The Liverpool Standard and General Commercial Advertiser.
Liverpool, Merseyside, England, 1839-03-15 00:00:00

LIVERPOOL MECHANICS' INSTITUTION.

LECTURES ON ORGANIC CHEMISTRY.

On Saturday evening Dr. Brett delivered the second of his
valuable lectures upon this important subject, in which he
entered fully into the nature and composition of organic
acids and bases, exemplifying by striking experiments the
theories which he propounded. The elegance of these ex-
periments was only equalled by the neatness of the manipu-
lation, which, as it is only to be acquired by long and con-
tinued practice, is an unfailing distinction to the eye between
a theoretical and a practical chemist.
In the last lecture I introduced to your notice the different
substances which constitute organic bodies, and I endea-
voured to demonstrate several elements which constitute
these substances. I attempted to show that organic bodies were
constituted of four separate elements, one of which is solid,
the three others gaseous. I also introduced to your notice
the mode in which organic substances are ultimately analyzed,
and I explained, by experiment, the method by which the
elementary constituents of such organic substances are to be
eliminated, demonstrating the existence of carbon, hydrogen,
and nitrogen. In the present lecture I shall introduce to
your notice the proximate principles which arc derived from
the organic kingdom of nature ; and when I speak of proxi-
mate principles, it is necessary that I should state to you
what is understood by the term. The different substances
which are obtained from the vegetable or animal kingdom
are resolved into a variety of what are called proximate prin-
ciples. The various secretions of plants, as well as those
occurring in animals, are by no means simple elementary
substances, but are constituted of a variety of substances
called proximate principles, and these substances are sepa-
rated one from another by means of certain solvents. These
solvents are water, alcohol, and ether, and by means of these
fluids we are capable of separating the various proximate
principles which enter into the constitution of animal and
vegetable substances. If for example we take the root of a
plant, we find that we are capable of separating from it a
variety of principles. Mere cold water will abstract starch
and sugar. Spirits of wine will remove from this solution of
starch and sugar the sugar alone, and leave the starch. And
that substances which' is found to be insoluble both in the
water and in the spirit, is called for the most part ligneous
fibre or lignia. Now this process is termed a proximate
analysis. It is the mode by which these principles are sepa-
rated from the plant without suffering any change. They are
closely associated with each other in the organization of the
plant, and are separated by means of the solvents to which I
have alluded ; we find, therefore, that starch is not readily
removed by means of cold water, that sugar and gum are
readily soluble in these menstruum ; but when our object is to
separate each principle from the other, we have recourse to
hot water, with a view of separating the starch. Cold water,
with a view of separating the gum and sugar ; and alcohol,
with a view of separating the gum from the sugar. The
sugar being soluble whilst the gum is left behind, and that
principle which is not soluble in either of these menstrua, is
termed ligneous fibre. I have introduced this familiar mode
of proximate analysis, in order that you might understand
what is meant by the terms proximate analysis and proximate
principles. The proximate principles are constituted of
oxygen, hydrogen, and carbon, and sometimes, but not
essentially so, of nitrogen. Independently, however, of
these principles which enter largely into the consti-
tution of organic substances, we have a variety of
others, and they may very conveniently be divided into
three classes. We have, in the first place, those principles
which are of an acid character : secondly, we have those which
have basic properties ; and, thirdly, we have those which are
neutral, possessing neither an acid or a basic character. The
term acid must be familiar to all. We know that it., possesses
peculiar properties, such as exciting an acid taste. It pos-
sesses the property reddening vegetable blues :it also pos-
sesses, and which is the most essential property of acids, the
property of neutralizing alkalies or basic substances. Now,
such substances are to be met with in the vegetable kingdom,
and they, therefore, constitute one class of proximate prin-
ciples. The second class are those which, to a certain ex-
tent, are analagous to the alkaline bodies which are met with
in the mineral kingdom. We know that in the mineral king-
dom potash, soda, lime, and magnesia abound ; but these
substances are recognized as alkalies, as they convert vege-
table blues and reds into greens, and possess the power of
saturating acids. The same thing occurs in vegetable struc-
tures. We are able to recognise in plants substances pos-
sessing the same properties as those of the inorganic king-
dom. The neutral bodies belonging to the organic kingdom,
which are neither acid-or alkaline, are exceedingly abundant,
as in this class we rank gum, starch, &c.
It is my purpose, in the present lecture, to consider more
especially those substances which are of an acid nature, and
which may be termed the organic acids. They occur very
abundantly in the organic kingdom, and there are very few
plants which do not contain certain quantities of these orga-
nic acids. They are met with both in a free state, uncom-
bined with any base, but in general combined with a base.
The oxalic, carbonic, and mellitic acids are simply constitut-
ed of oxygen and carbon, and in this respect are very re-
markable, as the organic acids are generally composed of
three elements. We then come to the formic acid, which is
an acid derived from the animal kingdom, and also capable
of being produced artificially by the action of certain re-agents
upon vegetable substances. The acetic acid and the benzoic
belong to the vegetable kingdom, as do the succinic, tartaric,
citric, malic, and gallic.
I shall first consider oxalic acid, as it is one of extreme
interest, from a variety of circumstances. It is abundantly
met with in the vegetable kingdom. There are certain va-
rieties of plants which especially yield this acid, which rank
under the class of sorrels, and contain a large quantity of
oxalic acid, combined with potash. It is found also in mi-
nerals, and in some quantities, combined with lime, in the
roots of several plants. But the oxalic acid of commerce is
obtained from the action of nitric acid upon sugar or starch,
and is exactly the same acid as exists in plants and in some
minerals. A large quantity of oxalic acid is made both for
the purposes of the arts, as well as for medicine, by the means
I have alluded to, namely, the action of nitric acid upon
sugar or starch. Sugar and starch are composed of carbon,
oxygen, and hydrogen. Oxalic acid consists of a combina-
tion of carbon and oxygen. The action of the acid upon the
sugar and starch is to cause the separation of hydrogen, to
which the nitric acid gives up oxygen, so as to give water,
whilst another portion of oxygen unites with a portion of
carbon, forming carbonic acid ; and oxalic acid is formed
by the combination of the remaining elements of the sugar.
I have a portion of sugar, to it I shall add some nitric acid,
and after the application of heat, in'a few moments we shall
find that considerable action will take place, that the elements
of the sugar, consisting of carbon, oxygen, and hydrogen, as
well as those of the nitric acid, will be decomposed, and enter
into new combinations, by which carbonic acid, oxalic acid
and nitrous acid gas will be found, as I have before stated.
The oxalic acid will crystallize after evaporation of the residual
fluid. It crystallizes in prisms of a white colour, very like
Epsom salts, with which it is sometimes confounded. Oxalic
acid is composed of two prop.ortions of carbon and three of
oxygen, or carbon and oxygen 24-36. It will therefore be
seen that oxalic acid might be decomposed into carbonic
oxide and carbonic acid, carbonic oxide 14, and carbonic acid
22-36, and we are able to effect this by means of certain
agents. If, for example, we apply heat to oxalic acid alone,
we shall convert it into carbonic acid and carbonic oxide, and
nothing else. If we employ the agency of an acid, which has
a strong affinity for water, the same result will happen, for
oxalic acid in a state of crystallization contains a quantity of
water, and the other elements, carbon and oxygen, being in a
free condition to form other gaseous compounds, resolve
themselves into carbonic acid and carbonic oxide. I shall
endeavour to prove by experiment that carbonic oxide and
carbonic acid are produced during the decomposition of
oxalic acid, by means of sulphuric acid. By collecting the
gaseous products over lime water, the water will be rendered
turbid and white from formation of carbonate of lime, whilst
the gas which displaces the lime water, and is not absorbed
by it, is carbonic 'oxide : and it may be observed that when
oxalic acid is perfectly pure, and the sulphuric acid which
acts upon it is also perfectly pure, the only substances which
remain in the retort after decomposition, are sulphuric acid
and water, so that we demonstrate in this manner the exis

ence of these two substances in oxalic acid, and that the
water which was contained in the crystals is retained by the
sulphuric acid. Carbonic oxide presents a blue flame when
burnt, and, as it is the only gaseous substance which does so,
we can readily detect its presence. Oxalic acid combines with
alkalies and with earths, and forms salts, and these salts are
of some interest, inasmuch as they are employed not only in
chemical analysis, but also in the arts and for medicinal pur-
poses. When oxalic acid is combined with ammonia the
volatile alkali, it produces a beautiful crystalline salt called
the oxalate of ammonia, and this salt is of very great impor-
tance in chemistry, because it is used to indicate the presence
of lime, and is one of the most delicate tests for the existence
of that substance. I shall add to b. salt of lime a solution of
this oxalate of ammonia, and we shall find that the oxalate of
ammonia will suffer decomposition, as will also the salt of
lime. The lime in this solution is combined with muriatic
acid. When then I add the oxalate of ammonia to this mu-
Hate of lime, the muriatic acid will go to the ammonia, and
the oxalic acid from the ammonia will combine with the lime
and fall as an insoluble substance. Oxalic acid is capable of
combining with potash and with soda. With potash it unites
and forms a salt which is extremely abundant in those vege-
table substances to which I before alluded, namely, the
various species of sorrel, and is termed the salt of sorrel. It
is a salt extrarted from the juice of those plants combined
with potass, and is termed the oxalate of potass, an extremely
poisonous salt. Oxalic acid combines with certain metals,
with silver, forming an insoluble oxalate of silver, and with
lead, forming an insoluble oxalate of lead. In this glass I
have a solution of acetate of lead, to which I shall add a so-
lution of oxalate of ammonia, and we shall find that the
oxalic acid will be transferred to the oxide of lead, forming
an insoluble precipitate, whilst the acetic acid will combine
with the ammonia to form acetate of ammonia. When oxalic
acid or a combination of oxalic acid and a base is added to a
salt of silver, we shall also obtain a precipitate of the same
character.

In this glass I have a solution of nitrate of silver, to which
I shall add a solution of oxalate of ammonia, and we shall
perceive an abundant white precipitate. This oxalate of
silver differs very materially from the other oxalates in pos-
sessing slight detonating properties. If we take a portion of the
salt and apply heat to it upon an iron spatula, we shall find that
it will be dissipated with a very slight detonation. The oxalic
acid is decomposed, and dissipated in a gaseous state, while
the silver will remain in a finely divided state. This, is one
of the most striking modes of ascertaining the existence of
oxalic acid, as, there is no other acid with which we are

acquainted which produces the same effect when combined
with silver. I may observe, that oxalic acid has extremely•
poisonous properties, and it is one of those acids not unfre-
quently had recourse to for suicide or murder, in a variety of
forms. The best antidote in such cases is a substance which

shall combine with the oxalic acid to render it insoluble, and

there is no substance which possesses this property so com-
pletely as lime or chalk, which will unite completely with the
oxalic acid, and render it completely insoluble, so that when
an individual has taken oxalic acid, lime will be the best

antidote. The croconic acid is one of artificial production,
and is obtained by passing the gas which 1 have shown you
over potassium, by which a portion of the carbonic oxide
is converted_ into croconic and oxalic oxides, the croconic

acid only differing from the oxalic in containing a lesser pro-
portion of oxygen. The mellitic acid, besides being an
organic compound, is found in that peculiar mineral called
the honey stone, from which it may be separated by strong
acids. Formic acid is an acid of peculiar interest, and has a
claim upon the animal as well as the mineral kingdom. We
first obtained it from ants. It is stated, with some gravity,
by the French and German chemists, that " if we take the

red ant, and cause him to walk over blue litmus paper, that
he will leave behind him in his footsteps a red mark." And
this is a fact. This insect secretes a considerable quantity of

an extremely pungent acid, which, from the circumstance of

its being first observed in it, has been termed the formic
acid, and was procured originally by crushing ants, in a whole-

sale manner, in a mortar and extracting the acid from them.
We are now able to obtain formic acid by artificial means, as

upon analyzing the acid it was found not to vary very ma-
terially from certain substances of vegetable origin, such, for

example, as tartaric acid ; and it was found ethic if we admit

to this substance an extra quantity of oxygen, we should be
able to procure formic acid__ The method of obtaining it

now, is extremely simple. If we take sugar or starch, we
shall find that, by supplying them with an extra quantity of
oxygen, we are able to obtain formic acid. When, therefore,

we mix sugar or starch with the oxide of manganese and sul-
phuric acid, and submit them to heat, the oxygen obtained
fromlihe manganese is capable of converting the sugar into
the formic acid. Now formic acid consists of carbon 2,

oxygen 3, and hydrogen 1 ; and it is certain that these
elements can be made to form two proportions of carbonic

oxide and one of water, these products being equal to the
elements obtained by the analysis of formic acid. Formic

acid possesses stronjacid properties, very like those of acetic
acid ; but when submitted to the action of sulphuric acid it
is converted into carbonic oxide and water, and not into car-

bonic acid and carbonic oxide. By leading the gas evolved