THERMO ELECTRIC EFFECTS AND VOLTAIC CONTACT COMPARED. 
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tact (2056.), 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, when- 
ever dilute sulphuric or nitric acid, or strong nitric acid, or solution of potassa (2012.) 
are used ; so that metallic contact like that of the thermo circle, can at all events have 
vei'y 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 hydrosulphuret 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 anti- 
mony to silver at the junctions. 
2059. 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 (2012.). 
2060. 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 render them only 
a feeble voltaic combination with each other : and with respect to silver, which 
stands between tin and zinc thermo-electrically, not only must the same departure 
be required, but how great must the effect of this, its incongruous contact, be to 
overcome so completely as it does, and even powerfully reverse the differences which 
the metals (according to the contact theory) tend to produce. 
2061. In further contrast with such an assumption, it must be remembered that, 
though the series of thermo-electric bodies is different from the usual voltaic order 
(2012.), it is perfectly consistent with itself, i. e. that if iron and antimony be weak 
with each other, and bismuth be strong with iron, it will also be strong with anti- 
mony. Also that if the electric current pass from bismuth to rhodium at the hot 
junction, and also from rhodium to antimony at the hot junction, it will pass far more 
powerfully from bismuth to antimony at the heated junction. To be at all consistent 
with this simple and true relation, sulphuric acid should not be strongly energetic 
with iron or tin and weakly so with silver, as it is in the voltaic circuit, since these 
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