1826.] t)r, Colquhoim on anew Form 0/ Carbon. 9 



frequently happens from the causes above-mentioned, it is often 

 an object to continue still to employ it for some time longer in 

 the distillation of coal, so long as the fissure remains of minute 

 dimensions. In these cases the gas which issues through the 

 rent gradually deposits, on the inner surface of that crust of ' 

 brickwork with which all such retorts are originally coated, or 

 on the arch of brickwork by which the retort is supported, a 

 carbon formation in general of the most perfect kind of the 

 mammillated variety, in form and in metallic lustre. It is fre- 

 quently composed of distinct columnar concretions, lying appa- 

 rently nearly parallel to each other, but more correctly in the 

 direction of the radii of a circle, the curvature of which is coin- 

 cident with the surface of that particular part of the retort to 

 which they are attached. The form of these concretions is 

 stalactitic ; and they closely resemble in beauty and appearance 

 the grey stalactitic ores of oxide of manganese. These mammil- 

 lations differ from those formed within the retort, both by being 

 of a more friable composition, so as to be more easily reduced 

 to powder, and in the powder of the former always possessing a 

 distinct shining micaceous aspect, which in the latter is hardly 

 discernible. 



Such are a few of the formations of carbon found in coal gas 

 manufactories, in so far as they are parallel in point of form, 

 texture, and colour, to specimens of the same substance obtained 

 from the steehfying process. It has been unnecessary to parti- 

 cularize minutely the points of resemblance between the indivi- 

 duals of the two sorts, for there is none of the aggregations 

 generally mentioned to be met with in the one process, which 

 does not find at least its miniature counterpart in the other. It 

 is probable, however, that besides the coal gas retort, there 

 may be many other situations in which a more extensive 

 acquaintance with the arts would discover carbon formations of 

 the same character with those we are now considering. And in 

 particular I have more than once had occasion to remark a 

 simultaneous production, both of the filamentous and of the 

 mammillated varieties, take place in the close ovens in which coal 

 is converted into coke for the use of the iron founder. On 

 charging one of these ovens with a coal of the caking species, it 

 first agglutinates into a sinole mass, and remains stationary for 

 some time, till by and bye it sustains a general contraction and 

 shrinkage, the consequence of which is that it becomes traversed 

 by numerous wide clefts or rents. When the manufacture is 

 complete, it is by no means unfrequent to find the sides of these 

 fissures incrusted by beautiful specimens of the mammillated 

 variety of carbon, and also, on the surface of this latter body, a 

 small collection of delicate filamentous carbon. At the same 

 time this filamentous variety was decidedly inferior in every 

 characteristic to that which occurred in the steelifying process. 



