70 
POPULAR SCIENCE REVIEW. 
The uninitiated reader must be informed that the cinders 
used are those which are produced in the processes of refining 
and puddling. They are often very beautifully crystallized, are 
rich in iron, but contain variable quantities of silicon, alumina, 
manganese, sulphur, phosphorus — in fact, all the impurities of 
the iron which are not dissipated by heat. 
The difference between the “cold-blast” and “hot-blast” iron, 
just now referred to, is produced by a contrivance for heating 
the air before it is urs'ed into the blast-furnace. The intro- 
o 
duction of hot, in the place of cold air, in iron manufacture, was 
effected in 1827, by Mr. Janies Beaumont Neil son, of Glasgow. 
It will be evident, upon consideration, that a fire urged with ah' 
heated to 572° Fahrenheit's scale, must be more intense than a 
fire imged by air at the ordinary atmospheric temperature. The 
result, in practice, has been, that whereas formerly, by the cold 
blast, to produce one ton of pig-iron, 8 tons 1 cwt. of coal, con- 
verted into coke, were required ; now a ton of iron can be made 
from the same ore with 2 tons 6 cwt. of coal. 
It was contended by many persons, on the introduction of 
the system of smelting iron by the hot blast, that, although the 
process might enable the ironmaster to produce a larger quantity 
of metal economically, yet, in many of the qualities most desir- 
able, the hot-blast iron was deficient. Long-, and often angry, 
discussions ensued, yet cold-blast furnaces went gradually out 
of use, and the liot-blast apparatus was generally applied. The 
matter was, at length, submitted to experimental examination 
at the request of the British Association, Mr. William Fairbairn 
and Mr. Eaton Hodgkinson having charge of the inquiry. 
The points to be determined were — 1 . Direct tensile strength ; 
2. Compressive strength; 8. Transverse strength; 4. Power to 
resist impact ; 5. Modulus of elasticity, or stiffness ; and 6. Spe- 
cific gravity. The report furnished, shows, conclusively that the 
sum of the advantages are in favour of hot-blast iron. The 
mean ratio of strength in cold-blast iron being represented by 
1,000 ; hot- blast was 1,024'8; and the mean ratio of power, to 
sustain impact,* being in cold-blast as 1,000, it was 1 ,22(ro in 
hot-blast iron. One cause has been indicated, which, no doubt, 
leads, in some cases, to an inferiority. Heated air exerts a 
greater reductive power than cold air; consequently, in some 
furnaces blown with hot ah’, refractory iron ores, which could 
not otherwise have been employed, have been introduced into 
the furnace. They generally contain many impurities, and, 
consequently, inferior iron has been made. The advantages of 
hot over cold air, in iron-making, are many; and, 'without it, 
the anthracite coal of South Wales and of the United States 
could never have been employed ; whereas this fuel is now be- 
coming every year more valuable. 
* The power to resist blows. 
