Thermo-electric Action of Metals in Electrolytes. 269 



of the chemico-electric ones, are much more distributed, those of each 

 particular metal occupying about double the number of lines. This 

 probably indicates that in these thermo-electric actions voltaic influ- 

 ence modified the effects ; also that heating one of the pieces of metal 

 only of a voltaic pair usually increased the amount of their electric 

 difference, making most metals more positive and some more negative, 

 whilst heating the second one also, usually neutralised to some extent 

 the effect of heating the first one only. 



Tabulating the members thus also shows that gold and platinum 

 are the least distributed of the metals of the thermo-electric series, 

 they are also the least corrodible. Platinum, gold, palladium, and 

 silver occupy in all cases the lower half only of the table in the voltaic 

 series, and in nearly all cases also in the thermo series. Aluminium, 

 tin, and iron preponderate in the upper section of both tables. These 

 facts also indicate that voltaic influence operates in most of these 

 thermo-electric actions. An examination of Table II further supports 

 this conclusion. 



As the electrical effect of heating a voltaic couple may be viewed 

 as being in a greater degree composed of the united consequences of 

 heating each of the two metals separately (see pp. 270, 271, and 281), 

 I have compared the chemico-electric series in the weak solutions at 

 60 F., Table X, p. 267, side by side with the thermo-electric ones of 

 the same metals in the same liquids of Table I, in a similar manner as 

 the two chemico series are themselves compared. By such a com- 

 parison it was found that magnesium, zinc, and cadmium suffered 

 usually very great depressions of position and electromotive force in 

 the series by the influence of heat (see pp. 276, 278). In such a table 

 of comparison, magnesium was depressed 21 times through a total 

 of 144 places ; zinc was lowered 20 times through a sum of 123, and 

 raised through 1 only; and cadmium sank 17 times through 87, and 

 rose 3 times through a total of 8. All these numbers follow the same 

 order as the specific gravities, atomic weights, and specific heats of 

 those metals. All the other metals behaved in a very different manner 

 from this. The same effects may be rendered evident in another way 

 by tabulating the number of instances in which each of those metals 

 respectively occurs in the several lines of Table I and of the cold 

 columns of Table X. Tables I and II also show that, notwithstand- 

 ing the highly volta-positive character of this group of metals, mag- 

 nesium was thermo-negative 10, cadmium 8, and zinc 7 times, and 

 that they were nearly as often thermo-negative as silver. This effect 

 is least conspicuous with the weak solutions of potassic chloride, carbo- 

 nate, and hydrate, and was not manifestly affected by increased strength 

 of liquid. The similar behaviour in this respect of the whole of the 

 magnesium group of metals, suggests the conclusion that the frequent 

 and great depressions in position of magnesium in the thermo-electric 



T 2 





