484 Dr. Gore on the Greater Influence of First Quantities 



have also shown that very minute proportions of dissolved 

 acids, salts, &c. exercise a relatively great influence upon 

 the electric conduction-resistance of pure water ; and I have 

 found " that a much greater increase of electromotive force is 

 usually caused by the first amount of substance added to the 

 water than by the subsequent amounts " (" On a New Method 

 and Department of Chemical .Research," Phil. Mag. May 1890, 

 p. 421), and have given a number of instances. According 

 to the researches of M. Lindeck also {Ann. Phys. Chem. [2] 

 vol. xxxv. pp. 311-331), whilst the first portion of zinc added 

 to mercury increases its electromotive force in electrolytes, 

 further additions have scarcely any effect. 



In the present research I have extended the inquiry, and 

 have not only examined the effect of adding equal quantities 

 in succession of acids and salts to a fixed amount of water, 

 but of water to fixed amounts of acids and salts, and of bases 

 to acids, upon the electromotive force of a simple voltaic 

 couple immersed in the water at ordinary atmospheric tempe- 

 ratures. The electromotive force was measured by the method 

 of balance, with the aid of a suitable thermoelectric pile of 

 iron and German silver (see Proc. Birm. Phil. Soc. vol. iv. 

 p. 130 ; < The Electrician/ 1884, vol. xii. p. 414), and a dif- 

 ferential astatic galvanometer having 50 ohms' resistance in 

 each coil. 



In consequence of the following circumstances very little 

 error or inconvenience was caused by polarization: — (1) all 

 the measurements were made at the null-point, when no per- 

 ceptible current was passing ; (2) by experience in working, 

 the null-point could be almost instantly attained ; (3) the 

 metals were only immersed during a very short period of time; 



(4) the positive metal was cleaned each time before immersion; 



(5) the platinum was washed each time, and heated to redness 

 occasionally ; and (6) to test whether the energy of the couple 

 remained unchanged, it was occasionally balanced in distilled 

 water by a similar freshly prepared one in distilled water. 



The relatively great increase of electromotive force with a 

 zinc-platinum couple, on adding the first unit quantity of 

 chlorine, bromine, iodine, hydrochloric, hydrobromic, hy- 

 driodic, nitric, and sulphuric acid, and tbe chlorides, bromides, 

 iodides, and sulphates of potassium and sodium, and certain 

 other salts, to a fixed amount of water, have already been shown 

 in the paper referred to (Phil. Mag. May 1890, p. 421). 



The similar large effects upon a cadmium-platinum couple 

 in the reverse process of adding the first unit quantity of water 

 to a fixed amount of hydrochloric, sulphuric, and nitric acid 

 are shown by the following curve?. The electromotive force 



