1823.] Matter in Cavities found in certain Crybtals. 46 



which would render it impossible to draw any conclusion as to 

 the exact temperature, yet still the experiments appeared to 

 offer, on any view, interesting results ; and I was the more 

 desirous of performing them, as I believe the nature of t'ye fluid 

 and aeriform matters included in rock crystals and other silice- 

 ous stones, has never been accurately ascertained. 



Having purchased some crystals, and having had others com- 

 mitted to my care by the liberality of my Brother Trustees of the 

 British Museum, and of my friend Prof. Buckland, I proceeded 

 to make the necessary experiments upon them. It will be 

 improper for me to take up the time of the Society by a minute 

 description of my manipulations. Holes were drilled in the 

 crystals by the use of diamonds, generally by Mr. Newman, 

 under distilled water, or mercury, the gas was expelled by the 

 introduction of wires, and the fluids included in the cavities 

 were drawn out by means of fine capillary tubes, and experi- 

 ments were afterwards made to determine the space they occu- 

 pied, which had been accurately measured and marked upon 

 the crystal. The chemical nature of the fluid and gas was 

 determined by processes which were necessarily difficult from 

 the smallness of the quantities operated upon ; but which are 

 too well known to the chemical philosophers of this Society to 

 need description. 



The first three crystals that I examined were from Schemnitz, 

 in Hungary ; the cavities that they contained were proved not to 

 be permeable to the atmosphere, by exposure to rarefied air, 

 alone, and under water, in the receiver of an air-pump, a cir- 

 cumstance which it was necessary always to attend to, in order 

 to render the experiment availing. 



A cavity in one of the crystals was pierced under oil, three 

 under distilled water, and one under mercury. In all of them 

 the fluid rushed in when the cavity was opened, and the globule 

 of elastic fluid contracted so as to appear from six to ten times 

 less than before the experiment. The fluid in all the crystals 

 (in two it was minutely examined) was found to be water nearly 

 pure, containing only a minute portion of the alkaline sulphates. 

 The elastic fluid, as well as I could ascertain from the very 

 minute quantities 1 could procure, appeared to be azote, unmixed 

 with any other substance. 



The largest cavity, which was in the crystal put into my hands 

 by Prof. Buckland, contained a space equal to 74*5 grains of 

 mercury; the water in it equalled in volume 48*1 grain mea- 

 sures of mercury ; and the globule of air, after the experiment, 

 equalled in diameter a globule of mercury weighing 4-2 grains, 

 so that the elastic fluid had contracted at least between six and 

 seven times. 



In the other experiments, the cavities being much smaller the 

 quantities of air and fluid could not be accurately measured ; but 

 there seemed to be nearly the same relation between the space 



