14 



LEAD ARSENATE. 



been dissolved complete the neutralization with sodium bicarbonate, 

 adding it in considerable excess. Add a few drops of starch indicator 

 (made by boiling 1 gram of pure starch in 100 cc of water) and run in 

 standard iodin solution till all arsenite has been oxidized to arsenate 

 as will be shown by the appearance of the blue color. Calculate the 

 amount of arsenic present in terms of arsenic oxid (As 2 O 5 ) from the 

 volume of the standard iodin solution required for the oxidation. 



The strength of the standard iodin solution is determined by 

 titrating against a solution containing a known amount of arsenious 

 oxid, in the same manner. 



Chlorin (Volhard's method). Acidify with nitric acid 50 cc of the 

 solution used for determining total arsenic, then add an excess of 

 standard silver nitrate solution and make up to 200 cc. Filter through 

 a dry filter and determine the excess of silver in 100 cc of the filtrate 

 by titrating with standard ammonium sulphocyanate solution, using 

 solution of ferric alum as indicator. Twice the amount of silver in 

 this 100 cc portion, subtracted from the total amount added, will give 

 the amount of silver equivalent to the chlorin in the 50 cc of the solu- 

 tion originally taken, from which the per cent of chlorin Dresent may 

 be calculated. 



COMPOSITION OF LEAD ACETATE. 

 RESULTS OF ANALYSES. 



In Table II are given the analyses of the samples of lead acetate 

 examined. In column four is given the equivalent of the lead oxid 

 found in crystallized lead acetate, Pb(C 2 H 3 O 2 ) 2 3H 2 O, in order to show 

 more clearly the relative value of the various samples for the purpose 

 of making lead arsenate. 



TABLE II. Composition of lead acetates . 



o Formula, Pb(C 2 H 8 O 2 )2 3HjO. 



