116 Scientific Proceedings, Royal Dublin Society. 



the normal pressure of the air and the temperature of lava, is a 

 gas ; and, like carbonic anhydride, may be rendered liquid or solid 

 by increasing pressure or lowering temperature. By removing 

 either of these secondary conditions the more volatile materials in 

 the two cases return to their gaseous state. Now, carbonic anhy- 

 dride in the presence of water is much more easily condensed, and 

 dissolves simultaneously in that liquid, the solubility propor- 

 tionally increasing with the pressure. Water is equally soluble 

 in molten silicates, as is shown by its escape from lava, and its 

 solubility likewise increases with the pressure, unless downright 

 opposed to known physical laws. Between these two cases of 

 gases soluble in liquids there is not only a physical, but also 

 a chemical, analogy, for in both cases we have to deal with gase- 

 ous oxides soluble in liquid ones. 



In the case of the solution of carbonic anhydride in water, 

 and, in fact, of solutions of all gases in liquids, we find that the 

 quantity of gas absorbed increases with the pressure, provided the 

 liquid does not solidify (as exhibited in the spitting of silver). 

 We find also that the pressure remaining fixed, an increase of 

 temperature has a tendency to reconvert the condensed, or, more 

 properly, dissolved gas, again into the gaseous state ; or, in other 

 words, we find that the tension of such a solution increases with 

 the temperature. The absorption of oxygen by molten silver, and 

 of the same gas and carbonic anhydride by iron and steel, as 

 demonstrated by Troost, are familiar examples of fluids at high 

 temperatures taking up gases. It is at the same time evident that 

 the critical point of water no longer enters into the question, as it 

 is held in solution like CO 2 in water, both occupying volumes 

 much nearer their liquid than their gaseous state. 



The conditions under which igneous matter commences its 

 course towards the surface may, no doubt, be very variable, and 

 whether such be due to secular cooling of our globe, and con- 

 sequent straining and fracturing of its outer surface, it is not our 

 present business to discuss. As already stated, we have every 

 reason to believe the volcanic magma, as it exists in its original 

 site, 1 contains dissolved in it little, if any, water, although many 



1 Whether this forms the centre of our globe, a stratum between the nucleus and 

 crust, or exists as isolated reservoirs, in no way affects that part of the question now 

 under discussion. 



