PROCEEDINGS OF THE POLYTECHNIC ASSOCIATION. 405 



mered a little. Subject it to the same process of tilting and 

 drawing, as tlie blistered steel passes through, and it will be 

 equal to it. Most of the steel in the market is too high, as they 

 call it; it contains too much carbon, and is too much like cast 

 iron. Iron cut from a Swedish bar is often enough like steel to 

 harden in the same manner. Mr. D. suggested that the function 

 of the nitrogen in the formation of steel might be to render the 

 carbon fusible, so that the iron may absorb it. Nothing can be 

 superior for cannon to the puddled steel made from a pure ore. 

 Some of the best ores are the magnetic oxides, often containing 

 seventy per cent, of iron. These can be reduced to puddled 

 steel much more cheaply than to cast steel by the old process of 

 cementation. And such steel will be more uniform in its texture 

 than blistered steel. The want of homogenity in blistered 

 steel render it unsuitable for cannon. 



Mr. Johnson. — Do not chemists consider the carbon and the 

 iron to be attomically combined? 



Dr. Vanderweyde. — We do not know. The strongest micro- 

 scope does not detect any detached carbon. Still we cannot say 

 that \Ji is a chemical combination. In chemical combinations we 

 find that the simple substances lose their former properties. 

 Sulphur and mercury combining form vermilla ; sulphur and cop- 

 per, blue vitriol. In that view I should be inclined to consider 

 it only an alloy. 

 Mr. Johnson. — Are not alloys, generally, chemical combinations ? 



Dr. Vanderweyde. — When the specific gravity of^^an alloy is 

 unchanged by the union, it is supposed to be only a mixture ; but 

 where it is materially changed, there is supposed to be a chemi- 

 cal combination, and the more it is changed the more intense is 

 that combination. Where the alloy has diflerent properties from 

 the two metals, the specific gravity is the most changed. For 

 instance, tin and copper are soft metals, but they compose bell- 

 metal, which is very hard. 



The Chairman. — Does magnetism furnish a test between cast 

 iron and steel ? 



Dr. Vanderweyde. — No sir ; the finer qualities of cast iron are 

 perfectly equal to the coarser qualities of steel in keeping mag- 

 netism. I have a good magnet made of thin iron plates cut in 

 the horse shoe form, hardened with the yellow prussiate of 

 potash. We can easily know pure iron by that test. Take a bar 

 of perfectly pure iron and rub it over with a steel magnet, and 



