Familiar Letters on Chemistry

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FAMILIAR LETTERS ON CHEMISTRY,

AND ITS RELATION TO COMMERCE, PHYSIOLOGY, AND AGRICULTURE,

BY JUSTUS LIEBIG, M.D., PH. D., F.R.S.,

PROFESSOR OF CHEMISTRY IN THE UNIVERSITY OF GIESSEN.

EDITED BY

JOHN GARDNER, M.D.,

MEMBER OF THE CHEMICAL SOCIETY.

Second Edition, Corrected.

LONDON:

MDCCCXLIV.

PREFACE

The Letters contained in this little Volume embrace some of the most
important points of the science of Chemistry, in their application
to Natural Philosophy, Physiology, Agriculture, and Commerce. Some
of them treat of subjects which have already been, or will hereafter
be, more fully discussed in my larger works. They were intended to
be mere sketches, and were written for the especial purpose of
exciting the attention of governments, and an enlightened public, to
the necessity of establishing Schools of Chemistry, and of
promoting, by every means, the study of a science so intimately
connected with the arts, pursuits, and social well-being of modern
civilised nations.

For my own part I do not scruple to avow the conviction, that ere
long, a knowledge of the principal truths of Chemistry will be
expected in every educated man, and that it will be as necessary to
the Statesman, the Political Economist, and the Practical
Agriculturist, as it is already indispensable to the Physician, and
the Manufacturer.

In Germany, such of these Letters as have been already published,
have not failed to produce some of the results anticipated. New
professorships have been established in the Universities of
Goettingen and Wuertzburg, for the express purpose of facilitating
the application of chemical truths to the practical arts of life,
and of following up the new line of investigation and research--the
bearing of Chemistry upon Physiology, Medicine, and
Agriculture,--which may be said to be only just begun.

My friend, Dr. Ernest Dieffenbach, one of my first pupils, who is
well acquainted with all the branches of Chemistry, Physics, Natural
History, and Medicine, suggested to me that a collection of these
Letters would be acceptable to the English public, which has so
favourably received my former works.

I readily acquiesced in the publication of an English edition, and
undertook to write a few additional Letters, which should embrace
some conclusions I have arrived at, in my recent investigations, in
connection with the application of chemical science to the
physiology of plants and agriculture.

My esteemed friend, Dr. Gardner, has had the kindness to revise the
manuscript and the proof sheets for publication, for which I cannot
refrain expressing my best thanks.

It only remains for me to add a hope, that this little offering may
serve to make new friends to our beautiful and useful science, and
be a remembrancer to those old friends who have, for many years
past, taken a lively interest in all my labours.

JUSTUS LIEBIG

Giessen, Aug. 1843.

CONTENTS

LETTER I

The Subject proposed. Materials employed for Chemical Apparatus:--
GLASS--CAOUTCHOUC--CORK--PLATINUM. THE BALANCE. The "Elements" of
the Ancients, represent the forms of matter. Lavoisier and his
successors. Study of the materials composing the Earth. Synthetic
production of Minerals--LAPIS LAZULI. Organic Chemistry.

LETTER II

Changes of Form which every kind of Matter undergoes. Conversion of
Gases into Liquids and Solids. Carbonic Acid--its curious properties
in a solid state. Condensation of Gases by porous bodies. By Spongy
Platinum. Importance of this property in Nature.

LETTER III

The Manufacture of Soda from Culinary Salt; its importance in the
Arts and in Commerce. Glass--Soap--Sulphuric Acid. Silver Refining.
Bleaching. TRADE IN SULPHUR.

LETTER IV

Connection of Theory with Practice. Employment of MAGNETISM as a
moving power--its impracticability. Relation of Coals and Zinc as
economic sources of Force. Manufacture of Beet-root Sugar--its
impolicy. Gas for illumination.

LETTER V

ISOMERISM, or identity of composition in bodies with different
chemical and physical properties. CRYSTALLISATION. AMORPHISM.
ISOMORPHISM, or similarity of properties in bodies totally different
in composition.

LETTER VI

ALLIANCE OF CHEMISTRY WITH PHYSIOLOGY. Division of Food into
nourishment, and materials for combustion. Effects of Atmospheric
Oxygen. Balance of CARBON and OXYGEN.

LETTER VII

ANIMAL HEAT, its laws and influence on the Animal Functions. Loss
and SUPPLY. Influence of Climate. Fuel of Animal Heat. Agency of
Oxygen in Disease. Respiration.

LETTER VIII

ALIMENTS. Constituents of the Blood. Fibrine, Albumen. Inorganic
Substances. Isomerism of Fibrine, Albumen, and elements of
nutrition. Relation of animal and vegetable organisms.

LETTER IX

Growth of Animals. Uses of Butter and Milk. Metamorphoses of
Tissues. Food of Carnivora, and of the Horse.

LETTER X

Application of the preceding facts to Man. Division of human Food.
Uses of Gelatine.

LETTER XI

CIRCULATION OF MATTER IN THE ANIMAL AND VEGETABLE KINGDOMS. The
Ocean. AGRICULTURE. RESTITUTION OF AN EQUILIBRIUM IN THE SOIL.
Causes of the exhaustion of Land. Virginia. England. Relief gained
by importation of bones. Empirical farming unsatisfactory. Necessity
for scientific principles. Influence of the atmosphere. Of Saline
and Earthy matters of the soil.

LETTER XII

SCIENCE AND ART OF AGRICULTURE. NECESSITY OF CHEMISTRY. Rationale of
agricultural processes. Washing for gold.

LETTER XIII

ILLUSTRATION OF THE NECESSITY OF CHEMISTRY TO ADVANCE AND PERFECT
AGRICULTURE. Manner in which FALLOW ameliorates the soil. Uses of
Lime. Effects of Burning. Of Marl.

LETTER XIV

NATURE AND EFFECTS OF MANURES. Animal bodies subject to constant
waste. Parts separating--exuviae--waste vegetable matters--together
contain all the elements of the soil and of food. Various value of
excrements of different animals as manure.

LETTER XV

SOURCE OF THE CARBON AND NITROGEN OF PLANTS. Produce of Carbon in
Forests and Meadows supplied only with mineral aliments prove it to
be from the atmosphere. Relations between Mineral constituents, and
Carbon and Nitrogen. Effects of the Carbonic Acid and Ammonia of
Manures. Necessity of inorganic constituents to the formation of
aliments, of blood, and therefore of nutrition. NECESSITY OF
INQUIRIES by ANALYSIS to advance AGRICULTURE.

LETTER XVI

RESULTS OF THE AUTHOR'S LATEST INQUIRIES. Superlative importance of
the PHOSPHATES OF LIME and ALKALIES to the cultivation of the
CEREALIA. Sources of a SUPPLY of these MATERIALS.

LETTERS ON CHEMISTRY

LETTER I

My dear Sir,

The influence which the science of chemistry exercises upon human
industry, agriculture, and commerce; upon physiology, medicine, and
other sciences, is now so interesting a topic of conversation
everywhere, that it may be no unacceptable present to you if I trace
in a few familiar letters some of the relations it bears to these
various sciences, and exhibit for you its actual effect upon the
present social condition of mankind.

In speaking of the present state of chemistry, its rise and
progress, I shall need no apology if, as a preliminary step, I call
your attention to the implements which the chemist employs--the
means which are indispensable to his labours and to his success.

These consist, generally, of materials furnished to us by nature,
endowed with many most remarkable properties fitting them for our
purposes; if one of them is a production of art, yet its adaptation
to the use of mankind,--the qualities which render it available to
us,--must be referred to the same source as those derived
immediately from nature.

Cork, Platinum, Glass, and Caoutchouc, are the substances to which I
allude, and which minister so essentially to modern chemical
investigations. Without them, indeed, we might have made some
progress, but it would have been slow; we might have accomplished
much, but it would have been far less than has been done with their
aid. Some persons, by the employment of expensive substances, might
have successfully pursued the science; but incalculably fewer minds
would have been engaged in its advancement. These materials have
only been duly appreciated and fully adopted within a very recent
period. In the time of Lavoisier, the rich alone could make chemical
researches; the necessary apparatus could only be procured at a very
great expense.

And first, of Glass: every one is familiar with most of the
properties of this curious substance; its transparency, hardness,
destitution of colour, and stability under ordinary circumstances:
to these obvious qualities we may add those which especially adapt
it to the use of the chemist, namely, that it is unaffected by most
acids or other fluids contained within it. At certain temperatures
it becomes more ductile and plastic than wax, and may be made to
assume in our hands, before the flame of a common lamp, the form of
every vessel we need to contain our materials, and of every
apparatus required to pursue our experiments.

Then, how admirable and valuable are the properties of Cork! How
little do men reflect upon the inestimable worth of so common a
substance! How few rightly esteem the importance of it to the
progress of science, and the moral advancement of mankind!--There is
no production of nature or art equally adapted to the purposes to
which the chemist applies it. Cork consists of a soft, highly
elastic substance, as a basis, having diffused throughout a matter
with properties resembling wax, tallow, and resin, yet dissimilar to
all of these, and termed suberin. This renders it perfectly
impermeable to fluids, and, in a great measure, even to gases. It is
thus the fittest material we possess for closing our bottles, and
retaining their contents. By its means, and with the aid of
Caoutchouc, we connect our vessels and tubes of glass, and construct
the most complicated apparatus. We form joints and links of
connexion, adapt large apertures to small, and thus dispense
altogether with the aid of the brassfounder and the mechanist. Thus
the implements of the chemist are cheaply and easily procured,
immediately adapted to any purpose, and readily repaired or altered.

Again, in investigating the composition of solid bodies,--of
minerals,--we are under the necessity of bringing them into a liquid
state, either by solution or fusion. Now vessels of glass, of
porcelain, and of all non-metallic substances, are destroyed by the
means we employ for that purpose,--are acted upon by many acids, by
alkalies and the alkaline carbonates. Crucibles of gold and silver
would melt at high temperatures. But we have a combination of all
the qualities we can desire in Platinum. This metal was only first
adapted to these uses about fifty years since. It is cheaper than
gold, harder and more durable than silver, infusible at all
temperatures of our furnaces, and is left intact by acids and
alkaline carbonates. Platinum unites all the valuable properties of
gold and of porcelain, resisting the action of heat, and of almost
all chemical agents.

As no mineral analysis could be made perfectly without platinum
vessels, had we not possessed this metal, the composition of
minerals would have yet remained unknown; without cork and
caoutchouc we should have required the costly aid of the mechanician
at every step. Even without the latter of these adjuncts our
instruments would have been far more costly and fragile. Possessing
all these gifts of nature, we economise incalculably our time--to us
more precious than money!

Such are our instruments. An equal improvement has been accomplished
in our laboratory. This is no longer the damp, cold, fireproof vault
of the metallurgist, nor the manufactory of the druggist, fitted up
with stills and retorts. On the contrary, a light, warm, comfortable
room, where beautifully constructed lamps supply the place of
furnaces, and the pure and odourless flame of gas, or of spirits of
wine, supersedes coal and other fuel, and gives us all the fire we
need; where health is not invaded, nor the free exercise of thought
impeded: there we pursue our inquiries, and interrogate Nature to
reveal her secrets.

To these simple means must be added "The Balance," and then we
possess everything which is required for the most extensive
researches.

The great distinction between the manner of proceeding in chemistry
and natural philosophy is, that one weighs, the other measures. The
natural philosopher has applied his measures to nature for many
centuries, but only for fifty years have we attempted to advance our
philosophy by weighing.

For all great discoveries chemists are indebted to the
"balance"--that incomparable instrument which gives permanence to
every observation, dispels all ambiguity, establishes truth, detects
error, and guides us in the true path of inductive science.

The balance, once adopted as a means of investigating nature, put an
end to the school of Aristotle in physics. The explanation of
natural phenomena by mere fanciful speculations, gave place to a
true natural philosophy. Fire, air, earth, and water, could no
longer be regarded as elements. Three of them could henceforth be
considered only as significative of the forms in which all matter
exists. Everything with which we are conversant upon the surface of
the earth is solid, liquid, or aeriform; but the notion of the
elementary nature of air, earth, and water, so universally held, was
now discovered to belong to the errors of the past.

Fire was found to be but the visible and otherwise perceptible
indication of changes proceeding within the, so called, elements.

Lavoisier investigated the composition of the atmosphere and of
water, and studied the many wonderful offices performed by an
element common to both in the scheme of nature, namely, oxygen: and
he discovered many of the properties of this elementary gas.

After his time, the principal problem of chemical philosophers was
to determine the composition of the solid matters composing the
earth. To the eighteen metals previously known were soon added
twenty-four discovered to be constituents of minerals. The great
mass of the earth was shown to be composed of metals in combination
with oxygen, to which they are united in one, two, or more definite
and unalterable proportions, forming compounds which are termed
metallic oxides, and these, again, combined with oxides of other
bodies, essentially different to metals, namely, carbon and
silicium. If to these we add certain compounds of sulphur with
metals, in which the sulphur takes the place of oxygen, and forms
sulphurets, and one other body,--common salt,--(which is a compound
of sodium and chlorine), we have every substance which exists in a
solid form upon our globe in any very considerable mass. Other
compounds, innumerably various, are found only in small scattered
quantities.

The chemist, however, did not remain satisfied with the separation
of minerals into their component elements, i.e. their analysis; but
he sought by synthesis, i.e. by combining the separate elements and
forming substances similar to those constructed by nature, to prove
the accuracy of his processes and the correctness of his
conclusions. Thus he formed, for instance, pumice-stone, feldspar,
mica, iron pyrites, &c. artificially.

But of all the achievements of inorganic chemistry, the artificial
formation of lapis lazuli was the most brilliant and the most
conclusive. This mineral, as presented to us by nature, is
calculated powerfully to arrest our attention by its beautiful
azure-blue colour, its remaining unchanged by exposure to air or to
fire, and furnishing us with a most valuable pigment, Ultramarine,
more precious than gold!

The analysis of lapis lazuli represented it to be composed of
silica, alumina, and soda, three colourless bodies, with sulphur and
a trace of iron. Nothing could be discovered in it of the nature of
a pigment, nothing to which its blue colour could be referred, the
cause of which was searched for in vain. It might therefore have
been supposed that the analyst was here altogether at fault, and
that at any rate its artificial production must be impossible.
Nevertheless, this has been accomplished, and simply by combining in
the proper proportions, as determined by analysis, silica, alumina,
soda, iron, and sulphur. Thousands of pounds weight are now
manufactured from these ingredients, and this artificial ultramarine
is as beautiful as the natural, while for the price of a single
ounce of the latter we may obtain many pounds of the former.

With the production of artificial lapis lazuli, the formation of
mineral bodies by synthesis ceased to be a scientific problem to the
chemist; he has no longer sufficient interest in it to pursue the
subject. He may now be satisfied that analysis will reveal to him
the true constitution of minerals. But to the mineralogist and
geologist it is still in a great measure an unexplored field,
offering inquiries of the highest interest and importance to their
pursuits.

After becoming acquainted with the constituent elements of all the
substances within our reach and the mutual relations of these
elements, the remarkable transmutations to which the bodies are
subject under the influence of the vital powers of plants and
animals, became the principal object of chemical investigations, and
the highest point of interest. A new science, inexhaustible as life
itself, is here presented us, standing upon the sound and solid
foundation of a well established inorganic chemistry. Thus the
progress of science is, like the development of nature's works,
gradual and expansive. After the buds and branches spring forth the
leaves and blossoms, after the blossoms the fruit.

Chemistry, in its application to animals and vegetables. endeavours
jointly with physiology to enlighten us respecting the mysterious
processes and sources of organic life.

LETTER II

My dear Sir,

In my former letter I reminded you that three of the supposed
elements of the ancients represent the forms or state in which all
the ponderable matter of our globe exists; I would now observe, that
no substance possesses absolutely any one of those conditions; that
modern chemistry recognises nothing unchangeably solid, liquid, or
aeriform: means have been devised for effecting a change of state in
almost every known substance. Platinum, alumina, and rock crystal,
it is true, cannot be liquified by the most intense heat of our
furnaces, but they melt like wax before the flame of the
oxy-hydrogen blowpipe. On the other hand, of the twenty-eight
gaseous bodies with which we are acquainted, twenty-five may be
reduced to a liquid state, and one into a solid. Probably, ere long,
similar changes of condition will be extended to every form of
matter.

There are many things relating to this condensation of the gases
worthy of your attention. Most aeriform bodies, when subjected to
compression, are made to occupy a space which diminishes in the
exact ratio of the increase of the compressing force. Very
generally, under a force double or triple of the ordinary
atmospheric pressure, they become one half or one third their former
volume. This was a long time considered to be a law, and known as
the law of Marriotte; but a more accurate study of the subject has
demonstrated that this law is by no means of general application.
The volume of certain gases does not decrease in the ratio of the
increase of the force used to compress them, but in some, a
diminution of their bulk takes place in a far greater degree as the
pressure increases.

Again, if ammoniacal gas is reduced by a compressing force to
one-sixth of its volume, or carbonic acid is reduced to one
thirty-sixth, a portion of them loses entirely the form of a gas,
and becomes a liquid, which, when the pressure is withdrawn, assumes
again in an instant its gaseous state--another deviation from the
law of Marriotte.

Our process for reducing gases into fluids is of admirable
simplicity. A simple bent tube, or a reduction of temperature by
artificial means, have superseded the powerful compressing machines
of the early experimenters.

The cyanuret of mercury, when heated in an open glass tube, is
resolved into cyanogen gas and metallic mercury; if this substance
is heated in a tube hermetically sealed, the decomposition occurs as
before, but the gas, unable to escape, and shut up in a space
several hundred times smaller than it would occupy as gas under the
ordinary atmospheric pressure, becomes a fluid in that part of the
tube which is kept cool.

When sulphuric acid is poured upon limestone in an open vessel,
carbonic acid escapes with effervescence as a gas, but if the
decomposition is effected in a strong, close, and suitable vessel of
iron, we obtain the carbonic acid in the state of liquid. In this
manner it may be obtained in considerable quantities, even many
pounds weight. Carbonic acid is separated from other bodies with
which it is combined as a fluid under a pressure of thirty-six
atmospheres.

The curious properties of fluid carbonic acid are now generally
known. When a small quantity is permitted to escape into the
atmosphere, it assumes its gaseous state with extraordinary
rapidity, and deprives the remaining fluid of caloric so rapidly
that it congeals into a white crystalline mass like snow: at first,
indeed, it was thought to be really snow, but upon examination it
proved to be pure frozen carbonic acid. This solid, contrary to
expectation, exercises only a feeble pressure upon the surrounding
medium. The fluid acid inclosed in a glass tube rushes at once, when
opened, into a gaseous state, with an explosion which shatters the
tube into fragments; but solid carbonic acid can be handled without
producing any other effect than a feeling of intense cold. The
particles of the carbonic acid being so closely approximated in the
solid, the whole force of cohesive attraction (which in the fluid is
weak) becomes exerted, and opposes its tendency to assume its
gaseous state; but as it receives heat from surrounding bodies, it
passes into gas gradually and without violence. The transition of
solid carbonic acid into gas deprives all around it of caloric so
rapidly and to so great an extent, that a degree of cold is produced
immeasurably great, the greatest indeed known. Ten, twenty, or more
pounds weight of mercury, brought into contact with a mixture of
ether and solid carbonic acid, becomes in a few moments firm and
malleable. This, however, cannot be accomplished without
considerable danger. A melancholy accident occurred at Paris, which
will probably prevent for the future the formation of solid carbonic
acid in these large quantities, and deprive the next generation of
the gratification of witnessing these curious experiments. Just
before the commencement of the lecture in the Laboratory of the
Polytechnic School, an iron cylinder, two feet and a half long and
one foot in diameter, in which carbonic acid had been developed for
experiment before the class, burst, and its fragments were scattered
about with the most tremendous force; it cut off both the legs of
the assistant and killed him on the spot. This vessel, formed of the
strongest cast-iron, and shaped like a cannon, had often been
employed to exhibit experiments in the presence of the students. We
can scarcely think, without shuddering, of the dreadful calamity
such an explosion would have occasioned in a hall filled with
spectators.

When we had ascertained the fact of gases becoming fluid under the
influence of cold or pressure, a curious property possessed by
charcoal, that of absorbing gas to the extent of many times its
volume,--ten, twenty, or even as in the case of ammoniacal gas or
muriatic acid gas, eighty or ninety fold,--which had been long
known, no longer remained a mystery. Some gases are absorbed and
condensed within the pores of the charcoal, into a space several
hundred times smaller than they before occupied; and there is now no
doubt they there become fluid, or assume a solid state. As in a
thousand other instances, chemical action here supplants mechanical
forces. Adhesion or heterogeneous attraction, as it is termed,
acquired by this discovery a more extended meaning; it had never
before been thought of as a cause of change of state in matter; but
it is now evident that a gas adheres to the surface of a solid body
by the same force which condenses it into a liquid.

The smallest amount of a gas,--atmospheric air for instance,--can be
compressed into a space a thousand times smaller by mere mechanical
pressure, and then its bulk must be to the least measurable surface
of a solid body, as a grain of sand to a mountain. By the mere
effect of mass,--the force of gravity,--gaseous molecules are
attracted by solids and adhere to their surfaces; and when to this
physical force is added the feeblest chemical affinity, the
liquifiable gases cannot retain their gaseous state. The amount of
air condensed by these forces upon a square inch of surface is
certainly not measurable; but when a solid body, presenting several
hundred square feet of surface within the space of a cubic inch, is
brought into a limited volume of gas, we may understand why that
volume is diminished, why all gases without exception are absorbed.
A cubic inch of charcoal must have, at the lowest computation, a
surface of one hundred square feet. This property of absorbing gases
varies with different kinds of charcoal: it is possessed in a higher
degree by those containing the most pores, i.e. where the pores are
finer; and in a lower degree in the more spongy kinds, i.e. where
the pores are larger.

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