THE PHARMACEUTICAL JOURNAL AND TRANSACTIONS. 
[December 23,1872. 
of current derived from the oxidation of iron in con¬ 
junction with carbon, silver, and copper respectively. 
But the whole subject of the relations between heat 
and electricity is one w r hich requires deep and accu¬ 
rate investigation. M. Favre, in France, and Dr. Joule, 
in England, are the principal experimenters on this 
subject, and having spent very much time in carefully 
examining the published records of their experiments 
T have no hesitation in saying that the conclusions they 
deduce cannot be accepted till they are repeated and 
varied with the most oareful precautions, either by them¬ 
selves or by others. It is much to be regretted that 
the Committee of the British Association appointed 
rthree years since to investigate and report on the 
•question in which these points are involved, and since 
reappointed from year to year, have not yet made public 
.a single syllable by way of report as to their proceed¬ 
ings or conclusions. 
I will only make one observation more before I leave 
this part of my subject, and that is, that chemical ac¬ 
tions which produce cold create a galvanic current, and 
therefore produce heat, as much as those actions which 
primarily produce heat. Thus copper and carbon, act¬ 
ing on water, produce a current exactly the same in 
kind as zinc and carbon, although the heat produced by 
the oxidation of copper is less than the cold produced 
*by the separation of the hydrogen and oxygen of the 
water. Again, you will see that while the combination 
of sulphuric acid with water, which produces heat, 
produces a galvanic current, the combination of 
acetic acid and water, which produces cold instead 
-of heat, produces also a'galvanic current of exactly the 
■same kind as the combination of the sulphuric acid and 
water. Let me then show you these facts by actual 
experiment. And I may note, by the way, that it is 
a curious circumstance that the combination of many 
acids and other substances with water, while they pro¬ 
duce a contraction of volume, at the same time produce 
cold, not heat. In the combination of an alkali with an 
-acid, which also produces much heat, you will see that 
a strong galvanic current is produced, and in this case 
the alkali, like the water in the former case, acts as 
the positive, and the acid as the negative. These cir¬ 
cumstances, with many others, illustrate the fact that 
the view of heat, as given in Tait’s ‘ Thermodynamics ’ 
nnd other better- known treatises, namely, that there is 
a certain absolute zero of temperature, fixed at - 272 C., 
where heat finally ceases to exist (just as there is a 
certain absence of motion w T hen a body is at rest), and 
that all heat above this point is equivalent to a cer¬ 
tain amount of mechanical force, is a view utterly er¬ 
roneous ; that, on the contrary, any variation of tempe¬ 
rature, either upward or downward, involves mechanical 
force, and that the true zero of temperature is, when 
all contiguous bodies are of equal temperature, just 
as the true electrical zero is when all contiguous bodies, 
are of an equal medium of electrical tension. 
But I now turn to the more practical view of the sub¬ 
ject. And here let me begin by saying that, in order 
•to understand practically the action of a battery, the 
most essential thing of all is thoroughly to comprehend 
what is called Ohm’s law. I have no hesitation in say¬ 
ing that the discovery of Ohm’s law was to electricity 
mot a whit less important, indeed, I should say more 
important, than Newton’s law of gravitation in astro¬ 
nomy and general physics ; in fact, it has been like the 
.rising of the sun to travellers groping their way in 
-darkness. It is now, of course, universally acknow¬ 
ledged as the great law of electrical action, though I 
meed hardly say that when first enounced it was received 
iby the scientific men of the day with the utmost scorn, 
mnd actually denounced as the wild ravings of a mad¬ 
man. But Ohm was then an unknown man—now’ his 
same is a household word with all electricians. This 
great law then is, that the quantity of electricity pass¬ 
ing through each part of a circuit in a given time is 
proportional directly to what is called the potential or 
electro-motive power of the elements, and inversely to the 
total resistance of the circuit. Thus, to express it alge¬ 
braically, 
Q- E 
2 “ R- 
Again, the resistance of the circuit consists of two 
parts—the internal resistance of the battery, and the re¬ 
sistance of the rest of the circuit. Calling these R' and 
R', we have the equation, 
Q — * 
1 ~ R' + R" ’ 
and in the practical comprehension of this equation un¬ 
der the different circumstances to which it is applicable 
consists the wdiole difference betwmen a good and a bad 
electrician; everything as regards the relation between 
batteries, the work they have to do, and the cost of doing 
it, depends upon this equation. If we have many similar 
cells in a battery, say n cells, then the equation becomes 
Q = 
n E 
n R' + R" • 
Q represents the amount of chemical action going on 
in a given time in each cell, and if R ;/ be small, it is 
plain that, though with many cells we get many times 
the waste of zinc and other elements of the battery, 
we get no addition to the current; on the other hand, 
if R" be large, we want a good many cells to produce 
the same current, and, in fact, as I said before, in the 
practical application of this equation to every varying 
case lies the whole art of the proper or improper use 
of a battery, and the art of using such batteries as are 
properly suited to the object desired to be attained. It 
will be obvious, from what I have said, that the main 
points of merit in a battery are— 
1st. A large potential, or electro-motive force. 
2nd. A small internal resistance, for w T here there is 
much internal resistance a large part of the power of the 
battery is wasted in itself, in overcoming—if I may so 
speak—its own friction. To these two points I may add 
two more, viz.:— 
3rd. Constancy, or a power of keeping up an action 
nearly uniform. 
4th. Permanency, or the power of working for a long 
time without attention or fresh making up of the bat¬ 
tery. 
When I say that the heat produced in a given time— 
and in some cases the magnetic power—is as the square 
of the quantity, and not simply as the quantity, you will 
see at once the great importance of having a large po¬ 
tential. 
The two instruments I have here will serve to show 
the first three points in different batteries, namely, the 
potential, the internal resistance, and the constancy for at 
least a short time. The permanency must, of course, be 
a matter of time to ascertain. The first instrument, a 
galvanometer with a large resistance, will, I think, show 
practically better than any other the potential of a bat¬ 
tery. By either observing the degree of deflection with 
the same resistance, or the resistance through which the 
same degree of deflection is produced, we get a good 
practical idea of the potential of a battery. And this is 
really all we want; an exact theoretical determination 
is valueless, as it is always varying, more or less, from 
moment to moment. 
I will now show you the practical potential of a large 
number of combinations. Let us take, as a convenient 
standard, zinc in sulphate of zinc, copper in sulphate of 
copper. 
It is more convenient in practice, though a little larger 
than the British Association unit, which they call a 
“Volt,” in which the negative is copper in nitrate of 
copper. 
You see the degree to which it attains; now let us 
compare with this the following elements:— 
