C.— GEOLOGY. 61 
Hall began his experiments as already stated in 1798. ‘They were 
interrupted for about a year (March 1800 to March 1801), and on 
March 31, 1801, he had obtained a considerable measure of success. A 
_eharge of forty grains of powdered chalix was converted into a firm 
granular crystalline mass of limestone. The loss on weighing was 
approximately 10 per cent. Another charge of eighty grains was con- 
yerted into marble (on March 3, 1801), with a loss of approximately 
5 per cent., and the crystalline mass showed distinct rhombohedral 
cleavage. 
* Though it cannot be said that his success was easily won he was by 
no means satisfied, and for another four years he continued his 
researches. Many different methods were tried in order to ascertain the 
most satisfactory and reliable; his ambition was to attain complete 
control of the process so that he could always be certain of the result. 
Porcelain tubes were tried, which he obtained from Wedgwood. They 
were very liable, however, to allow escape of the gases through pores. 
Many different methods of obtaining gas-tight stoppers were experl- 
mented on, but he does not seem to have found anything really better 
than the fusible metal. A slight loss of weight in the chalk used seemed 
inevitable, and the amount of loss varied irregularly; after long trials 
he ultimately succeeded in reducing this to less than 1 per cent. 
Various kinds of carbonate of lime were used, including chalk, lime- 
stone, powdered spar, oyster shells, periwinkles, and each of these was 
erystallised in turn. Many experiments showed that a reaction might 
take place between the chalk powder and the glass of the tube in which 
it was contained. The result was a white deposit often crystalline, and 
a certain amount of uncombined carbonic acid gas which escaped when 
the tube was opened. No doubt the white mineral was wollastonite. 
Fall proved that it was a silicate of lime which dissolved in acid and 
left a cloud of gelatinous silica. Thereafter he used platinum vessels 
instead of glass to contain the charge of carbonate of lime which he 
wanted to fuse. ‘The effect of impurities in the material used was also 
investigated. Critics had urged that his limestone was not pure. Hall 
aptly replied that this was so much the better ; natural limestones were 
seldom pure, and his point was that limestone might be fused under 
heat and pressure. He obtained the purest precipitated carbonate of 
lime, and used also perfectly transparent crystalline spar; the results 
_ were, as we might expect, that the pure substances and the fairly coarse 
erystalline powder were more difficult to fuse than the very finely 
ground natural chalk. These results show that Hall had very complete 
control of his experimental processes, and that even small differences 
in fusibility did not escape his observation. 
; As natural limestones are always moist, Hall’s attention was next 
directed to the influence of water on the crystallisation of his powders. 
This added greatly to the difficulty of the experiments, but by wonderful 
“skill he succeeded in using a few grains of water (apparently up to 
5 per cent. of the weight of the chalk). The result was to improve the 
crystallisation, for the reason, as Hall believed, that the pressure was 
inereased. He noticed atthe same time that hydrogen was produced, 
which took fire when the gun-barrel was discharged. Probably there 
