evolved on heating Mineral Substances, Meteorites, Sfc. 135 



forming sulphuretted hydrogen, which at the temperature of the 

 reaction is decomposed into sulphur and hydrogen. 



It is known that certain crystalline minerals contain liquid hydro 

 carbons enclosed in cavities. It is also possible that the methane, and 

 other hydrocarbons sometimes present in the gases obtained by heating 

 mineral substances, may be produced by the destructive distillation of 

 bituminous matter infiltrated into it, or from vegetable matter, par- 

 ticularly if the specimen has been long exposed on the surface. 



Nitrogen I have only rarely obtained by heating minerals. Mala- 

 cone* yields it in larger quantity, compared with the total quantity of 

 gas evolved, than any other mineral which I have examined, but even 

 in that particular case only a very small quantity of the gas is 

 obtained. It is possible that a finely powdered mineral may on stand- 

 ing condense air on its surface. Dr. G. McGowan tells me that when 

 a sample of china clay was heated in a current of hydrogen a small 

 quantity of ammonia was given off. Certain bituminous shales, in 

 which the organic matter is certainly of animal origin, are known to 

 contain large quantities of ammonium salts; the gases evolved under 

 the influence of heat would certainly contain nitrogen. Nitrogen and 

 its oxides might also be the product of the interaction at a high tem- 

 perature of nitrates infiltrated into the rock, and silica. That Davy- 

 obtained nitrogen from quartz is highly improbable. It is more likely 

 that the gas was introduced accidentally in the course of the experiment. 



I stated earlier in this paper that the felspar from Peterhead granite 

 exhibited certain peculiarities, and that I should describe it separately. 

 The granite consisted of very large crystals of quartz and felspar with 

 a comparatively small quantity of mica of a dark colour. On heating, a 

 mixture of carbon dioxide, carbon monoxide, and hydrogen was given off. 



In order to ascertain whether these gases were derived from each of 

 the minerals, or whether any particular one gave more gas on heating 

 than the others, I crushed a large quantity of the granite in an iron 

 mortar and picked out the constituents, separating them from one 

 another as far as possible. The mica was easily obtained quite pure, 

 but the quartz and felspar could not without very great trouble be 

 separated from one another ; in fact, the felspar always contained a 

 considerable quantity of the latter mineral. 



By heating weighed quantities of the component minerals to red 

 heat in hard glass tubes, and collecting and analysing the gases, the 

 following results were obtained. The results are expressed in cubic 

 centimetres of gas per gram of mineral : 



Quartz. Mica. Felspar. 



Carbon dioxide O225 none 0-172 



Carbon monoxide ) >- 4 [ none 0'059 



Hydrogen ) C 0-164 0-218 



* ' Eoy. Soc. Proc.,' 1897, vol. 60, p. 444. 



VOL. LXIV. M 



