British Association for the Advancement of Science. 23 



The constant constituents were iron, carbon, silicon, and alu- 

 minium ; and manganese was a pretty frequent ingredient. The 

 average proportions were 



3 J atoms of iron and manganese, 

 1 do. of carbon, silicon, and aluminium. 

 The atomic proportions of the carbon, silicon, and aluminiiun, 

 were 4, 1, 1, so that cold blast cast iron may be considered as 

 composed of 21 atoms iron and manganese, 

 4 do. carbon, 

 1 do. silicon, 

 1 do. aluminium. 

 The following table exhibits the composition of hot blast cast 

 iron. No. 1 : — 



Carbon, &c. 



1 atom. 

 1 atom. 



These constituents are in the proportion of 



6^ atoms iron and manganese, 



1 do. carbon, silicon, and aluminium. 



Iron. 



In the cold blast we have 3^ atoms + 



In the hot blast 6^ atoms -f- 



Thus, it appears, that hot blast iron contains only about half 

 the foreign matter that exists in cold blast iron. 



Ceist steel made from the best Dannemora iron, had a specific 

 gravity of 7.8125. Its constituents were 



Iron, - - - - - - 99.288 



Manganese, ----- 0.190 



Carbon, 0.388 



99.866 



or it contained 



55.7 atoms iron, 

 1 atom carbon. 



In reply to questions. Dr. Thomson stated, that he had made 

 no experiments on the comparative composition of bar iron from 



