92 THE SCIENTIFIC PAPERS OF 



The olefiant gas and tar vapour are well known to deposit carbon 

 on being heated to redness, which is immediately taken up by the 

 carbonic acid and vapour of water, the former being converted 

 into carbonic oxide and the latter into carbonic oxide and pure 

 hydrogen. The ammoniacal vapours and sulphuretted hydrogen 

 are also decomposed, and permanently elastic gases with a pre- 

 ponderance of hydrogen are formed. The specific gravity of the 

 mixture is reduced in consequence of these transformations to 

 0'70, showing an increase of volume from 64,000 to nearly 72,000 

 cubic feet per ton of fuel, taken at the same temperature. This 

 chemical change represents a large absorption of heat from the 

 regenerator, but the heat is given out again by combustion in the 

 furnace, enhancing the heating power of the fuel beyond the 

 increase due to elevation of temperature alone. 



The chemical transformation is also of importance in preventing 

 " sulphuring ; " for it is believed that the sulphur in separating 

 from its hydrogen takes up oxygen supplied by the carbonic acid 

 and water, formiug sulphurous acid, a firm compound, which is 

 not decomposed on meeting with metallic oxides in the furnace. 

 This view is so far borne out by experience that glass containing a 

 moderate proportion of lead in its composition may be melted in 

 open crucibles without injury, instead of requiring covered pots 

 for the purpose as in ordinary furnaces. In dealing with the 

 highest quality of flint glass, however, it is found necessary to 

 retain covered pots ; but every other description of glass is melted 

 in open pots. In all branches of glass manufacture, saving 

 of fuel is of relatively small moment as compared with the im- 

 provement effected in the colour and general quality of the glass 

 by the use of the regenerative gas furnace, owing to the absence 

 of dust and cinders and the high degree of temperature which 

 may with safety be maintained throughout the heating chamber. 



These advantages of the regenerative gas furnace are of equal 

 value in the case of puddling and welding iron. Plates 1C and 17 

 represent a puddling furnace constructed on this plan. Fig. 13 is 

 a longitudinal section of the furnace, Fig. 14 a sectional plan of 

 the puddling chamber, and Fig. 15 a sectional plan of the re- 

 generators ; Fig. 16 is a transverse section at the end of the 

 furnace, and Figs. 17 and 18 are vertical sections through the 

 gas and air passages. 



