PROCEEDINGS OFj iHE POLYTECHNIC ASSOCIATION. 313 



quantity of coal, is nearly double that usually realized by the common pro. 

 cesses. The flame is allowed to pass to the chimney too rapidly ; if more 

 time was given for the gases to be intermingled and reverberated, the pro- 

 ducts of combustion could be secured, and very few would be allowed to 

 escape up the chimney. The smoke which escapes is mostly carbon oxide 

 and line particles of coal. If these could be consumed, there would be much 

 additional heat. To consume the smoke, it is essential that ox^'geu should 

 be supplied very freely, and that the heat should be intense enough for 

 proper ignition. Accqrdiag to Beurne, Prideaux, and other authors, nearly 

 half of the oxygen passes through our cumiiion furnac(;s without being com- 

 bined with the fuel. This is owing to the rapid draft. 



The Chairman remarked that no subject had been discussed before this 

 Association of more importance than the disengaging of heat by chemical 

 combination. Heat as a motor, as a chemical agent, and as the source of 

 artificial temperature, is indispensable, and every person is directly or indi- 

 rectly benefited by the most economical generation of it. It is not essential 

 to speak of all the combinations which will produce heat, for it is settled, 

 beyond all question, that of the sixty-odd elements, only three can be 

 used with safety, economy and convenience. These are Oxygen, Carbon 

 and Hydrogen. The chemical change which produces heat is the combi- 

 nation of oxygen with carbon or with hj'drogen. About one -fifth of the 

 common air, by measure, is oxygen. This element always presents itself 

 at our bidding in any desired quantity ; the actual cost of the fire, there- 

 fore, is the cost of the carbon or hydrogen consumed. In some kinds of 

 fuel — in wood, for example — we find a certain portion of oxygen already 

 conil)ined with these elements. This portion has already done its heat- 

 work, and is of no service during the process of burning such fuel. Now 

 the plain but most important question to be settled is, what is the exact 

 quantity of heat generated by substances composed chiefly of carbon and 

 hydrogen? The experiments of MM. Fabre and Silbermann, conducted with 

 great care and accuracy, and corresponding in the main with those made 

 by Dulong and Petit, will furnish us the desired answer. The tables of 

 these experimenters include a great range of combinations, but only those 

 relating to the union of oxygen with substances containing carbon or hy- 

 drogen are selected. Taking as the thermal unit the quantity of heat re- 

 quired to raise the temperature of one pound of water from 0*^ to 1*^ C, we 

 have in the following table the units of heat generated from the union of 

 one pound of the several substances mentioned with all the oxygen required 

 for perfect combustion. 



ITydrogcn, .34,462 



Marsh Gas 13,0(53 



OleGant Gas 11,858 



Ainylene ,. 11,491 



Oil or Turpentine 10,852 



Olive Oil 9,800 



Ether 9,0.30 



Anthracite Coal 8,400 



Charcoal 8,080 



Bituminous Coal 8,000 



Tallow 8,000 



Diamond 7,700 



Absolute Alcohol 7,180 



Coke 7,000 



