52 THE GASES IN ROCKS. 



Equal volumes of hydrogen and carbon dioxide heated at 850 for 

 one hour gave C0 2 44.3 per cent, CO 8.3, H 2 42.0, and H 2 5.4 per cent. 

 Heated for three hours under the same conditions, the proportion of carbon 

 monoxide rose to 18 per cent. When rocks are heated for analysis, the 

 gas is usually pumped off at short intervals, and this reaction, because of 

 its slowness, becomes less important. Hiittner has appealed to this reaction 

 to explain the presence of carbon monoxide in minerals. 



But metallic iron also has a penchant for absorbing carbon monoxide 

 at the proper temperature. This process is usually called occlusion, and 

 may perhaps partake of the nature of a combination in which the gas 

 temporarily unites with the iron as iron carbonyl, Fe(CO) 4 / an unstable 

 compound readily giving up carbonic oxide. It seems likely that a portion 

 of the carbon monoxide developed from these irons, particularly those of 

 meteoritic origin, actually exists in the iron as monoxide, and that not all 

 of it has been formed by reduction of the dioxide. 



SULPHUR DIOXIDE. 



Certain rocks, when heated, disengaged sulphur dioxide in considerable 

 quantities. 2 These were ferruginous rocks of rusty appearance, generally 

 metamorphosed pyritiferous shales which had undergone much weather- 

 ing. By oxidation, the original pyrite had been partially converted into 

 ferrous sulphate (FeS0 4 ) and basic ferric sulphate (Fe 2 S 2 9 ), both of which 

 were decomposed by the heat of the combustion-furnace. 



2FeS0 4 = Fe 2 3 + S0 2 + S0 3 Fe 2 S 2 O 9 = Fe 2 O 3 + 2SO 3 



The sulphur trioxide was reduced to the dioxide either by hydrogen sul- 

 phide, hydrogen, ferrous oxide, or sulphur. 



It has been my observation that whenever sulphur dioxide was evolved 

 a slight sublimate of sulphur collected toward the cool end of the tube. 

 This may have been derived from the reaction above, or from hydrogen 

 sulphide and sulphur dioxide, coming from ferrous disulphide and sulphate, 

 respectively, and which can not exist together. 



2H 2 S+S0 2 = 2H 2 + 3S 



The sulphur dioxide obtained in the study of rocks is all assigned to 

 these reactions, though it is not impossible that this compound may occur 

 in small quantities, as a gas or a liquid, imprisoned in minute cavities. 



HYDROGEN SULPHIDE. 



When iron pyrites (FeS 2 ) is heated in a stream of hydrogen, ferrous 

 sulphide (FeS) and free sulphur result. 3 Though no hydrogen sulphide 



1 Fe and CO also exist feebly united in other proportions, as iron pentacarbonyl, 

 Fe(CO) 5 , and heptacarbonyl, Fe(CO) 7 . 



2 Analyses Nos. 43, 65, 93, and 109. 



3 Rose, Pogg. Ann., vol. 5, p. 533. 



