28 Transactions. — Miscellaneous. 



dynamic force required to work the blast than could be obtained from the 

 heat which disappears in a chimney. It has been calculated that lib. of coals 

 employed to raise steam will do the work of 500Ibs. expended in rarefying air, 

 such air being discharged through a chimney 35 ft. high. 



After proving that there is no real loss of power by the using of the blast, 

 we will proceed to consider how it now opens up a way to utilize a large 

 portion of the waste heat after it leaves either the tubes of the steam boiler or 

 the super-heater and hot-air jackets of the engine. It has been calculated that 

 IB), of coal should vaporize 14Ibs. of water from 212° F., whereas about 

 lOBbs. only are evaporated in Cornish boilers ; this is ascribed mainly to the 

 large amount of heat which passes up the chimney. Taking the temperature 

 of the contents of the boiler to be 300° F., that of the gases leaving the tubes 

 is considerably more than this, being in locomotives as high as 600° F., or 

 about one-fourth of the total heat of the furnace. Now, in common boilers, if 

 we cool this heated air in the chimney by attempting to utilize this heat, we 

 at once impair the draught, but the use of the blast allows us to exhaust all 

 the heat we can the moment that it leaves the boiler. The way that I 

 propose to utilize this heat, is to cause it to raise the temperatvire of all the 

 large volume of air which is required for the combustion of the fuel in the 

 furnace. The apparatus — which we may call, for convenience, a thermo- 

 convector — corresponds to the ordinary smoke-box somewhat enlarged, and 

 divided horizontally into a series of narrow compartments, the connections of 

 which alternate as in the figure {Plate V.), so that the discharged products of 

 combustion pass along those spaces marked bb in the direction of the arrows, 

 while the current of fresh air is conveyed in the opposite direction within the 

 other spaces aa. These latter spaces also communicate with one another by 

 broad lateral arches not shown in the figure. We have, now, virtually two 

 broad and narrow tubes. The walls or partitions of these tubes should be of 

 material specially selected, either for its transmitting power, or else for its 

 conducting power, such as a metal with its surfaces so prepared as to facilitate 

 the absorption and radiation of heat, as, for instance, thin unpolished sheet- 

 iron, which is usually covered with oxide of iron, which oxide Tyndall has 

 shown to be almost as efiective an absorber and radiator for obscure heat as 

 lampblack, which is, as we know, capable of absorbing nearly all the heat from 

 any source, luminous or obscure. 



Experiment No. 2. — A common thermometer at 60° was placed 1 in. 

 distant from a heated mass of iron, forming a constant source of obscure 

 radiant heat ; in seven minutes it rose to 118°. A lai'ge piece of the oxidized 

 iron was then interposed midway between, and the thermometer (previously 

 cooled to 60°) was returned, when in seven minutes it rose to 104°. The 

 thermometer was then removed to a place where the temperature was 60° j 



