﻿2 KNECHT, On some Constituents of Manchester Soot. 



circumstances at the time did not permit of the further 

 working out of details, and as I do not see my way to 

 enter into the matter again (at all events in the near 

 future), I take the liberty of bringing before you the 

 results which we have so far obtained. 



It is popularly supposed that the visible products of 

 the incomplete combustion of coal and other fuel consist 

 merely of finely-divided carbon ; and this view is 

 frequently supported in works of a scientific or semi- 

 scientific character. There can be no doubt that this view 

 is to a large extent correct in the sense that these visible 

 products contain finely-divided carbon, but that other 

 solid constituents are met with in not inconsiderable 

 amounts in the soot which is deposited from smoke, has 

 been well known for a long time to the manufacturer of 

 carbon blacks. 



The manner in which smoke forms from coal burning 

 in our open fire-grates cannot have escaped the atten- 

 tion of even the most casual observer. It will be quite 

 evident from the voluminous disengagement of gases or 

 vapours that in the first instance dry distillation takes 

 place. Where such disengagement is moderate, the 

 vapours take fire and burn with a bright luminous flame ; 

 but if the disengagement becomes violent, the vapours 

 either do not burn at all, or only suffer partial combustion, 

 and their bulk finds it way, mixed with a large excess of 

 air, into the chimney. When the first violent disengage- 

 ment of gas has ceased, the coal burns quietly with a 

 lurid flame, from which no dry distillation products, but 

 only products of incomplete combustion, result. From 

 these considerations I think we may take it that our 

 smoke and soot consist partly of dry distillation products 

 and partly of the products of incomplete combustion, to 

 which must be added the mineral matter, which is partly 



