December 23, 1872.] THE PHARMACEUTICAL JOURNAL AND TRANSACTIONS. 
505 
difficult to define individually, because it was evidently 
saturated with solid santonol. Analysis gave— 
Found. Calculated. 
C. 84-1 84-1 
II.8*9 8-4 
O (difference) . . . 7'0 7"5 
100-0 100-0 
The author is continuing his investigation of this 
body, and of the other derivatives of santonin. 
GALVANIC BATTERIES.* 
BY THE REV. H. HIGHTON, M.A. 
I shall not attempt to give any ultimate explanation 
of the phenomena of galvanism. It appears to me that 
it is true wisdom in science not to attempt to do more 
than to give an intelligent and comprehensive classifi¬ 
cation of the phenomena themselves. Deeper theories 
may sometimes be useful in suggesting experiments, if 
it be borne in mind that those theories must always be 
doubtful, and mere matters of guess, and, at best, simply 
provisionary. Thus Maxwell has shown that the laws 
of hydraulics may be applied to electrical currents, 
though he cautiously and wisely guards us against sup¬ 
posing that it follows from this that there is any real 
electric fluid similar to ordinary fluids. It would have 
been well if other well-known scientific men had been 
content to follow his example. In the same way I 
should object to the assumption of any ultimate theory 
of galvanism, beyond the mere intelligent and classified 
expression of the laws of the phenomena. 
In the kindred subject of heat, I think great injury 
has been done by asserting that it is “a mode of mo¬ 
tion,” which has introduced many wild and visionary 
ideas. If the word “motion” be meant simply as a 
translation of the Greek word klvtjctis, which includes 
nearly all kinds of change, and it also be meant that a 
change of temperature is a mode of motion in the ordi¬ 
nary English sense of the word, the assertion is, in a 
certain sense, true, but deceptive; if it be meant that 
simple heat, without change of temperature, is motion 
of any kind, this is not only extremely doubtful, but, I 
believe, absolutely untrue.f With regard to galvanism, 
then, I would merely say that it would appear that 
wherever there is a chemical there is also a galvanic ac¬ 
tion, which only requires proper arrangements to be 
made for exhibiting it. 
Perhaps the simplest method of producing a galvanic 
current is by the formation or decomposition of water. 
Ihus, it we have two plates of platinum, the surface of 
one of which is covered with a film of hydrogen, and 
the other with oxygen, on making a metallic connection 
between the two, a galvanic current passes, and the hy¬ 
drogen and oxygen unite and form water. Conversely, 
if we take two metals, one of which has a greater affinity 
for oxygen than the other, and place them in water, then, 
on metallically connecting them, the water is separated 
into oxygen and hydrogen, the oxygen uniting with the 
more oxidizable metal, and the hydrogen being evolved 
on the surface of the other metal, and a galvanic cur¬ 
rent flows. I will show you both these actions by actual 
experiment. In both cases one pole of the battery is 
* Lecture delivered before the Society of Arts, Wednesday. 
December 11th, 1872. 
t Aristotle,. in his ‘ Physics,’ suggests an important prin¬ 
ciple which might with advantage be studied by our modern 
theonsts on the subject of heat. He says (•' Physics,’ v. 1, 5), 
AAA icrow o v% tj X^\jk6tt]s Kivrjffis aWa t) A evKavcns. 
That is, “But perhaps whiteness is not a mode of motion, but 
whitening is so by analogy heat and cold are not modes of 
motion, but heating and cooling are so—that is in the Aris¬ 
totelian sense of the word. 
said to become positive and the other negative, and the 
action passing between the two is commonly called a 
galvanic current. 
1 4Take, again, the simplest of all forms of a galvanic 
battery—zinc and carbon, with a dialyte, as it is called, 
of dilute sulphuric acid between them ; the oxygen of 
the water unites with the zinc, and forms oxide of zinc ; 
the sulphuric acid unites with the oxide, and forms a 
sulphate of zinc, and the hydrogen is evolved on the 
surface of the carbon. This double chemical action 
gives rather more electricity than the single action, as 
you see. 
_ Now, it is a well-known fact that chemical combina¬ 
tions frequently produce heat, and it is also a well- 
known fact that an electrical current in passing through 
a homogeneous conductor also produces heat; and it is 
an exceedingly interesting problem to ascertain what 
relation the heat of the chemical combination bears to 
the heat produced in the conductor of the current. An 
investigation of this kind requires the most delicate and 
expensive apparatus, much more delicate and expensive 
than I possess ; but in searching into the records of the 
most trustworthy experimenters on this point, and com¬ 
paring the results obtained by them, I have arrived at 
the folio wing conclusions:— 
1. That, in all cases of galvanic action, the heat 
evolved in the battery, plus that in the exterior circuit, 
is exactly equal to the heat produced by the chemical 
action. 
2. That, in most cases, a certain portion of that heat 
is retained exclusively in the battery, besides what is 
due to the internal resistance of the battery, and is not 
transmitted through the circuit. 
3. That the potential of the battery varies, not only 
with the total chemical heat produced, but also with the 
proportion which that part of the heat which is trans¬ 
mitted through the circuit bears to the total chemical 
heat produced by the action of the elements of the 
battery. Indeed, the potential of a battery is exactly 
proportional to the amount of heat transmitted through 
the circuit by each unit of the atomic weight of the 
metal or other substance consumed or chemically 
changed. Thus, if we take two batteries, one of zinc, 
sulphuric acid and carbon, and another of zinc, sul¬ 
phuric acid and copper, the heat evolved by the sul- 
phoxidation of the zinc is the same in both cases; but 
the potential of the former, and consequently the heat 
evolved in the circuit, is greater ;—what becomes of the 
difference P Is the heat in some mysterious way lost ? 
No ; the surplus heat is not evolved in the circuit at all, 
but remains in the liquid of the battery, useless for the 
production of electricity. Now, it is an exceedingly 
remarkable circumstance that the only battery yet exa¬ 
mined in which the whole of the heat produced is trans¬ 
mitted through the circuit, is that form of the Daniell’s 
battery in which zinc, in a solution of sulphate of zinc, 
is used for the positive, and copper, in a solution of 
sulphate of copper, for the negative, and in which the 
sulphuric acid and oxygen are transferred from the cop¬ 
per to the zinc. 
With zinc, strong sulphuric acid and platinum, about 
five-sixths of the heat produced is transmitted through 
the circuit, but this varies somewhat with the strength 
of the acid; with iron in sulphate of iron and copper 
in sulphate of copper, only about two-thirds are trans¬ 
mitted ; with copper in nitrate of copper, and silver in 
nitrate of silver, about £§. In this way we account for 
the circumstance that, with the same positive metal, the 
potential varies with the character of the negative 
metal, less of the heat of the oxidation of the posi¬ 
tive metal being transmitted through the circuit, and 
more retained in the battery itself. I may as well say 
that I obtained these results by comparing some well- 
known experiments of M. A. Favre with some very im¬ 
portant ones of M. Soret, which are scarcely known at 
all. I will illustrate this by showing you the amount 
