+ 
86 W. P. Trowbridge—LKfficiency of Steam Boilers. 
law of change of temperature, or of transfer of heat, might then 
be ascertained for the flues and for the furnace separately. 
If the laws of Dulong and Petit be true for high temperatures, 
it is apparent that the influence of the furnace at high tem- 
peratures must preponderate. Under any circumstances, it 
seems impossible to find a scientific solution of the important 
problem of efficiency of boilers in the generation and transfer 
of heat, until these questions are solved. 
e laws of Dulong and Petit have not been verified for high 
temperatures. At very low temperatures the quantity of heat 
transferred by contact of a gas and by radiation, agcording to 
these laws, will be nearly identical, and the higher the tem- 
perature the greater becomes the difference in the effects. 
Common observation shows that to heat or cool a body 
rapidly by contact of a gas, the gas must be supplied and 
removed rapidly. It seems improbable, therefore, that there 
can be any general expression for the quantity of heat trans- 
ferred in this manner which does not involve this idea in somé 
other way than by the constants which have been adopted 
The mode of determining the initial temperatures of the fur- 
nace and gaseous products of combustion generally employed, 
up to the present time, has been to assume, from the partial ex- 
periments of Péclet and others, that half the heat of combustion 
is usually imparted to the gases, while half passes off as radiant 
heat, and then to estimate the temperatures on the further 
assumption that a definite known amount of air passes through 
the furnace for each pound of coal burned. From the nature 
and phenomena of combustion it can hardly be supposed that 
any such law as that assumed by Péclet can be universally true. 
The temperature of the residue of the solid combustible must 
depend on the special circumstances of combustion in each 
case, and especially on the law of radiation, at different tem- 
peratures. 
If it were possible to observe accurately the temperatures of 
initial temperatures, analysis. A e mode of inves- 
tigation herein suggested is offered as one which apparently 
theory of heat, are questions which such investigation may — 
help to solve. . 
