



280 Dr. 0. I\. A.Wright on the Determination of 



S$. Figs. 2 and 3 represent the curves thus obtained, the 

 curves numbered 1, 2, 3, and 4 being those respectively ob- 

 tained with the voltameters thus numbered ; in fig. 2 the cur- 

 rents are plotted as abscissa), and the values of e as ordinates. 

 Evidently, from the nature of these curves, the following con- 

 elusions may be drawn : — 



(1) As the current increases with a given voltameter the 

 value of e increases, but at a less rapid rate ; so that the 

 curves are concave downwards. 



(2) For a given current the value of e is the greater the 

 smaller the electrode surface. 



In fig. 3 the abscissaa are the quantities of electricity flowing 

 per second per square centimetre of electrode surface*; evi- 

 dently the four curves obtained with the four voltameters do 

 not differ more from one another than may reasonably be 

 ascribed to the not absolute uniformity of the conditions of 

 the surface of the electrodes (Nos. 1 and 2 being chiefly foil, 

 No. 3 partly foil partly wire, and No. 4 wholly platinum wire), 

 and to the unavoidable experimental errors ; whence it may 

 be concluded that 



(3) for a given rate of flow of electricity per unit area of 

 electrode, the value of e is independent of the size of the 

 electrodes and of the current passing; i. e., e remains the 

 same when both electrode surface and current are altered 

 in the same ratio. 



Effect of Variation in the Strength of the dilute Acid used. 



89. It has been concluded by previous experimenters that 

 increasing or decreasing the strength of the dilute sulphuric 

 acid electrolysed makes little or no difference in the value of 

 e, and that, if any difference exist, it is in this direction — that 

 the stronger acid gives, cceteris paribus, a smaller value for 

 e, the effect being less nearly imperceptible with very weak 

 solutions indeed, and being well marked when distilled water 

 is compared with weak acid. The following experiments 

 were made with the above-described voltameters, from which 

 it results that as the strength of the acid is increased (from 

 0*2 to 4O0 grammes per 100 cubic centims.) a progressive 

 diminution in the value of e ensues. 



Acid containing 40'0 grammes of H 2 S0 4 per 100 cubic cen- 

 tims. — Voltameter No. 1 was used : from Kohlrausch's numbers 

 (Pogg. Ann. Ergbd. viii. p. 1, and clix. p. 233) it results 



* Those determinations in which no hydrogen was evolved are omitted 

 in every case, inasmuch as the effects of diffusion discharge are unequal for 

 the different voltameters, and hence unequally reduce the value of «?, 

 leading" to marked difference in the curves. 



