226 THE SCIENTIFIC PAPERS OF 



a higher heat. On again reversing, this higher heat is communi- 

 cated to the gas and air passing in, and a still hotter flame is the 

 result. 



The temperature that may be attained in this way by the 

 gradual accumulation of heat in the furnace and in the upper 

 part of the regenerators appears to be quite unlimited, and the 

 heat at which a suitably designed furnace can be worked is 

 limited in practice only by the difficulty of finding a material 

 sufficiently refractory of which it can be built. 



Welsh Dinas brick, consisting of nearly pure silica,* is the only 

 material, of those practically available on a large scale, that I have 

 found to resist the intense heat at which steel-melting furnaces 

 are worked ; but though it withstands perfectly the temperature 

 required for the fusion of the mildest steel, even this is melted 

 easily if the furnace is pushed to a still higher heat. 



As the gas flame is quite free from the suspended dust which 

 is always carried over from the fuel by the keen draught of an 

 ordinary furnace, the brickwork exposed to it is not fluxed on the 

 surface and gradually cut away, but fails, if at all, only from abso- 

 lute softening and fusion throughout its mass. A Stourbridge 

 brick, for example, exposed for a few hours to the heat of the 

 steel-melting furnace, remains quite sharp on the edges, and is 

 little altered even in colour ; but it is so thoroughly softened by 

 the intense heat, that on attempting to take it out,, the tongs 

 press into it and almost meet, and it is often pulled in two, the 

 half-fused material drawing out in long strings. It results from 

 this perfect purity of the flame, that where the heat is not suffi- 

 cient to effect the absolute fusion of the bricks employed, the 

 length of time is almost unlimited during which a gas furnace 

 will work without repairs. 



* Analysis of Dinas " clay " from Pont-Neath, Vaughan, Vale of Neath (Percy's 

 Metallurgy, Vol. I. p. 237). 



Silica . 



Alumina . 



Protoxide of iron 



Lime 



Potass and soda 



Water combined 



98-31 

 0-72 

 0-18 

 0-22 

 0-14 

 0-35 



99-92 

 The " clay " is mixed with 1 per cen\ of lime in making the bricks. 



