Heath — Determination of Arsenic and Antimony. 511 



Art. LIT. — The lodometric Determination of Arsenic and 

 Antimony Associated with Copper ; by F. H. Heath. 



[Contributions from the Kent Chemical Laboratory of Yale Univ. — clxxv.] 



It has been said that the iodometrie process for the deter- 

 mination of copper can be used without error in the presence 

 of arsenic and antimony provided that the latter elements are 

 in the higher condition of oxidation. A. H. Low* makes this 

 statement and gives careful directions for the complete oxida- 

 tion of the arsenic and antimony. There appears, however, 

 to be no record of any attempt to determine arsenic and anti- 

 mony iodometrically after the separation of copper from a 

 mixture containing the three elements. 



It has been thought worth the while, therefore, to attempt 

 the determination of arsenic and antimony in the filtrate from 

 cuprous iodide after titration of the free iodine by means of 

 sodium thiosulphate, and filtration. To this end, the attempt 

 has been made to reduce the arsenic and antimony by boiling 

 with potassium iodide and sulphuric acid according to the 

 method of Gooch and Gruenerf and determining these ele- 

 ments by reoxidation with a standard -solution of iodine. The 

 reactions involved in these processes may be expressed by the 

 general symbols, 



M 2 5 + 4HI = M 2 3 + H 2 + 2I„ 

 and M 2 3 + 41 + 2K 2 = M 2 5 + 4KI. 



The trials of the method were made with tartar emetic and 

 potassium arseniate. The tartar emetic was dissolved in water 

 and the antimony oxidized to the higher condition by means 

 of standard iodine solution in presence of sodium or potassium 

 bicarbonate. The amount of iodine required was taken as a 

 measure of the amount of antimony used. The solution of 

 antimony thus obtained, or the solution of arsenic taken in the 

 higher condition of oxidation, was acidified and a known 

 volume of a standard solution of copper nitrate was added. 

 The copper was determined iodometrically with precautions 

 previously recommended by Gooch and Heath. ;{: 



A special precaution to be observed is the choice of the acid 

 used during the determination of copper. Mineral acids must 

 not be present on account of their tendency to bring about 

 reduction of the arsenic and antimony by action of the excess 

 of potassium iodide used in throwing out the copper. Such 

 action causes high results on copper and low results on arsenic 

 and antimony. A mixture of acetic acid and potassium iodide 



*Jour. Amer. Chem. Soc, xxiv, p. 1083. 



fThis Journal, xlii, Sept., 1891. ^Ibid., xxiv, 65, 1907. 



