378 MEETING OF THE BRITISH ASSOCIATION. 



use this oxygen .we must consume some omdizable substance, and 



coal is the cheapest we can procure. 



% % % % yz * ^ . * • '* . * ?fc 



MISCELLANEOUS USES OP COAL. 



I have hitherto spoken of coal only as a source of mechanical 

 power, put it is also extensively used for the kindred purpose of 

 relaxing those cohesive forces which resist our efforts to give new 

 forms and conditions to solid substances. In these appli- 

 cations, which are generally of a metallurgical nature, the same 

 wasteful expenditure of fuel is everywhere observable. In an or- 

 dinary furnace employed to fuse or soften any solid substances, it 

 is the excess of the heat of combustion over that of the heated 

 body which alone is rendered available for the purpose intended ; 

 the rest of the heat, which in many instances constitutes by far 

 the greater proportion of the whole, is allowed to escape uselessly 

 into the chimney. The combustion also in common furnaces is so 

 imperfect that clouds of powdered carbon, in the form of smoke, 

 envelope our manufacturing towns ; and gases, which ought to be 

 completely oxygenized in the fire, pass into the open air with two- 

 thirds of their heating power undeveloped. Some remedy for this 

 state of things, we may hope, is at hand in the gas regenerative 

 furnaces recently introduced by Mr. Siemens. In these furnaces 

 the rejected heat is arrested by a so-called "regenerator," as in 

 Stirling's air engine, and is communicated to the new fuel before 

 it enters the furnace. The fuel, however, is not solid coal, but 

 gas previously evolved from coal. A stream of this gas raised to 

 a high temperature by the rejected heat of combustion is admitted 

 into the furnace, and there meets a stream of atmospheric air also 

 raised to a high temperature by the same agency. In the combi- 

 nation which then ensues, the heat evolved by the combustion is 

 superadded to the heat previously accpiired by the gases. Thus, 

 in addition to the advantage of economy, a greater intensity of 

 heat is attained than by the combustion of unheated fuel. In fact, 

 as the heat evolved in the furnace, or so much of it as is not com- 

 municated to the bodies exposed to its action, continually returns 

 to augment the effect of the new fuel, there appears to be no limit 

 to the temperature attainable except the powers of resistance in 

 the materials of which the furnace is composed. With regard to 

 smoke, which is at once a waste and a nuisance, having myself 

 taken part with Dr. Richardson and Dr. Longridge in a series of 

 experiments made in this neighbourhood in the years 1857-58, for 



