Chemical Affinity in terms of Electromotive Fore . 263 



from -009 to '113 gramme of silver per 100 hours ('000022 

 to '00027 weber) evolved quantities of hydrogen usually only 

 differing by less than '05 cubic centim. from the quantities 

 calculated from the current passing when air-free solutions 

 of Glauber's salt, dilute sulphuric acid, or distilled water 

 were electrolysed for from 4^ to 26 hours, so that from - ll 

 to 1'09 cubic centim. were collected, the hydrogen pole being 

 a Wollaston point ; whilst a just visible evolution of 

 hydrogen was noticeable from a Wollaston point with a yet 

 smaller current, capable of depositing '001 gramme of silver 

 per 100 hours, and hence equal to '0000024 weber. Whilst 

 these experiments indicate that conduction without electrolysis 

 did not take place to any appreciable extent during the elec- 

 trolysis of the silver salt used, they are yet scarcely precise 

 enough to establish with certainty the same point in the case 

 of water, although they clearly point in that direction. 

 Accordingly the following experiments were made with a 

 view to supplementing Buff's work in this respect. 



78. Voltameters were constructed like the one represented 

 in PL III. fig. 1. A U-tube, AB, was drawn out and cut off 

 in the middle of one of the limbs, and the drawn-out part passed 

 through an indiarubber cork, C, smeared internally with 

 melted rubber to make an air-tight joint. Over this cork 

 (similarly smeared outside) was fixed a calibrated capillary 

 tube widened into a sort of thistle-funnel or bell -mouth D, 

 at the part into which the cork fitted ; this tube was bent to 

 a double right angle, so that the part used for measurement, 

 EF, pointed downwards, the lower end passing through an 

 indiarubber cork, H, into a second U-tube, G, the other end 

 of which was closed by another rubber cork through which a 

 stout glass rod, I, passed. The upper U-tube w T as provided 

 with electrodes, K and L, of platinum-foil of measured size 

 fixed to platinum wdres fused through the glass (or sometimes, 

 in the case of the longer limb, supported, as represented in 

 the figure, by a loosely fitting cork in the open mouth of the 

 tube), by means of a platinum wire sealed through a drawn- 

 out glass tube, M, which, being filled with mercury, served as 

 a mercury-cup. In order to fill the instrument, the corks 

 supporting I, and also H, were loosened, and recently 

 boiled, still hot, dilute sulphuric acid poured into the 

 longer limb of the U-tube, AB. This acid rapidly filled this 

 U-tube, and then passed over through the capillary tube, 

 DEF, into the lower U-tube, G, also filling it. A certain 

 amount of acid was allowed to run through the whole instru- 

 ment, so as to rinse out the first portion poured in, which had 

 probably absorbed air to some extent, after which the cork 



U2 



