50 



THE GASES IN ROCKS. 



When a finely powdered igneous rock is treated with hydrochloric 

 acid and gently warmed, a few small bubbles of carbon dioxide usually 

 are seen to rise to the surface of the acid. This gas comes from the action 

 of the acid upon small quantities of carbonate present in the rock. To 

 test the quantitative importance of this action and to discover whether 

 other gases are freed by acid, 25.13 grams of diabase from Nahant, Massa- 

 chusetts, 1 were placed in a flask connected with the mercury-pump, and the 

 air removed. Dilute sulphuric acid was introduced into the flask through 

 a dropping funnel. The gas developed in the cold during the first 2$ hours 

 was found to have the following composition: 



TABLE 35. 



Practically all of the carbon dioxide thus set free is to be assigned to 

 a carbonate. 



The apparatus was allowed to stand for three days, during which time 

 more gas came off. At the end of this period, the powder was washed, 

 dried, and then submitted to the ordinary process of heating in the tube. 

 Of the gas received, 38.19 per cent, or 0.62 volume per volume of rock, 

 was carbon dioxide. Powder from the same specimen of diabase, not 

 treated with acid, yielded 8.51 volumes of carbonic anhydride in the com- 

 bustion-tube. This amounted to 61.25 per cent of the total gas. 2 



While carbon dioxide, both gaseous and liquid, occurs in minute cavities 

 in certain minerals and rocks, and while rocks also, doubtless, contain 

 some of this gas in a state of occlusion, it seems probable, on account of 

 the wide dissemination of carbonates in small quantities through the 

 accessible rocks near the earth's surface, that the greater part of the carbon 

 dioxide obtained by the method of heating rock material in vacuo is derived 

 from the decomposition of carbonates in the combustion-tube. It may 

 be assumed that more of the carbonates in igneous rocks are secondary 

 than primary. But though a knowledge of this immediate source of much 

 of the carbon dioxide in the rocks does not lead far toward the elucidation 

 of the problem of the ultimate source of this gas, it imposes no restrictions 

 upon the more comprehensive view that the carbonic acid which is now 

 locked up in the rocks chemically, as a result of weathering and carbona- 

 tion, was given to the atmosphere and hydrosphere originally from the 

 magmas themselves. 



CARBON MONOXIDE. 



Metallic iron and ferrous salts reduce carbon dioxide to monoxide 

 under practically the same conditions that they liberate hydrogen from 

 water-vapor. 



Analysis No. 88. 



Analysis No. 86. 



