90 PROCEEDINGS OF THE AMERICAN ACADEMY. 



the magma. The powerful thermal effect of interaction between hydro- 

 gen or oxygen and the carbon or nitrogen atoms of cyanogen hardly 

 needs quantitative statement to show its value. 



In this connection it may be noted that the total melting heat of 

 ordinary rock-matter (measured from 0°C.) is only 400 to 450 cals. per 

 gram, and that the latent heat is only about 90 cals. per gram. 



Such examples emphasize the value of the conception that abyssal 

 injection, entailing a sharp change of pressure and a slower change of 

 temperature in primary magma, may set free a vast amount of energy 

 which is available for conserving the melting temperature in a lava 

 conduit. Very great superheat is, however, prevented by two-phase 

 convection, which tends to keep the volcanic furnace and the surface 

 lava at nearly the same temperature. 



The whole system, as imagined, is somewhat analogous to a modern 

 hot-water plant with an almost perfectly lagged vertical pipe running 

 up from the furnace. Or, again, the generation of heat in the conduit 

 is analogous to that in the gas-mixture of a blowpipe. In the first 

 case (two-phase convention) the rising gas is a passive agent in the 

 upward transfer of heat ; in the second case (chemical changes) the 

 gas is a positive heater. For a double reason juvenile gas has fluxing 

 power in the vent. 



Summary on the Heat Problem of an Active Central Vent. — A vol- 

 cano of the central-eruption type, like all others, depends on antecedent 

 abyssal injection of magma into the earth's crust, furnishing a magma 

 chamber whence the vent may draw its supply of energy. 



Three possibilities are open : (1) The primary magma may have 

 been initially saturated with juvenile gas at the original pressure of 

 10,000 atmospheres or more. (2) Only the upper part of the magma 

 may be saturated ^\•ith gas because of the change of pressure resulting 

 from the injection. (3) Or the magma may not be saturated immedi- 

 ately after injection, even at the pressure of one atmosphere. 



In the first case, bubbles must form throughout the chamber at all 

 levels above the original depth of the magma. In the second case, 

 bubbles must form at all levels above the lowest one where saturation 

 has been developed by change of pressure. In the third case, bubbles 

 will form only after other causes than mere change of pressure have 

 operated. At least three such causes are conceivable. (a) The 

 upper part of the magma chamber might become supersaturated 

 through the upward molecular diffusion of gases, whereby these are 

 concentrated. This is a reasonable expectation on the general princi- 

 ples of physical chemistry, though experimental or other proofs are 

 lacking, (b) The slow crystallization of the magma might be accom- 



