48 Sir H. Davy on the State of Water and Aeriform [Jaw. 



nious researches of Mr. Perkins show, that water is much more 

 compressible than was formerly imagined ; and the volume of 

 water, however high its temperature, must be influenced by the 

 pressure to which it is exposed ; so that a certain compressing 

 weight may not only impede, but altogether counteract, the 

 expansive force of heat. 



Many speculations might be indulged in on this subject, but I 

 shall not at present enter upon them ; and I shall conclude by 

 observing, that a fact, which has been considered by the Neptu- 

 nists, above all others as hostile to the idea of the igneous origin 

 of crystalline rocks, namely, the existence of water in them, 

 seems to afford a decisive argument in favour of the opinion it 

 has been brought forward to oppose. 



APPENDIX. 



Since the foregoing pages were communicated to the Royal 

 Society, I have made some new experiments on the same sub- 

 ject; all of them, except two, offered results of the same kind 

 as those 1 have detailed, and upon such 1 shall not enter; but 

 these iwo, from their peculiarity, will not, I trust, be thought 

 unworthy of a particular notice. 



In examining, with Mr. Heuland, the beautiful specimens of 

 rock crystals in the collection of Charles Hampden Turner, Esq. 

 I observed one crystal which, Mr. Heuland informed me, was 

 from La Gardette, in Dauphine, that contained a considerable 

 cavity, in which there v\as a viscid brownish liquid, resembling 

 in its appearance and consistence linseed oil. As the void space 

 or cavity filled with aeriform matter appeared considerable in 

 proportion to the fluid, I expressed a desire to pierce the crystal; 

 and Mr. Turner, hearing of my wish, was so kind as to gratify it 

 in the most polite and liberal manner, by presenting to me the 

 specimen. With Mr. Newman's assistance I made the usual 

 experiments upon it. The cavity was pyramidal, and nearly the 

 third of an inch in diameter. 1 soon ascertained that the fluid 

 was not water, as it congealed and became opaque at a temper- 

 ature of 56°. When the crystal was pierced under distilled 

 water, the water rushed in and entirely filled the cavity, so that 

 no other aeriform matter but the vapour of the substance could 

 have been present : the water was rendered white and cloudy, 

 apparently by the substance. I endeavoured to collect some of 

 it for chemical examination, but it was too small in quantity (not 

 equalling in volume one-sixth of the volume of the cavity), to be 

 submitted to analysis. It swam on the water, had no distinct 

 taste, but a smell resembling naphtha ; a portion of it taken out 

 mixed with the water, when exposed to heat acted like fixed oil, 

 and it seemed to have a high temperature of ebullition. It 

 inflamed, producing a white smoke. 



The fact, of almost a perfect vacuum existing in a cavity con- 





