PROCEEDINGS OF THE POLYTECHNIC ASSOCIATION. 485 



combustion — no soot or ashes — nothing but g-as and water. If this perfec- 

 tion of coinbusti(jn is attained, it will probabi}'' be by an excess of air; but 

 that is a part of my plan, which is to make an engine in which hot air is 

 one of the agents, as in Bennett's, Roper's, and others. The other agent 

 is steam. The products of combustion arc to go from the furnace, through 

 proper valves, into the water; and to pass through proper screens of wire 

 gauze, or other devices to cause the heat to be given to the water — such, 

 perhaps, as spraying the water. The condition I desire is, that there shall 

 be a mixture of hot gases and superheated steam, of about 130 lbs. pressure, 

 and of a temperature not over 500'^, or not too hot for the working parts. 



This idea of forcing air through the fire into the boiler, through the water 

 and through the engine, was carried out by Capt. Bennett in the old steam- 

 boat Nuvelty, in 1835 or 1836 ; but he was troubled by ashes and unburnt 

 fuel. The improvement now seemingly attainable will consist in perfect 

 gasification, and avoidance of all that can grind the cylinders and valves, 

 and foul the water in the boiler. 



It is doubtful whether we can retain the condenser. But perhaps we 

 may send the products of combustion in the usual way through a boiler, 

 and make pure stearn, and temper the gases with a little steam ou Mr. 

 Wethered's plan, and use the pure steam in a condensing engine, and the 

 mixed air and steam in a non-condensing engine. This practice may be 

 well for a long voj-age vessel, in which the freight-room occupied by fuel 

 is of buch value as to warrant the expense and complication of a condenser. 



The uses to which this method is most likely to be applied are for small 

 engines in buildings, and for steam rail-cars and carriages. The boilers 

 will be without tubes and very small, and safer than common boilers ; and 

 insurance premiums will not be much increased by them; and the consump- 

 tion of fuel can be economized or stopped at any instant. When the jets 

 of petroleum vapor are shut off, the generation of steam instantly ceases ; 

 and when the jets are throttled it is instantly diminished; and an automatic 

 safeguard may be made to operate on the throttle, so as to lessen the heat 

 as the steam pressure increases. 



As the advantages of this fuel, and this method of utilizing all the heat, 

 so as to use as little fuel as possible, and especially as little water as pos- 

 sible, are not all apparent, it may be well to indicate one of them. There 

 is now a new demand : underground railways are on the increase ; Mr. 

 Bazalgetttc, chief engineer of the English Board of Trade, reports that 258 

 new lines are already projected, their aggregate length to be 4n| miles, 

 and their estimated cost £70,000,000. These railways require engines that 

 use the best fuel and water, and make the least dust and sulphurous gas. 

 Now an ordinary locomotive wastes from 33 to 43 per cent of its fuel 

 through its chimney; that is, it pollutes the air with a hundred measures of 

 gas instead of 57 or 67 measures. And as to water, by superheating the 

 steam, and substituting air for it as far as may be without injuriously 

 heating the apparatus, it is probable that we may work with a third of the 

 water now used in locomotives. We can save a third of the gases, and 

 two-thirds of the vapor, that now pollute the air in tunnels. To meet this 

 new demand we have this new fuel — this essence of coal — which 1 hope is 

 to become cheap. 



