WILLIAM SIEMENS, F.R.S. 277 



advantages of the hot blast, but the permissible temperature was 

 limited to 960 Fahr., at which point it was considered that the 

 maximum effect could be had with a furnace of limited capacity. 

 This argument was based upon the supposition that iron ore was 

 reduced at 420 Fahr. ; and that the second action, which was that 

 of carbonic acid splitting up in contact with carbon, could only be 

 accomplished at a higher temperature. If, therefore, the carbonic 

 acid had all been split up in contact with carbon, and a zone had 

 now been reached at which no more unburning of carbonic acid 

 took place, the whole remaining capacity of the furnace would be 

 reserved for the final action that of the reduction of the ore to 

 the metallic condition, and the production of a large proportion of 

 carbonic acid gas in the gases leaving the furnace. He thought, 

 however, that iron ores, as a rule, were not reducible at the 

 extremely low temperature of 420 Fahr., which was really below 

 that of incandescence. In dealing with calcined Cleveland ore he 

 had no wish to doubt the fact, but if it was considered what this 

 ore consisted of, it would be seen why its reduction and carboniza- 

 tion took place at that low temperature. In calcining Cleveland 

 ore 25 per cent, of volatilised matter was evolved ; therefore the 

 calcined ore must be regarded as a sponge, consisting of extremely 

 divided particles of iron ore. This sponge being brought into 

 contact with the reducing gas, the carbonic oxide was mechanically 

 absorbed in large quantities, and the reduction of the ore facili- 

 tated. The sponge into which Cleveland ore was converted by 

 calcination might in effect be compared to platinum sponge, 

 which, when a current of hydrogen gas was directed upon it, 

 absorbed that gas so violently as to produce ignition. Again, 

 when a solid bar of iron was exposed to a dry atmosphere, no 

 appreciable oxidation would take place in one hundred or even in 

 one thousand years. There were iron bars which, in o.J Roman 

 buildings, had been exposed to the atmosphere for two thousand 

 years and were not oxidised ; but the same iron in a pulverulent 

 condition would take fire instantly in a room, showing that the 

 same material would behave differently under similar circum- 

 stances, according to its aggregate conditions. 



He had paid considerable attention to the reduction of iron ores, 

 and he had found that, whereas hydrated ores or spathose ores 

 were reducible at a low temperature, the peroxides required a 



