ISM.]- Royal Society. 6i> 



graduated, and plunged in mercury. When the diamond was once 

 kindled by the burning-glass it continued to burn for some time, 

 though the burning-glass was withdrawn, and even melted a pla- 

 tinum wire by which it was attached to the tray. No moisture was 

 produced by the combustion, and the diminution of the bulk of gas 

 was scarcely sensible. Nothing was produced but carbonic acid 

 gas, possessing all the properties of common carbonic acid gas. 

 When plumbago was burned, some moisture was produced, and 

 the bulk of the gas was sensibly diminished, indicating the presence 

 of a small portion of hydrogen as a constituent of this substance. 

 When two grains of plumbago were burnt the absorption amounted 

 to the bulk of 96 grains of mercury ; but as some oxide of iron was 

 left, the whole of this absorption cannot be ascribed to the formation, 

 of water. Charcoal from turpentine burnt all away, without leaving 

 any residue, and produced a greater quantity of water, and a 

 greater diminution of the gas, than plumbago. Charcoal from 

 alcohol, formed during the making of ether, left a small white 

 residue, owing .probably to the impurity of the sulphuric acid era- 

 ployed in the process, it formed more water, and occasioned a 

 greater absorption. Charcoal from oak left a white ash, consisting 

 chiefly of carbonate of lime. It formed the greatest quantity of 

 water, and occasioned the greatest absorption. These experiments 

 lead to the conclusion that diamond is pure carbon, and that the 

 other substances contain a little hydrogen in a state of chemical 

 combination. Sir H. Davy conceives, with Mr. Tennant, that the 

 difference between charcoal and diamond depends chiefly on the 

 crystallized state of the latter. 



At the same meeting a paper by Smithson Tennant, Esq. was 

 read, on an easier mode of procuring potassium than the process of 

 Gay-Lussac and Thenard. The method is this: A piece of gun- 

 barrel, about 18 inches long, shut at one end, is covered with a lute 

 composed of raw and baked Stourbridge clay. A piece of gun- 

 barrel, about nine inches long, open at both ends, is made to slip 

 into the upper end of the first gun-barrel. The lower end of this 

 piece has a narrow opening. It may be fixed on with sealing-wax, 

 or any common lute. Over the open end a third tube, or cap of 

 tin .plate, is luted, having a perforated cork, through which there 

 passes a bent tube of safety. A mixture of caustic potash and iron 

 turnings is put into the bottom of this gun-barrel, and it is then 

 heated violently i'or about an hour in a common smith's forge. The 

 jHjtasfcium is fouud sublimed pure in the interior iron tube. 



At th<- same meeting a paper by Sir Everard Home, Bart, was 

 read, giving an account of the skeleton of a fossil animal related to 

 the class of (Mies lately discovered on the south coast of England. 

 This specimen u in Mr. Bullock's museum. It was discovered in 

 a lioiestooe rock situated on the west of Lyme. The scull was 

 found in 181 J, and the other pails some months after. The author 

 shows that it must have been a .swimming animal, from the articu- 

 lations of the vertebrae. But it differs in its structure from all 



