278 
PROCEEDINGS 1849—1858. 
working index or pointer of the dial a second index, which couhl be 
entirely out of the control of the engineer, and which would remain 
fixed at the maximum pressure attained by advancing with the 
movable index but not receding. The second index could only be 
replaced or regulated by the employer, having a key for that purpose, 
My. Xasmytli also read a communication on a new system of 
puddling iron by steam. The difference between cast iron and 
malleable or wrought iron is chiefly due to the presence in the former 
of a considerable quantity of carbon in combination with the iron. 
To convert cast iron into malleable iron it is requisite that this carbon 
should be removed. This object is attained by what is termed 
puddling, a process wliich Mr. Nasmyth explained with some detail. 
The improvement he suggested consisted in employing a combined 
mechanical and chemical action of steam, which is driven beneath 
the surface of the molten cast iron, and not only throws the metal 
into violent agitation, but by the intimate contact of the steam with 
the molten iron the former is decomposed, and the liberated oxygen 
combines with the carbon and passes off in the form of carbonic acid 
and carbonic oxide gases, whilst the hydrogen combines with carbon 
to form carburetted hydrogen, and also with any sulphur which may 
be present and forms sulpliuretted hydrogen. The time necessary to 
complete this operation is only four or five minutes, and the resulting 
malleable iron is of first-rate quality. 
Mr. Richard Solly, of Sheffield, also contributed a paper, recording 
some Observations on the Manufacture of Iron, in which he 
enumerated the principal sourc?s of iron in Great Britain, tlieir com- 
parative values, and the purposes for which they are best adapted. 
He described the principal processes in the manufacture of iron, and 
indicated the several qualities resulting from different methods in 
manipulation. 
Mr. Robert Hunt, F.R.S., of London, communicated the result 
of some experiments which he had made to illustrate the structural 
characters of rock and of mineral deposits as effected by electricity. 
Between a zinc and copper plate, properly connected in a vessel 
prepared for that purpose, a mass of clay in a condition of thin mud 
was subjected to an electric current. After some weeks the mass of 
