No. 4.] GYPSY MOTH — APPENDIX. 365 



Adding the values of X and Z, we find that 1.5312 pounds 

 lead acetate are required for the reaction with .6396 pound 

 arsenate of soda of the grade specified. Expressing these 

 quantities in avoirdupois weights, 1 pound arsenate lead re- 

 quires 1 pound S^ ounces acetate of lead and 10|^ ounces 

 arsenate soda. 



The following equation represents the reaction between 

 arsenate of soda and nitrate of lead : — 



5Pb(N03) 2+ iNa^HAsO^ (H20)'' = 

 Pb3(AsOj.,4-2PbHAsO^-f 8NaN03+2HN03+„(H20). 



The essential features of this reaction may be summarized 

 as follows : — 



5PbO-}-2As2064-H20 = Pb5H2(As04)4, 



One part Pb5H2(As04)4 requires .70 part PbO and .30 

 part AS2O5. A proper excess of lead oxide may be obtained 

 by increasing the quantity mentioned to .7914, which will 

 insure the complete precipitation of the arsenic. 



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



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



containing respectively QQ per cent. PbO and 40 per cent. 



AsoOg : — 



.7914 



X=^^ -zzz 1 . 1990 pounds lead nitrate. 



.66 ^ 



= . 7500 pound arsenate of soda. 



.40 



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

 as in the preceding case, the additional amount of lead 

 nitrate (Z) required may be determined as follows : — 



„ . 7600 X. 07X3. 1408 „,._^ .. a ; , 



Zi= ■ = .2498 pound lead nitrate. 



.66 



Adding the values of X and Z, we find that 1.4488 pounds 

 lead nitrate and .75 pound arsenate of soda are required for 

 the preparation of 1 pound arsenate of lead. In avoirdupois 

 terms the relative weights stand as follows : 1 pound 2| 

 ounces nitrate of lead and 12 ounces arsenate of soda. 



