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— in the cavities of topazes, in rock crystal, and in chryso-beryls. 
He was led to the investigation by reason of the violent explo- 
sion of a topaz which he was heating in order to observe its 
change of colour. He also became acquainted with the fact 
that a Mr. Sanderson, a jeweller in Edinburgh, placed a topaz in 
his mouth, upon which it exploded with great violence, the 
fragments inflicting a wound. Under the title of 66 Explosive 
Grems,” a note occurs in Brewster’s “ Natural Magic ” giving an 
account of his researches. 
In the year 1860 Mr. Alexander Bryson, of Edinburgh, having- 
made a microscopic examination of rock sections during the 
previous ten years, published a note on the formation of granite. 
Fluid-cavities were noticed in many specimens, the gas-bubbles 
in which disappeared when warmed on a hot stage to 35° C. 
(97° F.), and returned on cooling to 29° (84°*2 F.), the liquid un- 
dergoing at the same time a sort of boiling movement . This appa- 
rent ebullition had previously been noticed likewise by Brewster. 
Not knowing the nature of the liquid, Bryson concluded that 
granite was crystallised from aqueous solutions at a temperature 
not exceeding 29° C. (84°*2 F.) He remarked the same liquid in 
hexagonal prisms of quartz, in porphyry from Dun Dhu in the 
Isle of Arran, in the schorl of Aberdeen granite, and also in the 
trap tufa of the Calton Hill, the basalt of Samson’s Bibs, and in 
greenstone from the Crags in the Queen’s Park, Edinburgh. 
There is a particular line of research which bears on these 
liquids. First of all the experiments of the Count Cagniard de 
la Tour, who, in the year 1822, showed the possibility of con- 
verting a liquid into vapour, in spite of any high pressure it 
may be subjected to, if only the temperature be sufficiently 
high. The most successful experiments in sealed glass tubes 
were made with ether, and, when the liquid occupied even as 
much as half the capacity of the tube, it ceased to be a liquid at 
a temperature of 150° C. (302° F.) Experiments with water simi- 
larly conducted always resulted in a disruption of the tube, most 
probably because of the solvent action of water upon the glass 
at high temperatures. In order to overcome this difficulty 
Cagniard de la Tour made use of a gun-barrel, closed com- 
pletely by an accurately fitting screw plug. At the upper part 
of the tube was placed a marble, and when the lower end, 
containing water, had been heated to about the temperature of 
melted zinc, it was found that the marble on shaking rattled 
when it fell against the lower end. There was nothing within 
to u break its fall,” as there otherwise would have been if the 
tube had contained a liquid. When the tube had cooled the 
conditions were altered, and the water itself could be heard. 
This remarkably ingenious and striking experiment proved the 
possibility of converting even water entirely into vapour despite 
