in Crystalline Rocks and Minerals. 



455 



reduced to coarse powder, and as a result of experiment in one or two 

 cases, I find that practically the same amount of gas is evolved on 

 heating the rock whether it is used in small lumps or in powder. 

 In the first series of experiments undertaken with the object of a 

 rapid survey of the materials, the gases were not completely analysed. 

 They were collected, measured, the carbon dioxide removed by potash, 

 and the residue examined by the spectroscope. When ignited in the 

 air it always burned with a pale flame resembling that of hydrogen. 



The table (p. 456) shows the results of these experiments. 



A selection of these was then subjected to more careful and exact 

 analysis. For this purpose fresh masses of the rock were taken, 

 and the gas extracted in the usual way. The following are the 

 results : 



To account for the large proportion of hydrogen and carbonic oxide 

 in these gases, it is only necessary to suppose tha,t the rock enclosing 

 them was crystallised in an atmosphere rich in carbon dioxide and 

 steam which had been, or were at the same time, in contact with 

 some easily oxidisable substance, at a moderately high temperature. 

 Of the substances capable of so acting, carbon, a metal, or a 

 protoxide of a metal, present themselves as the most probable. 



The reduction of carbon dioxide or of water vapour by carbon 

 gives rise to the formation of carbon monoxide, and if carbon had 

 been the agent the proportion of this gas in the mixture must have 

 been greater than is found to be the case. It is, of course, well 

 known that carbon dioxide and water vapour are both dissociated at 

 moderately high temperatures, but the greater part of the liberated 

 oxygen recombines at lower temperatures, though a small portion 

 may remain free in the presence of a large quantity of an indifferent 

 gas or vapour. No free oxygen has been found in any of the gases 

 analysed. 



Direct experiments, made with ferrous oxide (obtained by gently 

 heating pure chalybite) and with magnetic oxide of iron, show that 

 while the former, at a red-heat, decomposes both steam and carbon 

 dioxide quite freely, liberating hydrogen and carbon monoxide, and 

 becoming itself oxidised into m agnetic oxide ; the latter has no action 



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