FRANCIS — -ON COAL D1POSITS. 
129 
been consulted, but from its frequent contiguous occurrence 
with asphaltic deposits in Trinidad it is likely to prove a 
common impurity. 
It must further be pointed out that the unusual brittleness 
of the mineral is probably caused by this ingredient, for it is 
stated that sulphur added in the proportion of about 1 per 
cent, to asphaltic mastic makes it very brittle (Ure's Diet. 
6th edit., i., 238). If sulphur thus modifies the cohesion of 
asphalt, the determination of its presence or absence in a 
sample will become a matter of importance. 
Although the Williamsville mineral would form but an 
inefficient substitute for coal as fuel, it might be advantage- 
ously employed for the manufacture of illuminating gas. 
The gas obtained from it appears to be of excellent quality, 
as a rough experiment will prove. Moreover, the yield is 
considerable, being about 10,000 cubic feet per ton, — a quan- 
tity unsurpassed by many of the best gas coals of Great 
Britain. The following table by Hughes will show that this 
statement is not exaggerated. 
TABLE I. 
Quantity of Illuminating Gas yielded by British Coals. 
NAME OF COAL. 
Cubic feet per ton. 
Newcastle, aver. 10 samp 
11336 
Wigan Cannel... 
9500 
Scotch Parrot. 
9500 
Lesmahago Cannel 
11312 
Ince Hall Cannel 
11400 
Boghead Cannel 
15000 
Derbyshire 
9400 
Derbyshire, soft, 3 samp 
7166 
Neath, South Wales ... 
11200 
West Bromwich, (Parliamentary return, 
Birming- 
ham Gas Co.) 
6500 
Staffordshire, aver. 4 samp 
10467 
