428 



Profs. John Perry and W. E. Ayrton. [May 27, 



As a further example of the reduction by our method of the results 

 of observation, we give five tables of experiments made with a special 

 form of voltameter devised so as to enable experiments to be made 

 with a gas-freed liquid, or a liquid more or less saturated with any 

 particular gas, and with the platinum plates previously free from gas, 

 or made to occlude any special gas. The voltameter itself was some- 

 thing like the upper part of a Geissler's mercury pump ; that is, by 

 lowering a column of mercury the electrolyte could be lowered from 

 the platinum plates, leaving them in a vacuous space. The electrolyte 

 of course commenced to boil, and to rapidly free itself from gas. By 

 a valve this gas was allowed to escape, on again raising the mercury 

 column, and the liquid above it. This operation being repeated a 

 number of times, the liquid being left for a considerable period under 

 the vacuous space towards the end of the operation, a large portion of 

 the gas in the liquid could be removed. In order to remove the gas 

 occluded in the platinums they were not, as is usual in voltameters, 

 made in the form of plates, but each was a platinum spiral, the two 

 ends of which protruded to the outside of the voltameter. By means 

 of a small Grove's battery, each of these spirals could be made red hot 

 in the vacuous space produced when the electrolyte was lowered, and 

 thus a voltameter was obtained with gas-freed platinums in a gas- 

 freed liquid, or by subsequently bubbling through a stream of a par- 

 ticular gas, with platinums in a liquid, with more or less at will of 

 that gas occluded. 



As these platinum spirals presented but a small surface, and as they 

 were necessarily some little distance apart, the currents charging and 

 discharging such a voltameter, when only one Minotto's cell was em- 

 ployed, were rather small, so that it was necessary to employ a fairly 

 delicate reflecting galvanometer. From the first elongation of the 

 spot of light on charging or discharging the voltameter, we could 

 calculate the time integral of the current in the first half swing of the 

 needle, and the subsequent time readings of the diminishing deflection 

 were ascertained by an experienced observer, dotting with a pencil on 

 the horizontal cylinder revolving uniformly (referred to at tne com- 

 mencement of the paper) the limits of the excursions of the spot of 

 light in the successive swings about the varying mean position, the 

 locus of which was subsequently drawn in by our method already 

 referred to. 



In the following table u is the observed current flowing into the 

 voltameter to charge it at the time t, from the moment of applying one 

 Minotto's cell ; the voltameter contained distilled water well freed 

 from gas, and the platinum spirals were kept red hot for some time in 

 the vacuous space, before immersion in the liquid. The solution of the 

 general differential equation leads to 



u / =86'2 + 857 6 -o-o6245^ 



