46 Sir H. Davy on the State of Water and Aeriform [Jan. 



filled by fluid, and that containing aeriform matter ; and in all 

 of them the contraction of the globule of aeriform matter was 

 evidently greater, and in one instance to less than l-10th of its 

 original bulk. 



The fourth crystal that I experimented upon was of unknown 

 locality ; but I have reason to believe that it was from Gua- 

 naxuato, in Mexico, as it strongly resembled some that Mr. 

 Heuland showed me from that place. The cavity in it was 

 extremely small, and when pierced into, under distilled water, 

 the globule of gas, from being one-eighth of an inch in diameter,* 

 diminished so as to be less than l-25th ; so that its rarefaction 

 was much greater in this than in the other instances ; the water 

 was too small in quantity to be minutely examined ; it seemed to 

 be nearly pure, producing a cloudiness barely perceptible in 

 solutions of nitrate of silver and muriate of baryta. 



It was an interesting point to ascertain whether the same 

 circumstances occurred in productions found in rocks which 

 have been generally considered as of igneous origin, such as the 

 basaltic rocks in the neighbourhood of Vicenza, the chalcedo- 

 nies of which so often aftbrd included water. I found it much 

 more easy to make experiments of this kind, and to procure 

 specimens, which were abundantly supplied to me from the same 

 sources as those I have just referred to ; and though some of 

 these specimens proved to be permeable to the atmosphere, and 

 to have been filled with water artificially, yet many occurred, in 

 which the sides of the cavity were absolutely impervious to air 

 or water. 



The results that I obtained were very analogous. Water con- 

 taining very minute quantities of saline impregnations, occa- 

 sioning barely a visible cloudiness in solutions of silver and of 

 muriate of baryta, was found to be the fluid ; the gas was azote, 

 but it was in a much more rarefied state than in the rock crys- 

 tals, being between 60 and 70 times as rare as atmospheric air. 



The quantity of water was to the void space in greater propor- 

 tion than in the rock crystals. In the instance in which the 

 most accurate experiment was made ; namely, on the great spe- 

 cimen preserved in the collection of the British Museum, and 

 which weighed 380 grains, the quantity of water was 29-9 grains, 

 the space occupied by aeriform matter was equal to 1 1*7 grains 

 of water, the volume of the globule of gas at the common pres- 

 sure was to that of its rarefied volume as 1 to 63. 



It occurred to me that atmospheric air might have been origi- 

 nally the elastic fluid included in these siliceous stones and in the 

 crystals, and that the oxygen might have been separated from 

 the azote by the attraction of the water, and a direct experiment 



* I have not thought it necessary to refer to the heights of the barometer and ther- 

 mometer in these experiments, as it is impossible to gain any other than general 

 results, upon quantities in which differences arising from atmospheric temperature and 

 pressure, would be quite unappreciable. 



