22 British Association for the Advancement of Science. 



In the poorest specimens of iron-stone, the carbonate of iron, 

 amounts to only 29 per cent., but such specimens are rejected by 

 the iron-masters. The ore is roasted to drive off the carbonic 

 acid ,• this, at an average, reduces the weight about 31 per cent. ; 

 it is then mixed with hmestone and coal, and smelted. 



When the Clyde iron-works were established, above forty 

 years ago, ten tons of coal were requisite to produce one ton of 

 iron. This coal was previously coked, by which rather more 

 than half its weight was driven off under the form of gas, &c. 

 By various improvements, the quantity of coal requisite was di- 

 minished from ten tons to seven tons thirteen cwt., and the quan- 

 tity of limestone requisite for smelting one ton of iron was ten 

 and a half cwt. When hot air (or air heated to above 607°,) 

 was blown into the furnace instead of cold air, it was found that 

 coal could be used without being coked, and the quantity re- 

 quisite to smelt a ton of iron was reduced to two tons nineteen 

 cwt. ; the lime was reduced to seven cwt., and the produce of 

 iron in a given time from a furnace was more than doubled. The 

 reason of this superiority of hot air over cold seems to be, that 

 when the hot air enters the furnace it is immediately united to 

 the coal, and is all consumed ; whereas, the cold air partly passes 

 up through the materials, and produces, as it ascends, a scattered 

 and useless combustion. Hence, when hot air is introduced, the 

 heat at the point of combustion is greater than when cold air is 

 used, and hence, the smaller quantity of limestone requisite, and 

 the greater produce in iron in a given time. The specific gravity 

 of cold blast iron is lower than that of hot blast, the average of 

 the former being 6.7034, and that of the latter 7.0623. 



The following table shows the composition of six specimens of 

 cold blast iron from different localities : — 



