Iron, 
109 
This great weight thus lost is chiefly carried off in 
smoke. If a vessel is placed, filled with cold water, in 
the midst of one of these massy columns of vapour, before 
the fire has penetrated to the surface of the heap, a consi- 
derable quantity of tar will condense upon its external sur- 
face : this will continue to increase till such time as the 
water assumes the temperature of the smoke. At many 
iron works from 300 to 1000 tons of coals are thus weekly 
reduced to cinder. What a prodigious quantity of bitw 
minous vapour, surcharged with tar, ammoniac and oil, 
must for the present be lost ! !f (Mushet.) 
Pitcoal contains always an empyreumatic oil, moisture, 
earburetted hydrogen or coal gas, and ashes ; and fi§~ 
quently sulphur. The quantity of oil, moisture, and gas 
can be ascertained by distillation ; the quantity of incom- 
bustible matter or ashes, by burning the coal in contact 
with air ; the quantity of saline matter in the ashes by 
lixiviation, filtration and evaporation. The quantity of 
combustible matter in coal, can be found out by reducing 
100 grains into powder, also 100 grains of pure salt petre 
into powder : throw by small quantities (a grain or two) 
at a time, first the coal, and immediately after the salt pe- 
tre into a red hot crucible. The salt petre will deflagrate 
while there is any inflammable matter to decompose it ; 
when the deflagration ceases, the quantity of inflammable 
matter may be determined by the quantity of salt petre 
employed. Lampblack may be used as a standard, for it 
contains of ashes not more than one part in about 250. 
The ashes in coaks vary from 3 to 45 per cent. Hence 
it is manifest that the coal meant to be employed ought to 
be analysed before they are used ; to ascertain 1st. what 
quantity of coak can be obtained from a certain weight of 
coal : 21y. what quantity of ashes or incombustible mat- 
t This is the basis of Lord Dundonald’s patent for collecting 
coal tar. Becher as early as the reign of Ch. 1st had suggested 
the propriety of saying these products. T. C, 
