Flotation o/ Minevdls. 573 



In the case of the products from actual flotation processes 

 the samples of the concentrates were taken from the scum 

 overflowing from the spitz boxes, and put into air-tight bottles 

 in the form of a froth. The bottles were filled as nearly as 

 possible with this scum, together with some of the solution, 

 and kept air-tight till ready for analysis. All the bottles were 

 found to be under reduced pressure. In some cases a sample 

 of the gas above the solution covering the concentrates in the 

 bottles was taken. The results are given in the table B, page 

 (576), and showed that the oxygen content was very low in 

 almost every case. When the zinc concentrates were being 

 tested, the flask was filled as full as possible with the sulphide 

 wetted by the original solution in which they had been floated. 

 After drawing off as much as possible of this solution with a 

 pipette, the flask was filled to the top with air-free distilled 

 water, very little of the original solution remaining in the 

 flask. When the concentrates are taken out of the flask, after 

 being subjected to the reduced pressure, and boiled in water 

 or acid solution, they will as a rule float, this treatment ap- 

 parently not affecting the flotation properties of the mineral. 

 All the samples in table B would float when heated in their 

 own solution, or if this solution was poured oft' and water 

 added. 



If the sp. gr. of zinc blende is taken as 4, then 4 gms. 

 would displace 1 c.c. of water. Therefore to float 4 gms. of 

 zinc blende 3 c.c. of gas (neglecting its weight) would be re- 

 quired, and 1 gm. would require 0.75 c.c. of gas. On heat- 

 ing this to 100 deg. the volume would be greater, so that if 

 less gas than 0.75 was attached in . the gold solution, the 

 mineral would still float on heating. 



By collecting the gas evolved in stages it was noticed that the 

 first portion of the gas collected was usually air, and the last 

 to come off was COg, which apparently showed that the CO^ 

 clung more tenaciously to the minerals than did air. 



In some cases if the exhausting and heating was continued 

 till the mineral in the flask was perfectly dry, it was found 

 that, even if several c.c. of gas had been trapped in the col- 

 lecting burette, the gas went back into the flask and could 

 not be a^ain drawn off into the burette unless the mineral was 



