1896.] on Electric Besearch at Low Temperatures, 



Electrical Resistivity op Alloys. 



247 



Alloy. 



Aluminium-copper . . 



Alumiuium-titunium 



Aluminium-silver 



Gold-silver 



Copper-aluminium .. 

 Copper-nickel-aluminium 

 Platinum-rhodium . . 



Nickel-iron 



German silver . . 

 Platinum-iridium 

 Platinum-silver .. 



Platinoid 



Manganin 



Iron-manganese . . 



Composition. 



94 : 6 



94 : 6 



90 : 10 

 97 : 3 

 87 : 61 : 6h 

 90 : 10 "^ 



95 : 5 



Ptjr 



: 12 



Resistivity Percentage 



in C.G.S. increment, 



units at 0° C. O'^ C. to 100° C. 



2,904 



3,887 



4,641 



6,280 



8,847 



14,912 



21,142 



29,452 



29,982 



30,896 



31,582 



41,731 



46,678 



67,148 



38-1 

 29-0 

 23-8 

 12-4 

 8-97 

 6-45 

 14-3 

 20-1 

 2-73 

 8-22 

 2-43 

 31 

 0- 

 12-7 



The first thing which strikes us on looking at the chart (Fig. 6) is 

 that the lines for the pure metals all converge downwards in such a 

 manner as to indicate that their electrical resistance would vanish at 

 the absolute zero of temperature, but that no such convergence is 

 indicated in the case of alloys. We have found that the slightest 

 impurity in a metal changes the position of the resistance line. lu 

 the next place, note that the order of conductivity is different at low 

 temperatures to that at ordinary temperatures. At 13° C. pure 

 silver is the best conductor, but at - 200° pure copper is better 

 than silver, and the position of mercury is, of course, very 

 different. 



Again, the lines of some metals are very much curved. The 

 principal magnetic metals, iron and nickel, have lines which are 

 very concave upwards, and this is a characteristic apparently of many 

 magnetic alloys. The mean temperature coefficient of these magnetic 

 metals between 0° C. and 100° C. is much larger than that of other 

 metals, and the percentage decrease in resistance in cooling them 

 from + 200° C. to — 200° C. is greater than in the case of any other 

 metal. It is worth noting in passing that these magnetic metals, 

 iron and nickel, have smaller atomic volumes than any other metal, 

 and that, generally speaking, the worst conductors amongst the metals 

 are those that have the large atomic volumes and large valency. 



Next turning to alloys, we may make mention of a few general 

 facts with regard to their resistance. If to one pure metal we add a 

 small quantity of any other metal the result is always to raise the 

 resistance line almost parallel to that of the predominant constituent. 

 Thus, in our own chart, the alloy consisting of 6 per cent, of copper 

 with 94 per cent, of aluminium is parallel to the aluminium line, but 

 higher up. Three per cent, of aluminium added to 97 per cent, of 

 copper yields an alloy with a resistance line parallel to that of 



