86 PROCEEDINGS OF THE AMERICAN ACADEMY. 



the non-hygroscopic water determined in the analysis of quite unal- 

 tered gabbro or basalt may be as much a primary constituent as the 

 silica or the alumina. We must believe that hydrogen and oxygen, in 

 the proportion characteristic of water, are present in primary basaltic 

 magma. It does not follow that, under volcanic conditions, these ele- 

 ments will issue from the vent in combination as water. In his able 

 monograph on " The Gases in Rocks," R. T. Chamberlin indicates the 

 general reaction to be expected in the Kilauean or other basaltic magma 

 chamber. He writes : 



" The effect of pressure on chemical equilibrium is to favor the for- 

 mation of that system which occupies the smaller volume, but if there 

 is no change in volume, in passing from one system to the other, the 

 increase of pressure presumably has no influence on equilibrium. In 

 the reaction 



3FeO -f H2O ^ FesOi + H2 



considered as a thermochemical equation, the number of gaseous mole- 

 cules, and hence the volume of gas, always remains the same, so that it 

 is not likely that this action will be influenced by change -of pressure. 

 A rise of temperature favors the formation of that system which ab- 

 sorbs heat when it is formed. A comparison of the amount of heat 

 liberated by oxidizing three molecules of FeO to Fe304 and one mole- 

 cule of Ha to H2O shows that, in the former case, 73,700 calories are 

 evolved, and in the latter, 58,300 ; that is, 3Fe() + H2O — >- FcsOi + 

 H2 + 15,400 calories. As heat is evolved in this process, a rise of 

 temperature would accelerate the reaction in this direction less than in 

 the reverse. In other words, the higher the temperature, the more 

 would the formation of ferrous oxide and water be favored as compared 

 with the conditions at lower temperatures. 



"Because of this, there is much reason to suppose that, at the 

 depths where lavas originate, hydrogen and oxygen exist combined as 

 water, since up to temperatures of 2000° C, the dissociation of water 

 takes place only to a limited extent. If a state of equilibrium between 

 hydrogen, water, and the iron compounds were established in the 

 heated interior where a magma originated, as soon as it commenced its 

 way upward and began to lose heat the condition of equilibrium 

 would be destroyed. With the falling temperature the tendency to re- 

 establish equilibrium would favor the formation of that system which 

 was produced with the liberation of heat, i. e., magnetic oxide and free 

 hydrogen. In ascending lavas which are losing heat, the tendency, 

 therefore, is to produce hydrogen and magnetite, or ferroso-ferric com- 

 pounds. This is doubtless an important source for the hydrogen which 



