90 



Barrett, Brown & Hadfield — On the Elecirical Conrlnctivitu and. 



could be nioi-e accurately determined and the variation of resistance with 

 temperature ascertained. Here is the result: — 



Specific Ricsistance of NiCKEL-MANOiNKSE Steels (Tested ia the Form of No. 20, B. "W. G. "Wire). 



The specific i-esistance of most of these alloys is practically the same in 

 the form of wire as that deduced from the conductivity of the rods of similar 

 specimens. The considerably larger resistance of the last two specimens given in 

 the above table is due to the particular samples from which the wires were drawn 

 containing rather more carbon: viz. 1414 A wire had 1 per cent, of carbon; 

 and ]414:B wire was found to have 1"18 per cent, of carbon, nearly double the 

 amount of that in another earlier casting from which the rods were made. 



The sp. resistance of the wire 1414 B is the largest yet found in any of 

 these alloys of iron ; and we believe it has the highest resistance of any metallic 

 conductor yet obtained as wire in a commercial form. It is sixty times greater 

 than the resistance of pure copper, nearly ten times as great as the best iron 

 (S.C.I.), and 41 times greater than German silver. 



The temperature coefficient of these two alloys, 1414 A and B, and also of 

 1449 A and E was found to be fairly low, being less than a sixth of that of 

 iron, and not very much greater than German silver. Hence these alloys, if 

 they do not deteriorate with use, will prove extremely valuable materials for 

 resistance coils and for the purpose of electric-heating. We have not put them 

 to a prolonged test, but so far as our observations have gone they do not appear 

 to undergo any serious change by moderate heating and cooling. f 



Turning to the analysis of these nickel-manganese steels given in Group 12 

 (p. 89), it will be observed that 1109 D, 1414 A, and 1414 B contain the same 

 percentage of manganese, differing mainly in the amount of nickel. 1414 A 



* This alloy was received and tested in the form of strip. 



f Upwards of four years have elapsed since the nickel-manganese alloy, 1109 D, now kno-wn as 

 reostene, -was made hy one of us; its electric resistance, determined by us on November 8, 1895, 

 ■was found to be 83 microhms per c.c, with a temperature variation of a little over 0-1 per cent. 

 Various samples of reostene have been made, and the resistance measured by us from time to time with 



