6 H. HENS0LDT OX FLUID CAVITIES IN METEORITES. 



before the Chemical Society, which was subsequently printed in 

 the Journal of that Society (March, 1877), in which he gave a 

 most interesting account of his observations on this subject. After 

 a series of elaborate experiments in order to establish the nature 

 of the contents of cavities in topazes, sapphires, &c, he came to 

 the conclusion (as others had already done before him) that in very 

 many instances the imprisoned liquids consisted of the gas known 

 as carbon-dioxyde, or carbonic acid, which, under certain conditions, 

 can exist in a liquid state. 



As a rule, the fluid occurring in the cavities of crystals had 

 been found to be water, often containing high percentages of 

 saline matter in solution. Sometimes, as Prof. Judd points out 

 in his recently published work on Volcanoes, the saline matters are 

 present in such quantities that they cannot all pass into solution, 

 but crystallize out ; and thus we frequently find cubic crystals of 

 the chlorides of sodium and potassium floating in the liquids. In 

 several cases the liquids have been found to be hydro-carbons, oily 

 substances analogous to naphtha and petroleum. 



From experiments I have made, similar, though not so exhaus- 

 tive as those conducted by Mr. Hartley, I have ascertained 

 that the liquid contained in the minute cavities of this 

 meteorite is neither water nor a hydro-carbon, but that there can 

 be hardly any doubt that it is liquefied carbonic acid. On warming 

 the slide the gaseous bubbles disappear when a temperature of 

 about 30° C. is reached, but return again on cooling, without any 

 apparent diminution in size or moving capacity. Now, between 

 30° and 31° C. lies the so-called " critical point " of carbonic acid ; 

 that is, above this temperature carbonic acid cannot exist in its 

 liquid condition, however great the pressure may be to which it is 

 exposed. This is in accordance with an interesting law, the exist- 

 ence of which has been proved beyond any doubt by recent in- 

 vestigation. After certain temperatures are reached liquids enter 

 into the gaseous state, no matter what the pressure may be. The 

 temperature under which a certain liquid is no longer able to retain 

 its characteristic features, but transforms itself into a gas, has 

 been called by Prof. Andrews, of Belfast, its " critical point ;" and 

 from experiments made by him it has been convincingly shown 

 that it is not possible to maintain the liquid condition of carbonic 

 acid at any temperature beyond 30° 92' C. 



In all the cavities contained in the meteoric sections which have 



