STATES OF THE GASES. 55 



in the combustion-tube. Such a carbide must have withstood the action 

 of water, both magmatic and meteoric, ever since the solidification of the 

 rock. The other hypothesis seeks to avoid this difficulty by postulating 

 carbides in the very hot rocks where the hydrogen and oxygen may not be 

 combined as water; then, at a later stage, it allows water to decompose 

 the carbides with the evolution of marsh-gas, which is retained within the 

 rock. In this case the gas itself would exist in the rock specimen tested. 

 It is to be noted that several of these carbides, including that of the 

 widespread element calcium and the less stable sodium and potassium 

 compounds, 1 give acetylene when decomposed by water. In none of the 

 rocks examined, with one exception, has acetylene been detected. This 

 may possibly eliminate calcium carbide from the gas-contributing com- 

 pounds in the rocks. The absence of acetylene also carries with it some 

 slight evidence against carbides in general, since calcium plays a very 

 important role in rock evolution, and it is not likely that acetylene, if 

 formed, would pass into methane. However, it is not impossible that 

 aluminum carbide, which yields methane with water, may exist in the 

 earth's crust while calcium carbide is lacking. According to F. W. Clarke, 2 

 aluminum constitutes 8.16 per cent of the solid crust of the earth, while 

 iron and calcium comprise 4.64 and 3.50 per cent, respectively. Aluminum 

 also forms very stable compounds in nature. Moreover, aluminum oxide 

 fused in the electric furnace with calcium carbide gives yellow crystals of 

 aluminum carbide. 3 Perhaps at high temperatures iron carbide might 

 be decomposed by steam with the formation of marsh-gas. 



Besides carbides, organic matter suggests itself as a possible source of 

 the methane. This organic matter may have been either (1) accidentally 

 introduced into the combustion-tube, or (2) have been incorporated in the 

 rocks from life which inhabited the earth during the later stages of growth, 

 as outlined by the planetesimal hypothesis. The first possibility may be 

 practically dismissed, since great care was exercised to avoid the intro- 

 duction of any foreign matter with the rock powder. If dependent upon 

 such accidental conditions, this gas would only occasionally be present. 

 Under the planetesimal hypothesis, life may have existed long before the 

 growth of the planet was completed and its present size attained. Organic 

 deposits buried in sedimentary beds which have since undergone exten- 

 sive metamorphism should furnish marsh-gas. These rocks, worked over 

 and reworked by the volcanic activity in Archean times, might perhaps 

 account for the widespread occurrence of this gas. Formed in this way, 

 it may be retained in the rocks as a free or occluded gas, since it is very 

 stable at high temperatures. 



Other theoretical sources of methane are high-temperature reactions 

 within the combustion-tube, in which hydrogen and the oxides of carbon 

 participate. Brodie produced 6 per cent of marsh-gas by submitting 



1 Moissan, Jour. Chem. Soc., vol. 64, 2, p. 332. 

 z F. W. Clarke, Bull. 168 U. S. G. S. (1900), p. 15. 



3 Moissan, Comptes Rendus, 125 (1897), pp. 839-844; Jour. Chem. Soc., vol. 64 

 (1898), 2, p. 161. 



