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. 
Ee es Rasomnbustibe $¢£ (Evaporative power of 1{ © g2 
22/55 n 100) € 5... | Part by weightof coal, | 5 3% 
' g8is3 of coal. seo- Sl Sel ee Tel eee 
ui ss|Qo2 Ua| #28 |)a8 su} eo8 
a esis | a goes] £3) &8 | 32 | oes 
. asics | = gezs| se /S3 | eo | ees 
= Kind of coal. QH Sb] os fes6°| 34 Fre ee g 3 
4 aslo 23] © sage| &¢ | 6s | o> | ors 
S Gelso] ; S38 gsciig BS. be 
be § vol HQ} 8S o Went 8 33 108 Ere. 
beg eS 5 (228! BB i 2as| ES | Pass 
: sslege| 8) & (ESe3] SS | S03] 28 | ges) 
3 Cee te ° 2s as R22] 29 Sets 
rs sio< zis Z2&se <c gee pd mos? 
Pennsylvania an- pele ‘ I sks 
thra 5 | 3-84! 7-37; 1-34 | 12 | 9-508) 1-996) 17-4 | 12:59 
2. Natural ara ‘of Vir- 
SeNS eae 1 (13-75/18-46; 2-81 5 | 8-662| 1-517) 15-2 | 12-92 
3 Mi sxylen d free burn- 
F ing bitumin’us coals,) 5 |15-80) 9-94) 1-25 |. 12 | 9-894) 1-738) 15-0 | 13-09 
ennsylvani ree 
ban eee ituminous 
oe eae 4 |17-01}13-35} 0-82 9 | 9-620) 1-470) 13:3 | 12-92 
Virginia 
a (Midlothian) coal, | 1 |17-15/16-54) 2-81 | 1. | 8-632} 1-193] 12:2 | 12-10 | 
Foreign bitaminous,| 3 |31-75} 8-14) 2-16 8 | 8-252] 1-756) 1 tad 11-18 
5° |36-63}10-74| 1-64 | 12 | 8-482) 1-746) 17-1 | 11-51 
Z Niegnia bituminous 
ey 2 |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, 
