abstracts: electricity 81 



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'Annealed Copper Standard." The advantages of ohms per meter- 

 gram as a unit of resistivity are stated. The desirability of an inter- 

 national standard of copper conductivity is urged. J. H. D. 



ELECTRICITY.- — The temperature coefficient of resistance of copper. 

 J. H. Dellinger. Bulletin Bureau of Standards, 7 : 71-101. 1911. 

 Abstracted in the Journal of the Franklin Institute. 170: 243. 

 1910. 



Standard values for the temperature coefficient of copper have varied 

 greatly, and anaccurately determined value on representative samples 

 was needed. Samples were investigated from 14 of the leading copper 

 refiners and wire manufacturers in the United States, Germany, France, 

 and Austria. The measurements were of especially high relative accu- 

 racy, as the wires were all compared against a copper auxiliary wire in the 

 same oil bath. The principal result was the discovery of a proportional 

 relation between conductivity and temperature coefficient, which holds 

 substantially for samples chemically different, and holds within the 

 errors of measurement for differences in conductivity due to differences 

 in hardness. The change of resistivity per degree C. of a sample of 

 copper is 0.000598 ohm per meter-gram or 0.00683 micro-ohm per cen- 

 timeter cube, these constants holding for any temperature of reference 

 and any sample of copper. 



Bending and twisting a wire produce no material change in the tem- 

 perature coefficient, although they increase the resistance. It may 

 therefore be assumed with greater confidence than heretofore that the 

 temperature coefficient of a copper wire is not changed by winding. In 

 virtue of the proportionality between temperature coefficient and con- 

 ductivity, the measurement of temperature coefficient may in certain 

 cases be substituted for the direct measurement of conductivity. 



The relation of resistance to temperature was found to be linear, for 

 the temperatures investigated, 10° C. to 100°C. If this relation actually 

 held continuously down to zero resistance, there would be a set of differ- 

 ent temperatures, all higher than — 273°C, at which the resistances of 

 copper samples of various conductivities would vanish, and these "in- 

 ferred absolute zeros" of resistance are sometimes used as an aid in 

 remembering the temperature coefficient. But this investigation indi- 

 cated nothing of the actual resistance of copper at very low or very high 

 temperatures. 



The proportionality between temperature coefficient and conductivity 

 has been confirmed by results obtained at the Reichsanstalt. J. H. D. 



