490 



REroRT— 1884. 



f' 



proceeds to fonnd a number of statements which arc true,' thongh 

 scarcely simple ; in fact, they perhaps rather tend to complicate what may 

 be held to be a simple matter. 



(Schonbein, in a letter to Fiiraday published in the ' Philosophical 

 Magazine ' for 1838,- throws out a remarkable suggestion with regard to 

 ' chemical tendency ' as the possible source of a current, or rather of 

 ' force electromotive.' His language and ideas are in many respects old- 

 fashioned and erroneous; he uses such phrases as 'a current of tendency,' 

 he supposes currents with no electrolytic i)Owor to exist, and of course is 

 not troubled about energy considerations. But I feel little doubt that 

 had ho lived later he would have held that, while cAirrcnts were due to 

 chemical action, ehctromotict' force was due to 'chemical tendency'; 

 and this is pretty exactly my own view of the matter. 



I have only just discovered this Schonbein letter, and I have also 

 found some paragraphs in Faraday which more in detail, and with fair 

 <listinctness, express what I believe to be the true view, (See §§ 803-000, 

 ' Exp. lies.' vol. i.) 3 



' Except, indeed, a doubtful statement at the end of Number 2, .nnd an ermncoiis 

 bit of re.-isoning at the end of Number 1, though the eonchision dr.iwn is correct. 



" S^'hiinbein : I'hil. J/c///. vol. xii. pp. 2'la and llll. The two motst striking' sen- 

 tences are here extracted : — 



M'.efore elosins? my letter, allow nie to communicate to you in a general nianiii'i- 

 the view which I have taken of the subject in question. In the iirst place, I nui^t 

 tell you that I am by no means inclined to consider mere contact in any case as the 

 cause of the exeiteuient of even the most feeble current. I maintain, on the 'on- 

 trary, in accordance with the priuci])les of the chemical tlieory, that any current 

 j)roduced in a hydro-electric voltaic circle is always due to .some chemical action. 

 I'ut as to tlie idea which I .attach to the term "chemical action," I go further than yoii 

 and i\l. de la Kive seem to go; i'oi- I maintain that any tendencj' of tw<j dilfcrcnt 

 sul)stances to unite chemically with one another must be considered as a cheniitiil 

 action, be that tendency followed uji by the actual combination of those substances 

 or bo it not, aiul that such a teiulency is capable of putting electricity into circulaticm.' 

 And on page ;>1 1 he exjilains this last phrase, which he has elsewhere called a 

 current of tendency, thus : — 



' As what I term a current of tendency is no doubt in some cases nothing but that 

 electrical state which the voltaists consider to be the elfect of their " force electro- 

 motive," or of contact, it ajipears to me that, from some of the facts above staletl, a 

 specific and most important conclusion regarding the theory of the pile can be drawn. 

 Even if we grant to the voltaists our current of tendency to be the effect of more 

 ■contact, the facts alluded to prove that such a current iloes not po.sscss a sensibk' 

 <legree of electrolysing power, consequently that the chemical effects of the common 

 voltaic arrangements have nothing to ilo witli current elcctricitj' excited by contact.' 

 •' Extract from Furuihn/H Expi'rimenial Itcseavchcs^, vol. i.; — 

 ' (89l{.) The use of victullic contact in a single pair of plates, and the cause of it> 

 great superiority above contact made by other kinds of matter, become now very 

 i'vident. When an amalgamated zinc jilate is dipped into dilute sulphuric aeiil, thi' 

 force of chemical aflinity exerted between the metal and the fluid is not auflicientl.v 

 powerfid to cause sensible action at fh(! surfaces of contact, and occasion the (teconi- 

 position of water by the oxidation of the metal, although it is suflicicnt to prodmc 

 t<uch a condition of the electricity (or the power upon which chemical atliniiv 

 depends) as would produce a current if there were a path o])en for if; and tiiat 

 contact would complete the conditions necessary, under tlie circumstances, for tlu' 

 flecomposition of water. 



' (894.) Now the jircsence of a piece of platina touching both the zinc and the llui 1 

 to be decomposed opens the path required for the electricity. Its direct com in ii»i- 

 cation, with the zinc is effectual, far beyond any comnmnication made between it ami 

 that metal {i.e. between the i)latina and zinc) by means of decomposable comUictirn.^ 

 bodies, or, in other words, electrolytes, as in the experiment already described [that ot 

 decomposing iodide of potassium without metallic contact by interposing it f^" 

 blotting paj)er between the platinum and the zinc of a simple voltaic cell]. 



