Review of Prof. Johnson’s Report on American Coals. 329 
‘Table exhibiting the per centage of volatile matter in the 
combustible part of several classes of coals, and the evaporative 
power of the same part, with the proportion which was expend- 
ed respectively on the boiler and on the gases passing to the 
chimney. 
oes ‘ nto Saeed is CR Tem ae 
=S|/S$e |Incombustible)?&<s j|Evaporative powerof1l| °8& 
ean S15 matter in 100}%5~ .| partby weightof coal, | = 3% 
2 Ener y weig ees 
a 5leS of coal. pay a — = gus 
p=] 0° 0) : ew - 509 
3 . 92l5 2 Poss no oe ran Bos 
| ~ new = =o 
a SRS : Ae WEAN Sa Fd N= 
s (e 3 we Q2an2 @ ; rea os 
cs asia PS SeESe! oo ee | 8h | bot 
© mele s | esao] 32 |soe I S25 
: Eee israel a Bie.0 s a e2 | sFs 
Net Kind of coal. Melo Ray) os Reiesace oS os a3 ead 
ve) a°0\|3 WE Sy wo ee te 62 ct OPS 
S celzss| 3 ssgo] = |S | > | aes 
i) on Eas S 3 Tae Prey He : oF Seo 4 
5 cata Kool e [S28] BS | ts8| ES | Osss 
Kee |S > cS Ss o.5 o as 5 
E Ssl/see| 2 | B |ES23) 3] 8a3a| 22 | goes 
|e Salssz| @ | 2 |Zsea| &s | ¥e5| 22 | Sess 
SLE TEE WR ORR ey (| ed = a | a ad Ace oe 
1.Pennsylvania an- 
5 = 
thracites, ..... | 5 | 3-84) 7-37] 1:34 12 9-508] 1-996] 17-4 | 12:59 
’ i - 
2. Natural coke of Vir- 
TILE A a ee ee 1 |13-75)18-46) 2-81 5 8-662) 1-517} 15-2 | 12:92 
? 
3.|Maryland free burn- 
ing bitumin’us coals,| 5 |15-80) 9-94) 1-25 | 12 | 9-894] 1-738) 15-0 | 13-09 
4.\Pennsylvania free 
burning bituminous 
CEs CE 4 |17-01|13-35) 0-82 9 | 9-620] 1-470) 13:3 | 12-92 
5.\Coke of Virginia 
(Midlothian) coal, | 1 |17-15/16-54) 2-81 1 | 8-632} 1-193) 12-2 | 12-10 
6.|Foreign bituminous,} 3 |31-75| 8-14) 2-16 8 | 8-252) 1-756} 17-6 | 11-18 
7.|Virginia bituminous,| 5 |36-63)10-74| 1-64 | 12 | 8-482) 1-746) 17-1 | 11-51 
S.\Cannel,.-. 9... : 39:37| 7:61] 2:80 5 | 7-219] 1-501) 17-2 | 9-73 
) 
If there be one peculiarity more striking than another in Prof. 
Johnson’s labors it is their useful tendency. After invoking the 
most profound principles of natural and chemical philosophy for 
the investigations, the result is depicted in such a manner as to 
admit of application by the merest practical inquirer. It may 
perhaps, by persons who have not duly reflected on the matter, 
be charged against this, as we believe it has been against some 
reports on other subjects of a somewhat similar character, that he 
indulges too much in detail in the publication of his facts. This 
we think an unfounded charge, tending only to encourage a course 
of loose investigations, injurious to the rigid laws of truth. No 
man should undertake the investigation of any important subject 
without being thoroughly prepared in every respect ; but however 
conscious he may be of having made that preparation, he is bound 
to convince the rest of the scientific world of the fact before he 
can demand confidence in his deductions. Professor Johnson 
has, we think, very properly pursued this course. He presents 
a full description of the apparatus, of the subjects operated upon, 
