330 PROCEEDINGS OF SECTION B. 



the addition of a dro]) of dilute sodium chloride before plating 

 out will prevent its deposition. 



In the copper ores coming before us containing large 

 quantities of silver, arsenic, or antimony, or both, are always 

 present, and for the determination of the copper such ores are 

 treated with aqua regia, evaporated to dryness, taken up with 

 hydrochloric acid, filtered, and copper separated from arsenic and 

 antimony, and plated out as above described. 



(2.) DETERMINATION OF ANTIMONY IN ANTIMONIAL 

 PYRITES. 



We have recently had occasion to make a considerable number of 

 antimony determinations in pyritic ores containing large quantities 

 of both antimony and arsenic. 'J'he ordinary methods of separa- 

 tion and determination of the former constituent involve the 

 expenditure of a considerable amount of time. By the method 

 which we shall now describe it is possible to complete an estima- 

 tion in an ordinary working day. 



The process is a combination of the methods proposed by Clark, 

 (J. S.C.I. 10. 444 and J.C.S. 46,424), and by Paul Fr. Zeits (31,537). 

 Clark shows that on heating antimony and arsenic sulphides with 

 hydrochloric acid and ferric chloride the arsenic distils over as 

 chloride and the antimony is dissolved and remains in solution as 

 trichloride. From this solution the antimony is precipitated as ti i- 

 sulphide with sulphuretted hydrogen in the ordinary manner. Clark 

 then collects this precipitate on a weighed filter, washes free from 

 sulphur with carbon bisulphide, dries at 130°, and weighs as tri- 

 sulphide of antimony. We do not collect and weigh the sulphide 

 in this manner, but, instead, make use of the very convenient 

 process of Paid referred to above The antimony sulphide is 

 filtered off and washed on an asbestos filter in a Gooch crucible, 

 gently dried, and finally heated in a stream of dry carbon dioxide. 

 By this means all fi*ee sulphur is expelled and there remains pure 

 trisulphide of antimony, which is allowed to cool and weighed. 

 The process is carried on as follows : — Half a gram of the finely- 

 ground ore is weighed out into 4|in. jjorcelain dish, covered with 

 funnel w^ith bent stem ; there is then added 5c. c. of a solution of 

 ferric chloride (made by dissolving 20 grams of ferric chloride in 

 lOOc.c. of strong hydrochloric acid), together with 20c. c. of strong 

 hydrochloric acid, and the dish and contents are heated on the 

 water bath for half an hour ; the funnel cover is then washed down 

 with a little hot water and the solution evaporated to about 7c. c. 

 to 10c. c. Care must be taken not to carry the evaporation too far, 

 as, if all the hydrochloric acid is exjjelled, the trichloride of 

 antimony will volatilise. Another 20c. c. of hydrochloric acid is 

 now added and the evaporation carried to the same extent ; then a 

 third quantity of 'hydrochloric acid and the evaporation again 



