168 Bibliography. 
_'The existence; in bituminous coals, of variable proportions of nearly 
peal ‘charcoal, is referred to as furnishing evidence of a want of homo- 
geneousness in this class of bodies. A diversity of results may conse- 
quently be expected when ultimate analysis is resorted to for the pur- 
pose of establishing a theory of trunsmutations, or of demonstrating 
what changes have occurred in bringing vegetable substances into the 
state of bituminous coal.. Those who assume woody fibre as the sole 
basis from which it has been derived, do not pretend to prove that the 
other proximate constituents of vegetables, the resinous matter, for 
example, and the oily component of seeds, have been wholly removed. 
Hence analyses of coal applied to this purpose may not always lead to 
unobjectionable inferences. But as means of determining the calorific 
power of combustible bodies, they may, especially when performed on 
average samples, or multiple specimens, afford information both inter- 
esting to science and valuable to the arts 
The relation between the calorific power calculated from analysis, 
and the practical heating power decided by evaporating water, is deter- 
mined for six different varieties of bituminous coals, varying considera- 
bly in their composition. 
Drawings of the apparatus employed for both these purposes were 
exhibited, and their action explained. ‘That used in evaporation is so 
constructed as to determine the proportion of heat expended on the pro- 
ducts of combustion, as well as that employed to generate steam. 
- In applying calculations to the ultimate analyses of coals, as well as 
to the products of combustion, the atomic weight of carbon is assumed 
to be six, of oxygen eight, and of nitrogen fourteen times that of hydro- 
gen, in accordance with the recent determinations of Dumas. In cal- 
culating evaporative powers, the latent heat of steam is taken at 1030° 
Fahr., according to Prof. J.’s own investigations of that subject. 
In ascertaining the relative efficiencies and values of combustible 
bodies, with a view to economical applications, it is necessary to 
them either as found in nature, or as supplied to commerce, including, 
of course, whatever impurities they may chance to-contain. But in 
order to deduce general relations between bodies differently constituted, 
in regard particularly to their combustible constituents, the comparison 
must be made after deducting the waste, or incombustible matter found 
in the crude state of the fuel. This principle is applied both to the ulti- 
mate analysis and to the evaporative experiments; and hence in the 
following table both the calculated evaporative power of the carbon con- 
stituent, (column 15,) and the total evaporative efficiency by experiment, 
(column 18,) are referred to, and calculated for, one me by Mig of 
co 
