300 Messrs. Sorby and Butler on the Structure of [Feb. 18, 



fortunately he does not state the temperature at which this occurs, nor does 

 he seem to have tried to ascertain the exact limit of the volume, which must, 

 however, lie between one-half and one-third. Cagniard-Latour # found 

 that when ether and other liquids sealed up in small strong tubes, with a 

 certain space left empty, were heated, they expanded very much, and sud- 

 denly passed into the state of vapour. The temperature, pressure, and vo- 

 lume at which this change took place varied very considerably. Ether ex- 

 panded to nearly double its volume, and passed into vapour at about 200° C, 

 with an elastic force of 37 or 38 atmospheres. Alcohol expanded to about 

 three times its volume, and passed into vapour at about 260° C, with an 

 elastic force of 119 atmospheres; whereas water appeared to expand to 

 nearly four times its volume, and required a temperature near that at which 

 zinc melts (328° C, Daniel). "When in this highly expanded state, the 

 liquids were very mobile, and seemed much more compressible than under 

 other circumstances ; for they did not burst the tube, if too much had been 

 sealed up in it, until after their normal volume would have been decidedly 

 greater than its capacity. No one could fail to see that these phenomena 

 have much in common with what occurs at a lower temperature in the case 

 of the liquid inclosed in sapphire, and that they are of great importance 

 in connexion with the origin of fluid-cavities. Since they become full of 

 liquid at a comparatively low temperature, it was not unreasonable to sup- 

 pose that the minerals in which they occur must have been formed where 

 the heat was scarcely above that of the atmosphere ; but these facts seem 

 to show that the occurrence of such fluid-cavities is quite reconcilable with 

 a very high temperature ; for it is obvious that if, at a great depth below 

 the surface, heated, highly compressed gaseous carbonic acid were inclosed 

 in growing crystals, it might condense on cooling so as to more or less com- 

 pletely fill the cavities with the liquid acid. 



If the same principles could be applied in the case of water, we should 

 be led to infer that it could not exist in a liquid state at a higher tempe- 

 rature than that of dull redness, corresponding closely with what Mr. Sorby 

 deduced from the fluid-cavities in some volcanic rocks. In that case, ac- 

 cording to Cagniard-Latour, the liquid when condensed would occupy 

 only one-fourth part of the cavity, and it would scarcely be likely to con- 

 tain any fixed salt in solution ; whereas the fluid- cavities in the minerals 

 of ejected blocks are often two-thirds full of what seems to have been a 

 supersaturated solution of alkaline chlorides. The phenomena now under 

 consideration should certainly be borne in mind in studying volcanic action ; 

 arid it is possible that some cavities now containing water may have been 

 formed by the inclosure of very highly compressed steam. In some cases 

 the requisite pressure would be enormous, and other facts seem to show that 

 it was more generally caught up in a liquid state. 



The cavities in emerald are very interesting in connexion with this subject, 

 and also furnish strong evidence against the opinion that the liquid was not 

 * Ann. de Chimie, 1822, t. xxi. pp. 127 & 178 ; t. xxii. p. 410. 



