Iron and Steel in the Construction of Ships and Bridges. 259 



former times, imparted to the product qualities which it now 

 rarely possesses, but set very narrow limits to its production. 

 When the value of that metal began to be properly understood, 

 and the demand for it, in consequence, became considerable, 

 the rapid destruction of the forests which ensued had so in- 

 jurious an effect upon its manufacture, that the quantity of 

 iron made in this country fell to one-fourth of what it had 

 previously been. 



A mode of escape from this embarrassment, also, was soon 

 devised. It might be supposed that mineral coal, in the form 

 of coke, would be universally employed as a substitute for 

 wood, when its applicability to the purpose was once ascer- 

 tained. Such, however, was not the case. The use of coke is 

 attended with difficulties which were not suddenly overcome — 

 which were not, indeed, entirely surmounted before the .power 

 of the blowing-machine was augmented by the invention of 

 the steam engine : until then blowing had been effected by 

 that clumsy and imperfect contrivance, the bellows. When 

 steam power came into use, the bellows gave place to the 

 cylinder and piston, the capabilities of which were, practically, 

 unlimited. 



The progress of the iron manufacture towards perfection, 

 once begun, was very rapid. It was again almost revolu- 

 tionised by the introduction of the hot blast. Though the 

 saving effected by this may, at least plausibly, be disputed, 

 there can be no doubt that it is accompanied by peculiar advan- 

 tages. Thus it renders possible the employment of coal, and 

 even anthracite, and it enables us to utihze inferior ores. The 

 adoptiou of coal instead of coke leads to an immense saving*, 

 on account of the gases, which are the most valuable portions 

 of the fuel, and which formerly were wasted, being economized. 



There are, it is true, certain serious objections to the use of 

 coal in the smelting of iron. Thus, the sulphur it usually 

 contains, and from which even coke is not free, causes the iron 

 made with it to be red short — that is, to have the very objec- 

 tionable property of being brittle under the hammer at a red 

 heat. So little as 0.03375 sulphur destroys the property of 

 welding, and a still smaller amount of it renders the metal 

 utterly unsuitable for armour plates. The phosphorus, which 

 also is likely to be present in coal, causes the iron to be crys- 

 tallized — that is, renders it cold sliort, or brittle when cold. It 

 is worthy of observation, that phosphorus, to a certain extent, 

 counteracts the effect of sulphur ; it sets free carbon, which 

 combines with and removes the sulphur. It is possible, how- 

 ever, to get rid of all these mischievous ingredients : but the hot 

 blast cannot yet be entirely depended on for the production 

 of superior iron. 



