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 l-emoved by potash, and the residue examined by the spectroscope. W hen 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 tbe gas extracted in the usual way. The following are the results :—
in Crystalline Bocks and Minerals. CO,. CO. c h 4. No. h 2.
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Granite from Skye..................... 23-60 6*45 3-02 5 13 61-68 Gabbro from Lizard................... 5-50 2-16 2-03 1 -90 88 -42 Pyroxene gneiss, Ceylon.. . . . . . 77-72 8-06 0-56 1-16 12-49 Gneiss from Seringapatam........ 31 -62 5-36 0-51 0-56 61 -93 Basalt from Antrim................... 32-08 20-08 10-00 1-61 36-15
To account for the large proportion of hydrogen and carbonic oxide in these gases, it is only necessary to suppose th at 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 magnetic oxide ; the latter has no action
