44 Transactions Tennessee Academy of Science. 



Voltaic Action in Combination TeetK 



lings 



Filli 



By John Daniel, Vanderbilt University. 



My attention was directed by personal experience to the prac- 

 tice among Nashville dentists, and, presumably, among dentists 

 in general, of using what they call "combination fillings ;" that is, 

 tin fillings topped with gold. This combination gives no serious 

 voltaic or electrical disturbance in case the base metal is entirely 

 covered by the gold, and is at no point left exposed to the saliva. 

 This is probably the way it was intended to be used by the origina- 

 tor of the combination fillings ; but the case is very different when 

 both metals are left exposed at any point to the saliva. 



In my own experience, which is a case in point, I had ordered 

 gold fillings and thought I had them ; but in a very short time the 

 base metal was dissolved away, undermining the gold cap. A dis- 

 cussion of the case with my dentist disclosed the fact that the 

 fillings were combination fillings. My experience of having the 

 base metal dissolved away when placed in contact with the gold 

 is exactly what should be expected, and is fully explained by the 

 well established laws of electricity. 



On page 305 et seq. of General Physics, by Henry Crew, Pro- 

 fessor of Physics in Northwestern University, is found the fol- 

 lowing statement concerning voltaic action : "The simple and well 

 estabHshed facts of the voltaic cell are as follows : At the very 

 close of the eighteenth century it was discovered by the Italian 

 physicist, Volta, that all conductors of electricity can be divided 

 into two classes. This division is based upon the following ex- 

 periments. If we make a closed circuit out of several different 

 metals, i. e., if we make an endless chain in which each link is 

 composed of a different simple substance, such as zinc, copper, 

 gold, or tin, we see tliat no electric ciu"rcnt is i^roduced. All sub- 

 stances which when joined together at the same temperature in 

 any order, produce no current, are called conductors of the first 

 class. 



