 2 HAsO 4 (H 2 O) n := 

 Pb 3 (AsO 4 ) 2 +4NaC 2 H 3 2 +2C 2 H 4 O 2 + n (H 2 0). 



In order to prepare arsenate of lead successfully, great care 

 must be taken to establish an exact ratio between the quan- 

 tities of the soluble lead and arsenic salts, otherwise injury 

 to the foliage may result. The reaction between acetate of 

 lead and arsenate of soda may be summarized as follows : 



3PbO + As 2 O 5 Pb 3 (AsO 4 ) 2 . 



One part Pb 3 (AsO 4 ) 2 requires .74416 part PbO and 

 .25584 part A& 2 O 5 . Experience has shown that it is advis- 

 able to increase the amount of lead oxide to .77812, in order 

 to insure an excess of lead. A single example will suffice to 

 show how the relative amounts of soluble lead and arsenic 

 salts may be fixed. 



Let it be required to prepare 1 pound of arsenate of lead 

 from samples of lead acetate (X) and sodium arsenate (Y), 

 containing respectively 60 per cent, lead oxide (PbO) and 

 40 per cent, arsenic pentoxicle 



Xr=: - 1 . 2969 pounds lead acetate. 

 .60 



25584 



Y = - = . 6396 pound arsenate of soda . 

 .40 



Should the arsenate of soda contain 7 per cent, chlorine, 

 in addition to the arsenic pentoxide, there would be required 

 an additional amount of lead acetate (Z) to complete the 

 reaction between the two salts. One part chlorine is equiv- 

 alent to 3.1408 parts PbO, and the amount of lead acetate 

 required is determined as follows : 



.6396 X.07X 3.1408 

 .60 



