COAL: ITS COMPOSITION 123 



The trouble with coal is that it is not simply a hydrocar- 

 bon of even unknown proportion, or a mixture of hydro- 

 carbons. It contains oxygen built into its solid structure, 

 and this oxygen is not necessarily there as water with some 

 of the hydrogen as H 2 0. But it is there, and it comes off 

 in distillation, and forms that complex substance tar. 

 Tar contains phenols carbolic acid, C 6 H 5 OH, is one of 

 them and there are phenols with eight and nine carbon 

 atoms, and even ten. 



It would fill this whole paper only to name the known 

 carbon or organic compounds containing the three elements 

 C, H and variously hooked together. But with all the 

 knowledge of the many substances given out from tar, it 

 cannot be said they are present in coal in the form they 

 take on. But the main facts of physics can be relied on. 

 Heat is swallowed up when solids are liquefied or liquids 

 gasified, and these are the things that happen to coal when 

 burned. They retard its perfect combustion, and the 

 engineer who can best fit practice to meet nature's laws on 

 proper conditions will best utilize coal as regards economy 

 and cleanliness. The knowledge of what happens thermo- 

 chemically in the life history of the hydrocarbons furnishes 

 ample explanation of the failure of ordinary methods of 

 burning it without heat or temperature conservation. The 

 behavior and properties of the gaseous hydrocarbons may 

 be regarded as the gaps in the bounding walls of knowledge 

 through which glimpses may be had sufficient to serve as 

 the jumping-off points of the flying machines of specu- 

 lative imagination ; and after all it is imagination which 

 differentiates the engineer from the mere mechanic. 

 Armies are never likely to be conveyed by either balloon 

 or flying machine, but both these frail craft may serve to 

 point the way by which an army may best proceed. The 

 mere speculative engineer will not perhaps carry out work 

 so well as the constructional man who follows beaten paths, 

 but his speculative habit of mind does enable him to point 

 the way for others to follow. 



