THE PROPERTIES OF METALLIC SUBSTANCES 385 



in connection with inter-metallic compounds is the large number of 

 compounds derivable from a single pair of elementary substances. The 

 constitution of these compounds does not harmonize well with our pres- 

 ent conceptions of valence. The study of these substances is attended 

 with many experimental difficulties and their nature at the present time 

 is little understood. 



Metallic substances are characterized by certain well-defined prop- 

 erties, chiefly electrical and optical, which are common to all. 4 This 

 community of property among metallic substances indicates some com- 

 mon element within their constitution. During the past few decades the 

 view has been gaining ground that the properties of metallic substances 

 are primarily due to the presence of charged particles, presumably nega- 

 tive electrons, which are relatively free to move within the body of the 

 metal. While this theory of the constitution of metals is in good agree- 

 ment with observed facts from a qualitative point of view, it has not 

 been found possible to elaborate a detailed theory of metallic substances 

 which accounts successfully for the major portion of their characteristic 

 properties. 



2. The Conduction Process in Metals. Metallic conductors are dif- 

 ferentiated from electrolytic conductors in that the passage of the cur- 

 rent through them is unaccompanied by an appreciable transfer of mat- 

 ter. If a current is passed for an indefinite period of time through a 

 series of metallic conductors, no material effects are observable, either 

 within the conductors themselves or at the boundaries between them. 

 If the conduction process in metals is due to the motion of negative 

 electrons, then there must likewise be present in the metals positively 

 charged constituents or ions which, conceivably, may take part in the 

 conduction process. In all likelihood the amount of matter transferred 

 by these carriers is extremely small, and may under ordinary conditions 

 escape observation. Experiments carried out with amalgams of sodium 

 and potassium indicate that in these systems an appreciable transfer of 

 matter actually takes place. 5 Curiously enough, in these amalgams, the 

 electropositive constituent, that is, the alkali metal, was found to be 

 carried toward the anode and not toward the cathode as might have 

 been expected. The data are as yet too meager to warrant drawing 



* A very complete summary of the literature relating to metallic substances is given 



by J. Koenigsberger in Handbuch d. Elektrizitat u. d. Magnetismus by L. Graetz, Leipzig 



J. A. Earth (1920), Vol. 3, pp. 597-724. The older literature is also summarized in 



Winkelmann's Handbuch d. Physik, Vol. 4, pp. 344-384, and Baedeker's Elektrische 



Erscheinungen in Metallischen Leitern, Vieweg, Braunschweig (1911). 



8 Lewis, Adams and Lanman, J. Am. Chem. 8oc. 37, 2656 (1915). 



