September 3, 1870.] THE PHARMACEUTICAL JOURNAL AND TRANSACTIONS. 
185 
The behaviour of glass tears affords a good ex¬ 
ample of such internal tension ; if they are scratched 
at any part of the surface so as to disturb the equili¬ 
brium of the parts, the tears fly to powder with 
great force. In this case there is no alteration in 
the composition of the glass; the state of tension 
obtained only in regard to the homogeneous particles 
of glass, not in regard to its constituents. In the 
case of fulminating silver or of nitroglycerin, this 
tension obtains especially in regard to the dis¬ 
similar particles or the constituents of the sub¬ 
stances. 
Nitroglycerin, or fulminating silver, may be heated 
above 100° C. without undergoing decomposition, 
wliile the breaking of a small crystal of fulminating 
silver, or a slight blow upon nitroglycerin, at once 
causes the constituents of those substances to assume 
a state of stabile equilibrium with violent explosion. 
If nitroglycerin is dropped upon a red-hot iron it 
burns completely with a slight hissing, but without 
any explosion. 
In the one case an enormous motive force is de¬ 
veloped by the blow, while in the other case heat is 
generated by combustion. The motive force is the 
result of an internal molecular motion; the heat is 
a consequence of perfect combustion of the consti¬ 
tuents of nitroglycerin. 
Tliesa examples are evidently quite inappropriate 
for elucidating the exercise of muscular force in the 
animal body, which takes place in a totally different 
manner; they are intended merely to show that by 
the alteration of internal arrangement of the consti¬ 
tuents of certain compounds great mechanical effects 
may be produced without any action of oxygen from 
without. 
The albuminates of the plant world are the most 
complex nitrogen compounds that we know. All 
the constituents of the animal body are produced 
from the albumen of the body by an altered internal 
arrangement of the parts of albumen, or by their se¬ 
paration. In these changes oxygen exercises a deter¬ 
mining influence without being the cause of them; 
and it may be assumed that if these products of 
albumen be sources of power, the motion they pro¬ 
duce depends upon the tension accumulated in them 
during their formation and liberated in their decom¬ 
position, not upon their combustion or upon the 
conversion of heat into motive force. 
It is quite certain that the substance of the mem¬ 
branes and those constituents of bone which furnish 
gelatin, that blood fibrin, the nitrogenous consti¬ 
tuents of brain, the acids of bile, liippuric acid and 
wine acid, are products of the transformation and 
breaking up of albumen; but we have no evidence 
that albumen yields urea,^carbonic acid and water 
as the result of combustion. 
All attempts to produce urea from albuminates 
by oxidation have failed as completely as the attempt 
to produce alcohol from sugar by chemical means; 
and probably the conversion of uric acid into urea 
and carbonic acid may afford a good example of the 
processes and changes which the albuminates un¬ 
dergo in the animal body. 
Uiic acid, like albumen, is one of the most difficult 
substances to burn directly; it is not broken up by 
concentrated sulphuric acid, or by boiling with hy¬ 
drochloric acid or potash; but there is probably no 
other substance of which the constituents are so 
readily moveable under the simultaneous influence 
of oxygen and acids or alkalies, none that is suscep¬ 
tible of conversion into such a multitude of products 
as uric acid is. 
By addition of two equivalents of oxgyen in the 
presence of an acid, uric acid breaks up into urea 
and alloxan; by further addition of oxygen, alloxan 
breaks up into urea and carbonic acid. In the pre¬ 
sence of a strong base and oxygen, uric acid breaks 
up into oxalic acid, allantoin and urea; by a further 
addition of oxygen allantoin breaks up into urea and 
allanturic acid, this latter substance containing the 
elements of carbonic acid and urea. 
In all these cases urea is produced from uric acid 
by addition of oxygen; but it is not, in any case, a 
product of .direct oxidation; it is produced by the 
breaking up of a newly formed and more highly 
oxidized compound. 
{To be continued.) 
WHAT IS ENERGY ?* 
BY BALFOUR STEWART. 
It is only of late years that the laws of motion 
have been fully comprehended. No doubt it has 
been known since the time of Newton that there can 
be no action without reaction; or, in other words, if 
we define momentum to be the product of the mass 
of a moving body into its velocity of motion, then 
whenever this is generated in one direction an equal 
amount is simultaneously generated in the opposite 
direction, and whenever it is destroyed in one direc¬ 
tion an equal amount is simultaneously destroyed in 
the opposite direction. Thus the recoil of a gun is 
the appropriate reaction to the forward motion of the 
bullet, and the ascent of a rocket to the downrush of 
heated gas from its orifice; and in other cases where 
the action of the principle is not so apparent, its truth 
has notwithstanding been universally admitted. 
It has, for instance, been perfectly well understood 
for the last 200 years that if a rock be detached from 
the top of a precipice 144 feet high it will reach the 
earth with the velocity of 96 feet in a second, wliile 
the earth will in return move up to meet it, if not 
with the same velocity yet with the same momentum. 
But inasmuch as the mass of the earth is very great 
compared with that of the rock, so the velocity of the 
former must be very small compared with that of the 
latter, in order that the momentum or product of 
mass into velocity may be the same for both. In 
fact, in this case, the velocity of the earth is quite 
insensible and may be disregarded. 
The old conception of the laws of motion was thus 
sufficient to represent what takes place when the 
rock is in the act of traversing the air to meet the 
earth; but, on the other hand, the true physical con¬ 
comitants of the crash which takes place when the 
two bodies have come together were entirely ignored. 
They met, their momentum was cancelled; that was 
enough for the old hypothesis. 
So, when a hammer descends upon an anvil, it 
was considered enough to believe that the blow was 
stopped by the anvil; or when a break was applied 
to a carriage-wheel it was enough to imagine that 
* Reprinted from Nature. This is the first of a series of 
papers on a subject that is daily becoming more important in 
its general scientific bearing, while it is treated in so clear 
and instructive a way that the papers cannot fail to be use¬ 
ful to all who read them carefully.—E d. Pn. J. 
