Chemistry. 307 



per cent, of carbonic acid in excess above that ordinarily 

 contained in air; and although it was thought similar ferns 

 growing under the same conditions, but without carbonic 

 acid in excess, were the most luxuriant, it appeared that 

 they thrived well in this artificial atmosphere. Mr R. Hunt 

 stated that he found the diversified influences of light mate- 

 rially to affect the quantity of carbonic acid which the plants 

 could absorb without immediate injury. 



Professor Voelcker read a paper on " the per-centage of 

 nitrogen as an index to the nutritive value of food,** which 

 was highly important, as shewing the objections which apply 

 to the present method of determining the nutritive value of 

 food by chemical analysis. The nature of the paper, how- 

 ever, does not admit of abstract. 



A paper was then read from Mr Henry Taylor, on " the 

 chemical composition of the rocks of the coal formations ;'* 

 and another by Mr J. P. Joule, F.R.S., *' on some amal- 

 gams." 



Mr J. P. Gassiot, F.R.S., the well-known electrician, read 

 a paper on " a peculiar form produced in a diamond under 

 the influence of the voltaic arc." He exhibited to the Sec- 

 tion a diamond which had been exposed to the intense heat 

 produced by the voltaic battery when arranged as in the de- 

 vice for the electric light. The diamond had apparently been 

 fused, but instead of changing into coke, as in such circum- 

 stances diamonds generally do, it had become a glassy mass, 

 and seemed to consist of a multitude of small crystals ad- 

 hering to each other. The diamond was examined with 

 much interest and curiosity. 



The last paper read was by Mr H. C. Sorby, F.G.S., on 

 " the trimorphism of carbon," the object of which was to 

 establish the fact that coke was in reality crystallised when 

 very hard, and in the same form as the diamond, from which, 

 however, it was stated to diff^er in crystallographic volume. 

 Mr Sorby stated that he had also observed anthracite or blind- 

 coal in the form of crystals, belonging to the square prisma- 

 tic system. 



u2 



