[This is one of the _Naturo-Philosophical_ volumes of the
_Cabinet Cyclopaedia_, and is therefore to be viewed as a
portion of that series rather than as a substantive work. Its
preparation has been entrusted to Mr. M. Donovan, Professor of
Chemistry to the Company of Apothecaries in Ireland; so that
it comes to us with some share of recommendatory experience
on the part of the editor. It would, however, be difficult to
point out the advantages of Mr. Donovan's volume over others
of the same description. Neither will such distinction be
looked for but in a scientific journal. The arrangement is
clear and satisfactory; the manner plain and illustrative; and
the matter in accordance with the science of the present day;
though in a few cases the nomenclature is somewhat overloaded
with hard names, and presumes more previous acquaintance with
the subject than is consistent. We subjoin a few extracts of
popular interest.]
_Caloric, or the matter of Heat._
Heat is admitted by the philosophers of the present day to be the
principle concerned in repulsion; and heat and cold are known to
produce expansion and contraction in all bodies. Heat is, therefore,
the antagonist of cohesion. Chemists have thought it necessary to make
a distinction between the senses in which the word heat may be taken.
In its usual acceptation, it merely means the effect excited on the
organs of sensation by a hot body. But as this must be produced by
a power in the hot body independent of sensation, that power is what
chemists understand by the word _heat_: and to distinguish between
the effect and its cause, the term _caloric_ has been substituted.
The introduction of this term appears altogether unnecessary, when
the sense in which the word _heat_ should be understood is explained.
Caloric means the _cause_ of the _sensation_ heat: and there seems no
reason to fear that the perception of heat by the organs of sensation
can ever be misunderstood to be the agent in chemical phenomena.
_Omniscience displayed in the constitution of the Atmosphere._
In the constitution of the atmosphere we have ample scope to admire
the design and execution of a structure calculated, with such wondrous
precision, to fulfil its purposes. Were the atmosphere to consist
wholly of oxygen; and the different kinds of objects which compose,
and are found upon, the globe, to remain what they are; the world
would run through its stages of decay, renovation, and final
destruction, in a rapid cycle. Combustion, once excited, would proceed
with ungovernable violence; the globe, during its short existence,
would be in a continual conflagration, until its ashes would be its
only remains: animals would live with hundred-fold intensity, and
terminate their mortal career in a few hours. On the other hand,
were the atmosphere wholly composed of azote, life could never have
existed, whether animal or vegetable, and the objects of the Creator
in forming this world would not be fulfilled. But the atmosphere is a
wholesome mixture of these two formidable elements, each neutralizing
the other's baneful influence. The life of animals quietly runs
through its allotted space; and the current of nature flows within
prescribed limits, manageably and moderately.
_Tartaric Acid._
Every one knows, that when a large quantity of the juice of grapes is
left to spontaneous fermentation, the result is wine. When wine has
been kept some time to depurate in wooden vessels, it deposits, on the
side of the vessel, a hard crust of dark coloured matter, the taste
of which is sour. This matter is impure; but, when purified by various
crystallizations, it becomes perfectly white and crystalline; and
then it is known in commerce by the name of _cream of tartar_. The
etymology of the singular name, tartar, is uncertain: it is derived
from _tártaros_, as some say, because it occasions pains equal to
those endured in the infernal regions; and, as others say, merely
because this substance deposits itself in the inferior parts of the
cask. Tartaric acid may be obtained from cream of tartar by a
process analogous to that given for obtaining citric acid. It has an
exceedingly acid taste: it dissolves readily in water, and is soluble
in alcohol. Its crystals are of a very irregular shape. In 100 parts,
by weight, there are 12 of water; the remaining 88 parts are the pure
anhydrous acid, composed of 32-39 parts of carbon, 52-97 of oxygen,
and 2-64 of hydrogen. This acid exists abundantly in other fruits, but
especially in the tamarind; in the grape it exists along with citric,
malic, and an acid called _vinic_, which resembles tartaric acid
in many respects, but differs from it in others, and concerning the
nature of which almost nothing is known: these four constitute the
agreeable tartness of the juice of that fruit.
_Oxalic Acid_.
The plant called sorrel is valued for its acidulous taste. This
acidity is owing to the presence of a peculiar acid, which may
be separated from the juice, and from the potash with which it is
combined, by a process analagous to that described for the preparation
of citric acid. It has obtained the name of _oxalic acid_, from
the generic name of the plant, _oxalis acetosella_. This acid forms
readily into regular crystals, of which one half the weight is water,
the other half being pure acid. It is a remarkable circumstance in
its constitution, that it contains no hydrogen, and that it consists
merely of carbon and oxygen--there being twice as much oxygen as
there is carbon. So that it differs from carbonic acid merely in the
relative quantities of its ingredients. Oxalic acid can be prepared by
an artificial process, with great ease, from sugar, and six times its
weight of nitric acid,--the former affording the carbon necessary to
its formation, and the latter the oxygen. It is only necessary to
heat the nitric acid on the sugar; the sugar dissolves, and there is
a violent effervescence, which must be moderated by immersion in
cold water: when the mixture cools, crystals of oxalic acid form in
abundance, which may be purified by a second crystallization.
Oxalic acid is an active poison; many persons have fallen victims to
its virulence, by having swallowed it in mistake for Epsom salt, which
it resembles in appearance. In all probability, this would not prove
to be the only vegetable acid capable of acting as a poison. Chalk
finely powdered, and diffused in water, is the proper antidote to the
poison of oxalic acid.
[The chapter on Combustion contains some new facts; and that
on the Atomic Theory is more attractive than might have been
expected.]
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