296 MR. J. B. DANCER ON COAL-ASH OR DUST. 



form of these bodies suggests that they have been thrown 

 off in scintillations, such as are seen during the combus- 

 tion of iron in oxygen gas, and whilst in a fluid state they 

 assume a spheroidal form. They are carried by the draught 

 into the flue, and being of greater specific gravity than the 

 carbonaceous matter forming the smoke, they fall before 

 the current of air has reached the chimney. Some of the 

 dust has been a considerable time in the flue, exposed to 

 the intensely heated circulating flame ; the reducing ac- 

 tion of this would probably convert some of the oxide into 

 metallic iron. Many of these balls have the appearance of 

 reduced oxides. The flue-dust contains a larger amount 

 of ferruginous matter than can be accounted for by the 

 analysis of coal-ash. I think the surplus may be regarded 

 as representing the wear and tear of the ironwork about 

 the furnace, such as fire-bars, boiler-plates, &c. The brick- 

 work and cement about the boiler and flues may also 

 supply some of the silica, alumina, and iron for these balls, 

 numbers of which are merely thin shells. The movements 

 of these objects, caused by the approach of a magnet under 

 the stage of the microscope, are somewhat amusing ; and it 

 is at times startling to see the crystalline objects, both 

 spherical and irregular, exhibit magnetic attraction : pro- 

 bably they contain particles of iron imbedded in them ; if 

 they do not, may we not imagine that there is some mag- 

 netic compound in which the crystalline matter predomi- 

 nates ? When we consider the accidental condition under 

 which this matter has combined, it is just possible that 

 some new molecular arrangement or combination of ele- 

 ments may have taken place. It is very probable that 

 many of these polished balls are much more complex in 

 their elementary constitution than I have stated. They 

 are, in fact, a kind of glass, and many of them merely bulbs. 

 Pelouze states that glass is probably an indefinite mixture 

 of definite silicates. Glass, containing small quantities of 



