182 Mr. T. Gray on the Application of the Electrolysis 



at the high temperatures a correction could be obtained by 

 keeping a plate of the same size as that used in the electrolysis 

 in a similar cell with no current passing through, showed that 

 this method of working was capable of giving approximately 

 correct results. They are hardly ever absolutely exact, but 

 they should not differ from the truth by as much as one tenth 

 per cent, if the current-density is greater than the hundredth 

 of an ampere per square centimetre of cathode surface. 



The curve for 2° C. is interesting as showing that, within a 

 considerable range of current-density, there is absolutely no 

 effect produced by variation in size of plate at this temperature. 

 Why there should be a somewhat pronounced effect when the 

 size of the plate passes about two hundred square centimetres 

 to the ampere is puzzling, and probably indicates a protect ing- 

 power in the passage of the current through the cell. There 

 is some slight evidence of such protection for high current- 

 densities at all temperatures. The curious shape of the curve 

 for the temperature 12°, which, as will be seen from Table I., 

 again becomes steeper for lower current-densities than those 

 shown in the curve, is very interesting. This result is certainly 

 genuine, as that curve is taken from the mean of a large 

 number of experiments made under varying conditions by 

 different persons, and the whole of the individual experiments 

 agree closely with the mean curve. 



Table I. and the diagram of curves which illustrate it 

 give the relative results for different sizes of cathode, the 

 point of crossing of the curves being reduced to 10,000 for 

 the purpose of rendering the appropriate percentage correction 

 for any particular size of plate easily estimated. With regard 

 to the curves at 2°, 23°, 28°, and 35° C, it should be stated 

 that the curve for 2° is the mean of three experiments, that 

 for 35° the mean of two experiments, while those for 23° and 

 28° are single experiments. 



Table I. 



Area of cathode, 

 in square centi- 



Tempera- 

 ture, 



Tempera- 

 ture, 



Tempcra- 



Tempera- 



Tempera - 



pere of current, 



2°C. 



12° C. 



23° C. 



28° C. 



oo°C. 



50 



10,000 



99964 



9995 



9993-5 



9980-6 



100 



10,000 



9987 



9983 



9979-5 



9958 



150 



9998 



9979-5 



9974 



9969-6 



9935 



200 



9990 



9973 



9966-6 



9957-5 



9912 



250 



9984 



H970 



9959-5 



9939-3 



9890 



300 



9980 



99685 



9952 



9920 



9868-5 



400 





9961 









500 







9949 









