386 PROPERTIES OF ELECTRICALLY CONDUCTING SYSTEMS 



conclusions as to the part which the positive constituent plays in metallic 

 conduction. It appears probable, however, that in suitable metallic 

 systems an appreciable transfer of matter accompanies the passage of 

 the current. 



The view that the conduction process in metals is an ionic one is the 

 only one in agreement with our present notions regarding the constitu- 

 tion of matter. The absence of material effects accompanying the trans- 

 fer of electricity indicates a common carrier in all metallic substances. 

 The fact that no positively charged carrier of sub-atomic dimensions is 

 known lends probability to the view that metallic conduction is due to 

 the motion of the negative electron, the only known carrier of sub-atomic 

 dimensions. 



Direct evidence in support of the electron theory of metallic con- 

 duction is very meager. Tolman and Stewart 6 have studied the current 

 flow induced in metallic conductors under acceleration. From their meas- 

 urements, they have calculated the ratio of the effective mass of the 

 carriers to the quantity of electricity flowing. Their results indicate that 

 the current is due to the motion of a negative carrier, the ratio of whose 

 mass to the charge corresponds with that of the negative electron. For 

 copper, aluminum and silver conductors, Tolman and Stewart found for 

 the value of 1/ra, assuming = 16, the values 1660, 1590, and 1540 

 respectively. These are somewhat lower than corresponds to the mass 

 of a slowly-moving negative electron, but the difference lies within the 

 limits of experimental error. The results of investigations on the prop- 

 erties of solutions of the alkali metals in liquid ammonia, described in 

 the preceding chapter, likewise furnish striking evidence in support of 

 the electron theory of metallic conduction. Other properties of the 

 metals, such as the Hall effect, and particularly the emission of negative 

 electrons by metals at higher temperatures, lend support to this theory. 

 The precise nature of the conduction process of metals, however, still 

 remains very obscure. 



3. The Conductance of Elementary Metallic Substances. The 

 order of magnitude of the conductance of metals, in itself, furnishes 

 evidence in support of the electron theory of metallic conduction. In 

 Table CLIII are given values of the atomic conductance and the spe- 

 cific resistance, as well as of the mean temperature coefficient a of the 

 resistance of a number of elementary metals. 



Tolman and Stewart, Phys. Rev. 8, 97 (1916) ; i?w?., 9, 164 (1917), 



