AR8ENATE OF LEAD. 65 



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 84- ounces acetate of lead and 10^ ounces 

 arsenate soda. 



The following equation represents the reaction between 

 arsenate of soda and nitrate of lead : 



5Pb(NO 3 ) 2 +4Na 2 HAsO 4 (H 2 O) n 



Pb s (AsO 4 ) 2 + 2PbHAsO 4 + 8XaNO 3 + 2HNO 8 -f n (H,O) . 



The essential features of this reaction may be summarized 

 as follows : 



5PbO+2As 2 O 6 -f-H 2 Q=rPb 6 H 2 (AsO 4 ) 4 . 



One part Pb 5 H 2 (AsO 4 ) 4 requires .70 part PbO and .30 

 part As 2 O 5 . 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 66 per cent. PbO and 40 per cent. 



As A : 



7914 



X=: = 1 .1990 pounds lead nitrate. 

 .66 



.3000 



1 - - . i oOO pound arsenate of soda. 

 .40 



Should the arseuate 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 : - 



.7500X -07 X 3. 1408 



Z = = . 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 2f 

 ounces nitrate of lead and 12 ounces arseuate of soda. 



