264 EIGHTH REPORT — 1838. 



27. Now to the presence of these hydrocarbons I conceive we 

 are to look for the phenomenon of the spontaneous heating of 

 the phunbaginous matter, so many cases of the production of 

 which have been adduced. It appears to be owing to their fur- 

 ther oxidation, on exposure to air, presenting a great sui'face to 

 absorption as existing in the porous mass of plumbago, and to 

 be a strict analogue of the cases of spontaneous combustion- 

 produced by various fat oils, &c. exposed to air, in contact with 

 cotton, linen, &c. &c., or other carbonaceous bodies exposing 

 a large surface to absorption. The fact that cast iron, which 

 will produce spontaneously-heatingplumbago, when decomposed 

 by air and water, or by hydrochloric acid, when dissolved in 

 riitric acid, gives a plumbago which will not heat spontaneously, 

 favours this view of the subject; the nitric acid supplying the 

 oxygen in the first instance. 



This is at present but an hypothesis used in directing experi- 

 ments now in progress to determine the ultimate constitution of 

 these hydrocarbonous compounds, which have not yet been ana- 

 lyzed, or collected even in sufficient quantity to admit of ana- 

 lysis by others, and to discover the nature of the changes which 

 they suffer in presence of air or oxygen. 



28. The analogy of this substance with the carburets pro- 

 duced by the destructive distillation of the iron salts of the or- 

 ganic oxacids and cyanogene compounds, is obvious. These, 

 Berzelius is of opinion, are true carburets, while other chemists 

 conclude them to be mere mixtures of finely-divided carbon 

 with the base of the salt. 



I cannot, howevei', but coincide in the view of Boucharlat, 

 whose experiments lead him to believe them mixtures of car- 

 bon, with one or more definite carburets of iron whose pro- 

 perties he has described. If thus, they are analogous to the 

 conditions in which carbon exists in cast iron itself. 



29. It also bears a striking resemblance to the powders de- 

 scribed by Messrs. Stodart and Faraday, as obtained by the so- 

 lution of some of their alloys of steel in sulphuric and hydro- 

 chloric acids : these were not acted on by water, but oxidated in 

 air, and burnt like pyrophorus when heated to 300° or 400° 

 Fahr., leaving protoxide of iron and the alloying metal. They 

 conclude, that during the action of the acid, hydrogen entered 

 into combination with the metal and charcoal, and formed an 

 inflammable compound, as they found these powders sometimes 

 burnt with flame. By the action of nitric acid on these powders 

 they obtained some fulminating compounds. 



I have found that when borate of lead is decomposed by the 

 joint action of charcoal and platina with heat, a boruret of pla- 



