237 



natant liquid proceeds from the positive wire towards the negative 

 one, and negative flow, &c. when it passes in the opposite direction. 



5. The usual method of manipulation I have adopted has been to 

 take a watch-glass of about 2 inches diameter and place in it by means 

 of a small gutta-percha spoon capable of containing from 20 to 50 

 grains of mercury, a globule of that metal of about 30 grains weight, 

 adding sufficient of the electrolyte to just cover or nearly cover the 

 globule of metal, and sifting a few particles of finely powdered char- 

 coal or asphaltum upon the surface of the liquid, to facilitate obser- 

 vation of the movements ; next, using a Smee's battery of 22 pairs 

 of plates 4 inches deep and 2|- inches wide with terminal platinum 

 wires, charged with one measure of oil of vitriol and 15 measures of 

 water, I place the end of the negative wire in the liquid about ^th of 

 an inch from the mercury, and then carefully immerse the end of the 

 positive wire in the liquid on the opposite side of the globule, at a 

 greater distance from the mercury than the negative wire in the case 

 of an alkaline solution, and at a less distance in the case of an acid 

 one, in order to prevent the mercury from touching the electrodes 

 by its movement and thus vitiating the first and purest result. A 

 polished oval space 2 inches long, fths of an inch wide, and -f ths of 

 an inch deep, with a curved bottom, formed in a thick plate of glass 

 and substituted for the watch-glass, did not admit of such satisfactory 

 freedom of motion. In doubtful cases of movement, a small porcelain 

 boat, such as is used in organic chemical analysis, was sometimes 

 employed instead of the watch-glass ; and in certain special experi- 

 ments a V-tube was employed. In nearly all cases the mercury gra- 

 dually became impure, and therefore fresh mercury was taken for 

 each experiment. 



A. Conditions of the Movements. 



6. Two substances are always required in these experiments, with 

 one alone the movements never occur. 



7. To determine whether both the substances must be in a liquid 

 state: 1st. A portion of mercury in a watch-glass was connected 

 with the negative pole of a battery and covered with a flat piece of 

 platinum foil ; a drop of solution of sulphate of potash was placed 

 upon the foil and the end of the positive wire dipped into it. No move- 

 ment, either sudden or continuous, of the solution or mercury took 

 place. On substituting for the foil a circular piece of filtering paper 

 varnished all round its edge and covered with several drops of the 



s 2 



