324 Review of Prof. Johnson’s Report on American Coals. 
mined by Despretz and Dulong. In Peclet’s work, Pennsylvania an- 
thracite has assigned to it a heating power represented by 7211° centi- 
grade, or 12980° Fahr.; Newcastle coal 7866° cent., or 14159° Fahr. 
Now, in practice, 8 kinds of Pennsylvania anthracite gave a mean 
evaporative power of 9°56, and Newcastle coal gave 8-66.”—p. 586. 
Evincing his habitual care in expressing an opinion, Professor 
J. hesitates to assert at once that the “carbon alone in the coal is 
the only available element of its heating power.” ‘This certainly 
indicates a degree of prudence worthy of imitation, and it is ear- 
nestly to be hoped that he may be empowered “to complete the 
series of researches” on this as well as other subjects connected 
with this important material, coal. For it must be evident that 
the establishment of this law as unquestionable, is in the highest 
degree interesting. No other analytic process has yet been found 
satisfactory, and experiments on a practical scale require too much 
time and money to make them as these have been made under 
the direction of Prof. Johnson, to allow them to be undertaken on 
private account. 
With the view of showing the reader the manner in which 
Prof. Johnson treats that part of the subject which relates to the 
analysis of coals, we introduce the following extract, relating to 
the second specimen of the coals in the above table. 
“ Bituminous screened coal vom the mines of the Midlothian Coal Com- 
pany’s ‘new shaft, Virginia. 
“This sample was received and used in the lump form, which it re- 
tained with considerable force. Its fractures present a shining black 
resinous, scarcely conchoidal aspect, with distinct lines of the lamine 
of deposition. It is mostly free from incrustations of earthy matter, but 
occasionally presents some shaly or pyritous portions. 
“The powder is of a light brown, indicating a pretty high degree of 
bituminousness ; and its streak is nearly of the same color. 
“The specific gravity of two specimens (a and }) was found to be 
1:3495 and 1:3006, respectively ; the mean of which affords by calcu- 
lation the weight of one cubic foot of the coal in the solid state = 82°43 
pounds, 
“ By thirty one trials in the charge-box, the mean weight per cubic 
foot was ascertained to be 47:899 pounds—the lowest result being 42°79, 
and the highest 54:125. Hence the actual is to the calculated weight 
as 0°5811 to 1. 
, ‘“‘ The space required for the stowage of one gross ton is 46° 769 cubic 
eet. 
