on the Nature of certain Bodies. 1 1 3 



tn anntller experiment of a siuiikr kind, in which frag- 

 ments of diamonds were used in the quantity of four grains, 

 the polassiuni became extremely black from its action upon 

 them during qn exposure to he.it for three hours, and the 

 diamonds were covered with a grayish crust, and when acted 

 upon by water and dried, were found to have lost about 

 iVo-ths of a grain in weight. The matter separated by wash- 

 ing, and examined, appeared as a fine powder of a den^e 

 black colour. When a surface of platina wire was covered 

 with it, and made to touch another wire in the Voltaic cir- 

 cuit, a brilliant spark with combustion occurred. It burnt, 

 when heated to redness in a green glass tube filled with oxy- 

 gen gas, and produced carbonic acid by its combustion. 



These general results seem to show, that in phmibago the 

 carbonaceous element exists merely in combinatitin with iron, 

 anil in a iorm which may be regarded as approaching to that 

 of a metal in its nature, being conducting in a high degree, 

 opaque, and possessing considerable lusue. 



Charcoal appears to contain a minute quantity of hydro- 

 gen in combination. Possibly likewise, the alkalies and 

 earths produced during its comhustion, exist in it not fully 

 combined with oxygen; and according to these ideas, it is a 

 verv compounded substance, though in the main it consists 

 of the pure carbonaceous element. 



The experiments on the diamond render it extremely likely 

 that it contains oxygen ; but the quantity must be exceed- 

 inglv minute, (houoh probably sufficient to render the com- 

 pound non-conducting : and if the carbonaceou-* element in 

 charcoal and the diamond be considered as united to still less 

 foreign matter in quantity, than in plumbago, which con- 

 tains about -^uth of iron, the results of their coni'oustioii, as 

 examined independently of hygrometrical tests, will nof 

 differ perceptibly. 



Whoever considers the difference between iron and steel, 

 in which there does not ejcist more than-^^-jj-th of plumbago, 

 or the difference between the amalgam of ammonium, and 

 mercury, in which the quantit) of new matter is not more 

 tlian y^^'p^ih, or tliat between the inttals and their sub- 

 oxides, some, of which contain less than -^\h of oxygen, 

 will not be disposed to question the principle, that minute 

 difltrenecs in chemical composition may produce great diffe- 

 rences in external and physical characters. 



VI. Experimcut.'i on the Decomposition and Composition of 

 tkn Boraac ykid. 

 Tn the last Bakerian Lecture, 1 have given an account of 

 Vol. 34. No. 136. /It/iiUit iboy. H au 



