376 Dr Clark on the Application of the Hot Blast 



through cast-iron vessels, kept at a red heat. In the specifica- 

 tion of the patent, Mr Neilson 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 Neilson'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^ cwt. 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 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 8 cwt. The 

 nett saving thus was 2^ 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 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. 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. 



