STATES OF THE GASES. 



43 



ferrous iron present before and after heating. Another test with feldspar 

 from the Peterhead granite not showing correspondence, seemed to Travers 

 to be explained by the presence of both metallic iron and ferrous oxide in 

 the feldspar. The presence of a considerable amount of metallic iron in 

 a feldspar which crystallized from an acidic magma containing an excess 

 of silica is quite unusual. This feldspar treated with dilute sulphuric 

 acid yielded about four volumes of hydrogen. 



Against the theory that the hydrogen was largely derived from the 

 action of water-vapor on ferrous compounds, may be placed the very 

 marked change in color which the rock undergoes during the process of 

 heating. I have observed that whenever a rock powder, before being 

 placed in the tube, possesses an orange, brownish, or reddish tint due to 

 ferric oxide, the combustion invariably alters the tone to a greenish gray. 

 This suggests a reduction of ferric oxide to ferrous oxide, a process con- 

 suming hydrogen. In order to test this question, a specimen of bright-red 

 Permian sandstone from the Garden of the Gods near Colorado Springs 1 

 was powdered. These Red Beds are supposed to consist of thoroughly 

 oxidized material; this opinion was partially confirmed by chemical tests 

 which gave a weak reaction for ferrous iron, but indicated much ferric. 

 After heating, the brick-red sand had become dull gray-green in color. The 

 gray sand from the combustion-tube gave a stronger reaction for fer- 

 rous iron. Later, a quantitative determination of the ferrous iron present 

 before and after heating was undertaken. Equal weights of the two sands 

 were boiled with strong sulphuric acid 2 for two hours and then allowed to 

 stand overnight. In each case the solution was effected in an atmosphere 

 of carbon dioxide to prevent oxidation by oxygen from the air. The two 

 solutions were then titrated with potassium permanganate solution. 3.09 

 grams red sand required 1.97 cubic centimeters N/10 KMn0 4 ; 3.09 grams 

 gray sand required 2.52 cubic centimeters N/10 KMn0 4 . 0.55 cubic centi- 

 meter N/10 KMnO 4 is equivalent to 0.015 gram of iron, which is the 

 weight of the metal reduced from the ferric to the ferrous state. For the 

 total weight of sand used in the gas analysis (85 grams), the increase in 

 ferrous iron should be 0.423 gram, which would correspond to an oxidation 

 of approximately 85 cubic centimeters of hydrogen. Yet both hydrogen 

 and carbon monoxide were obtained from this sandstone in considerable 



quantities. 



TABLE 29. 



1 Analysis No. 78. 



2 3 parts cone, acid to 1 part water. 



