54 THE GASES IN ROCKS. 



known "oil rock" from a lead and zinc mine near Platteville, Wisconsin, 

 produced 6.79 per cent hydrogen sulphide, corresponding to 3.90 volumes 

 per volume of rock. 1 How prolific a source of hydrogen sulphide the organic 

 matter in certain shales may be, is indicated by these two experiments. 

 If a shale of this sort, undergoing extensive metamorphism, did not lose 

 all of its sulphur compounds during the transforming process, the meta- 

 morphic product might still be distinguished by a high content of hydrogen 

 sulphide. Perhaps the specimen of Baltimore gneiss obtained from Spring 

 Mill, on the Schuylkill River, 2 from which 4.91 per cent, or 0.30 volume, 

 of sulphureted hydrogen was extracted, may have been derived from such 

 a shale. Other sulphur compounds in small amounts have been noted 

 in the gases from rocks. The potassium hydroxide solution in the Lunge 

 nitrometer, after having absorbed whatever hydrogen sulphide and carbon 

 dioxide there may have been in the gas under analysis, frequently emits 

 an odor suggesting a mercaptan. When air is let into the pump and tubes, 

 after the removal of the gas for analysis, and then pumped out, it usually 

 is charged with odors of more or less offensive nature. These suggest 

 that other complex reactions prevail at the high temperatures employed 

 in extracting the gas. Gautier detected a trace of ammonium sulphocyanide 

 in the gas from a granitoid porphyry from Esterel. 3 



METHANE. 



Moissan believed that the hydrocarbons of the petroleum type which 

 occur in the earth's crust were, in many cases, derived from the action of 

 water upon metallic carbides in the deep interior. 4 His important researches 

 upon carbides form the experimental basis for the hypothesis that the 

 methane obtained by heating igneous rocks has resulted from these com- 

 pounds. Even with cold water, the carbides of barium, strontium, calcium, 

 and lithium give pure acetylene, while under the same conditions aluminum 

 and beryllium carbides generate pure methane. 



CaC 2 + 2H 2 O = Ca(OH) 2 + C 2 H 2 A1 4 C 3 + 12H 2 O = 4A1(OH) 3 + 3CH 4 



The carbides of the rarer metals, cerium, lanthanum, yttrium, and 

 thorium, yield various mixtures of acetylene and marsh-gas; from manga- 

 nese carbide, marsh-gas and hydrogen result. But the most remarkable 

 of the carbides is that of uranium, which with water at ordinary tempera- 

 tures produces (in addition to a gaseous mixture of methane, hydrogen, 

 and ethylene) both liquid and solid hydrocarbons. Under ordinary condi- 

 tions water does not decompose the carbides of molybdenum, tungsten, 

 chromium, or iron. 



These reactions suggest two alternative hypotheses to explain the 

 occurrence of methane in the gas obtained from igneous rocks. The most 

 limited of these supposes the marsh-gas to be produced from a carbide 



1 Analysis No. 42. 



2 Analysis No. 28. 



3 Gautier, Comptes Rendus, vol. 132, pp. 61-62. 



4 Moissan, Proc. Roy. Soc., vol. 60 (1897), pp. 156-160. 



