154 
Transactions of the Society. 
few years, during which time hundreds of analyses have been made, 
and I can say that this similarity occurs fairly frequently. From 
considerations already stated, it is obvious that this must be the 
case. It is, in fact, the converse of similar coals having different 
analyses. 
These groupings are useful, and would be more so, were it not 
for the fact that the sharp distinctions of such classifications are 
not met with. In nature there is a gradual transition from one 
type to another. It is because of constantly recurring difficulties 
of this nature that the microscope was first brought into use in 
the hope that a better understanding in fuel selection might be 
reached. 
The micro-structure was first applied to the selection of coal 
for a large twenty-two unit recovery gas plant, gasifying some 
2,500 tons of coal per week, with the production of some 
350,000,000 cubic feet of gas. In this plant, worked on the Mond 
principle, superheated steam and air are blown through a deep fuel 
bed. Excess of steam is used, and so the temperature of the pro- 
ducer is low, the out-going gases not being above 500° C. The 
coal is therefore subjected to a primary comparatively low-tem- 
perature distillation, and much of the “resinic” portion, which causes 
coking, is distilled off. It is possible in this type of plant to 
gasify practically any class of coal. A strongly coking slack, 
however, would necessitate a very slow rate of gasification and a 
large excess of steam, probably as much as two and a half tons per 
ton of coal, so that it would not be a commercial proposition to use 
such a coal. In practice as high a rate of gasification with as low 
a steam consumption as possible consistent with good gas and a 
high ammonia yield is aimed for. The producer is then running 
economically. Careful selection of fuel goes a long way towards 
obtaining efficiency and the satisfactory running of such a plant. 
The coals used are between the coking and non-coking types, and 
are consequently difficult to select ordinarily. Two coals may look 
alike, and give practically the same results in the laboratory, but 
when put into use one of them may be quite satisfactory and the 
other unsatisfactory. 1 give below the analyses of two such 
coals ; one was used successfully in the recovery plant already 
mentioned, but the other could not be used economically : — 
Volatiles 
Fixed 
Carbon 
Total 
Carbon 
Hydrogen 
Oxygen 
( 
Nitrogen 
Calorific 
Value, 
B. Th. Units 
per lb. 
No. 1 .. .. 
“ pTc. 
38-2 
p.c. 
.61-8 
p.c. 
82-2 
p.c. 
5-83 
p.c. 
11-21 
p.c. 
0-76 
14,750 
No. 2 .. .. 
38-1 
61-9 
81-2 
5-60 
11-93 
1-27 
14,750 
