4G4 Analyses of Boohs. 



nious 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. It is remarkable, that in this country, the 

 practice is almost universally adopted ; but hitherto it has been 

 scarcely noticed in English books. The French and Americans, on 

 the contrary, have collected and published a great mass of informa- 

 tion, chiefly, of course, derived from practical sources in this coun- 

 try. Dr. Clark has supplied the void which we have noticed, con- 

 cisely — but distinctly. 



His paper investigates the subject under three heads. 1st. The 

 process of making iron as formerly practised. 2nd. Mr. Neilson's 

 alteration in that process. 3rd. The effect of that alteration. And, 

 4th. The cause of that effect. 



1. The original process consisted in introducing a charge of coke, 

 limestone, and mine, or burned ironstone, 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 

 blowing apparatus. The iron was thus separated from carbonic 

 acid, alumina, and silica ; and was allowed to run off at the bottom. 



2. 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 at a red heat. 



3. 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 SOD 3 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 

 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 sav- 

 ing of coal was greatly increased, insomuch that, about the begin- 

 ning 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 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 iron-works. The temperature of the 

 air under blast had now been raised so as to melt lead, and some- 

 times zinc, and therefore was above 600° Fahr., instead of being 

 300°, as in the year 1830. 



" During the first six months of the year 1833, when all these 

 changes had been fully brought into operation, one ton of cast-iron 

 was made by means of 2 tons S| cwt. of coal, which had not pre- 



