1823.] Matter in Cavities found in certain Crystals. 47 



seemed to confirm this idea. A chalcedony which had been 

 bored was placed in water free from air under a receiver, which 

 was exhausted till a portion of gas from the interior of the crys- 

 tal had escaped into a proper receptacle. This gas examined 

 by nitrous gas was found to contain nearly as much oxygen as 

 atmospheric air ; so that there is every reason to believe that 

 the water had emitted oxygen during the exhaustion. 



I endeavoured to find some calcareous secondary rocks, or 

 crystals belonging to them, containing cavities, on which expe- 

 riments of the same kind might be made ; but in a number of 

 trials, I have as yet found none impermeable to the atmosphere ; 

 and the cavities of such, when bored, are always found to con- 

 tain atmospheric air in a common state of density. 



I was surprised to find that this was the case even with cavi- 

 ties in calcareous spar in the centre of a limestone rock ; yet 

 these cavities which contained atmospheric air did not fill with 

 water when the stone was placed in water under an exhausted 

 receiver. When, however, it was dry, and placed in a receiver 

 alternately exhausted and filled with hydrogen, the air that was 

 produced by piercing the cavities, was found mixed with hydro- 

 gen; proving that the substance of the stone was permeable to 

 elastic fluid. 



I hope soon to be able to make further researches on this 

 subject ; but in reasoning upon the vacuum, or rarefied state of 

 the aeriform matter in the cavities of these rock crystals and 

 chalcedonies, it appears difficult to account for the phenomenon, 

 except on the supposition of their being formed at a higher tem- 

 perature than that now belonging to the surface of the globe ; 

 and the most probable supposition seems to Jje, that the water 

 and the. silica were in chemical union, and separated from each 

 other by cooling. 



Water in the temperature of the arctic winter is constantly a 

 crystallized body. As a fluid, its solvent powers are increased as 

 its heat becomes higher, and, when elastic, the density of its 

 vapour is exalted in proportion to its heat ; so that an atmosphere 

 of steam, supplied from an indefinite source above water, would 

 render it capable of receiving a very high degree of heat. Lime 

 retains water in combination at a heat above 250° Fahrenheit ; 

 baryta retains it (even under ordinary pressures) at a strong red 

 heat, and fuses with it. It is extremely likely that a liquid 

 hydrate of silica would exist, under pressure, at high tempera- 

 tures ; and like all liquid bodies in the atmosphere, would pro- 

 bably contain small quantities of atmospheric air ; and such a 

 supposition only is necessary to account for the phenomena pre- 

 sented by the water in rock crystal and chalcedony. 



As, however, steam or aqueous vapour may be considered as 

 having a share in these results, if it be supposed included in the 

 cavity, no exact conclusions can be drawn from the apparent 

 degree of contraction of the water ; particularly as the late inge- 



