376 
fore employed not platinum plate, but plates composed of a 
metal (copper) which is more easily corroded. 
The following are the general results arrived at. 
The chief fact brought out conspicuously by the experiments 
with copper dishes is, that in many cases an increase of chemical 
action produced by heat instead of making the hot metal electro- 
positive makes it considerably negative. 
The results show that hot copper was positive to cold copper 
in the following liquids :— hydrochloric, hydrocyanic, boracic, 
and tribasic ortho-phosphoric acids ; chloride of copper (weak 
solution) ; chloride of cobalt ; chloride of manganese ; chromie 
acid ; chloride of chromium ; sulphate of zinc (weak solution) ; 
sulphate of magnesia ; chloride of calcium ; nitrate and chloride 
of strontium ; chloride of barium; nitrate of sodium (strong 
solution) ; chloride, iodide, carbonate, and biborate of sodium ; 
sulphate of sodium (strong solution) ; tribasic phosphate of 
sodium ; nitrate, chloride, and chlorate of potassium ; bromide 
of potassium (strong solution); iodide of potassium (strong 
solution) ; carbonate, acid carbonate, and bichromate of 
potassium ; aqueous ammonia; chloride of ammonium; cya- 
nide and ferrocyanide of potassium ; acetate of zinc ; and acetate 
of sodium. And negative in the following ones :—nitric, chloric, 
hydrobromic, hydrofluosilicic, and sulphuric acids ; ferrous sul- 
phate; chloride of copper (strong solution); sulphate of cop- 
per ; sulphate of zinc (strong solution); nitrate and iodide of 
sodium (weak solutions); bromide and iodide of potassium 
(weak solutions) ; iodate of potassium; chrome alum ; nitrate 
of ammonium ; oxalic, acetic, tartaric, and citric acids. The 
number of liquids in which hat copper was positive was 
thirty-six, and those in which it was negative was twenty. 
In several instances where the hot metal was negative with a 
weak solution, it became positive with a strong one ; for in- 
stance, with sulphate of zinc, nitrate, iodide, and sulphate of 
sodium, bromide, and iodide of potassium ; but with chloride of 
copper the reverse occurred, These results may be connected 
with the fact that in weak neutral solutions the chemical action 
is generally the most feeble, and therefore interferes the least with 
the direct influence of the heat in producing electric currents. 
The influence of free hydrochloric, hydrocyanic, boracic, 
ortho-phosphoric, and chromic acids, was to make the hot copper 
positive ; whilst that of nitric, chloric, hydrobromic, hydro- 
fluosilicic, sulphuric, and some of the organic acids was to make 
it negative. 
In consequence probably of the small amount of interference 
by chemical action in solutions of oxalic, acetic, tartaric, and 
citric acids, the direct influence of the heat made the copper 
negative, similar to its influence on platinum, in all acid liquids 
which do not attack that metal. 
The nature of the acid in a salt appears to exert much more 
influence than that of the base on the direction of the current ; 
for instance, in nearly all chlorides, including those of a con- 
siderable variety of bases, hot copper was positive, probably be- 
cause copper is more readily attacked by acids than by bases. 
In all decidedly alkaline liquids the hot copper was positive ; 
this is similar to the behaviour of platinum in such solutions, 
and is probably due to the same course, viz. the direct influence 
of the heat, as well as to chemical action. 
The results also show that the quantity of the current obtained 
with any given liquid generally increases with the number of 
molecules of the substance contained in the solution ; in some 
cases, however, as with sulphuric acid, carbonate of potossium, 
chloride of ammonium, and acetate of zinc, there was a limit to 
this increase ; and beyond that limit the quantity of the current 
decreased up to the point of saturation of the liquid. 
In the great majority of cases the value of the deflection increased 
much more rapidly than the strength of the solution, particularly 
with solutions of sulphate of magnesia, and also of hydrochloric 
acid and of chloride of sodium, probably because two causes 
operated, viz. increased strength of solution and diminished re- 
sistance ; in a very few cases, however, the opposite result took 
place, as with solutions of chloride and nitrate of strontium. 
Inversions of the direction of the deflection by difference of 
strength of the liquid occurred with solutions of chloride of cop- 
per, sulphate of zinc, nitrate, iodide, and sulphate of sodium, 
bromide, and iodide of potassium. 
Irregularities of the amount of deflection were very apt to take 
place with liquids which gave strong deflections, or which acted 
much upon the copper plates (for instance, nitric acid), especially 
if bubbles of air remained under the plates, or the dishes were 
wetted on their side above the liquid by the solution. 

NATURE 


[March 9, 187% 

In certain acid liquids, viz., nitric, chloric, hydrobromic, 
hydrofluosilicic, and sulphuric acids, the hot copper was strongly 
negative (notwithstanding the chemical action upon it was dis- 
tinct, and in some cases even strong) ; this is similar to the elec- 
trical behaviour of platinum in such liquids, and may be 
attributed either to the more direct influence of the heat alone 
(such as occurs with platinum plates), or to a different influence 
of the chemical action produced by the heat. Both these causes 
probably operate in such cases. 
It is probable that in all cases where the hot copper was posi- 
tive in liquids of strongly acid reaction, the positive condition 
was due to chemical action alone. 
With some liquids, especially with solutions. of hydrocyanic, 
boracic, acetic, tartaric, and citric acids, the deflections were very 
feeble, and the chemical action on the plates not perceptible ; 
whilst with others, such as nitric and chloric acid, solutions of 
the chlorides of strontium, sodium, potassium, and ammonium, 
and of carbonate, acid carbonate, and eyanide of potassium, the 
deflections were considerable, and the chemical action distinct, 
and in some cases strong, In none of the liquids (except hydro- 
bromic and chromic acids) did the hot plates appear to be /ess 
stained or corroded than the cold one; probably, in all cases, it 
was the most corroded, although in some cases the corrosion was 
not perceptible. 
The amount of deflection was not always proportionate to the 
amount of chemical action ; for instance, with solutions of chlo- 
ride of copper and iodate of potassium there was considerable 
corrosion, but only feeble currents, prebably because the plates 
became covered with a badly conducting film, whilst with hydro- 
chloric acid, chloride of cobalt, chloride of manganese, and nitrate 
of potassium, the reverse occurred. 
I consider the currents in all these experiments of difference 
of temperature to be due either (1) to the direct influence of 
heat, the effect of which is to make the hot copper negative in 
acid liquids and positive in alkaline ones (see PAi/. Mag. 1857, 
vol. xiii. p. 1) ; (2) to chemical action, which sometimes over- 
powers the direct influence of heat and reverses the effect ; or 
(3) to both these influences combined. The more ultimate cause, 
however, of the phenomena in these causes must be sought for 
in the molecular movemtents produced by heat in the metals and 
liquids. 
The current obtained with copper plates were no doubt in- 
fluenced in their amounts (if not also in their direction) by the 
oxidising action of the air upon the liquid and metal at their 
line of mutual contact, for we know that metals in contact with 
liquids oxidise much more quickly if oxygen has access to their 
wet surfaces ; and the currents were also influenced by the action 
of unequal temperature upon the air-contact line, for we know 
that-wet metals oxidise still more rapidly if heat is applied. 
General Conclusion.—The electric currents produced by the 
direct influence of unequal temperature or friction of platinum 
or copper electrodes, in conducting liquids which do not act 
chemically upon those metals, have their origin in temporary 
changes of cohesion of the layers of metal and liquid which are 
in immediate and mutual contact, and may be considered as a 
very delicate test of the kind and amount of temporary molecular 
movements produced by those causes. 
‘Further Experiments on the effect of Diet and Exercise on 
the Elimination of Nitrogen,” by E. A. Parkes, M.D., F.R.S. 
“* Magnetic Observations made during a Voyage to the North 
of Europe and the Coasts of the Arctic Sea in the Summer of 
1870,” by Capt. Ivad Belavenetz, I.R.N., Director of the Im- 
perial Magnetic Observatory, Cronstadt. 
“On the Mutual Relations of the Apex Cardiograph and 
the Radial Sphygmograph Trace,” by A. H. Garrod, of 
St. John’s College, Cambridge. 
Geological Society, February 22.—Mr. Joseph Prestwich, 
F.R.S., president, in the chair. Mr. John Thornton Har- 
yison, C.E., and Mr. M. Hawkins Johnson, were elected 
Fellows of the Society. — The following communications 
were read :—1. “On supposed Borings of Lithodomous 
Mollusca,” by Sir W. €. Trevelyan, Bart., M.A., F.G.S. 
The author referred to Mr, Mackintosh’s paper on _ this 
subject (0. ¥ G. S. vol. xxv. p. 280), and stated his con- 
viction, from examination of specimens, that the holes in 
question are the work of /Yezices, or other terrestrial Mollusca, 
He ascribed the same origin to the so-called ‘‘ Pholas-borings” 
in the limestone at Orme’s Head and elsewhere. He considered 
length of time to be a necessary element in the formation of these 

