316 
MR. WHEATSTONE ON NEW INSTRUMENTS AND PROCESSES FOR 
Amalgam of zinc . . Sulphate of copper . . Copper . . 30 turns. 
Amalgam of zinc . . Dilute sulphuric acid . Copper . . 20 turns. 
Amalgam of zinc . . Chloride of platinum . Platinum . 40 turns. 
Amalgam of zinc . . Dilute sulphuric acid . Platinum . 27 turns. 
6. The proportion of zinc in the liquid amalgam does not appear to alfect the 
electro-motive force of the voltaic element of which it forms part ; the number of 
turns of the rheostat remains the same although the quantity of zinc may vary very 
considerably. I was therefore led to think that tolerably accurate measures might 
be made of the comparative electro-motive forces of the alkaline and earthy bases. 
An element was formed of liquid amalgam of potassium, sulphate of zinc, and zinc ; 
the potassium was in proportion to the mercury less than 2 per cent. ; there was no 
apparent local action, and the current was remarkably constant and continuous. 
The following were ascertained to be the electro-motive forces of different elements 
in which the positive metal was amalgam of potassium, and the negative metals re- 
spectively were zinc, copper and platinum. 
Amalgam of potassium . . Sulphate of zinc . . . Zinc. . . 29 turns. 
Amalgam of potassium . . Sulphate of copper . . Copper . . 59 turns. 
Amalgam of potassium . . Chloride of platinum . Platinum . 69 turns. 
The electro-motive force of the first combination nearly corresponds with that of 
zinc and copper, and when the resistance in the circuit is equivalent, produces a cur- 
rent having nearly the same degree of force. The third combination is one of great 
electro-motive energy, and when a voltameter with small electrodes is interposed in 
the circuit, decomposes the water in it abundantly. 
It would not be difficult to submit to experiments of this kind all the alkaline and 
earthy bases ; as the proportion in the amalgam does not seem to be of importance, 
they might be easily prepared by means of a voltaic battery. It would be interesting 
to know what rank the hypothetical base of ammonia would hold in this scale of 
electro-motive forces. 
7. A still higher electro-motive force may be obtained by employing, in conjunc- 
tion with the amalgam of potassium, a platinum plate covered with a film of peroxide 
of lead*. Such a plate is easily prepared by making it the positive electrode in a de- 
composing cell, charged with a solution of acetate of lead. The films thus formed exhibit, 
as Nobili has shown, according to their thickness, the colours of Newton’s rings. 
Amalgam of zinc . . Dilute sulphuric acid . . Peroxide of lead . 68 turns. 
Amalgam of potassium Dilute sulphuric acid . . Peroxide of lead . 98 turns. 
* A rheomotive series of ten such elements will have an electro-motive force equal to thirty-three elements 
of Daniell’s battery, or fifty of Wollaston’s arrangement in good action. Voltaic combinations, in which 
peroxide of lead is substituted for the negative metal, have been experimented with by Professors Schonbejn 
(Phil. Mag., 3rd Series, vol. xii. p. 225, March 1838) and De La Rive (Archives de l’Electricite, No. 7, April 
1843). 
