892 On the relative Proportions of Coals and 
jutt epitome of what takes place in the philofophy of exten- 
five manufaétories. The following table exhibits the quan- 
tity of carbon which may be ufed upon an average, with the 
relative quantity of carbonic acid formed, and air ufed :— 
In the manufacture of 1]b. — 1 ton of iron, 
The pure carbon requifite is 2°49 — 5585°44]b. 
Carbonic acid formed - 81°86 — 18336640 cub. feet 
Oxygen gasufed - - 75°89 — 169993°60 cub. feet 
Atmofpheric air employed 281°00 — 629440°00 cub. feet. 
From the foregoing particulars upon coal may be learned 
how much is dependent upon the native conftruétion of coal 
and its conftituent parts; I fhall next advert to the effects 
produced by its improper preparation. 
When coals intended for the blaft-furnace are faficiently 
charred, they ought, in point of colour, to be of a filver grey; 
their fracture will appear lamellated and porous if {plint-coals 
have been ufed; fofter coals form themfelves into branches 
ilightly curved, and, when properly prepared, are always very 
porous. I have frequently found that the better the cokes 
were charred, the more water they will abforb. Coals half 
burnt do not take up half fo much water, becaufe their frac- 
ture continues in part to be fmooth and lefs porous than 
when thoroughly burnt. 
When half-prepared cokes are introduced into the furnace, 
the metal formerly carbonated will lofe its grey fracture, and 
approach to the quality of oxygenated iron. Their prefence 
is eafily deteCted by the unufnal quantity of thick vapour 
arifing along with the flame, Befides, the water and fulphur, 
which raw coals introduce into the furnace, and which always 
impair the quantity of carbon by the various folutions ef- _ 
fected by the prefence of oxygen, hydrogen, &c. the fitnefs 
of the coal for combuftion, and the fupport of the ore, is 
much diminifhed by this fecond courfe of ignition. and dif- 
engagement of bitumen. The preflure of the incumbent ores 
alfo fraéture, and reduce the cokes into fmall pieces, which 
produce a confiderable portion of coke-duft; this is partly 
carried to the top of the furnace before the blaft: fometimes 
below it appears in immenfe quantities, ignited to whitenefs, 
and liquid as fand, Coal thus detached from the mafs, ex- 
ays pofed 
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