90 Barrett, Brown & Haprietp—On the Electrical Conductivity and 
could be more accurately determined and the variation of resistance with 
temperature ascertained. Here is the result :— 
Sprcrric Restsrance or Nicken-Mancanuse Streets (Tested in the Form of No. 20, B. W. G. Wire). 
Whores Specific resistance in Percentage variation of resistance 
: microhms at 15°C. | per 1°C., between 0° and 150°C. 
1420 B | 28°68 0:150 
1109D i 83:11 0-109 
1449 A | 86:60 0:090 
*1449 H 89°17 0:077 
1414 A | 90°62 0-104 
1414 B 97°52 | 0-085 | 
The specific resistance 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 1414 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.1.), and 45 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.t 
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 1414B 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. 
+ Upwards of four years have elapsed since the nickel-manganese alloy, 1109 D, now known as 
reostene, was made by one of us; its electric resistance, determined by us on November 8, 1895, 
was found to be 88 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 
