28 T'ransactions.— Miscellaneous. 
dynamie force required to work the blast than could be obtained from the 
heat which disappears in a chimney. It has been calculated that 10. of coals 
employed to raise steam will do the work of 500lbs. 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 
lib. of coal should vaporize l4lbs. of water from 212? F. whereas about 
101bs. 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. "Тһе way that I 
propose to utilize this heat, is to cause it to raise the temperature 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 вв 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 effective 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 large 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? ; 
