ON THE CHEMICAL NATURE OF CAST IRON. 15 



in lead, we should produce a solid mass similar to what we termed a solidified 

 solution. 



Again, if only a few per cent, of tin be added to the mixture, of, say, ten 

 parts zinc in lead, a perfect alloy will be formed. 



Applying these facts to the alloys of carbon and iron, we are led : — 



(1) To look upon white iron (containing small percentages) as a solidified 

 solution of carbon and iron ; 



(2) ^Tien containing larger percentages as a solidified solution of carbon 

 and iron, with carbon dilfused through the mass in a very fine state of divi- 

 sion ; 



(3) "When containing large percentages of carbon, together with certain 

 other substances (manganese, to wit), as a solidified solution of carbon, iron, 

 and the other substances. 



And to look on the grey modification as a solidified solution of carbon and 

 ii'on, vnth. carbon (varying amounts of the graphitic modification) mechani- 

 cally intermixed. 



Another point in favour of the above may be mentioned, namely, that it 

 has been observed that the eonducting-power of the pure metal may be 

 deduced from that of the impure one, where the conducting-power of the 

 impure metal difi"ers from that of the pure one by not more than 20 per cent. ; 

 this has been foimd to hold good only in cases where solidified solutions 

 exist. 



IS'ow some experiments* have been made in this direction with various 

 kinds of iron. The results obtained were as follows : — 



Specific conducting-power in terms of the B.A. unit foi* 



metre length and millimetre diameter. 



„ r\i 1 Deduced for 



N°- Observed. ^^^.^ ^^^^1 



5 7-472 8-207 



6 7-438 8-191 



7 6-75.5 7-863 



9 7-002 7-898 



13 0-322 7-855 



15 6-551 7-950 



The amount of impurities in 5, 6, 7 were, in 100 parts, — 



5. 6. 7. 



Sulphur 0-190 0121 0-104 



Phosphorus 0-020 0-178 0-106 



.Sihcium 0-014 0-160 0-122 



Carbon 0-230 0-040 0-020 



Manganese, | q.-^^q q.qoq 0-280 ' 

 JNickel, Cobalt J 



No. 9. From a piece of sheet-iron. 



No. 13. Pianoforte wire. 



No. 15. Commercial iron wire. 



These data show that the alloys of iron follow in this respect the same 

 laws as those, of other metals. 



« Phil. Trans. 1SG4, p. 369, 



