Page:Experimental researches in electricity.djvu/336

310 (fig. 80), and the junction x be heated, the current there is from the silver to the antimony. If silver and bismuth form a thermo series (fig. 81), and the junction x be heated, the current is from the bismuth to the silver; and assuming that heat increases the force of contact (1044), these results will give the

direction of contact force between these metals, antimony←silver, and bismuth→silver. But in the voltaic series the current is from the silver to both the antimony and bismuth at their points of contact, whenever dilute sulphuric or nitric acid, or strong nitric acid, or solution of potassa (1000) are used; so that metallic contact, like that in the thermo circle, can at all events have very little to do here. In the yellow sulphuret of potassium the current is from both antimony and bismuth to the silver at their contacts, a result equally inconsistent with the thermo effect as the former. When the colourless hydro- sulphuret of potassium is used to complete the voltaic circle, the current is from bismuth to silver, and from silver to antimony at their points of contact; whilst, with strong muriatic acid, precisely the reverse direction occurs, for it is from silver to bismuth, and from antimony to silver at the junctions.

1047. Again;—by the heat series copper gives a current to gold; tin and lead give currents to copper, rhodium, or gold; zinc gives one to antimony, or iron, or even plumbago; and bismuth gives one to nickel, cobalt, mercury, silver, palladium, gold, platinum, rhodium, and plumbago; at the point of contact between the metals: currents which are just the reverse of those produced by the same metals, when formed into voltaic circuits and excited by the ordinary acid solutions (1000).

1048. These, and a great number of other discrepancies, appear by a comparison, according to theory, of thermo contact and voltaic contact action, which can only be accounted for by assuming a specific effect of the contact of water, acids, alkalies, sulphurets, and other exciting electrolytes, for each metal ; this assumed contact force being not only unlike thermo-metallic contact, in not possessing a balanced state in the complete circuit at uniform temperatures, but also having no relation to it as to the order of the metals employed. So bismuth and antimony, which are far apart in thermo-electric order, must have this extra character of acid contact very greatly developed in an opposite direction as to its result, to