180 Miscellanies. 
comparative variations of the Barometer at Montreal, Albany, 
Flushing, L. I., Middletown, Conn., and Cincinnati, Ohio. 
6. On the Application of the Hot Blast, in the Manufacture of 
Cast-Iron, by Tuomas Cuark, M. D., &c. (Trans. Royal Soc. 
Edin. xiii.) —The substitution of hot for cold air, in the blast furnaces 
of the iron manufactory, is an improvement which suggested itself to 
the ingenious Mr. Neilson, of Glasgow, at a most seasonable period; 
when the great demand for iron in the construction. of railways is 
daily, nay, hourly, increasing. 
The original process consisted in introducing a charge of coke, 
limestone, and mine, or burned iron stone, into the top of the iron 
. furnace ; and this mixture was excited to combustion by air forcibly 
driven in, at about forty feet from the top, through pipes from a blow- 
ing apparatus. The iron was thus separated from carbonic acid, 
alumina, and silica; and was allowed to run off at the bottom. 
r. Neilson improved this process, by substituting for air at the 
temperature of the atmosphere, air heated up to 300° and upwards. 
This is effected by passing the air through the cast-iron pipes, 
through which the former passed, kept in a red heat. 
During the first six months of the year 1829, when all the cast- 
iron in Clyde iron-works, was made by means of the cold blast, a 
single ton of cast-iron required for fuel to reduce it, 8 tons 14 cwt. 
of coal converted into coke. During the first six months of the fol- 
lowing year, while the air was heated to near 300° Fahr.: one ton 
of cast-iron, required 5 tons 34 cwt. of coal, converted into coke. 
The saving amounts to 2 tons 18 cwt. on the making of one ton 
of cast-iron ; but from that saving comes to be deducted the coals 
used in heating the air, which were nearly eight cwt. The nett sav- 
ing thus was 24 tons of coal on a single ton of cast-iron, But dur- 
ing that year, 1830, the air was heated no higher than 300° Fabr. 
The great success, however, of these trials, encouraged Mr. Dunlop, 
and other iron masters, to try the effect of a still higher temperature. 
Nor were their expectations disappointed. The saving of coal was 
greatly increased, insomuch that about the beginning of 1831, Mr. 
Dixon, proprietor of Calder iron-works, felt himself encouraged to 
attempt the substitution of raw coal for the coke before in use. Pro- 
ceeding on the ascertained advantages of the hot blast, the attempt 
was entirely successful: and since that period, the use of raw coal 
has extended so far as to be adopted in the majority of the Scotch 
