30 



THE GASES IN ROCKS. 



they are more rapidly given off than the others. Carbon monoxide follows 

 the dioxide as the temperature is raised, and generally increases in relative 

 importance, as the latter begins to subside, toward the end of the com- 

 bustion. Hydrogen and marsh-gas are most conspicuous at high temper- 

 atures, and hence attain higher percentages in the last half of the gas than 

 in the first portion. Nitrogen appears to be disengaged with much difficulty, 

 requiring considerable time at an elevated temperature. These general 

 facts may be graphically represented by plotting the curves based on the 

 experiments with the Baltimore gneiss. 1 (See fig. 1.) 

 7 t 



6.82 



in 

 o 



E 



1.54 



too 



200 



700 800850 



300 400 500 600 

 Temperature 



FIG. 1. Plot of curves representing volume of each gas per volume of rock 

 obtained at different temperatures from Baltimore gneiss. 



Nitrogen is omitted from this diagram owing to an unfortunate leak- 

 age of air during a part of the experiment, which was sufficient to vitiate 

 the results for this gas. 



1 For tables, see pp. 36-37. 



