94 PROCEEDINGS OF THE AMERICAN ACADEMY. 



Though full experimental data for the testing of these conclusions 

 are not yet in hand, it is not difficult to see that the fluxing power of 

 even small masses of juvenile gas is great under these conditions. If 

 chemical reactions supply any large fraction of the heat lost by radia- 

 tion in the active period, they must raise the temperature of the lava 

 column under conditions of dormancy. This involves a slow melting 

 of the country-rock, and especially the plug. 



In most cases dormancy is ended by explosions so powerful as to 

 show pressures under the plugs of even higher order than the pres- 

 sures in the greatest modern cannon at the moment of discharge. These 

 pressures run Avell over 2,000 atmospheres. If a given plug, when frozen 

 to maximum thickness, is 1000 meters deep, the initial pressure on the 

 gas first collecting beneath it would be about 270 atmospheres. 

 Amagat's experiments furnish the data from which the temperature 

 effect of the adiabatic compression of the typical gases, carbon dioxide 

 and hydrogen, may be approximately computed. 



At the request of the writer Professor H. N. Davis has kindly de- 

 duced the thermodynamic equation for these two cases. If T^ is the 

 initial temperature ; J", the final temperature ; po, the initial pressure ; 

 and ^?, the final pressure, we have 



= ^« & 



in which n is an exponent approximately determined from Amagat's 

 curves. If the initial temperature and pressure are, respectively, 

 1273°C. absolute and 270 atmospheres, and the final pressure is 2700 at- 

 mospheres, the average value of n for carbon dioxide is about 0.17 ; and, 

 for hydrogen, n probably lies between 0.26 and 0.31. For carbon diox- 

 ide the computed value of 7" is 1880° absolute, and for hydrogen 2300° 

 to 2600° absolute. This adiabatic compression of carbon dioxide 

 would develop heat to the amount of about 200 calories per gram. 

 Similar compression of pure hydrogen would develop an amount of 

 heat ranging from 3000 to 4000 calories per gram. The compression of 

 the gaseous mixture actually formed under volcanic plugs would pro- 

 duce heat to amounts intermediate between those calculated for carbon 

 dioxide and for hydrogen. Since hydrogen is one of the most abundant 

 constituents of the mixture, it is possible that adiabatic compression 

 of the mixture, under the conditions above described, would produce 

 at least 1000 calories per gram of gas. Since the latent heat of holo- 

 crystalline igneous rock is about 90 calories (Vogt), this heat of com- 

 pression could fuse more than 10 grams of rock per gram of gas. 



