HOME-MADE LEAD ARSENATE. 



15 



DISCUSSION. 



Pure crystallized lead acetate contains theoretically 58.81 per cent 

 of lead oxid and 14.25 per cent of water of crystallization. A number 

 of these samples have lost much of their water of crystallization, as is 

 shown by the high lead content. The commercial " brown" acetate 

 of lead is cheaper than the pure crystallized salt and the samples 

 examined contained more lead, For these reasons the technical 

 grade is to be preferred rather than the pure salt for the preparation 

 of lead arsenate. None of the samples examined contained impuri- 

 ties which would in any way decrease their value for this purpose. 

 One hundred pounds of samples Nos. 4626 and 4627 would be equiva- 

 lent to over 113 pounds of the crystallized salt for this purpose, in 

 addition to being cheaper per pound. 



COMPOSITION OF LEAD NITRATE. 

 RESULTS OF ANALYSES. 



The results for total lead oxid in the samples of lead nitrate analyzed 

 are as follows : 



TABLE III. Composition of lead nitrates. 



( C. P." 

 'Commercial.' 



DISCUSSION. 



The theoretical per cent of lead oxid in pure lead nitrate is 67.35. 

 It will be seen that all of these samples contain very close to this 

 amount. The composition of lead nitrate is more uniform than lead 

 acetate, and it also contains more lead, though some of the partially 

 dehydrated samples of the acetate contain nearly as much. 



COMPOSITION OF SODIUM ARSENATE. 

 RESULTS OF ANALYSES. 



Pure crystallized sodium arsenate, or, chemically, disodium hydro- 

 gen arsenate, has the formula Na 2 HAsO 4 7H 2 O, and contains theo- 

 retically 36.84 per cent of arsenic oxid (As 2 O 5 ). One authority states 

 that this salt has the composition Na 2 HAsO 4 12H 2 O, and gives direc- 



