Flotation of Minerals, Part II. 321 



obtained before the mineral was heated. As the whole of the 

 gas before heating- was not collected, these figures have no 

 relation with the whole of the gas obtained, but simply relate 

 to a final product, the quantity and composition of which 

 depends upon the stage of exhaustion reached when it was col- 

 lected. Column lY. shows not only the composition, but also 

 the total quantities of the gas obtained from the mineral 

 under these conditions. The volume occupied by the different 

 minerals was approximately the same, except in the case of 

 calcite and cerussite. 



Before each test on the different minerals, the pump was care- 

 fully exhausted. As a rule the residual gas from the pump gave 

 negative results — i.e., it was of the same composition as atmo- 

 •spheric air. Some of the blank tests, however, showed the 

 presence of small quantities of carbon dioxide, with a higher 

 proportion of residual gas, after absorbing the oxygen, than 

 would be the case if the gas had been atmospheric air. The 

 blank tests were tried, both in the cold and in heating the 

 empty flask in boiling water. The deviation from the composi- 

 tion of atmospheric air in some of the blank tests may be 

 accounted for by the retention of some of the gas from a 

 previous experiment, on the glass walls of the apparatus or by 

 the mercury itself. 



Description of gas analysis apparatus.^ 



The gases were analysed in a Bonnier and Mangin gas 

 apparatus (shown in the adjoining text figure), capable of 

 analysing with accuracy very small volumes of gas. The 

 capacity of the apparatus is approximately 0.2 c.c. As can be 

 seen from the reproduced photograph, it consists of a metal 

 cylinder A, from which the mercury can be forced out, or 

 drawn in, from the glass reservoir F, by way of the graduated 

 capillary tube C, and through the large bulb of the capillary 

 tube at B. The movement of the mercury is controlled by 

 means of the small hand wheel E, which moves, on turning, a 

 screw piston, either backwards or forwards, as desired, in the 



1 This gas apparatus was kindly lent by Professor Ewart, of the Botajiical Department. 



