166 Dr. Gr. Gore on the Relation of Volta Electromotive 



electromotive force, it was evident that this increase could 

 not be due to absorption of energy in the form of heat. I 

 therefore examined the phenomena in another manner, to 

 ascertain whether they were related to changes of total volume 

 and of mean specific gravity of the two liquids during the act 

 of mixing. 



Different investigators have shown that when a concen- 

 trated aqueous solution of an acid, a salt, or an alkali, is 

 diluted with water, a contraction of the total volume 

 of the two liquids and an increase of the mean amount 

 of their specific gravities occur in nearly every case 

 (see Watts's ' Dictionary of Chemistry,' 2nd Supp. 

 pp. 596-604). Marignac, however, found an excep- 

 tion with a mixture of a solution of neutral sulphate 

 of sodium and sulphuric acid : in this case " expan- 

 sion always occurs " (ibid, p. 604) ; he further 

 observed that contraction takes place on diluting 

 solutions of hydrochloric acid, sulphuric acid, chlo- 

 ride of sodium, and sulphate of sodium (ibid. pp. 603, 

 604). J. Thomsen and others have also shown that 

 when a solution of caustic soda, and of various other 

 substances, is diluted, the total volume of the two 

 liquids becomes less (ibid. pp. 597-600). And Nicol 

 has 'obtained similar results by separately diluting 

 aqueous solutions of potassium chloride, potassium 

 nitrate, sodium chloride, and sodium nitrate (Phil. 

 Mag. vol. xv. 1883, p. 97 ; Journ. Chem. Soc. 1883, 

 vol. xliii. , Trans, p. 136). 



In order to ascertain w r hether contraction occurred 

 in the whole of the remainder of the cases in which 

 I had found an increased mean amount of electro- 

 motive force developed during the mixing, the follow- 

 ing arrangement (see figure) was employed : — A is 

 a glass tube about 12 inches high and ^ an inch in 

 diameter, with a perfectly fitting stopcock in the 

 middle. The lower end of this tube was closed by a 

 vulcanized rubber bung, and the upper end was fitted 

 with a perforated bung surmounted by a tall glass 

 tube of narrow bore open at both ends, and provided 

 with a scale or index capable of sliding up or down. 

 The stopcock and bungs were coated with grease, and 

 the apparatus was proved to be perfectly water-tight. 

 The entire portion of the apparatus below the index- 

 scale was immersed side by side with a sensitive ther- 

 mometer in a large vessel of water at about 16 Q 0., in 

 order to keep the apparatus at a sufficiently uniform 



