ELEMENTARY VITAL PHENOMENA 265 



soldered place back to the zinc and circulating as long as the 

 circuit is closed. This arrangement corresponds to Galvani's 

 original experiment in which the nerve represented the moist 

 conductor between the two metals, copper and iron. This principle 

 for the production of a galvanic current has been employed in 

 somewhat more perfect form in galvanic elements (Fig. 118, B), 

 in which a liquid is employed as the moist conductor, while the 

 two metals, the lower ends of which dip into the vessel containing 

 the liquid, are in contact with one another at their upper ends by 

 a copper wire in place of the soldering ; this has the advantage of 

 allowing the current to be conducted by means of the flexible wire 

 wherever it is needed. 



Following the views of Clausius upon the phenomena of 

 electricity in liquids, Sohncke ('88) has presented a very clear 

 idea of the origin of the galvanic current. According to Clausius 

 ('57) the molecules in a liquid are in constant motion and con- 

 stantly crowd upon one another, the result being that some split 

 into their constituent atoms while other atoms unite into mole- 

 cules. Hence simultaneously and at all times free atoms and 

 whole molecules are present in the liquid. But while the closed 

 molecule as a whole is electrically indifferent {e.g., water, HgO), its 

 various kinds of constituent atoms, when free, have different kinds 

 of electricity {e.g., hydrogen, H, positive, oxygen, 0, negative). 

 Within the liquid the free atoms retain their charge of electricity. 

 If they come in contact with atoms charged similarly they break 

 away from them ; if they meet those charged dissimilarly, they 

 remain no longer free but unite with the latter chemically into a 

 molecule which is electrically indifferent. But the situation is 

 changed when there is introduced into the liquid a metal plate 

 that exercises upon one kind of the free atoms a chemical 

 attraction. These atoms then accumulate on the surface of the 

 metal, which is non-electric and a conductor, and give off their 

 electric tension to it by conduction. 



If, therefore, into a vessel containing acidified water a zinc plate 

 be dipped, free atoms of oxygen accumulate upon its surface and 

 give off their negative electricity to it ; in other words, it becomes 

 negatively charged. If at the same time a copper plate be dipped 

 into the liquid, atoms of hydrogen collect upon it and give to 

 it their positive charge. There arises, therefore, an electric tension 

 between the two metals ; if now the free ends of the copper and 

 the zinc plates be joined by a metallic conductor, this tension is 

 able to equalise itself During this process, however, new atoms 

 become attracted to the place of contact of the metals with the 

 liquid and become chemically united ; thus the tension becomes 

 continually re-established, and in this way a continual galvanic 

 current is produced. 



As is known from the researches of electro-chemistry, especially 



