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XLIII. On the Determination of Chemical Affinity in terms of 

 Electromotive Force. — Part II.* By C. R. Alder Wright, 

 D.Sc.Lond., Lecturer on Chemistry and Physics, and E. H. 

 Rennie, M.A. (Syd.), B.Sc. (Lond.), Demonstrator of Che- 

 mistry in St. Mary's Hospital Medical School. 



Experimental Determination of the Electromotive Force corre- 

 sponding to the Work done in the Decomposition of Water 

 into Oxygen and Hydrogen at the ordinary temperature. 



38. ~|~N order to apply the principles described in Part I. 

 ~L (§ 11, 18, 32), the current from a Daniell battery 

 was passed through a voltameter placed in a calorimeter, and 

 the average difference of potential between the voltameter- 

 plates determined by connecting them with a quadrant elec- 

 trometer standardized by a Clark cell (verified for us by Dr. 

 Alexander Muirhead). The amount of decomposition being 

 determined ( = n grammes), and the quantity of heat, A, de- 

 veloped in the voltameter observed, the data were obtained 

 for the calculation of the E.M.F. representing the nett work 

 corresponding to the sum of the physical and chemical changes 

 taking place by the formula 



n 



a being the equivalent of the electrolyte. 



In the case of water acidulated with sulphuric acid, the 

 following results were obtained. The voltameter consisted of 

 a wide test-tube of about 30 millimetres diameter, into the neck 

 of which was fixed an india-rubber cork perforated with three 

 holes: through the centre one passed a delivery tube of small 

 bore for the collection of the evolved gases ; through the 

 other two, copper rods 5-6 millims. in diameter. To the lower 

 ends of these were soldered equally thick platinum rods, 

 the free ends of which were previously forged into spade-like 

 plates which w^ere arranged parallel to one another ; the sol- 

 derings and the portions of the copper rods inside the test-tube 

 were imbedded in a thick mass of gutta-percha, with the three- 

 fold object of keeping the plates at an invariable distance from 

 one another (the voltameter being also intended for some other 

 experiments in which this was essential), of protecting the 

 copper and soldering from corrosion by the acid and the con- 

 sequent introduction of metals into the solution electrolyzed, 

 and of filling up the upper space in the tube, so that any error 

 due to alteration in temperature of the voltameter and conse- 



* Part I., supra, pp. 237-266. 

 2B2 



