410 



SCIENCE 



[N. S. Vol. XLIII. No. 1108 



We stand at a point where the most prolific 

 error of electrochemistry begins, the combating of 

 which has from that time on occupied almost the 

 greater part of the scientific work in this field. 



This opinion tas undoubtedly been shared 

 by most chemists and by many physicists from 

 that day to this. 



It seems strange that those champions of 

 the theory of the chemical origin of the con- 

 tact charge who look upon Fabroni as the 

 founder of their theory have overlooked the 

 fact that what Fabroni especially undertook 

 to show in his paper was that the mere con- 

 tact of two metals weakens the cohesion be- 

 tween the molecules of at least one of them, 

 and that this change was precedent to the 

 chemical action which he regarded as the cause 

 of the electrical current. Since we now know 

 that cohesion is an attraction between the elec- 

 tropositive and electronegative ions of the 

 metal, or more definitely, between the positive 

 sub-atoms and the electrons within the metal, 

 if we accept the foundation hypothesis of 

 Fabroni we must conclude that the mere con- 

 tact of two different metals produces a change 

 in the electrical forces between their surface 

 atoms before any chemical action is set up. 



That this opinion was shared by Berthol- 

 let may be gathered from a translation in 

 Nicholson's Journal- of a part of Berthollet's 

 " Essai de Statique Chimique." 



After a discussion of a number of experi- 

 ments performed by Charles and Gay Lussac 

 for the purpose of deciding whether the dissi- 

 pation of a fine wire by the electric discharge 

 of a Leyden jar was due to the heating effect 

 of the spark or to some other cause, and their 

 conclusion that the wire was not vaporized by 

 heat, Berthollet concludes that the dispersion 

 of the metallic particles precedes their oxida- 

 tion, and says : 



Electricity favors this oxidation, inasmuch as 

 it diminishes the force of cohesion ; it is thus that 

 an alkali renders the action of sulphur on oxygen 

 much more powerful, by destroying the force of 

 cohesion opposed to it, and that a metal dissolved 

 in an amalgam is oxidized more easily than when 

 it is in the solid state. 



2 Vol. 8, 



80. 



All the chemical effects produced in substances 

 submitted to the action of electricity seem capable 

 of being deduced from these considerations, and 

 of being explained by the diminution of the force 

 of cohesion, which is the obstacle to the combina- 

 tions which their molecules tend to form. 



The fundamental question at issue in the 

 century-long battle which has been fought 

 over contact electrification has been: Are the 

 charges which are found upon two plates of 

 different metals when they have been placed in 

 contact and then separated due to some chem- 

 ical action which has taken place at the time 

 of contact, or were the two metals before they 

 were brought into contact already electrically 

 different with respect to each other ? Or, since 

 metals are said to be unelectrified when they 

 have been put into good metallic contact with 

 the earth while at a distance from other 

 bodies, may two metals which are unelectri- 

 fied with reference to the earth still be in 

 different electrical states relative to each 

 other ? 



Many physicists have maintained that two 

 metals which have been discharged to the 

 earth or to the inside of a hollow conductor 

 are in absolutely the same electrical state, i. e., 

 that they are in a condition of absolute elec- 

 trical neutrality. Others have believed that 

 the change in the electrical state of both 

 metals when they are brought into contact 

 with each other proves that they were not in 

 an electrically neutral condition before con- 

 tact. 



Among those who believe that before con- 

 tact the metals are in an electrically neutral 

 condition it is commonly held that the elec- 

 trical displacement which occurs when two 

 metals are brought into contact is due to 

 the greater afilnity of oxygen for one of the 

 metals than for the other. Those who hold 

 this view seem to overlook the fact that affinity 

 for oxygen must be, itself, an electrical attrac- 

 tion. If zinc has an affinity for oxygen, it is 

 because the zinc is either electropositive or 

 electronegative to oxygen. If zinc has a 

 greater affinity for oxygen than copper has, the 

 zinc must be more electropositive or electro- 

 negative to oxygen than is copper, and in con- 

 sequence it must be electropositive or electro- 



