376 Dr Criark on the Application of the Hot Blast 
through cast-iron vessels, kept at a red heat. In the specifica- 
tion of the patent, Mr Nrrxson states, that no particular form of 
heating-apparatus is essential to obtaining the beneficial effect of 
his invention ; and, out of many forms that have been tried, ex- 
perience does not seem to have yet decided which is best. At 
Clyde Iron-Works, the most beneficial of the results that I shall 
have occasion to state, were obtained by the obvious expedient 
of keeping red-hot the cast-iron cylindrical-pipes conveying the 
air from the blowing apparatus to the furnace. 
III. Such being the simple nature of Mr Neiuson’s inven- 
tion, I now proceed to state the effect of its application. 
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 ewt. of coal, converted into coke. During the first six months 
of the following year, while the air was heated to near 300° Fahr., 
one ton of cast-iron required 5 tons 34 ewt. 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 8 cwt. ‘The 
nett saving thus was 24 tons of coal on a single ton of cast-iron. 
But during that year, 1830, the air was heated no higher than 300° 
Fahr. The great success, however, of those trials, encouraged 
Mr Dunvor, 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 Drxoy, proprietor of Calder Iron- 
Works, felt himself encouraged to attempt the substitution of 
raw coal for the coke before in use. Proceeding on the ascer- 
tained advantages of the hot blast, the attempt was entirely suc- 
cessful ; and, since that period, the use of raw coal has extended 
so far as to be adopted in the majority of the Scotch iron-works. 
