Heath — Determination of Arsenic and Antimony. 519 



the free iodine with sodium thiosulphate solution. The 

 reactions involved in the copper determination are 



2CuS0 4 + 4KI -> 2K 2 S0 4 + Cu 2 I 2 + I 2 



and 21 +2Na 2 S 2 3 = 2NaI + Na 2 S 4 6 . 



Filter off the cuprous iodide on asbestos. To the filtrate add 

 l cmS of liquid bromine and boil the solution in an Erlenmeyer 

 flask, using a trap to prevent loss by spattering. If, after 

 boiling for a short time and allowing the large amount of free 

 iodine to volatilize, the solution does not become clear, cool it, 

 add a little more bromine (0*5 cm3 ) and boil again. When the 

 solution has become clear, concentrate it somewhat (to about 

 60 cm3 ) to expel excess of bromine. Dilute to about L00 om3 , add 

 2 grin, of potassium iodide and boil to a volume of 50 om3 . Cool 

 the solution, bleach the free iodine by adding sulphurous acid, 

 using starch as indicator. Dilute to 100 cm3 , add iodine solution 

 to color and just bleach by careful addition of dilute sulphur- 

 ous acid from a pipette. Neutralize the solution with sodium 

 or potassium bicarbonate and titrate the arsenic or antimony 

 with standard iodine solution in the usual way. 



From the results obtained it seems possible by this method 

 to separate and determine copper and arsenic, or copper and 

 antimony, with errors of only a few tenths of a milligram. It 

 is also possible to determine the sum of arsenic and antimony 

 present with a fair degree of accuracy, and to separate and 

 determine copper when associated with both arsenic and anti- 

 mony. In the latter case the sum of the arsenic and antimony 

 may also be determined, but the values here obtained for 

 copper tend to come a little too high and those for arsenic and 

 antimony a little too low. 



In conclusion, the author wishes to express his appreciation 

 of the kind assistance and many suggestions given by Profes- 

 sor F. A. Gooch during the course of these investigations. 



