﻿476 Intelligence and Miscellaneous Articles, 



of the electrodes ; and a flame kindled these bubbles, which showed 

 that the gas in them was hydrogen. Assuming that free sulphuric 

 acid was present in the solution, I saturated it with carbonate of 

 zinc by adding this to the solution, which I kept boiling for two or 

 three hours. This is necessary; for experiment showed me that a sim- 

 ple addition has but a slight action. The filtered solution contained 

 sulphate of zinc, an extremely small quantity of carbonate of zinc, 

 and basic sulphate of zinc, which had been formed during the boil- 

 ing. This mixture gave a far smaller polarization. 



I then compared the polarization and the inequality which occur 

 in ordinary sulphate of zinc and those which are exhibited by the 

 solution I had treated with carbonate of zinc, and measured these 

 various values. 



I took for this purpose glass troughs 80 millims. in length, 30 

 millims. in breadth and in height. The zinc electrodes measured 

 75 by 18 millims. By means of a tongue on the zinc plate the con- 

 ducting-wire could be fastened outside the liquid. 



By means of a commutator this trough could be inserted in a cir- 

 cuit consisting of a mirror-galvanometer and of a "Wheatstone's 

 bridge. The same commutator placed the electrodes in connexion 

 when the apparatus was outside the circuit. 



The resistance of the galvanometer was 694 Siemens's units, that 

 of the trough only 3 to 4. The latter could be neglected as com- 

 pared with the former. 



On the other hand, the Daniell's element which fed the bridge 

 was provided with a rheostat of 162 units, by which the variations 

 in the battery (the resistance of which amounted to about 1 unit) 

 could be neglected. This rheostat and the position of the slider 

 were so arranged that the battery could only yield a hundredth of its 

 electromotive force. 



Some preliminary experiments showed me that the battery was 

 sufficiently constant. 



First experiment. Crude sulphate of zinc. — 



The inequality gave the following numbers for the deflections of the 

 mirror : — 



millims. minutes. 

 18 after 1 



20 



„ 5 



23 



„ 10 



15 



„ 30 



12 



,, 20 



12 



„ 40 



12 



„ 60 



The number 1 2 may be regarded as constant after the lapse of a 

 certain time. We shall then further see how the electromotive force 

 may be deduced from this number. 



Polarization. — The current passed first through the trough, and 

 then directly gave, first, the force of the current minus the polari- 

 zation and, according to the direction, plus or minus the inequality ; 

 secondly, the current alone. 



