374 Dr Clark on the Application of the Hot Blast 



Fiist, To the process of making iron, as formerly practised, 

 Second, To Mr Neilson's alteration on that process, 

 Third, To the effect of that alteration, 

 Fourth, To the cause of that effect. 



I. In proceeding to advert to the process of making cast-iron, 

 as formerly practised, it cannot here be necessary to enter into 

 much detail in explanation of a process, long practised and ex- 

 tensively known, as this has been ; nor, indeed, shall I enter into 

 detail, farther than, to the general scientific reader, may be pro- 

 per to elucidate Mr Neilson's invention. 



In making cast iron, then, the materials made use of were 

 three,— 



The Ore, 



The Fuel, 



The Flux. 



The Ore was clay iron-stone, that is to say, carbonate of iron, 

 mixed, in variable proportions, with carbonates of lime, and of 

 magnesia, as well as with aluminous and siliceous matter. 



The Fuel made use of at Clyde Iron- Works, and in Scotland 

 generally, was coke, derived from splint-coal. During its conver- 

 sion into coke, this coal underwent a loss of 55 parts in the 100, 

 leaving 45 of coke. The advantage of this previous conversion 

 consisted in the higher temperature produced by the combustion 

 of the coke, in consequence of none of the resulting heat disap- 

 pearing in the latent form, in the vapours arising from the coal, 

 during its conversion into coke. 



The Flux was common limestone, which was employed to act 

 upon the aluminous and siliceous impurities of the ore, so as to 

 produce a mixture more easy to melt than any of the materials 

 of which it was made up, just as an alloy of tin and lead serves 

 as a solder, the resulting alloy being more easy to melt than 

 either the lead or the tin apart. 



