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 limestone 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 ewt., and the quan- 
tity of limestone requisite for smelting one ton of iron was ten 
and a half ewt. 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 
ewt.; 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 eegpatinn of six specimens of 
cold blast iron from different localities 
Muirkirk. | Do. | Do. | Pyrites, | Carron. | Ciyde, |_Mean._ | 
Iron, . . . | 90.98 (90.29 91.3889.442/94.010 90.824 91.154 
Copper, . SOW co. Cee eek eee 
7.14 | 2.00. . | 0.626, 2.458) 2.037 
Pe ES ee eee 8 
4 Bois. 02 
eee ee ek Sots PSY Seo eg 
