318 Kenneth A. Miclde : 



These samples were taken at ditferent stages in the concen- 

 trating operation. 



A sample was also obtained of a flotation product produced 

 by a process using acidulated solution without the addition of 

 oleic acid. The material being treated in this case was Broken 

 Hill slimes, which had been given a slight roast to oxidise the 

 lead sulphide to sulphate in order to prevent the latter float- 

 ing. An analysis of the disengaged gas from this flotation 

 product (the sample being obtained similarly to the previous 

 flotation product) was as follows: — -Nitrogen, 96 per cent,; 

 oxygen, 1 per cent. ; carbon dioxide, 4 per cent. 



6. The flotation product (mentioned in paragraph 5), in which 

 the zinc concentrate was produced by a process using a dilute 

 acid solution and a small amount of oleic acid, was then 

 treated as follows : — Some of the concentrate, after being de- 

 prived of all visible gas by allowing to settle, was placed in a 

 small flask. The flask was nearly filled with the sulphides, and 

 allowed to stand, the sight excess of solution beins: drawn off. 

 This solution was faintly acid to litmus. The flask was then 

 filled with air-free distilled water, and connected to a vacuum 

 pump, all the connections being also filled with air-free water. 

 On lowering the pressure in the flask the concentrates wei*^ 

 noticed to swell up, and completely fill the flask, and an evolu- 

 tion of gas was at once apparent. This gas was collected and 

 analysed. The volume was 1.7 c.c, and consisted of 58.8 per 

 cent, carbon dioxide, 27 per cent, nitrogen, and 14.1 per cent, 

 oxygen. The flask was then immersed in water, which was 

 brought* to the boiling point, at the same time continuing the 

 exhaustion by means of the vacuum pump. An additional 

 volume of 8.9 c.c. of gas collected, consisting of almost entirely 

 carbon dioxide. The .weight of the concentrates experimented 

 with was 70 gms. 



A sample of the second product referred to in paragraph 5 

 was then taken and similarly treated, except that the wet con- 

 centrate was made slio-htly alkaline with ammonia. On heat- 

 ing and subjecting to reduced pressure as before, the gas col- 

 lected amounted to 18.5 c.c, practically the whole of which 

 was carbon dioxide, only small quantities of nitrogen and 

 oxygen being present. 



