10 Dr, Colquhoun on a new Form of' Carbon, [July, 



It was smaller in quantity, its fibres were short, curled, and con- 

 fusedly interlaced among each other ; it was also generally with- 

 out lustre, and was therefore very different from the long parallel 

 and slender filaments of the more perfect formation. These 

 carbon formations among the rents otthe coke, which are hailed 

 by the manufacturer as the surest test of the success of his pro- 

 cess, are found to occur generally in dry frosty weather, and 

 seldom or never when the atmosphere is overcharged with 

 moisture. 



Those whose attention has been already attracted by the 

 formation of mammillary carbon in the coal gas manufactory in 

 the manner just related, have divided themselves into two par- 

 ties with regard to the question of its origin. One considers it 

 to be a deposition from volatilized coal tar, which certainly 

 cannot be said to seem at all an inadequate cause, while another 

 maintains that it is a precipitate from carburetted hydrogen gas; 

 founding tl\eir opinion on the well ascertained fact, that this gas 

 undergoes a partial decomposition when exposed to an elevated 

 temperature. It is the latter account which the facts we have 

 been detailing seem to prove to be in all probabihty the correct 

 one ; because the aggregations of carbon formed in the steelify- 

 ing process out of carburetted hydrogen gas completely depu- 

 rated from tar, are so congruous in their external characters to 

 the metallic- looking mammillary carbon, that it is scarcely possi- 

 ble not to ascribe them, under all the circumstances, to a 

 common origin. Besides, after subjecting the latter kind of 

 carbon to experiments similar to those already detailed in rela- 

 tion to the former, it appeared that their essential chemical 

 characters are the same. For both the compact variety of 

 mammillary carbon, which accumulates within the interior of the 

 gas retort, and those more beautiful mammillations deposited 

 upon the inner crust of that brickwork which coats the outside 

 of the retort, on being deflagrated with nitre, proved to be com- 

 posed wholly of pure carbon, with the exception of some mere 

 evanescent traces of earthy matter. 



In making this statement, I think it right to add, that the 

 results obtained by me in examining this mammillary carbon, are 

 certainly somewhat different from those of Mr. Conybeare, who 

 has given an interesting description of the varieties of car- 

 bon or plumbago, as they are commonly termed, which are 

 found to form and accumulate within the retorts of coal gas 

 manufactories. That gentleman mentions * that in deflagrating 

 portions of such carbon with nitre, he discovered in them traces 

 of iron. And he adds, that '* his experiments gave him reason 

 to think that the quantity of iron varies in different specimens, 

 and that it scarcely amounts, at the most, to the nine per cent, 



♦ Mnuli 0/ ^hU»so£hi/j JSew Series, Vi 5^. 



