one compared with most of the others. This arises in a great
measure from the circumstance that the Idea of Polarity has
only recently been apprehended and applied, with any great
degree of clearness, among physical philosophers; and is
even yet probably entertained in an obscure and ambiguous
manner by most experimental inquirers. I have been desirous
of not attempting to bring forward any doctrines upon the
subject, except such as have been fully illustrated and
exemplified by the acknowledged progress of the physical
sciences. If I had been willing to discuss the various
speculations which have been published respecting the
universal prevalence of Polarities in the universe, and
their results in every province of nature, I might easily
have presented this subject in a more extended form; but
this would not have been consistent with my plan of tracing
the influence of scientific Ideas only so far as they have
really aided in disclosing and developing scientific truths.
And as the influence of this Idea is clearly distinguishable
both from those which precede and those which follow, in the
character of the sciences to which it gives rise, and as it
appears likely to be hereafter of great extent and
consequence, it seemed better to treat of it in a separate
Book, although of a brevity disproportioned to the rest.
END OF VOL. I.
Cambridge: Printed at the University Press.
HISTORY
OF
SCIENTIFIC IDEAS.
VOLUME II.
Cambridge;
PRINTED BY C. J. CLAY, M.A.
AT THE UNIVERSITY PRESS.
HISTORY
OF
SCIENTIFIC IDEAS.
BY WILLIAM WHEWELL, D.D.,
MASTER OF TRINITY COLLEGE, CAMBRIDGE, AND
CORRESPONDING MEMBER OF THE INSTITUTE OF FRANCE.
BEING THE FIRST PART OF THE PHILOSOPHY
OF THE INDUCTIVE SCIENCES.
_THE THIRD EDITION._
IN TWO VOLUMES.
ΛΑΜΠΑΔIΑ ΕΧΟΝΤΕΣ ΔIΑΔΩΣΟΥΣIΝ ΑΛΛΗΛΟIΣ
VOLUME II.
LONDON:
JOHN W. PARKER AND SON, WEST STRAND.
1858.
CONTENTS
OF
THE SECOND VOLUME.
BOOK VI.
THE PHILOSOPHY OF CHEMISTRY.
PAGE
CHAP. I. ATTEMPTS TO CONCEIVE ELEMENTARY COMPOSITION 3
_Art._ 1. Fundamental Ideas of Chemistry.
2. Elements.
3. Do Compounds resemble their Elements?
4. The Three Principles.
5. A Modern Errour.
6. Are Compounds determined by the Figure of Elements?
7. Crystalline Form depends on Figure of Elements.
8. Are Compounds determined by Mechanical Attraction
of Elements?
9. Newton's followers.
10. Imperfection of their Hypotheses.
CHAP. II. ESTABLISHMENT AND DEVELOPMENT OF THE IDEA OF
CHEMICAL AFFINITY 15
_Art._ 1. Early Chemists.
2. Chemical Affinity.
3. Affinity or Attraction?
4. Affinity preferable.
5. Analysis is possible.
{vi}
6. Affinity is Elective.
7. Controversy on this.
8. Affinity is Definite.
9. Are these Principles necessarily true?
10. Composition determines Properties.
11. Comparison on this subject.
12. Composition determines Crystalline Form.
CHAP. III. OF THE IDEA OF SUBSTANCE 29
_Art._ 1. Indestructibility of Substance.
2. The Idea of Substance.
3. Locke's Denial of Substance.
4. Is all Substance heavy?
Note on Sir W. Hamilton's objections 37
CHAP. IV. APPLICATION OF THE IDEA OF SUBSTANCE IN CHEMISTRY 39
_Art._ 1. A Body is Equal to its Elements.
2. Lavoisier.
3. Are there Imponderable Elements?
4. Faraday's views.
5. Composition of Water.
6. Heat in Chemistry.
CHAP. V. THE ATOMIC THEORY 48
_Art._ 1. The Theory on Chemical Grounds.
2. Hypothesis of Atoms.
3. Its Chemical Difficulties.
4. Grounds of the Atomic Doctrine.
5. Ancient Atomists.
6. Francis Bacon.
7. Modern Atomists.
8. Arguments for and against.
9. Boscovich's Theory.
10. Molecular Hypothesis.
11. Poisson's Inference.
12. Wollaston's Argument.
13. Properties are Permanent.
{vii}
BOOK VII.
THE PHILOSOPHY OF MORPHOLOGY, INCLUDING CRYSTALLOGRAPHY.
CHAP. I. EXPLICATION OF THE IDEA OF SYMMETRY 67
_Art._ 1. Symmetry, what.
2. Kinds of Symmetry.
3. Examples in Nature.
4. Vegetables and Animals.
5. Symmetry a Fundamental Idea.
6. Result of Symmetry.
CHAP. II. APPLICATION OF THE IDEA OF SYMMETRY TO CRYSTALS 75
_Art._ 1. 'Fundamental Forms.'
2. Their use.
3. 'Systems of Crystallization.'
4. Cleavage.
5. Other Properties.
CHAP. III. SPECULATIONS FOUNDED UPON THE SYMMETRY OF CRYSTALS 80
_Art._ 1. Integrant Molecules.
2. Difficulties of the Theory.
3. Merit of the Theory.
4. Wollaston's Hypothesis.
5. Maxim for such Hypotheses.
6. Dalton's Hypothesis.
7. Ampère's Hypothesis.
8. Difficulty of such Hypotheses.
9. Isomorphism.
{viii}
BOOK VIII.
PHILOSOPHY OF THE CLASSIFICATORY SCIENCES.
CHAP. I. THE IDEA OF LIKENESS AS GOVERNING THE USE OF
COMMON NAMES 95
_Art._ 1. Object of the Chapter.
2. Unity of the Individual.
3. Condition of Unity.
4. Kinds.
5. Not made by Definitions.
6. Condition of the Use of Terms.
7. Terms may have different Uses.
8. Gradation of Kinds.
9. Characters of Kinds.
10. Difficulty of Definitions.
11. 'The Five Words.'
CHAP. II. THE METHODS OF NATURAL HISTORY, AS REGULATED
BY THE IDEA OF LIKENESS 108
_Sect._ I. _Natural History in General._
_Art._ 1. Idea of Likeness in Natural History.
2. Condition of its Use.
_Sect._ II. _Terminology._
_Art._ 3. Meaning of the word.
_Sect._ III. _The Plan of the System._
_Art._ 4. Its Meaning.
5. Latent Reference to Natural Affinity.
6. Natural Classes.
7. Artificial Classes.
8. Are Genera Natural?
9. Natural History and Mathematics.
10. Natural Groups given by Type, not by Definition.
11. Physiography.
12. Artificial and Natural Systems.
{ix}
_Sect._ IV. _Methods of framing Natural Systems._
_Art._ 13. Method of Blind Trial.
14. Method of General Comparison.
_Sect._ V. _Gradation of Groups._
_Art._ 15. Series of Subdivisions.
16. What is a Species?
17. The _words_ 'Species' and 'Genus.'
18. Varieties. Races.
_Sect._ VI. _Nomenclature._
_Art._ 19. Binary Nomenclature.
_Sect._ VII. _Diagnosis._
_Art._ 20. Characteristick and Systematick.
CHAP. III. APPLICATION OF THE NATURAL HISTORY METHOD
TO MINERALOGY 138
_Art._ 1. Mohs's System.
2. His 'Characteristick.'
3. Mineral _Species_ not yet well fixed.
4. _Orders_ of Minerals.
5. Nomenclature of Minerals.
6. M. Necker's 'Règne Mineral.'
7. Inconvenience of taking a Chemical Basis of
Mineral Systems.
8. Relation of Natural History and Chemistry.
9. What is a Mineralogical Individual?
10. A well-formed Crystal is an Individual.
11. Not the Integrant Molecules,
12. Nor the Cleavage Forms.
13. Compound Crystals are not Individuals.
14. Crystalline Forms are sufficiently complete for
this.
15. Including aggregate Masses.
16. Do Artificial Crystals belong to Mineralogy?
17. The Mineralogical Individual extends as far as
the same Crystalline Axes extend.
18. Artificial Crystals do belong to Mineralogy:
{x}
19. Cannot be excluded.
20. Species to be determined by the Crystalline Power.
21. Secondary Derivative Forms are Varieties:
22. Are not Species, as M. Necker holds.
CHAP. IV. OF THE IDEA OF NATURAL AFFINITY 159
_Art._ 1. The Idea of Affinity
2. Is not to be made out by Arbitrary Rules.
3. Functions of Living things are many,
4. But all lead to the same arrangement.
5. This is Cuvier's principle:
6. And Decandolle's.
7. Is this applicable to Inorganic Bodies?
8. Yes; by the agreement of Physical and
Chemical Arrangement.
BOOK IX.
THE PHILOSOPHY OF BIOLOGY.
CHAP. 1. ANALOGY OF BIOLOGY WITH OTHER SCIENCES. 169
_Art._ 1. Biology involves the Idea of Life.
2. This Idea to be historically traced.
3. The Idea at first expressed by means of other
Ideas.
4. Mystical, Mechanical, Chemical, and Vital
Fluid Hypotheses.
CHAP. II. SUCCESSIVE BIOLOGICAL HYPOTHESES 174
_Sect._ I. _The Mystical School._
_Sect._ II. _The Iatrochemical School._
_Sect._ III. _The Iatromathematical School._
_Sect._ IV. _The Vital Fluid School._
_Sect._ V. _The Psychical School._
{xi}
CHAP. III. ATTEMPTS TO ANALYSE THE IDEA OF LIFE 195
_Art._ 1. Definitions of Life,
2. By Stahl, Humboldt, Kant.
3. Definition of Organization by Kant.
4. Life is a System of Functions.
5. Bichat. _Sum_ of Functions.
6. Use of Definition.
7. Cuvier's view.
8. Classifications of Functions.
9. Vital, Natural, and Animal Functions.
10. Bichat. Organic and Animal Life.
11. Use of this Classification.
CHAP. IV. ATTEMPTS TO FORM IDEAS OF SEPARATE VITAL FORCES,
AND FIRST, OF ASSIMILATION AND SECRETION 203
_Sect._ I. _Course of Biological Research._
_Art._ 1. Observation and New Conceptions.
_Sect._ II. _Attempts to form a distinct Conception
of Assimilation and Secretion._
_Art._ 2. The Ancients.
3. Buffon. Interior Mould.
4. Defect of this view.
5. Cuvier. Life a Vortex.
6. Defect of this view.
7. Schelling. Matter and Form.
8. Life a constant Form of circulating Matter, &c.
_Sect._ III. _Attempts to conceive the Forces of
Assimilation and Secretion._
_Art._ 9. Assimilation is a Vital Force.
10. The name 'Assimilation.'
11. Several processes involved in Assimilation.
12. _Absorption_. Endosmose.
13. Absorption involves a Vital Force.
14. _Secretion_. Glands.
15. Motions of Vital Fluids.
{xii}
_Sect._ IV. _Attempts to conceive the Process of Generation._
_Art._ 16. 'Reproduction' figuratively used for Generation.
17. Nutrition different from
18. Generation.
19. Generations successively included.
20. Pre-existence of Germs.
21. Difficulty of this view.
22. Communication of Vital Forces.
23. Close similarity of Nutrition and Generation.
24. The Identity of the two Processes exemplified.
CHAP. V. ATTEMPTS TO FORM IDEAS OF SEPARATE VITAL
FORCES, _continued_.--VOLUNTARY MOTION. 222
_Art._ 1. Voluntary Motion one of the animal Functions.
2. Progressive knowledge of it.
3. Nervous Fluid not electric.
4. Irritability. Glisson.
5. Haller.
6. Contractility.
7. Organic Sensibility and Contractility not separable.
8. Improperly described by Bichat.
9. Brown.
10. Contractility a peculiar Power.
11. Cuvier's view.
12. Elementary contractile Action.
13. Strength of Muscular Fibre.
14. Sensations become Perceptions
15. By means of Ideas;
16. And lead to Muscular Actions.
17. Volition comes between Perception and Action.
18. Transition to Psychology,
19. A center is introduced.
20. The central consciousness may be obscure.
21. Reflex Muscular Action.
22. Instinct.
23. Difficulty of conceiving Instinct.
24. Instinct opposed to Insight.
{xiii}
CHAP. VI. OF THE IDEA OF FINAL CAUSES 239
_Art._ 1. Organization. Parts are Ends and Means.
2. Not merely mutually dependent.
3. Not merely mutually Cause and Effect.
4. Notion of _End_ not derived from Facts.
5. This notion has regulated Physiology.
6. Notion of Design comes from within.
7. Design not understood by Savages.
8. Design opposed to Morphology.
9. Impression of Design when fresh.
10. Acknowledgement of an End by adverse Physiologists.
11. This included in the Notion of Disease.
12. It belongs to organized Creatures only.
13. The term Final _Cause_.
14. Law and Design.
15. Final Causes and Morphology.
16. Expressions of physiological Ends.
17. The Conditions of Existence.
18. The asserted presumption of Teleology.
19. Final Causes in other subjects.
20. Transition to Palætiology.
BOOK X.
THE PHILOSOPHY OF PALÆTIOLOGY.
CHAP. I. OF PALÆTIOLOGICAL SCIENCES IN GENERAL. 257
_Art._ 1. Description of Palætiology.
2. Its Members.
3. Other Members.
4. Connexion of the whole subject.
5. We shall take Material Sciences only;
6. But these are connected with others.
CHAP. II. OF THE THREE MEMBERS OF A PALÆTIOLOGICAL SCIENCE 263
_Art._ 1. Divisions of such Sciences.
2. The Study of Causes.
3. Ætiology.
{xiv}
4. Phenomenology requires Classification. Phenomenal
Geology.
5. Phenomenal Uranology.
6. Phenomenal Geography of Plants and Animals.
7. Phenomenal Glossology.
8. The Study of Phenomena leads to Theory.
9. No sound Theory without Ætiology.
10. Causes in Palætiology.
11. Various kinds of Cause.
12. Hypothetical Order of Palætiological Causes.
13. Mode of Cultivating Ætiology:--In Geology:
14. In the Geography of Plants and Animals:
15. In Languages.
16. Construction of Theories.
17. No sound Palætiological Theory yet extant.
CHAP. III. OF THE DOCTRINE OF CATASTROPHES AND THE
DOCTRINE OF UNIFORMITY 284
_Art._ 1. Doctrine of Catastrophes.
2. Doctrine of Uniformity.
3. Is Uniformity probable _a priori_?
4. Cycle of Uniformity indefinite.
5. Uniformitarian Arguments are Negative only.
6. Uniformity in the Organic World.
7. Origin of the present Organic World.
8. Nebular Origin of the Solar System.
9. Origin of Languages.
10. No Natural Origin discoverable.
CHAP. IV. OF THE RELATION OF TRADITION TO PALÆTIOLOGY 297
_Art._ 1. Importance of Tradition.
2. Connexion of Tradition and Science.
3. Natural and Providential History of the World.
4. The Sacred Narrative.
5. Difficulties in interpreting the Sacred Narrative.
6. Such Difficulties inevitable.
7. Science tells us nothing concerning Creation.
{xv}
8. Scientific views, when familiar, do not disturb
the authority of Scripture.
9. When should Old Interpretations be given up?
10. In what Spirit should the Change be accepted?
11. In what Spirit should the Change be urged?
12. Duty of Mutual forbearance.
13. Case of Galileo.
CHAP. V. OF THE CONCEPTION OF A FIRST CAUSE 316
_Art._ 1. The Origin of things is not naturally discoverable;
2. Yet has always been sought after.
3. There must be a First Cause.
4. This is an Axiom.
5. Involved in the proof of a Deity.
6. The mind is not satisfied without it.
7. The Whole Course of Nature must have a Cause.
8. Necessary Existence of God.
9. Forms of the Proof.
10. Idea of a First Cause is Necessary.
11. Conception of a First Cause.
12. The First Cause in all Sciences is the same.
13. We are thus led to Moral Subjects.
Conclusion of this History.
{{1}}
BOOK VI.
THE
PHILOSOPHY
OF
CHEMISTRY.
A PHILOSOPHER was asked:--How much does smoke weigh? He
answered: Subtract from the weight of the fuel the weight of
the ashes, and thou hast the weight of the smoke. Thus he
assumed as incontrovertible that, even in the fire, the
Substance does not perish, only its Form undergoes a change.
In like manner the proposition, _Nothing can come of
Nothing_ was only another consequence of the Principle of
Permanence, or rather of the Principle of the Enduring
Existence of the same subject with different appearances.
Kant, _Kritik d. r. Vern._
{{3}}
BOOK VI.
THE PHILOSOPHY OF CHEMISTRY.
CHAPTER I.
ATTEMPTS TO CONCEIVE ELEMENTARY COMPOSITION.
1. WE have now to bring into view, if possible, the Ideas
and General Principles which are involved in Chemistry,--the
science of the composition of bodies. For in this as in
other parts of human knowledge, we shall find that there are
certain Ideas, deeply seated in the mind, though shaped and
unfolded by external observation, which are necessary
conditions of the existence of such a science. These Ideas
it is, which impel man to such a knowledge of the
Composition of bodies, which give _meaning_ to _facts_
exhibiting this composition, and _universality_ to _special_
truths discovered by experience. These are the Ideas of
_Element_ and of _Substance_.
Unlike the Idea of Polarity, of which we treated in the last
Book, these Ideas have been current in men's minds from very
early times, and formed the subject of some of the first
speculations of philosophers. It happened however, as might
have been expected, that in the first attempts they were not
clearly distinguished from other notions, and were
apprehended and applied in an obscure and confused manner.
We cannot better exhibit the peculiar character and meaning
of these Ideas than by tracing the form which they have
assumed {4} and the efficacy which they have exerted in
these successive essays. This, therefore, I shall endeavour
to do, beginning with the Idea of Element.
2. That bodies are composed or made up of certain parts,
elements, or principles, is a conception which has existed
in men's minds from the beginning of the first attempts at
speculative knowledge. The doctrine of the Four Elements,
Earth, Air, Fire and Water, of which all things in the
universe were supposed to be constituted, is one of the
earliest forms in which this conception was systematized;
and this doctrine is stated by various authors to have
existed as early as the times of the ancient Egyptians[1\6].
The words usually employed by Greek writers to express these
elements are ἀρχὴ a _principle_ or _beginning_, and
στοιχεῖον, which probably meant a _letter_ (of a word)
before it meant an _element_ of a compound. For the
resolution of a word into its letters is undoubtedly a
remarkable instance of a successful analysis performed at an
early stage of man's history; and might very naturally
supply a metaphor to denote the analysis of substances into
their intimate parts, when men began to contemplate such an
analysis as a subject of speculation. The Latin word
_elementum_ itself, though by its form it appears to be a
derivative abstract term, comes from some root now obsolete;
probably[2\6] from a word signifying _to grow_ or _spring up_.
[Note 1\6: Gilbert's _Phys._ 1. i. c. iii.]
[Note 2\6: Vossius _in voce_. "Conjecto esse ab antiqua voco
_eleo_ pro _oleo_, id est _cresco_: a qua signiflcatione
proles, _suboles_, _adolescens_: ut ab _juratum_,
_juramentum_; ab _adjutum_, _adjumentum_: sic ab _eletum_,
_elementum_: quia inde omnia crescunt ac nascuntur."]
The mode in which elements form the compound bodies and
determine their properties was at first, as might be
expected, vaguely and variously conceived. It will, I trust,
hereafter be made clear to the reader that the relation of
the elements to the compound involves a peculiar and
appropriate Fundamental Idea, not susceptible of being
correctly represented by any comparison or combination of
other ideas, and guiding us to clear and definite results
only when it is illustrated {5} and nourished by an abundant
supply of experimental facts. But at first the peculiar and
special notion which is required in a just conception of the
constitution of bodies was neither discerned nor suspected;
and up to a very late period in the history of chemistry,
men went on attempting to apprehend the constitution of
bodies more clearly by substituting for this obscure and
recondite idea of Elementary Composition, some other idea
more obvious, more luminous, and more familiar, such as the
ideas of Resemblance, Position, and mechanical Force. We
shall briefly speak of some of these attempts, and of the
errours which were thus introduced into speculations on the
relations of elements and compounds.
3. _Compounds assumed to resemble their Elements._--The
first notion was that compounds derive their qualities from
their elements by _resemblance_:--they are hot in virtue of
a hot element, heavy in virtue of a heavy element, and so
on. In this way the doctrine of the _four elements_ was
framed; for every body is either hot or cold, moist or dry;
and by combining these qualities in all possible ways, men
devised four elementary substances, as has been stated in
the History[3\6].
[Note 3\6: _Hist. Ind. Sc._ b. i. c. ii. sec. 2.]
This assumption of the derivation of the qualities of bodies
from similar qualities in the elements was, as we shall see,
altogether baseless and unphilosophical, yet it prevailed
long and universally. It was the foundation of medicine for
a long period, both in Europe and Asia; disorders being
divided into hot, cold, and the like; and remedies being
arranged according to similar distinctions. Many readers
will recollect, perhaps, the story[4\6] of the indignation
which the Persian physicians felt towards the European, when
he undertook to cure the ill effects of cucumber upon the
patient, by means of mercurial medicine: for cucumber, which
is cold, could not be counteracted, they maintained, by
mercury, which in their classification is cold also. Similar
views of the operation of medicines might {6} easily be
traced in our own country. A moment's reflection may
convince us that when drugs of any kind are subjected to the
chemistry of the human stomach and thus made to operate on
the human frame, it is utterly impossible to form the most
remote conjecture what the result will be, from any such
vague notions of their qualities as the common use of our
senses can give. And in like manner the common operations of
chemistry give rise, in almost every instance, to products
which bear no resemblance to the materials employed. The
results of the furnace, the alembic, the mixture, frequently
have no visible likeness to the ingredients operated upon.
Iron becomes steel by the addition of a little charcoal; but
what visible trace of the charcoal is presented by the metal
thus modified? The most beautiful colours are given to glass
and earthenware by minute portions of the ores of black or
dingy metals, as iron and manganese. The worker in metal,
the painter, the dyer, the vintner, the brewer, all the
artisans in short who deal with practical chemistry, are
able to teach the speculative chemist that it is an utter
mistake to expect that the qualities of the elements shall
be still discoverable, in an unaltered form, in the
compound. This first rude notion of an element, that it
determines the properties of bodies _by resemblance_, must
be utterly rejected and abandoned before we can make any
advance towards a true apprehension of the constitution of
bodies.
[Note 4\6: See _Hadji Baba_.]
4. This step accordingly was made, when the hypothesis of
the four elements was given up, and the doctrine of the
_three Principles_, Salt, Sulphur, and Mercury, was
substituted in its place. For in making this change, as I
have remarked in the History[5\6], the real advance was the
acknowledgment of the changes, produced by the chemist's
operations, as results to be accounted for by the union and
separation of substantial elements, however great the
changes, and however unlike the product might be to the
materials. And this step once made, chemists went on
constantly {7} advancing towards a truer view of the nature
of an element, and consequently, towards a more satisfactory
theory of chemical operations.
[Note 5\6: _Hist. Ind. Sc._ b. iv. c. 1.]
5. Yet we may, I think, note one instance, even in the works
of eminent modern chemists, in which this maxim, that we
have no right to expect any resemblance between the elements
and the compound, is lost sight of. I speak of certain
classifications of mineral substances. Berzelius, in his
System of Mineral Arrangement, places _sulphur_ next to the
_sulphurets_. But surely this is an errour, involving the
ancient assumption of the resemblance of elements and
compounds; as if we were to expect the sulphurets to bear a
resemblance to sulphur. All classifications are intended to
bring together things resembling each other: the sulphurets
of metals have certain general resemblances to each other
which make them a tolerably distinct, well determined, class
of bodies. But sulphur has no resemblances with these, and
no analogies with them, either in physical or even in
chemical properties. It is a simple body; and both its
resemblances and its analogies direct us to place it along
with other simple bodies, (selenium, and phosphorus,) which,
united with metals, produce compounds not very different
from the sulphurets. Sulphur cannot be, nor approach to
being, a sulphuret; we must not confound what it _is_ with
what it _makes_. Sulphur has its proper influence in
determining the properties of the compound into which it
enters; but it does not do this according to resemblance of
qualities, or according to any principle which properly
leads to propinquity in classification.
6. _Compounds assumed to be determined by the Figure of
Elements._--I pass over the fanciful modes of representing
chemical changes which were employed by the Alchemists; for
these strange inventions did little in leading men towards a
juster view of the relations of elements to compounds. I
proceed for an instant to the attempt to substitute another
obvious conception for the still obscure notion of
elementary composition. It was imagined that all the
properties of bodies and their mutual operations might be
{8} accounted for by supposing them constituted of
_particles_ of various _forms_, round or angular, pointed or
hooked, straight or spiral. This is a very ancient
hypothesis, and a favourite one with many casual speculators
in all ages. Thus Lucretius undertakes to explain why wine
passes rapidly through a sieve and oil slowly, by telling us
that the latter substance has its particles either larger
than those of the other, or more hooked and interwoven
together. And he accounts for the difference of sweet and
bitter by supposing the particles in the former case to be
round and smooth, in the latter sharp and jagged[6\6].
Similar assumptions prevailed in modern times on the revival
of the mechanical philosophy, and constitute a large part of
the physical schemes of Descartes and Gassendi. They were
also adopted to a considerable extent by the chemists. Acids
were without hesitation assumed to consist of sharp pointed
particles; which, 'I hope,' Lemery says[7\6], 'no one will
dispute, seeing every one's experience does demonstrate it:
he needs but taste an acid to be satisfied of it, for it
pricks the tongue like anything keen and finely cut.' Such
an assumption is not only altogether gratuitous and useless,
but appears to be founded in some degree upon a confusion in
the metaphorical and literal use of such words as _keen_ and
_sharp_. The assumption once made, it was easy to
accommodate it, in a manner equally arbitrary, to other
facts. 'A demonstrative and convincing proof that an acid
does consist of pointed parts is, that not only all acid
salts do crystallize into edges, but all dissolutions of
different things, caused by acid liquors, do assume this
figure in their crystallization. These crystals consist of
points differing both in length and bigness one from
another, and this diversity must be attributed to the keener
or blunter edges of the different sorts of acids: and so
likewise this difference of the points in subtilty is the
cause that one acid can penetrate and dissolve with one sort
of _mixt_, that another can't rarify at all: Thus _vinegar_
dissolves _lead_, {9} which _aqua fortis_ can't: _aqua
fortis_ dissolves _quicksilver_, which _vinegar_ will not
touch; _aqua regalis_ dissolves _gold_, whenas _aqua fortis_
cannot meddle with it; on the contrary, _aqua fortis_
dissolves _silver_, but can do nothing with gold, and so of
the rest.'
[Note 6\6: _De Rerum Natura_, ii. 390 sqq.]
[Note 7\6: _Chemistry_, p. 25.]
The leading fact of the vehement combination and complete
union of acid and alkali readily suggested a fit form for
the particles of the latter class of substances. 'This
effect,' Lemery adds, 'may make us reasonably conjecture
that an alkali is a terrestrious and solid matter whose
forms are figured after such a manner that the acid points
entering in do strike and divide whatever opposes their
motion.' And in a like spirit are the speculations in Dr.
Mead's _Mechanical Account of Poisons_ (1745). Thus he
explains the poisonous effect of _corrosive sublimate_ of
mercury by saying[8\6] that the particles of the salt are a
kind of lamellæ or blades to which the mercury gives an
additional weight. If resublimed with three-fourths the
quantity of mercury, it loses its corrosiveness, (becoming
_calomel_,) which arises from this, that in sublimation 'the
crystalline blades are divided every time more and more by
the force of the fire:' and 'the broken pieces of the
crystals uniting into little masses of differing figures
from their former make, those cutting points are now so much
smaller that they cannot make wounds deep enough to be
equally mischievous and deadly: and therefore do only
vellicate and twitch the sensible membranes of the stomach.'
[Note 8\6: P. 199.]
7. Among all this very fanciful and gratuitous assumption we
may notice one true principle clearly introduced, namely,
that the suppositions which we make respecting the forms of
the elementary particles of bodies and their mode of
combination must be such as to explain the facts of
crystallization, as well as of mere chemical change. This
principle we shall hereafter have occasion to insist upon
further.
I now proceed to consider a more refined form of assumption
respecting the constitution of bodies, yet {10} still one in
which a vain attempt is made to substitute for the peculiar
idea of chemical composition a more familiar mechanical
conception.
8. _Compounds assumed to be determined by the Mechanical
Attraction of the Elements._--When, in consequence of the
investigations and discoveries of Newton and his
predecessors, the conception of mechanical force had become
clear and familiar, so far as the action of external forces
upon a body was concerned, it was very natural that the
mathematicians who had pursued this train of speculation
should attempt to apply the same conception to that mutual
action of the internal parts of a body by which they are
held together. Newton himself had pointed the way to this
attempt. In the Preface to the _Principia_, after speaking
of what he has done in calculating the effects of forces
upon the planets, satellites, &e., he adds, 'Would it were
permitted us to deduce the other phenomena of nature from
mechanical principles by the same kind of reasoning. For
many things move me to suspect that all these phenomena
depend upon certain forces, by which the particles of
bodies, through causes not yet known, are either urged
towards each other, and cohere according to regular figures,
or are repelled and recede from each other; which forces
being unknown, philosophers have hitherto made their
attempts upon nature in vain.' The same thought is at a
later period followed out further in one of the Queries at
the end of the Opticks[9\6]. 'Have not the small particles
of bodies certain Powers, Virtues, or Forces, by which they
act at a distance, not only upon the rays of light for
reflecting, refracting and inflecting them, but also upon
one another for producing a great part of the phenomena of
nature?' And a little further on he proceeds to apply this
expressly to chemical changes. 'When Salt of Tartar runs
_per deliquium_ [or as we now express it, deliquesces] is
not this done by an _attraction_ between the particles of
the Salt of Tartar and the particles of the water which
float in the air in {11} the form of vapours? And why does
not common salt, or saltpetre, or vitriol, run _per
deliquium_, but for want of such an attraction? or why does
not Salt of Tartar draw more water out of the air than in a
certain proportion to its quantity, but for want of an
attractive force after it is saturated with water?' He goes
on to put a great number of similar cases, all tending to
the same point, that chemical combinations cannot be
conceived in any other way than as an attraction of
particles.
[Note 9\6: Query 31.]
9. Succeeding speculators in his school attempted to follow
out this view. Dr. Frend, of Christ Church, in 1710,
published his _Prælectiones Chymicæ, in quibus omne fere
Operationes Chymicæ ad vera Principia ex ipsius Naturæ
Legibus rediguntur. Oxonii habitæ_. This book is dedicated
to Newton, and in the dedication, the promise of advantage
to chemistry from the influence of the Newtonian discoveries
is spoken of somewhat largely,--much more largely, indeed,
than has yet been justified by the sequel. After declaring
in strong terms that the only prospect of improving science
consists in following the footsteps of Newton, the author
adds, 'That force of attraction, of which you first so
successfully traced the influence in the heavenly bodies,
operates in the most minute corpuscles, as you long ago
hinted in your _Principia_, and have lately plainly shown in
your _Opticks_; and this force we are only just beginning to
perceive and to study. Under these circumstances I have been
desirous of trying what is the result of this view in
chemistry.' The work opens formally enough, with a statement
of general mechanical principles, of which the most peculiar
are these:--'That there exists an attractive force by which
particles when at very small distances from each other, are
drawn together;--that this force is different, according to
the different figure and density of the particles;--that the
force may be greater on one side of a particle than on the
other;--that the force by which particles cohere together
arises from attraction, and is variously modified according
to the quantity of contacts.' But these principles are not
{12} applied in any definite manner to the explanation of
specific phenomena. He attempts, indeed, the question of
special solvents[10\6]. Why does _aqua fortis_ dissolve
silver and not gold, while _aqua regia_ dissolves gold and
not silver? which, he says, is the most difficult question
in chemistry, and which is certainly a fundamental question
in the formation of chemical theory. He solves it by certain
assumptions respecting the forces of attraction of the
particles, and also the diameter of the particles of the
acids and the pores of the metals, all which suppositions
are gratuitous.
[Note 10\6: P. 54.]
10. We may observe further, that by speaking, as I have
stated that he does, of the figure of particles, he mixes
together the assumption of the last section with the one
which we are considering in this. This combination is very
unphilosophical, or, to say the least, very insufficient,
since it makes a new hypothesis necessary. If a body be
composed of cubical particles, held together by their mutual
attraction, by what force are the parts of each cube held
together? In order to understand their structure, we are
obliged again to assume a cohesive force of the second
order, binding together the particles of each particle. And
therefore Newton himself says[11\6], very justly, 'The parts
of all homogeneal hard bodies which fully touch each other,
stick together very strongly: and for explaining how this
is, some have invented hooked atoms, _which is begging the
question_.' For (he means to imply,) how do the parts of the
hook stick together?
[Note 11\6: _Opticks_, p. 364.]
The same remark is applicable to all hypotheses in which
particles of a complex structure are assumed as the
constituents of bodies: for while we suppose bodies and
their known properties to result from the mutual actions of
these particles, we are compelled to suppose the parts of
each particle to be held together by forces still more
difficult to conceive, since they are disclosed only by the
properties of these particles, which as yet are unknown. Yet
Newton himself has not abstained from such hypotheses: thus
he says[12\6], 'A particle of {13} a salt may be compared to
a chaos, being dense, hard, dry, and earthy in the center,
and moist and watery in the circumference.'
[Note 12\6: _Opticks_, p. 362.]
Since Newton's time the use of the term _attraction_, as
expressing the cause of the union of the chemical elements
of bodies, has been familiarly continued; and has, no doubt,
been accompanied in the minds of many persons with an
obscure notion that chemical attraction is, in some way, a
kind of mechanical attraction of the particles of bodies.
Yet the doctrine that _chemical_ 'attraction' and
_mechanical_ attraction are forces of the same kind has
never, so far as I am aware, been worked out into a system
of chemical theory; nor even applied with any distinctness
as an explanation of any particular chemical phenomena. Any
such attempt, indeed, could only tend to bring more clearly
into view the entire inadequacy of such a mode of
explanation. For the leading phenomena of chemistry are all
of such a nature that no mechanical combination can serve to
express them, without an immense accumulation of additional
hypotheses. If we take as our problem the changes of colour,
transparency, texture, taste, odour, produced by small
changes in the ingredients, how can we expect to give a
mechanical account of these, till we can give a mechanical
account of colour, transparency, texture, taste, odour,
themselves? And if our mechanical hypothesis of the
elementary constitution of bodies does not explain _such_
phenomena as those changes, what can it explain, or what can
be the value of it? I do not here insist upon a remark which
will afterwards come before us, that even crystalline form,
a phenomenon of a far more obviously mechanical nature than
those just alluded to, has never yet been in any degree
explained by such assumptions as this, that bodies consist
of elementary particles exerting forces of the same nature
as the central forces which we contemplate in Mechanics.
When therefore Newton asks, 'When some stones, as spar of
lead, dissolved in proper menstruums, become salts, do not
these things show that salts are dry earth and watery acid
united by _attraction_?' we may {14} answer, that this mode
of expression appears to be intended to identify chemical
combination with mechanical attraction;--that there would be
no objection to any such identification, if we could, in
that way, explain, or even classify well, a collection of
chemical facts; but that this has never yet been done by the
help of such expressions. Till some advance of this kind can
be pointed out, we must necessarily consider the power which
produces chemical combination as a peculiar principle, a
special relation of the elements, not rightly expressed in
mechanical terms. And we now proceed to consider this
relation under the name by which it is most familiarly
known.
{{15}}
CHAPTER II.
ESTABLISHMENT AND DEVELOPMENT OF THE IDEA OF CHEMICAL
AFFINITY.
1. THE earlier chemists did not commonly involve themselves
in the confusion into which the mechanical philosophers ran,
of comparing chemical to mechanical forces. Their attention
was engaged, and their ideas were moulded, by their own
pursuits. They saw that the connexion of elements and
compounds with which they had to deal, was a peculiar
relation which must be studied directly; and which must be
understood, if understood at all, in itself, and not by
comparison with a different class of relations. At different
periods of the progress of chemistry, the conception of this
relation, still vague and obscure, was expressed in various
manners; and at last this conception was clothed in
tolerably consistent phraseology, and the principles which
it involved were, by the united force of thought and
experiment, brought into view.
2. The power by which the elements of bodies combine
chemically, being, as we have seen, a peculiar agency,
different from mere mechanical connexion or attraction, it
is desirable to have it designated by a distinct and
peculiar name; and the term _Affinity_ has been employed for
that purpose by most modern chemists. The word 'affinity' in
common language means, sometimes resemblance, and sometimes
relationship and ties of family. It is from the latter sense
that the metaphor is borrowed when we speak of 'chemical
affinity.' By the employment of this term we do not indicate
a resemblance, but a disposition to unite. Using the word in
a common unscientific manner, we might say that chlorine,
bromine, and iodine, have a great {16} _natural affinity_
with each other, for there are considerable resemblances and
analogies among them; but these bodies have very little
_chemical_ Affinity for each other. The use of the word in
the _former_ sense, of resemblance, can be traced in earlier
chemists; but the word does not appear to have acquired its
peculiar chemical meaning till after Boerhaave's time.
Boerhaave, however, is the writer in whom we first find a
due apprehension of the peculiarity and importance of the
Idea which it now expresses. When we make a chemical
solution[13\6], he says, not only are the particles of the
dissolved body separated from each other, but they are
closely united to the particles of the solvent. When _aqua
regia_ dissolves gold, do you not see, he says to his
hearers, that there must be between each particle of the
solvent and of the metal, a mutual virtue by which each
loves, unites with, and holds the other (_amat_, _unit_,
_retinet_)? The opinion previously prevalent had been that
the solvent merely separates the parts of the body
dissolved: and most philosophers had conceived this
separation as performed by mechanical operations of the
particles, resembling, for instance, the operation of wedges
breaking up a block of timber. But Boerhaave forcibly and
earnestly points out the insufficiency of the conception.
This, he says, does not account for what we see. We have not
only a separation, but a new combination. There is a force
by which the particles of the solvent associate to
themselves the parts dissolved, not a force by which they
repel and dissever them. We are here to imagine not
mechanical action, not violent impulse, not antipathy, but
love, at least if love be the desire of uniting. (Non igitur
hic etiam actiones mechanicæ, non propulsiones violentæ, non
inimicitiæ cogitandæ, sed amicitiæ, si amor dicendus copulæ
cupido.) The novelty of this view is evidenced by the mode
in which he apologizes for introducing it. 'Fateor, paradoxa
hæc assertio.' To Boerhaave, therefore, (especially
considering his great influence as a teacher of chemistry,)
we may {17} assign the merit of first diffusing a proper
view of Chemical Affinity as a peculiar force, the origin of
almost all chemical changes and operations.
[Note 13\6: _Elementa Chemiæ_, Lugd. Bat. 1732, p. 677.]
3. To Boerhaave is usually assigned also the credit of
introducing the _word_ 'Affinity' among chemists; but I do
not find that the word is often used by him in this sense;
perhaps not at all[14\6]. But however this may be, the term
is, on many accounts, well worthy to be preserved, as I
shall endeavour to show. Other terms were used in the same
sense during the early part of the eighteenth century. Thus
when Geoffroy, in 1718, laid before the Academy of Paris his
Tables of Affinities, which perhaps did more than any other
event to fix the Idea of Affinity, he termed them 'Tables of
the Relations of Bodies;' '_Tables des Rapports_:' speaking
however, also, of their 'disposition to unite,' and using
other phrases of the same import.
[Note 14\6: See Dumas, _Leçons de Phil. Chim._ p. 364. Rees'
_Cyclopædia_, Art. Chemistry. In the passage of Boerhaave to
which I refer above, _affinitas_ is rather opposed to, than
identified with, chemical combination. When, he says, the
parts of the body to be dissolved are dissevered by the
solvent, why do they remain united to the particles of the
solvent, and why do not rather both the particles of the
solvent and of the dissolved body collect into homogeneous
bodies by their _affinity_? 'denuo se affinitate suæ naturæ
colligant in corpora homogenea?' And the answer is, because
they possess another force which counteracts this affinity
of homogeneous particles, and makes compounds of different
elements. Affinity, in chemistry, now means the tendency of
_different_ kinds of matter to unite: but it appears, as I
have said, to have acquired this sense since Boerhaave's time.]
The term _attraction_, having been recommended by Newton as
a fit word to designate the force which produces chemical
combination, continued in great favour in England, where the
Newtonian philosophy was looked upon as applicable to every
branch of science. In France, on the contrary, where
Descartes still reigned triumphant, 'attraction,' the
watch-word of the enemy, was a sound never uttered but with
dislike and suspicion. In 1718 (in the notice of Geoffroy's
Table,) the Secretary of the Academy, after pointing out
some of the peculiar circumstances of chemical {18}
combinations, says, 'Sympathies and attractions would suit
well here, if there were such things,' 'Les sympathies, les
attractions conviendroient bien ici, si elles étaient
quelque chose.' And at a later period, in 1731, having to
write the _éloge_ of Geoffroy after his death, he says, 'He
gave, in 1718, a singular system, and a Table of
_Affinities_, or Relations of the different substances in
chemistry. These affinities gave an easiness to some
persons, who feared that they were _attractions in
disguise_, and all the more dangerous in consequence of the
seductive forms which clever people have contrived to give
them. It was found in the sequel that this scruple might be
got over.'
This is the earliest published instance, so far as I am
aware, in which the word 'Affinity' is distinctly used for
the cause of chemical composition; and taking into account
the circumstances, the word appears to have been adopted in
France in order to avoid the word _attraction_, which had
the taint of Newtonianism. Accordingly we find the word
_affinité_ employed in the works of French chemists from
this time. Thus, in the _Transactions of the French Academy_
for 1746, in a paper of Macquer's upon Arsenic, he
says[15\6], 'On peut facilement rendre raison de ces
phenomènes par le moyen des affinités que les différens
substances qui entrent dans ces combinaisons, ont les uns
avec les autres:' and he proceeds to explain the facts by
reference to Geoffroy's Table. And in Macquer's _Elements of
Chemistry_, which appeared a few years later, the 'Affinity
of Composition' is treated of as a leading part of the
subject, much in the same way as has been practised in such
books up to the present time. From this period, the word
appears to have become familiar to all European chemists in
the sense of which we are now speaking. Thus, in the year
1758, the Academy of Sciences at Rouen offered a prize for
the best dissertation on Affinity. The prize was shared
between M. Limbourg of Theux, near Liege, and M. Le Sage
{19} of Geneva[16\6]. About the same time other persons
(Manherr[17\6], Nicolai[18\6], and others) wrote on the same
subject, employing the same name.
[Note 15\6: _A. P._ 1746, p. 201.]
[Note 16\6: Thomson's _Chemistry_, iii. 10. Limbourg's
Dissertation was published at Liege, in 1761; and Le Sage's
at Geneva.]
[Note 17\6: _Dissertatio de Affinitate Corporum_. Vindob. 1762.]
[Note 18\6: _Progr._ I. II. _de Affinitate Corporum Chimica_.
Jen. 1775, 1776.]
Nevertheless, in 1775, the Swedish chemist Bergman, pursuing
still further this subject of Chemical Affinities, and the
expression of them by means of Tables, returned again to the
old Newtonian term; and designated the disposition of a body
to combine with one rather than another of two others as
_Elective Attraction_. And as his work on _Elective
Attractions_ had great circulation and great influence, this
phrase has obtained a footing by the side of _Affinity_, and
both one and the other are now in common use among chemists.
4. I have said above that the term _Affinity_ is worthy of
being retained as a technical term. If we use the word
_attraction_ in this case, we identify or compare chemical
with mechanical attraction; from which identification and
comparison, as I have already remarked, no one has yet been
able to extract the means of expressing any single
scientific truth. If such an identification or comparison be
not intended, the use of the same word in two different
senses can only lead to confusion; and the proper course,
recommended by all the best analogies of scientific history,
is to adopt a peculiar term for that peculiar relation on
which chemical composition depends. The word _Affinity_,
even if it were not rigorously proper according to its
common meaning, still, being simple, familiar, and well
established in this very usage, is much to be preferred
before any other.
But further, there are some analogies drawn from the common
meaning of this word, which appear to recommend it as
suitable for the office which it has to discharge. For
common mechanical attractions and {20} repulsions, the
forces by which one body considered as a _whole_ acts upon
another external to it, are, as we have said, to be
distinguished from those more intimate ties by which the
_parts_ of each body are held together. Now this difference
is implied, if we compare the former relations, the
attractions and repulsions, to alliances and wars between
States, and the latter, the internal union of particles, to
those bonds of affinity which connect the citizens of the
same state with one another, and especially to the ties of
Family. We have seen that Boerhaave compares the union of
two elements of a compound to their marriage; 'we must
allow,' says an eminent chemist of our own time[19\6], 'that
there is some truth in this poetical comparison.' It
contains this truth,--that the two become one to most
intents and purposes, and that the Unit thus formed (the
Family) is not a mere juxtaposition of the component parts.
And thus the Idea of Affinity as the peculiar principle of
chemical composition, is established among chemists, and
designated by a familiar and appropriate name.
[Note 19\6: Dumas, _Leçons de Phil. Chim._ p. 363.]
5. _Analysis is possible._--We must, however, endeavour to
obtain a further insight into this Idea, thus fixed and
named. We must endeavour to extricate, if not from the Idea
itself, from the processes by which it has obtained
acceptation and currency among chemists, some principles
which may define its application, some additional
specialities in the relations which it implies. This we
shall proceed to do.
The Idea of Affinity, as already explained, implies a
disposition to combine. But this combination is to be
understood as admitting also of a possibility of separation.
Synthesis implies Analysis as conceivable: or to recur to
the image which we have already used, Divorce is possible
when the Marriage has taken place.
That there is this possibility, is a conviction implied in
all the researches of chemists, ever since the true notion
of composition began to predominate in their investigations.
One of the first persons who clearly {21} expressed this
conviction was Mayow, an English physician, who published
his _Medico-Physical Tracts_ in 1674. The first of them _De
Sale-Nitro et Spiritu Nitro-Aerio_, contains a clear
enunciation of this principle. After showing how, in the
combinations of opposite elements, as acid and alkali, their
properties entirely disappear, and a new substance is formed
not at all resembling either of the ingredients, he
adds[20\6], 'Although these salts thus mixed appear to be
destroyed it is still possible for them to be separated from
each other, with their powers still entire.' He proceeds to
exemplify this, and illustrates it by the same image which I
have already alluded to: 'Salia acida a salibus
volatilibus discedunt, ut cum sale fixo tartari, tanquam
_sponso_ magis idoneo, _conjugium_ strictius ineunt.' This
idea of a synthesis which left a complete analysis still
possible, was opposed to a notion previously current, that
when two heterogeneous bodies united together and formed a
third body, the two constituents were entirely destroyed,
and the result formed out of their ruins[21\6]. And this
conception of Synthesis and Analysis, as processes which are
possible successively and alternately, and each of which
supposes the possibility of the other, has been the
fundamental and regulative principle of the operations and
speculations of analytical chemistry from the time of Mayow
to the present day.
[Note 20\6: Cap. xiv. p. 233.]
[Note 21\6: Thomson's _Chemistry_, iii. 8.]
6. _Affinity is Elective._--When the idea of chemical
affinity, or disposition to unite, was brought into view by
the experiments and reasonings of chemists, they found it
necessary to consider this disposition as _elective_;--each
element _chose_ one rather than another of the elements
which were presented to it, and quitted its union with one
to unite with another which it preferred. This has already
appeared in the passage just quoted from Mayow. He adds in
the same strain, 'I have no doubt that fixed salts choose
one acid rather than another, in order that they may
coalesce with it {22} in a more intimate union.'--'Nullus
dubito salia fixa acidum unum præ aliis _eligere_, ut cum
eodem arctiore unione coalescant.' The same thought is
expressed and exemplified by other chemists: they notice
innumerable cases in which, when an ingredient is combined
with a liquid, if a new substance be immersed which has a
greater affinity for the liquid, the liquid combines with
the new substance by election, and the former **ingredient
is _precipitated_. Thus Stahl says[22\6], 'In spirit of
nitre dissolve silver; put in copper and the silver is
thrown down; put in iron and the copper goes down; put in
zinc, the iron precipitates; put in volatile alkali, the
zinc is separated; put in fixed alkali, the volatile quits
its hold.'--As may be seen in this example, we have in such
cases, not only a preference, but a long gradation of
preferences. The spirit of nitre will combine with silver,
but it prefers copper; prefers iron more; zinc still more;
volatile alkali yet more; fixed alkali the most.
[Note 22\6: _Zymotechnia_, 1697, p. 117.]
The same thing was proved to obtain with regard to each
element; and when this was ascertained, it became the object
of chemists to express these degrees of preference, by lists
in which substances were arranged according to their
disposition to unite with another substance. In this manner
was formed Geoffroy's Table of Affinities (1718), which we
have already mentioned. This Table was further improved by
other writers, as Gellert (1751) and Limbourg (1761).
Finally Bergman improved these Tables still further, taking
into account not only the order of affinities of each
element for others, but the _sum_ of the tendencies to unite
of each two elements, which sum, he held, determined the
resulting combination when several elements were in contact
with each other.
7. As we have stated in the History[23\6], when the doctrine
of elective affinities had assumed this very definite and
systematic form, it was assailed by Berthollet, who
maintained, in his _Essai de Statique_ {23} _Chimique_,
(1803,) that chemical affinities are _not_ elective:--that,
when various elements are brought together, their
combinations do not depend upon the kind of elements alone,
but upon the quantity of each which is present, that which
is most abundant always entering most largely into the
resulting compounds. It may seem strange that it should be
possible, at so late a period of the science, to throw doubt
upon a doctrine which had presided over and directed its
progress so long. Proust answered Berthollet, and again
maintained that chemical affinity is elective. I have, in
the History, given the judgment of Berzelius upon this
controversy. 'Berthollet,' he says, 'defended himself with
an acuteness which makes the reader hesitate in his
judgment; but the great mass of facts finally decided the
point in favour of Proust.' I may here add the opinion
pronounced upon this subject by Dr. Turner[24\6]: 'Bergman
erred in supposing the result of the chemical action to be
in every case owing to elective affinity [for this power is
modified in its effects by various circumstances]: but
Berthollet ran into the opposite extreme in declaring that
the effects formerly ascribed to that power are never
produced by it. That chemical attraction is exerted between
different bodies with different degrees of energy, is, I
apprehend, indisputable.' And he then proceeds to give many
instances of differences in affinity which cannot be
accounted for by the operation of any modifying causes.
Still more recently, M. Dumas has taken a review of this
controversy; and, speaking with enthusiasm of the work of
Berthollet, as one which had been of inestimable service to
himself in his early study of chemistry, he appears at first
disposed to award to him the victory in this dispute. But
his final verdict leaves undamaged the general principle now
under our consideration, that chemical affinity is elective.
'For my own part,' he says[25\6], 'I willingly admit the
notions of Berthollet when we have to do with acids or {24}
with bases, of which the energy is nearly equal: but when
bodies endued with very energetic affinities are in presence
of other bodies of which the affinities are very feeble, I
propose to adopt the following rule: In a solution,
everything remaining dissolved, the strong affinities
satisfy themselves, leaving the weak affinities to arrange
matters with one another. The strong acids take the strong
bases, and the weak acids can only unite with the weak
bases. The known facts are perfectly in accordance with this
practical rule.' It is obvious that this recognition of a
distinction between strong and weak affinities, which
operates to such an extent as to determine entirely the
result, is a complete acknowledgement of the Elective nature
of Affinity, as far as any person acquainted with chemical
operations could contend for it. For it must be allowed by
all, that solubility, and other collateral circumstances,
influence the course of chemical combinations, since they
determine whether or not there shall take place that contact
of elements without which affinity cannot possibly operate.
[Note 23\6: _Hist. Ind. Sc._ b. xiv. c. iii.]
[Note 24\6: _Chemistry_, p. 199. 6th edition.]
[Note 25\6: _Leçons de Philosophie Chimique_, p. 386.]
8. _Affinity is Definite as to quantity._--In proportion as
chemists obtained a clearer view of the products of the
laboratory as results of the composition of elements, they
saw more and more clearly that these results were definite;
that one element not only preferred to combine with another
of a certain kind, but also would combine with it to a
certain extent and no further, thus giving to the result not
an accidental and variable, but a fixed and constant
character. Thus salts being considered as the result of the
combination of two opposite principles, acid and alkali, and
being termed _neutral_ when these principles exactly
balanced each other, Rouelle (who was Royal Professor at
Paris in 1742) admits of neutral salts with excess of acid,
neutral salts with excess of base, and perfect neutral
salts. Beaume maintained[26\6] against him that there were
no salts except those perfectly neutral, the other classes
being the results of mixture and imperfect {25} combination.
But this question was not adequately treated till chemists
made every experiment with the balance in their hands. When
this was done, they soon discovered that, in each neutral
salt, the proportional weights of the ingredients which
composed it were always the same. This was ascertained by
Wenzel, whose _Doctrine of the Affinities of Bodies_
appeared in 1777. He not only ascertained that the
proportions of elements in neutral chemical compounds are
definite, but also that they are reciprocal; that is, (to
express his results in a manner now employed by chemists),
that if A, a certain weight of a certain acid, neutralize
_m_, a certain weight of a certain base, and B, a certain
weight of a certain other acid, neutralize _n_, a certain
weight of a certain other base; the compound of A and _n_
will also be neutral; as also that of B and _m_. The same
views were again presented by Richter in 1792, in his
_Principles of the Measure of Chemical Elements_. And along
with these facts, that of the combination of elements in
multiple proportions being also taken into account, the
foundations of the Atomic Theory were laid; and that Theory
was propounded in 1803 by Mr. Dalton. That theory, however,
rests upon the Idea of Substance, as well as upon that Idea
of Chemical Affinity which we are here considering; and the
discussion of its evidence and truth must be for the present
deferred.
[Note 26\6: Dumas, _Phil. Chim._ p. 198.]
9. The two principles just explained,--that Affinity is
Definite as to the Kind, and as to the Quantity of the
elements which it unites,--have here been stated as results
of experimental investigation. That they could never have
been clearly understood, and therefore never firmly
established, without laborious and exact experiments, is
certain; but yet we may venture to say that being once fully
known, they may seem to thoughtful men to possess an
evidence beyond that of mere experiment. For how, in fact,
can we conceive combinations, otherwise than as definite in
kind and quantity? If we were to suppose each element
ready to combine with any other indifferently, and
indifferently in any quantity, we should have a world in
{26} which all would be confusion and indefiniteness. There
would be no fixed kinds of bodies. Salts, and stones, and
ores, would approach to and graduate into each other by
insensible degrees. Instead of this, we know that the world
consists of bodies distinguishable from each other by
definite differences, capable of being classified and named,
and of having general propositions asserted concerning them.
And as we cannot conceive a world in which this should not
be the case, it would appear that we cannot conceive a state
of things in which the laws of the combination of elements
should not be of that definite and measured kind which we
have above asserted.
This will, perhaps, appear more clearly by stating our
fundamental convictions respecting chemical composition in
another form, which I shall, therefore, proceed to do.
10. _Chemical Composition determines Physical
Properties._--However obscure and incomplete may be our
conception of the internal powers by which the ultimate
particles of bodies are held together, it involves, at
least, this conviction:--that these powers are what
determine bodies to be bodies, and therefore contain the
reason of all the properties which, as bodies, they possess.
The forces by which the particles of a body are held
together, also cause it to be hard or soft, heavy or light,
opake or transparent, black or red; for if these forces are
not the cause of these peculiarities, what can be the cause?
By the very supposition which we make respecting these
forces, they include all the relations by which the parts
are combined into a whole, and therefore they, and they
only, must determine all the attributes of the whole. The
foundation of all our speculations respecting the intimate
constitution of bodies must be this principle, that their
composition determines their properties.
Accordingly we find our chemists reasoning from this
principle with great confidence, even in doubtful cases.
Thus Davy, in his researches concerning the diamond, says:
'That some chemical difference must exist between the
hardest and most beautiful of the {27} gems and charcoal,
between a non-conductor and a conductor of electricity, it
is scarcely possible to doubt: and it seems reasonable to
expect that a very refined or perfect chemistry will confirm
_the analogies of nature_; and show that bodies cannot be
the same in their composition or chemical nature, and yet
totally different in their chemical properties.' It is
obvious that the principle here assumed is so far from being
a mere result of experience, that it is here appealed to to
prove that all previous results of experience on this
subject must be incomplete and inaccurate; and that there
must be some chemical difference between charcoal and
diamond, though none had hitherto been detected.
11. In what manner, according to what rule, the chemical
composition shall determine the kind of the substance, we
cannot reasonably expect to determine by mere conjecture or
assumption, without a studious examination of natural bodies
and artificial compounds. Yet even in the most recent times,
and among men of science, we find that an assumption of the
most arbitrary character has in one case been mixed up with
this indisputable principle, that the elementary composition
determines the kind of the substance. In the classification
of minerals, one school of mineralogists have rightly taken
it as their fundamental principle that the chemical
composition shall decide the position of the mineral in the
system. But they have appended to this principle,
arbitrarily and unjustifiably, the maxim that the element
which is _largest in quantity_ shall fix the class of the
substance. To make such an assumption is to renounce, at
once, all hope of framing a system which shall be governed
by the resemblances of the things classified; for how can we
possibly know beforehand that fifty-five per cent, of iron
shall give a substance its predominant properties, and that
forty-five per cent, shall not? Accordingly, the systems of
mineralogical arrangement which have been attempted in this
way, (those of Haüy, Phillips, and others,) have been found
inconsistent with themselves, ambiguous, and incapable of
leading to any general truths. {28}
12. _Chemical Composition and Crystalline Form
correspond._--Thus the physical properties of bodies depend
upon their chemical composition, but in a manner which a
general examination of bodies with reference to their
properties and their composition can alone determine. We
may, however, venture to assert further, that the more
definite the properties are, the more distinct may we expect
to find this dependence. Now the most definite of the
properties of bodies are those constant properties which
involve relations of space; that is, their figure. We speak
not, however, of that external figure, derived from external
circumstances, which, so far from being constant and
definite, is altogether casual and arbitrary; but of that
figure which arises from their internal texture, and which
shows itself not only in the regular forms which they
spontaneously assume, but in the disposition of the parts to
separate in definite directions, and no others. In short,
the most definite of the properties of perfect chemical
compounds is their _crystalline structure_; and therefore it
is evident that the crystalline structure of each body, and
the forms which it affects, must be in a most intimate
dependence upon its chemical composition.
Here again we are led to the brink of another theory;--that
of crystalline structure, which has excited great interest
among philosophers ever since the time of Haüy. But this
theory involves, besides that idea of chemical composition
with which we are here concerned, other conceptions, which
enter into the relations of figure. These conceptions,
governed principally by the Idea of Symmetry, must be
unfolded and examined before we can venture to discuss any
theory of crystallization: and we shall proceed to do this
as soon as we have first duly considered the Idea of
Substance and its consequences.
{{29}}
CHAPTER III.
OF THE IDEA OF SUBSTANCE.
1. _Axiom of the Indestructibility of Substance._--WE now
come to an Idea of which the history is very different from
those of which we have lately been speaking. Instead of
being gradually and recently brought into a clear light, as
has been the case with the Ideas of Polarity and Affinity,
the Idea of Substance has been entertained in a distinct
form from the first periods of European speculation. That
this is so, is proved by our finding a principle depending
upon this Idea current as an axiom among the early
philosophers of Greece:--namely, that _nothing can be
produced out of nothing_. Such an axiom, more fully stated,
amounts to this: that the substance of which a body consists
is incapable of being diminished (and consequently incapable
of being augmented) in quantity, whatever apparent changes
it may undergo. Its forms, its distribution, its qualities,
may vary, but the substance itself is identically the same
under all these variations.
The axiom just spoken of was the great principle of the
physical philosophy of the Epicurean school, as it must be
of every merely material philosophy. The reader of Lucretius
will recollect the emphasis with which it is repeatedly
asserted in his poem:
E nilo nil gigni, in nilum nil posse reverti;
Nought comes of nought, nor ought returns to nought.
Those who engaged in these early attempts at physical
speculation were naturally much pleased with the clearness
which was given to their notions of change, composition, and
decomposition, by keeping steadily hold of the Idea of
Substance, as marked by this {30} fundamental axiom. Nor has
its authority ever ceased to be acknowledged. A philosopher
was asked[27\6], What is the weight of smoke? He answered,
'Subtract the weight of the ashes from the weight of the
wood which is burnt, and you have the weight of the smoke.'
This reply would be assented to by all; and it assumes as
incontestable that even under the action of fire, the
material, the substance, does not perish, but only changes
its form.
[Note 27\6: Kant, _Kritik der R. V._ p. 167.]
This principle of the indestructibility of substance might
easily be traced in many reasonings and researches, ancient
and modern. For instance, when the chemist works with the
_retort_, he places the body on which he operates in one
part of an inclosed cavity, which, by its bendings and
communications, separates at the same time that it confines,
the products which result from the action of fire: and he
assumes that this process is an analysis of the body into
its ingredients, not a creation of anything which did not
exist before, or a destruction of anything which previously
existed. And he assumes further, that the total quantity of
the substance thus analysed is the sum of the quantities of
its ingredients. This principle is the very basis of
chemical speculation, as we shall hereafter explain more fully.
2. _The Idea of Substance._--The axiom above spoken of
depends upon the Idea of Substance, which is involved in all
our views of external objects. We unavoidably assume that
the qualities and properties which we observe are properties
of _things_;--that the adjective implies a
substantive;--that there is, besides the external characters
of things, something _of which_ they are the characters. An
apple which is red, and round, and hard, is not merely
redness, and roundness, and hardness: these circumstances
may all alter while the apple remains the same apple. Behind
or under the appearances which we see, we conceive something
of which we think; or, to use the metaphor which obtained
currency among the ancient philosophers, the {31} attributes
and qualities which we observe are supported by and inherent
in something: and this something is hence called a
_substratum_ or _substance_,--that which stands _beneath_
the apparent qualities and supports them.
That we have such an _Idea_, using the term 'Idea' in the
sense in which I have employed it throughout these
disquisitions, is evident from what has been already said.
The Axiom of the Indestructibility of Substance proves the
existence of the Idea of Substance, just as the Axioms of
Geometry and Arithmetic prove the existence of the Ideas of
Space and Number. In the case of Substance, as of space or
number, the ideas cannot be said to be borrowed from
experience, for the axioms have an authority of a far more
comprehensive and demonstrative character than any which
experience can bestow. The axiom that nothing can be
produced from nothing and nothing destroyed, is so far from
being a result of experience, that it is apparently
contradicted by the most obvious observation. It has, at
first, the air of a paradox; and by those who refer to it,
it is familiarly employed to show how fallacious common
observation is. The assertion is usually made in this
form;--that nothing is created and nothing annihilated,
_notwithstanding_ that the common course of our experience
appears to show the contrary. The principle is not an
empirical, but a necessary and universal truth;--is
collected, not from the evidence of our senses, but from the
operation of our ideas. And thus the universal and
undisputed authority of the axiom proves the existence of
the Idea of Substance.
3. _Locke's Denial of the Idea of Substance._--I shall not
attempt to review the various opinions which have been
promulgated respecting this Idea: but it may be worth our
while to notice briefly the part which it played in the
great controversy concerning the origin of our ideas which
Locke's _Essay_ occasioned. Locke's object was to disprove
the existence of all ideas not derived from Sensation or
Reflection: and since the idea of substance as distinct from
external qualities, is {32} manifestly not derived directly
from sensation, nor by any very obvious or distinct process
from reflection, Locke was disposed to exclude the idea as
much as possible. Accordingly, in his argumentation against
Innate Ideas[28\6], he says plainly, 'the idea of substance,
which we neither have nor can have by sensation or
reflection.' And the inference which he draws is, 'that we
have no such clear idea at all.' What then, it may be asked,
do we mean by the word _substance_? This also he answers,
though somewhat strangely, 'We signify nothing by the word
_substance_, but only an uncertain supposition of we know
not what, _i. e._ of something whereof we have no particular
distinct positive idea, which we take to be the substratum,
or support, of those ideas we know.' That while he indulged
in this tautological assertion of our ignorance and
uncertainty, he should still have been compelled to
acknowledge that the word substance had some meaning, and
should have been driven to explain it by the identical
metaphors of 'substratum' and 'support,' is a curious proof
how impossible it is entirely to reject this idea.
[Note 28\6: _Essay_, b. i. c. iv. s. 18.]
But as we have already seen, the supposition of the
existence of substance is so far from being uncertain, that
it carries with it irresistible conviction, and substance is
necessarily conceived as something which cannot be produced
or destroyed. It may be easily supposed, therefore, that
when the controversy between Locke and his assailants came
to this point, he would be in some difficulty. And, indeed,
though with his accustomed skill in controversy, he managed
to retain a triumphant tone, he was driven from his main
points. Thus he repels the charge that he took the being of
substance to be doubtful[29\6]. He says, 'Having everywhere
affirmed and built upon it that man is a substance, I cannot
be supposed to question or doubt of the being of substance,
till I can question or doubt of my own being.' He attempts
to make a stand by saying that _being_ of things does not
depend upon our {33} _ideas_; but if he had been asked how,
without having an _idea_ of substance, he _knew_ substance
to _be_, it is difficult to conceive what answer he could
have made. Again, he had said that our idea of substance
arises from our 'accustoming ourselves to suppose' a
substratum of qualities. Upon this his adversary, Bishop
Stillingfleet, very properly asks, Is this custom grounded
upon true reason or no? To which Locke replies, that it is
grounded upon this: That we cannot conceive how simple ideas
of sensible qualities should subsist alone; and therefore we
suppose them to exist in, and to be supported by some common
subject, which support we denote by the name substance. Thus
he allows, not only that we necessarily assume the reality
of substance, but that we cannot conceive qualities without
substance; which are concessions so ample as almost to
include all that any advocate for the Idea of Substance need
desire.
[Note 29\6: _Essay_, b. ii. c. ii. and _First Letter to the
Bishop of Worcester_.]
Perhaps Locke, and the adherents of Locke, in denying that
we have an idea of substance in general, were latently
influenced by finding that they could not, by any effort of
mind, call up any _image_ which could be considered as an
image of substance in general. That in this sense we have no
idea of substance, is plain enough; but in the same sense we
have no idea of space in general, or of time, or number, or
cause, or resemblance. Yet we certainly have such a power of
representing to our minds space, time, number, cause,
resemblance, as to arrive at numerous truths by means of
such representations. These general representations I have
all along called Ideas, nor can I discover any more
appropriate word; and in this sense, we have also, as has
now been shown, an Idea of Substance.
4. _Is all Material Substance heavy?_--The principle that
the quantity of the substance of any body remains unchanged
by our operations upon it, is, as we have said, of universal
validity. But then the question occurs, how are we to
ascertain the quantity of substance, and thus, to apply the
principle in particular cases. In the case above mentioned,
where {34} smoke was to be weighed, it was manifestly
assumed that the quantity of the substance might be known by
its weight; and that the total quantity being unchanged, the
total weight also would remain the same. Now on what grounds
do we make this assumption? Is all material substance heavy?
and if we can assert this to be so, on what grounds does the
truth of the assertion rest? These are not idle questions of
barren curiosity; for in the history of that science
(Chemistry) to which the Idea of Substance is principally
applicable, nothing less than the fate of a comprehensive
and long established theory (the Phlogiston theory) depended
upon the decision of this question. When it was urged that
the reduction of a metal from a calcined to a metallic form
could not consist in the _addition_ of phlogiston, because
the metal was lighter than the calx had been; it was replied
by some, that this was not conclusive, for that phlogiston
was a principle of levity, diminishing the weight of the
body to which it was added. This reply was, however,
rejected by all the sounder philosophers, and the force of
the argument finally acknowledged. But why was this
suggestion of a substance having no weight, or having
absolute levity, repudiated by the most reflective
reasoners? It is assumed, it appears, that all matter must
be heavy; what is the ground of this assumption?
The ground of such an assumption appears to be the
following. Our idea of substance includes in it this:--that
substance is a quantity capable of addition; and thus
capable of making up, by composition, a sum equal to all its
parts. But substance, and the quantity of substance, can be
known to us only by its attributes and qualities. And the
qualities which are capable constantly and indefinitely of
increase and diminution by increase and diminution of the
parts, must be conceived inseparable from the substance. For
the qualities, if removable from the substance at all, must
be removable by some operation performed upon the substance;
and by the idea of substance, all such operations are only
equivalent to separation, junction, and union of parts.
Hence those characters {35} which thus universally increase
and diminish by addition and subtraction of the things
themselves, belong to the substance of the things. They are
measures of its quantity, and are not merely its separable
qualities.
The weight of bodies is such a character. However we
compound or divide bodies, we compound and divide their
weight in the same manner. We may dismember a body into the
minutest parts; but the sum of the weights of the parts is
always equal to the whole weight of the body. The weight of
a body can be in no way increased or diminished, except by
adding something to it or taking something from it. If we
bake a brick, we do not conceive that the change of colour
or of hardness, implies that anything has been created or
destroyed. It may easily be that the parts have only assumed
a new arrangement; but if the brick have lost weight, we
suppose that something (moisture for instance) has been
removed elsewhere.
Thus weight is apprehended as essential to matter. In
considering the dismemberment or analysis of bodies, we
assume that there must be some criterion of the quantity of
substance; and this criterion can possess no other
properties than their weight possesses. If we assume an
element which has no weight, or the weight of which is
negative, as some of the defenders of phlogiston attempted
to do, we put an end to all speculation on such subjects.
For if weight is not the criterion of the quantity of one
element, phlogiston for instance, why is weight the
criterion of the quantity of any other element? We may, by
the same right, assume any other real or imaginary element
to have levity instead of gravity; or to have a peculiar
intensity of gravity which makes its weight no index of its
quantity. In short, if we do this, we deprive of all
possibility of application our notions of element, analysis,
and composition; and violate the postulates on which the
questions are propounded which we thus attempt to decide.
We must, then, take a constant and quantitative property of
matter, such as weight is, to be an index {36} of the
quantity of matter or of substance to which it belongs. I do
not here speak of the question which has sometimes been
proposed, whether the _weight_ or the _inertia_ of bodies be
the more proper measure of the quantity of matter. For the
measure of inertia is regulated by the same assumption as
that of substance:--that the quantity of the whole must be
equal to the quantity of all the parts: and inertia is
measured by weight, for the same reason that substance is so.
Having thus established the certainty, and ascertained the
interpretation of the fundamental principle which the Idea
of Substance involves, we are prepared to consider its
application in the science upon which it has a peculiar
bearing.
{{37}}
NOTE TO CHAPTER III.
[3rd Ed.]--[THE doctrine here propounded, that All Matter is
Heavy, has been opposed by Sir William Hamilton of
Edinburgh. (_Works of Reid_, note, p. 853.) This writer is a
man of unquestionable acuteness and of very extensive
reading; but his acuteness shows itself in barren
ontological distinctions, which appear to me to be of the
same character as the speculations of the eminent Schoolmen
of the most sterile periods of the dark ages. That he should
have no conception of progressive or inductive science is
not wonderful, when we recollect that he holds, as an
important part of his philosophy, that the study of
mathematics perverts and obscures the mind. But it may be of
some interest to consider his objections to the doctrine
here maintained.
He says, 1st, that our reasoning assumes that we must
necessarily have it in our power to ascertain the Quantity
of Matter; whereas this may be a problem out of the reach of
human determination.
To this I reply, that my reasoning _does_ assume that there
is a science, or sciences, which make assertions concerning
the Quantity of Matter: Mechanics and Chemistry are such
sciences. My assertion is, that to make such sciences
possible, Quantity of Matter must be proportional to Weight.
If my opponent deny that Mechanics and Chemistry can exist
as sciences, he may invalidate my proof; but not otherwise.
2. He says that there are two conceivable ways of estimating
the Quantity of Matter: by the Space occupied, and by the
Weight or Inertia; and that I assume the second measure
gratuitously.
To which I reply, that the most elementary steps in
Mechanics and in Chemistry contradict the notion that {38}
the Quantity of Matter is proportionate to the Space. They
proceed necessarily on a distinction between Space and
Matter:--between mere Extension and material Substance.
3. He allows that we cannot make the Extension of a body the
measure of the Quantity of Matter, because, he says, we do
not know if 'the compressing force' is such as to produce
'the closest compression.' That is, he assumes a compressing
force, assumes a closest compression, assumes a peculiar
(and very improbable) atomic hypothesis; and all this to
supply a reason why we are not to believe the first simple
principle of Mechanics and Chemistry.
4. He speaks of 'a series of apparent fluids (as Light or
its vehicle, the Calorific, the Electro-galvanic, and
Magnetic agents) which we can neither denude of their
character of substance, nor clothe with the attribute of
weight.'
To which my reply is, that precisely because I cannot
'clothe' these agents with the attribute of Weight, I _do_
'denude them of the character of Substance.' They are not
substances, but agencies. These Imponderable Agents are not
properly called 'Imponderable Fluids.' This I conceive that
I have proved; and the proof is not shaken by denying the
conclusion without showing any defect in the reasoning.
5. Finally, my critic speaks about 'a logical canon,' and
about 'a criterion of truth, subjectively necessary and
objectively certain;' which matters I shall not waste the
reader's time by discussing.]
{{39}}
CHAPTER IV.
APPLICATION OF THE IDEA OF SUBSTANCE IN CHEMISTRY.
1. _A Body is Equal to the Sum of its Elements._--FROM the
earliest periods of chemistry the balance has been
familiarly used to determine the proportions of the
ingredients and of the compound; and soon after the middle
of the last century, this practice was so studiously
followed, that Wenzel and Richter were thereby led to the
doctrine of Definite Proportions. But yet the full value and
significance of the balance, as an indispensable instrument
in chemical researches, was not understood till the gaseous,
as well as solid and fluid ingredients were taken into the
account. When this was done, it was found that the
principle, that the whole is equal to the sum of its parts,
of which, as we have seen, the necessary truth, in such
cases, flows from the idea of substance, could be applied in
the most rigorous manner. And conversely, it was found that
by the use of the balance, the chemist could decide, in
doubtful cases, which was a whole, and which were parts.
For chemistry considers all the changes which belong to her
province as compositions and decompositions of elements; but
still the question may occur, whether an observed change be
the one or the other. How can we distinguish whether the
process which we contemplate be composition or
decomposition?--whether the new body be formed by addition
of a new, or subtraction of an old element? Again; in the
case of decomposition, we may inquire, What are the ultimate
limits of our analysis? If we decompound bodies into others
more and more simple, how far can we carry this succession
{40} of processes? How far can we proceed in the road of
analysis? And in our actual course, what evidence have we
that our progress, as far as it has gone, has carried us
from the more complex to the more simple?
To this we reply, that the criterion which enables us to
distinguish, decidedly and finally, whether our process have
been a mere analysis of the proposed body into its
ingredients, or a synthesis of some of them with some new
element, is the principle stated above, that the weight of
the whole is equal to the weight of all the parts. And no
process of chemical analysis or synthesis can be considered
complete till it has been verified by this fact;--by finding
that the weight of the compound is the weight of its
supposed ingredients; or, that if there be an element which
we think we have detached from the whole, its loss is
betrayed by a corresponding diminution of weight.
I have already noticed what an important part this principle
has played in the great chemical controversy which ended in
the establishment of the oxygen theory. The calcination of a
metal was decided to be the union of oxygen with the metal,
and not the separation of phlogiston from it, because it was
found that in the process of calcination, the weight of the
metal increased, and increased exactly as much as the weight
of ambient air diminished. When oxygen and hydrogen were
exploded together, and a small quantity of water was
produced, it was held that this was really a synthesis of
water, because, when very great care was taken with the
process, the weight of the water which resulted was equal to
the weight of the gases which disappeared.
2. _Lavoisier._--It was when gases came to be considered as
entering largely into the composition of liquid and solid
bodies, that extreme accuracy in weighing was seen to be so
necessary to the true understanding of chemical processes.
It was in this manner discovered by Lavoisier and his
contemporaries that oxygen constitutes a large ingredient of
calcined metals, of acids, and of water. A countryman of
Lavoisier[30\6] {41} has not only given most just praise to
that great philosopher for having constantly tested all his
processes by a careful and skilful use of the balance, but
has also claimed for him the merit of having introduced the
maxim, that in chemical operations nothing is created and
nothing lost. But I think it is impossible to deny that this
maxim is assumed in all the attempts at analysis made by his
contemporaries, as well as by him. This maxim is indeed
included in any clear notion of analysis: it could not be
the result of the researches of any one chemist, but was the
governing principle of the reasonings of all. Lavoisier,
however, employed this principle with peculiar assiduity and
skill. In applying it, he does not confine himself to mere
additions and subtractions of the quantities of ingredients;
but often obtains his results by more complex processes. In
one of his investigations he says, 'I may consider the
ingredients which are brought together, and the result which
is obtained as an algebraical equation; and if I
successively suppose each of the quantities of this equation
to be unknown, I can obtain its value from the rest: and
thus I can rectify the experiment by the calculation, and
the calculation by the experiment. I have often taken
advantage of this method, in order to correct the first
results of my experiments, and to direct me in repeating
them with proper precautions.'
[Note 30\6: M. Dumas, _Leçons de la Philosophie Chimique_.
1837. p. 157.]
The maxim, that the whole is equal to the sum of all its
parts, is thus capable of most important and varied
employment in chemistry. But it may be applied in another
form to the exclusion of a class of speculations which are
often put forwards.
3. _Maxim respecting Imponderable Elements._--Several of the
phenomena which belong to bodies, as heat, light,
electricity, magnetism, have been explained hypothetically
by assuming the existence of certain fluids; but these
fluids have never been shown to have weight. Hence such
hypothetical fluids have been termed _imponderable
elements_. It is however plain, that so long as these fluids
appear to be without weight, they are not _elements_ of
bodies in the same {42} sense as those elements of which we
have hitherto been speaking. Indeed we may with good reason
doubt whether those phenomena depend upon transferable
fluids at all. We have seen strong reason to believe that
light is not matter, but only motion; and the same thing
appears to be probable with regard to heat. Nor is it at all
inconceivable that a similar hypothesis respecting
electricity and magnetism should hereafter be found tenable.
Now if heat, light, and those other agents, be not matter,
they are not _elements_ in such a sense as to be included in
the principle referred to above, That the body is equal to
the sum of its elements. Consequently the maxim just stated,
that in chemical operations nothing is created, nothing
annihilated, does not apply to Light and Heat. They are not
_things_. And whether heat can be produced where there was
no heat before, and light struck out from darkness, the
ideas of which we are at present treating do not enable us
to say. In reasoning respecting chemical synthesis and
analysis therefore, we shall only make confusion by
attempting to include in our conception the Light and Heat
which are produced and destroyed. Such phenomena may be very
proper subjects of study, as indeed they undoubtedly are;
but they cannot be studied to advantage by considering them
as sharing the nature of composition and decomposition.
Again: in all attempts to explain the processes of nature,
the proper course is, first to measure the facts with
precision, and then to endeavour to understand their cause.
Now the facts of chemical composition and decomposition, the
weights of the ingredients and of the compounds, are facts
measurable with the utmost precision and certainty. But it
is far otherwise with the light and heat which accompany
chemical processes. When combustion, deflagration,
explosion, takes place, how can we measure the light or the
heat? Even in cases of more tranquil action, though we can
apply the thermometer, what does the thermometer tell us
respecting the _quantity_ of the heat? Since then we have no
measure which is of any value as {43} regards such
circumstances in chemical changes, if we attempt to account
for these phenomena _on chemical principles_, we introduce,
into investigations in themselves perfectly precise and
mathematically rigorous, another class of reasonings, vague
and insecure, of which the only possible effect is to
vitiate the whole reasoning, and to make our conclusions
inevitably erroneous.
We are led then to this maxim: that _imponderable fluids
are_ not _to be admitted as chemical elements of bodies_[31\6].
[Note 31\6: See the answer to Sir William Hamilton's
objections, at the end of the last chapter.
Since we are thus warned by a sound view of the nature of
science, from considering chemical affinity as having any
hold upon imponderable elements, we are manifestly still
more decisively prohibited from supposing mechanical impulse
or pressure to have any effect upon such elements. To make
this supposition, is to connect the most subtle and
incorporeal objects which we know in nature by the most
gross material ties. This remark seems to be applicable to
M. Poisson's hypothesis that the electric fluid is retained
at the surface of bodies by the pressure of the
atmosphere.]
4. It appears, I think, that our best and most philosophical
chemists have proceeded upon this principle in their
investigations. In reasoning concerning the constitution of
bodies and the interpretation of chemical changes, the
attempts to include in these interpretations the heat or
cold produced, by the addition or subtraction of a certain
hypothetical 'caloric,' have become more and more rare among
men of science. Such statements, and the explanations often
put forwards of the light and heat which appear under
various circumstances in the form of fire, must be
considered as unessential parts of any sound theory.
Accordingly we find Mr. Faraday gradually relinquishing such
views. In January, 1834, he speaks generally of an
hypothesis of this kind[32\6]: 'I cannot refrain from
recalling here the beautiful idea put forth, I believe by
Berzelius, in his development of his views of the
electro-chemical theory of affinity, that the heat and light
evolved during cases of powerful combination {44} are the
consequence of the electric discharge which is at that
moment taking place.' But in April of the same year[33\6],
he observes, that in the combination of oxygen and hydrogen
to produce water, electric powers to a most enormous amount
are for the time active, but that the flame which is
produced gives but feeble traces of such powers. 'Such
phenomena,' therefore, he adds, 'may not, cannot, be taken
as evidences of the nature of the action; but are merely
incidental results, incomparably small in relation to the
forces concerned, and supplying no information of the way in
which the particles are active on each other, or in which
their forces are finally arranged.'
[Note 32\6: _Researches_, 870.]
[Note 33\6: _Researches_, 960.]
In pursuance of this maxim, we must consider as an
unessential part of the oxygen theory that portion of it,
much insisted upon by its author at the time, in which when
sulphur, for instance, combined with oxygen to produce
sulphuric acid, the combustion was accounted for by means of
the _caloric_ which was supposed to be _liberated_ from its
combination with oxygen.