13 REPORT 18G6. 



on the Chemical Nature of Alloys," I have defined the terms " solution of one 

 metal in the other, as one Hke that of ether and alcohol ; for these two liquids 

 may be mixed in any proportion, and they will not separate, by standing, into 

 two layers," and " solidified solutions as a most intimate mixture, such as 

 would occur in the sudden conversion of a solution of two liquids into a solid, 

 and a much more intimate mixture than can be obtained by ordinary mecha- 

 nical means — in fact a perfectly homogeneous diffusion of one body in another. 

 An excellent example of homogeneous diffusion is furnished by glass, which 

 is formed in a liquid state at a high temperature, and solidifies on cooling 

 Avithout separation of the different silicates." 



Before deducing the chemical nature of cast iron from what is already 

 known, it will be as well to compare the physical deportment of the alloys 

 of carbon and iron with that of other aUoys ; for instance, with those of tin 

 and copper, and zinc and copper. Pure u'on is said to be very malleable, so 

 is pure copper; iron alloyed with small quantities of carbon (malleable, wrought 

 iron) is less malleable and harder than the pure metal ; so is copper, when 

 alloyed with small quantities of tin or zinc, less malleable and harder than 

 the piirc metal. Iron alloj-ed with from 1 to 2 per cent, of carbon has 

 obtained its maximum state of hardness in conjunction with a certain 

 degree of malleability and ductility (steel) ; copper alloyed with certain 

 quantities of tin or zinc possesses similar properties, forming gun-metal 

 and brass. 



Again, increase the amount of carbon in the iron and the mass becomes 

 brittle and unworkable (cast iron) ; so also do the alloys of cojiper, and tin or 

 zinc, when the amount of the latter exceeds that contained in gun-metal or 

 brass by a few per cent. 



Leaving out of consideration the impurities of cast iron, let us first discuss 

 the alloys of carbon and iron, and these we find may bo divided into two 

 classes, viz. the white and the grey cast iron. 



Now the essential difference between these two forms is the state in which 

 the carbon exists in them. In the one (white) it is said to be chemically 

 combined with the iron, in the other (grey) mechanically mixed with the 

 iron. As these, the white and the grey iron, may be converted into one 

 another by re-fusion (for if certain sorts of white iron be fused at a low 

 temperature and allowed to cool slowly, grey will be produced, and conversely, 

 if grey iron be fused at a high temperature and cooled rapidly, white iron), 

 it follows that the chemical combination of carbon and iron may be made to 

 split up into its component elements simply by slowly cooling the molten mass. 

 Bearing on this point are the following experiments made by Karstcn : he took 

 a mass of cast iron and determined the amounts of so -called chemically com- 

 bined and uncombined (graphitic) carbon in it ; ho then melted it and cast it 

 in a mould, analyzed the outer and inner portion of it. The following are 

 the results he obtained : — 



Carbon per cent. 



Combined. Uncombined. 



Before melting 0-78 3-25 



Outer (white) portion of casting 5" 10 i 



Inner (grey) portion of casting 0-Ql 3-16 



Now, can it be possible that the carbon is really chemically combined with 

 the outer portion of the casting and not in the inner ? if this be so, it is I 

 think the only case known of a chemical combination in which the elements 



