168 ROYAL SOCIETY OF CANADA 



Data and curves, corresponding to those shown for Constantin, 

 were also obtained for mangamin, rheotin, German silver, copper, and 

 aluminium; but as the result is the same in every case they are not 

 shown here. In order to give an idea of the nature of the materials 

 tested the following descriptions are given: 



Manganin. 



This is the familiar alloy so much used for resistance standards 

 on account of its low temperature coefficient and other good physical 

 qualities. It is usually considered to 1)e the best and most reliable 

 of alloys for standard purposes. Its composition, perhaps, is variable, 

 but it is likely to be something about Cu. 84- Ni. 12, Zn. 3-5. 



The test-specimen was -0235" (= -0597 cm.) diameter; its modu- 

 lus was 21-60 X 10*' ins-lb. units, or 1518 x 10" cm.-kgm. units. 



After the elastic limit is passed the material exhibits the same 

 property in slowly pulling out as Constantin does. 



Rheotin. 



One of the latest resistance alloys. It is a material much harder 

 and stiffer than Constantin and manganin, and is very much stronger. 

 It breaks under a load not much greater than the elastic limit load, 

 and there is only a very little pulling out when the elastic limit is 

 passed. 



The specimen was of -0226" diameter, elastic limit corresponding 

 to a stress of 101,500 lbs. per sq. inch (= 7,350 kgm. per sq. cm.), 

 and a strain of 00607. The modulus of elasticity was 17-20 x 10® 

 inch-lbs. units or 1-209 x 10^ cm.-kgm. units. 



German Silver. 



The specimen, -023" diameter, was of the ordinary German silver 

 wire that is so much used for resistance purposes ; composition was 

 approximately Cu. 60, Mn. 26, ISTi. 14. The stress-strain curve showed 

 it to be not as strong as rheotin, thougîi much stronger than Constantin 

 and manganin. t 



As in the case of rheotin there is not much pulling out just after 

 the elastic limit is passed, but this effect increases as the load is in- 

 creased. In most physical properties the material seems to come between 

 rheotin and Constantin. 



The elastic limit corresponded to a stress of 46,050 lbs. per sq. 

 inch (= 3,328 kgm. per sq. cm.), with a corresponding strain of 



