8 Professor Berzelius on [July, 



of the cyanurets by heat is entirely determined by the affinity of 

 carbon for the metals ; if it were otherwise, the cyanogen would 

 either remain combined with them, as, for example, with the 

 alkalifiable metals, or would separate without decomposition, as 

 occurs with the metals reducible per se. 



In the foregoing experiments, we have not only seen bi, tri, and 

 quadricarburets, but we have also discovered double carburets 

 analogous to double sulphurets and arseniurets, numerous exam- 

 ples of which are met with in the interior of our globe. The 

 existence of these carburets depends probably upon the same 

 affinity as that which gives rise to double cyanurets. 



In distilling vegetable salts with a metallic base, the metal- 

 lic carburets are also obtained, and which have been in general 

 considered as mixtures of carbon and metal ; but it is very cer- 

 tain that in a great number of cases, if not in all, these residues 

 are metallic carburets of determinate composition, and that the 

 quantity of carbon which is found in the volatile products of the 

 distillation is in part determined by the affinity of the metal for 

 this element. 



The phenomenon of combustion which is observed in the 

 greater number of the above-mentioned experiments is an inte- 

 resting addition to those which have been before presented by 

 some metallic antimoniates, gadolinite, hydrate of zircon, as well 

 as the oxides of chrome, rhodium, and iron. This combustion 

 appears to arise from a more intimate combination between the 

 iron and the carbon than that which existed in the cyanuret. 

 Every sudden rise of temperature which occurs in these bodies 

 consequently appears in the form of an eruption of fire. 



For those who have not yet attended to this singular pheno- 

 menon, I will here relate an experiment which is very easily 

 repeated. A solution of sulphate or muriate of deutoxide of 

 iron is to be decomposed by ammonia added slightly in excess, 

 in order to prevent the oxide of iron from carrying down any 

 acid in the form of subsalt. The oxide is to be well washed and 

 dried. It is afterwards to be slowly heated in a small platina 

 crucible, by exposure to the flame of a good spirit lamp, until the 

 crucible begins to become red, and the water and ammonia conse- 

 quently driven off. The fire is then suddenly increased to red- 

 ness ; the pieces of oxide of iron begin to increase in volume ; 

 slight motion is perceived here and there ; all at once they take 

 fire, and intense ignition pervades them from one end to the 

 other. The oxide neither gains nor loses any thing by this 

 phenomenon ; and if there is any change of weight, it is always 

 diminution, occasioned by not having left it long enough exposed 

 to a moderate heat, to expel all the water and ammonia which it 

 had retained. After having undergone this apparent combus- 

 tion, the oxide of iron is rendered more difficulty soluble in acids ; 

 it is dissolved, nevertheless, by continued digestion in concen- 

 trated muriatic acid; but if it be precipitated again, fire isrepro- 

 t)«iced under similar circumstances. 



