Review of Prof. Johnson’s Report on American Coals. 323 
mining. analytically the same question. The facts resulting 
from these experiments are recorded in the two last columns of 
these synoptical tables. They are collected in a tabulated form 
in other parts of the Report, and show unfortunately that im- 
plicit confidence cannot be placed in this process. 
The following extract indicates a much more plausible means 
of determining this question by analysis than that of Berthier or 
others, and is in every respect worthy the attention of experi- 
menters. 
“ Heating powers derived from ultimate analyses of coals. 
“The comparisons which in the course of this Report I have been 
enabled to make between the practical steam-generating power of the 
combustible matter of several kinds of coal, and that derived from their 
ultimate analysis, and thence calculated from the quantity of carbon 
which they severally contain, enable me to offer at present the following 
cases illustrative of this subject. Should I be hereafter empowered to 
complete the series of researches so as to obtain ultimate analyses of all 
the coals which have been tested by evaporation, a mass of evidence 
would be accumulated, which might, in all probability, set the question 
finally at rest. 
Evaporative power Power calculated 
of 1 of combus- from carbon as- 
tible matter by certained by ul- 
Steaming appa- timate analysis. 
ratus. 
Cambria county, Pennsylvania, - - 11:550 11:522 
Midlothian, (new shaft,) Virginia, - - 11:460 11-731 
Newcastle, England, - - - 10-898 10:545 
Clover Hill, Virginia, = - - - 10°537 10-445 
Scotch, - - - - - 10:206 10°393 
Indiana (Cannelton), . - -  9°557 9-509 
Mean, - . - 10°701 10691 © 
*¢ Notwithstanding this very remarkable approximation (or, I may say, 
identity) of the two numbers in these six instances, I would not be under- 
stood as announcing the universality of the law that the weight of car- 
bon alone in coal is the only available element of its heating power. 
I only bring forward this number of facts, all tending in the same direc- 
tion, all in harmony with each other and with preéxisting experience, 
so far as any tolerable degree of exactness has been given to researches 
in relation to this subject. 
“In the works of European chemists, the calculated ‘ heating power’ 
of coals is ascertained by the numbers for hydrogen and carbon deter- 
