1883.] 



Action of Metals in Electrolytes. 



53 



Whilst also variation of strength of liquid caused only a moderate 

 amount of change of order in the volta tension series, it produced 

 more than three times that amount of change in the thermo-electric 

 tension series. The usual effect of increasing the strength of the 

 liquid upon volta-electro-motive force was to considerably increase it, 

 but its effect upon thermo-electro-motive force was to largely decrease 

 it. The degree of potential of a metal and liquid thermo-couple was 

 not always exactly the same at the same temperatures during a rise 

 as during a fall of temperature ; this is analogous to the variation of 

 melting and fusing points of bodies under such conditions, and also 

 to that of supersaturation of a liquid by a salt, and is probably due to 

 some hindrance to change of molecular movement. 



The rate of ordinary chemical corrosion of each metal varied in 

 every different liquid ; in each solution also it differed with every 

 different metal. The most chemically positive metals were usually 

 the most quickly corroded, and the corrosion of each metal was 

 usually the fastest with the most acid solutions. The rate of corro- 

 sion was dependent both upon the nature of the metal and upon that 

 of the liquid, and was limited by the most feebly active of the two — 

 usually the electrolyte. The order of rate of corrosion of metals also 

 differed in every different liquid. The more dissimilar the chemical 

 characters of two liquids, the more diverse usually was the order of 

 rapidity of corrosion of a series of metals in them. The order of rate 

 of simple corrosion in any of the liquids examined differed largely 

 from that of degree of chemico-electric, and still more from that 

 of thermo-electro-motive force. Corrosion was not the cause of pure 

 thermo-electric action of metals in liquids. 



Out of fifty-eight cases of rise of temperature the rate of ordinary 

 corrosion was increased in every instance except one, and that was 

 only a feeble exception ; the increase from 60° to 160° F. with different 

 metals was extremely variable, and was from 15 to 321*6 times. 

 Whether a metal increased or decreased in thermo -electro or chemico- 

 electro-motive force by being heated, it increased in rapidity of corro- 

 sion. The proportions in which the most corroded metal was also the 

 most thermo-electro-positive one was 65*87 per cent, in liquids at 

 60° F., and 69*12 in the same at 160° F. ; and the proportion in which 

 it was the most chemico-electro-positive at 60 F. was 84*44 per cent., 

 and at 160° F. 80*77 per cent. The proportion of cases therefore in 

 which the most chemico- electro-negative metal was the most corroded 

 one increased from 15*56 to 19*23 per cent, by a rise of temperature of 

 100 F. degrees. Comparison of these proportions shows that corrosion 

 usually influenced in a greater degree chemico-electric than thermo- 

 electric actions of metals in liquids. Not only was the relative 

 number of cases in which the volta negative was the most corroded, 

 increased by rise of temperature, but also the average relative loss by 



