part 3.] Mallet: Recent Coal explorations in the Darjiling District. 
.147 
About 3| cwt. of coal in its natural state, i. e., in coarse powder and fragile lumps, 
was introduced into a retort, which was already at a red heat. The charge was kept at this 
temperature by means of an external furnace, for fire hours, and then drawn. The coal 
came out in powder just as it went in. It lost its volatile matter, of course, but did not 
cake in the slightest degree. 
Three and a half cwt. of coal, previously saturated with water, was treated in the same 
way for seventeen hours. The result was the same as in the last experiment. 
In a subsequent series of experiments I sought to determine, as far as can be done 
on a small scale, what proportion of pitch added to the coal was required to give the coke 
a sufficient degree of firmness. Two pounds of the coal powder, passed through a sieve, of 
6 holes to the inch linear, were intimately mixed with different proportions of coal-tar pitch 
(passed through a sieve of 20 holes to the inch linear), the mixture somewhat shaken down 
in the crucible, covered over with a, thick layer of sand and ihe crucible lid. and then heated 
for an hour and a half. When withdrawn, the crucible had been for some time at a full 
red heat, and the evolution of gas had ceased. The results were as follow :— 
Quality of coke. 
^ Coke hard and firm. 
{ Coke of good quality, 
but less firm than 
No. 1. 
... f Coke fairly good ; 
...1 somewhat tender. 
j Coke inferior; fragile. 
... r-Coke very inferior; 
... X easily crumbled. 
In a sixth experiment the coal was tightly rammed into the crucible without admixture 
of pitch. It coked to some extent, being about equal in that respect to No. 5. 
It apppears, then, that the Tindharia coal will not coke at all when heated in a loose 
state, but that it will coke, although in a very inferior way, when previously compressed. 
It is also to he remarked that the Tindharia coal contains tbe largest proportion of combusti¬ 
ble volatile matter (on the presence of which in sufficient quantity the coking mainly 
depends) of any Darjiling coal assayed, as shown in the following table.* 
Proportions. 
j C Coal 4 parts by weight 
<- Pitch 1 „ 
2 C Coal 8 parts by weight 
<• Pitch 1 „ 
3 C Coal 12 parts by weight 
<■ Pitch 1 „ 
4 j Coal ] 6 parts by wei ght 
t Pitch 1 „ „ 
6 C Coal 32 parts by weight 
<- Pitch 1 „ 
Fixed carbon. 
Volatile matter. 
Ash. 
Rakt naddi, 5'6" seam 
79 3 
7*6 
131 
Cart road, 6'0" seam 
741 
9-0 
16-9 
Chirankhola naddi, 7' 0" seam... 
69-6 
5*2 
252 
Tindharia ravine, IP 0" seam ... 
66-3 
12-4 
21'3 
Ravine south of Pankabari, O' 9" seam ... ... 
64-0 
11*8 
24-2 
Average 
70-66 
9-20 
20-14 
* Memoirs, G. S. I., Vol. XI, p. 54. 
