PRINCIPLES OF COMBUSTION. 153 



The neglect of chemistry when treating of combustion, and 

 the results of this neglect in these smoke-burning furnaces, can- 

 not be too strongly exposed ; neither can its study be too strongly 

 enforced, seeing that it is practically within the reach of all. 

 For chemistry is no longer the mysterious alchemy that it was 

 a century ago ; it is now a mere rigid inquiry into nature's pro- 

 cesses and laws, by the aid of those proofs and illustrations 

 which nature herself has supplied. It has taken its place among 

 the exact sciences, and now recognizes no man's dictum or opin- 

 ion, apart from experimental tests, and strict, substantial evidence. 



Looking, then, to chemistry, we would add, in reference to 

 these smoke-burning expedients, that, in seeking to obtain heat 

 from gas, (or smoke,) the bringing it into connection with ignited 

 carbonaceous matter, or to anything approaching the temper- 

 ature of incandescence, is absolutely useless, if not injurious, 

 until we are assured of having the means of contact with air 

 fully provided for. 



The mere enunciation of a plan " for consuming smoke" is 

 prima facie evidence that the inventor has not studied and con- 

 sidered the subject in its chemical relations. Chemists can 

 understand a plan for the prevention of smoke ; but as to its 

 combustion, it is so unscientific, not to say impossible, (if there 

 be any truth in chemistry,) that such phraseology should be 

 avoided. The popular phrase, " A furnace burning its own 

 smoke," may be justifiable, as conveying an intelligible mean- 

 ing ; but, in a work having any pretensions to science, or from 

 any one pretending to teach those who are unable to distinguish 

 for themselves, and who may easily be led into error, is wholly 

 objectionable. 



6. Construction of Furnaces. From what has been already 

 said, in the preceding part of this section, it will be seen that 

 the construction of furnaces is a matter of great importance in 

 the economy of heat. To investigate the various varieties of 

 furnaces which have been recommended, would occupy too much 

 of our space at present, especially as we shall have to refer to 

 them hereafter, when treating of the different methods of heat- 

 ing; besides, in small apparatuses, the intense heat required 



