108 



tating the coloring matter with sodium carbonate a varying amount of arsenic is 

 carried down in the precipitate. 



The determinations made by Method IV, while not agreeing as closely as might be 

 desired, are close enough to justify a more extended trial of the method in the hands 

 of different analysts. The writer has found it very satisfactory and, when properly 

 carried out, a perfectly clear solution can almost always be obtained. Of course it is 

 desirable to be able to determine both forms of arsenic on the same solution, but if 

 it Ls found tiiat this can not be done accurately thjb objection to the method becomes 

 of minor importance. 



LEAD ARSENATE. 



The methods used for lead arsenate were proposed by Haywood at the meeting of 

 the association in 1906 and were tried last year. They may be found in Bureau of 

 Chemistry Bulletin 105, page 165; also Bulletin 107, revised, page 239. 



The sample sent out for the work was made by the referee from C. P. di-sodium 

 arsenate and lead acetate. 



Lead arsenate. 



a Porcelain gooch used in all determinations of lead oxid. 

 DISCUSSION. 



C. D. Woods states that in the determination of total arsenic oxid it was not found 

 necessary to add thiosulphate to use up free iodin because if care is used in boiling 

 the solution a colorless point is easily obtained. 



The results on lead arsenate are not so uniform as might be desired, particularly on 

 total lead oxid. However, the difference between the highest and lowest determina- 

 tion of arsenic oxid is only 3 per cent of the total amount present and for lead oxid 5 

 per cent of the total amount present. The method is certainly the best that has thus 

 far been proposed and if carefully followed good results should be obtained. 



SODA LYE. 



METHOD I. This is the precipitation method, and may be found in Circular 10, 

 revised, page 8, and Bulletin 107, revised, page 31. 



METHOD II. This is the same as Method I except that the titration for hydroxid 

 is made without removing the barium carbonate precipitate. 



The acid potassium sulphate method was not submitted for trial, as satisfactory 

 results had not been obtained by it in previous years and the association voted that 

 it be dropped, as recommended by the referee in 1907. 



