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 Thomas Clabk, 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 w^as allowed to run off at the bottom. 



Mr. 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 1| cwt. 

 of coal converted into coke. During the first six months of the fol- 

 lowing year, w'hile the air was heated to near 300° Fahr. : one ton 

 of cast-iron, required 5 tons 3| 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- 

 ino- thus was 2J tons of coal on a single ton of cast-iron. But dur- 

 ing that year, 1830, the air was heated no higher than 300° Fahr. 

 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 



