loG Dr. M. W. Travers. The Oriyin of the Gases 



These results show that the mica and felspar are responsible for 

 nearly the whole of the hydrogen, while the greater part of the carbon 

 dioxide is derived from the quartz. The carbon dioxide is probably 

 present in cavities in the quartz, but if the hydrogen were also- 

 present in cavities, one would expect that it would be also obtained in 

 greatest quantity from the quartz, the only mineral of the three which 

 has no cleavage ; one would not certainly expect to obtain it from the 

 mica. 



As the felspar gave off gas in the cold when treated with dilute 

 sulphuric acid, a weighed quantity of the mineral was placed in a thick- 

 walled tube, with a second tube containing 50 per cent, sulphuric acid. 

 The tube was drawn to a point, exhausted, and sealed in the manner 

 already described. After heating for twenty-four hours to 170 the 

 gas was pumped out and analysed, and the ferrous sulphate in the solu- 

 tion was determined. 



The following results were obtained from two samples of felspar 

 from different parts of the same block of granite. The quantities of 

 gas are expressed in 'cubic centimetres per gram : 



Ferrous oxide in solution (a) 4'02 p.c. (b) 2'05 p. c. 



Hydrogen with trace of hydrocarbon 3*50 1*99 ,, 



Carbon dioxide 0'20 0*90 



From these results I was led to suppose that the felspar contained 

 both free iron and ferrous oxide, since if we calculate the amount of 

 iron which would be equivalent to the hydrogen evolved, we find that 

 expressed in terms of ferrous oxide, 



3'50 c.c. of hydrogen per gram = 2'25 per cent, of ferrous oxide. 

 1-99 = 1-23 



Quantities which are considerably less than the quantity of ferrous 

 oxide found by titration. On the other hand, it is possible that some 

 of the hydrogen is taken up by the ferric compounds present, lessening 

 the yield of hydrogen, and increasing the quantity of ferrous sulphate 

 in the solution. 



There is, unfortunately, no accurate method of estimating the free 

 iron in minerals. The copper method apparently fails in the presence 

 of hydrated ferric oxide, on account of the secondary reactions which 

 take place between that compound and copper sulphate, and subse- 

 quently between the ferric sulphate and precipitated copper. 



In order to prove that a considerable amount of free iron was 

 present in the felspar, two weighed quantities of felspar from the same 

 sample were heated with 50 per cent, sulphuric acid and 96 per cent, 

 acid respectively. The gases were subsequently pumped out of the 

 tubes and analysed, and the ferrous sulphate was estimated in the 

 liquid. 



