42 THE GASES IN ROCKS. 



it is reduced to ferrous oxide, and when heated above 300, to the metal. 1 

 The more recent studies of Moissan give different figures; 2 Fe 2 O 3 is reduced 

 by hydrogen at 300 to Fe 3 O 4 in 30 minutes; at 500 to FeO in 20 minutes; 

 at 600 to 700 to metallic iron. 



If the hydrogen or water-vapor produced by these reactions is not 

 removed, the process continues only until a condition of equilibrium is 

 established. In extracting the gases from rocks, the products of these 

 reactions were rapidly removed, so that final equilibrium was probably 

 never attained. Hence, in these experiments the direction in which the 

 reaction will proceed depends upon whether there is ferrous oxide and 

 water, or ferric oxide and hydrogen, most abundantly stored in the rock. 

 Ferrous and ferric salts behave, in general, like the oxides. 



Since most igneous rocks contain ferrous as well as ferric salts, the 

 possibility that, when heated in the presence of steam, hydrogen will be 

 produced, must always be taken into account. In terrestrial rocks water 

 of constitution is generally present and often is not expelled below a bright 

 red heat. Thus, a rock containing a ferrous compound in appreciable 

 amount, together with water of crystallization, a portion of which is re- 

 tained up to red heat, will be in a condition to furnish hydrogen upon the 

 application of heat. 



In general, the analyses show that the greater the amount of iron present 

 in the rock, the more hydrogen may be expected. This may be the result 

 of chemical action, or a selective occlusion of hydrogen manifested by iron 

 and its compounds. Magnetite, being the end product of the reaction of 

 water upon iron, can not produce hydrogen by this chemical interaction, 

 though it might possess the occlusive properties of iron compounds. Anal- 

 ysis of the black sand from the bed of the Snake River, Idaho, 3 indicates 

 that iron in the form of magnetite does not yield much hydrogen. How- 

 ever, these figures have no great significance, for, even though an abundance 

 of hydrogen existed in the ore, either occluded or mechanically imprisoned, 

 the magnetite would, at red heat, quickly oxidize it to water, with the 

 exception of a small portion of free hydrogen maintained by the reverse 

 reaction. The analyses show that basic diabases and basalts yield the 

 most gas, while acidic rhyolites give but little. These are also among the 

 maximum and minimum iron-bearing lavas. But the difference in hydro- 

 gen is much greater proportionately than the difference in ferrous salts. 

 Table 13 4 also shows that andesites, which are nearer the basic end of the 

 scale than the acidic, do not greatly exceed the rhyolites in hydrogen. 

 The difference between the two types of rocks, acidic and basic, in point 

 of volume of the individual gases, while somewhat more conspicuous in 

 the case of hydrogen, is generally true of the other gases as well. 



Endeavoring to prove that the hydrogen obtained by heating minerals 

 came entirely from chemical reactions, Travers experimented with the 

 secondary mineral chlorite, calculating how much ferrous iron should have 

 been oxidized to give the quantity of hydrogen and carbon monoxide 

 evolved. 5 This he found to agree closely with the difference in amount of 



1 Siewert, Jahresbericht d. Chem., 1864, p. 265. Ante, p. 27. 



2 Moissan, Comptes Rendus, vol. 84, p. 1296. 8 Travers, Proc. Roy. Soc., vol. 64, p. 132. 



3 Analvsis No. 46. 



