1879.] Aqueous Solutions ivith Mercurial Electrodes. 481 



in 5, and had no effect in 7. The effects of stirring upon the amount 

 of deflection were greater in alkaline liquids than in those of acid 

 reaction. 



Influence of previously heating the Solution. 



Having observed, even with solutions formed with water which 

 had been preboiled to expel dissolved air, that unless such liquids had 

 been further heated to 180° F. (and cooled), after the salt, &c, had 

 dissolved, the currents obtained in successive experiments with such a 

 solution were not quite uniform in amount, but always decreased, I 

 examined this circumstance. 



Twenty ounces of distilled water was boiled and cooled ; the salt to 

 be employed was then dissolved completely in it, and the solution 

 shaken with pure mercury. The mixture was then divided into two- 

 equal portions, one of those portions raised to a temperature of 180° F. 

 in a covered glass vessel, and the evaporated water condensed and 

 returned to the mixture, so that the solution remained unaltered in 

 composition ; the liquid was then cooled. These preheated and non- 

 preheated portions were employed respectively to charge the two appa- 

 ratuses already described. The two thermo-pairs were then simul- 

 taneously excited, their currents allowed to circulate in opposite 

 directions through the coils of the galvanometer, and the deflection 

 noted when the hot portions of the two liquids had simultaneously 

 acquired a temperature of 160° F. The following is a brief statement 

 of the results. 



Twenty ounces of distilled water, and 200 grs. of crystals of sodic 

 phosphate. The non-preheated portion of solution yielded the strongest 

 current ; deflection 1°. 



Twenty ounces of water and 2 drms. of sulphuric acid. The non- 

 preheated portion gave the strongest current ; deflection '25°. 



Twenty ounces of water and 100 grs. of partly dehydrated sodic 

 carbonate. The non-preheated portion gave the strongest current ; 

 deflection '33° at 140° F., and '25° at 160° F. 



Twenty ounces of water and 200 grs. of baric nitrate. The non- 

 preheated portion yielded the strongest current ; deflection 1°. 



The same mixture as the last ; one portion of the solution was pre- 

 heated with mercury, instead of being preheated alone. The non- 

 preheated portion gave the strongest current ; deflection 1° at 180° F. 



In each of these five experiments the non-preheated portion of liquid 

 yielded the current of greatest electromotive force. This accords with 

 the original observation that repetition experiments always yielded 

 weaker currents (see p. 480). 



In order to ascertain whether preheating the one portion of salt 

 before dissolving it had the same effect upon the current as heating it 

 after having been dissolved, the following experiments were made : — 



