THE CHEMICAL ELEMENTS CONTRASTED WITH THE ALCHEMICAL PRINCIPLES.
It was known to many observers in the later years of the 17th century
that the product of the calcination of a metal weighs more than the
metal; but it was still possible, at that time, to assert that this
fact is of no importance to one who is seeking to give an accurate
description of the process of calcination. Weight, which measures mass
or quantity of substance, was thought of, in these days, as a property
like colour, taste, or smell, a property which was sometimes
decreased, and sometimes increased, by adding one substance to
another. Students of natural occurrences were, however, feeling their
way towards the recognition of some property of substances which did
not change in the haphazard way wherein most properties seemed to
alter. Lavoisier reached this property at one bound. By his
experimental investigations, he taught that, however greatly the
properties of one substance may be masked, or altered, by adding
another substance to it, yet the property we call mass, and measure by
weight, is not affected by these changes; for Lavoisier showed, that
the mass of the product of the union of two substances is always
exactly the sum of the masses of these two substances, and the sum of
the masses of the substances whereinto one substance is divided is
always exactly equal to that mass of the substance which is divided.
For the undefined, ever-changing, protean essence, or soul, of a thing
which the alchemists thought of as hidden by wrappings of properties,
the exact investigations of Lavoisier, and those of others who worked
on the same lines as he, substituted this definite, fixed,
unmodifiable property of mass. Lavoisier, and those who followed in
his footsteps, also did away with the alchemical notion of the
existence of an essential substratum, independent of changes in those
properties of a substance which can be observed by the senses. For the
experimental researches of these men obliged naturalists to recognise,
that a change in the properties of a definite, homogeneous substance,
such as pure water, pure chalk, or pure sulphur, is accompanied (or,
as we generally say, is caused) by the formation of a new substance or
substances; and this formation, this apparent creation, of new
material, is effected, either by the addition of something to the
original substance, or by the separation of it into portions which are
unlike it, and unlike one another. If the change is a combination, or
coalescence, of two things into one, then the mass, and hence the
weight, of the product is equal to the sum of those masses, and hence
those weights, of the things which have united to form it; if the
change is a separation of one distinct substance into several
substances, then the sum of the masses, and hence the weights, of the
products is equal to that mass, and hence that weight, of the
substance which has been separated.
Consider the word _water_, and the substance represented by this word.
In Chapter IV., I gave illustrations of the different meanings which
have been given to this word; it is sometimes used to represent a
material substance, sometimes a quality more or less characteristic of
that substance, and sometimes a process to which that substance, and
many others like it, may be subjected. But when the word _water_ is
used with a definite and exact meaning, it is a succinct expression
for a certain group, or collocation, of measurable properties which
are always found together, and is, therefore, thought of as a distinct
substance. This substance can be separated into two other substances
very unlike it, and can be formed by causing these to unite. One
hundred parts, by weight, of pure water are always formed by the union
of 11.11 parts of hydrogen, and 88.89 parts of oxygen, and can be
separated into these quantities of those substances. When water is
formed by the union of hydrogen and oxygen, in the ratio of 11.11
parts by weight of the former to 88.89 of the latter, the properties
of the two substances which coalesce to form it disappear, except
their masses. It is customary to say that water _contains_ hydrogen
and oxygen; but this expression is scarcely an accurate description of
the facts. What we call _substances_ are known to us only by their
properties, that is, the ways wherein they act on our senses. Hydrogen
has certain definite properties, oxygen has other definite properties,
and the properties of water are perfectly distinct from those of
either of the substances which it is said to contain. It is,
therefore, somewhat misleading to say that water _contains_
substances the properties whereof, except their masses, disappeared at
the moment when they united and water was produced. Nevertheless we
are forced to think of water as, in a sense, containing hydrogen and
oxygen. For, one of the properties of hydrogen is its power to
coalesce, or combine, with oxygen to form water, and one of the
properties of oxygen is its ability to unite with hydrogen to form
water; and these properties of those substances cannot be recognised,
or even suspected, unless certain definite quantities of the two
substances are brought together under certain definite conditions. The
properties which characterise hydrogen, and those which characterise
oxygen, when these things are separated from all other substances, can
be determined and measured in terms of the similar properties of some
other substance taken as a standard. These two distinct substances
disappear when they are brought into contact, under the proper
conditions, and something (water) is obtained whose properties are
very unlike those of hydrogen or oxygen; this new thing can be caused
to disappear, and hydrogen and oxygen are again produced. This cycle
of changes can be repeated as often as we please; the quantities of
hydrogen and oxygen which are obtained when we choose to stop the
process are exactly the same as the quantities of those substances
which disappeared in the first operation whereby water was produced.
Hence, water is an intimate union of hydrogen and oxygen; and, in this
sense, water may be said to contain hydrogen and oxygen.
The alchemist would have said, the properties of hydrogen and oxygen
are destroyed when these things unite to form water, but the essence,
or substratum, of each remains. The chemist says, you cannot discover
all the properties of hydrogen and oxygen by examining these
substances apart from one another, for one of the most important
properties of either is manifested only when the two mutually react:
the formation of water is not the destruction of the properties of
hydrogen and oxygen and the revelation of their essential substrata,
it is rather the manifestation of a property of each which cannot be
discovered except by causing the union of both.
There was, then, a certain degree of accuracy in the alchemical
description of the processes we now call chemical changes, as being
the removal of the outer properties of the things which react, and the
manifestation of their essential substance. But there is a vast
difference between this description and the chemical presentment of
these processes as reactions between definite and measurable
quantities of elements, or compounds, or both, resulting in the
re-distribution, of the elements, or the separation of the compounds
into their elements, and the formation of new compounds by the
re-combination of these elements.
Let us contrast the two descriptions somewhat more fully.
The alchemist wished to effect the transmutation of one substance into
another; he despaired of the possibility of separating the Elements
whereof the substance might be formed, but he thought he could
manipulate what he called the _virtues_ of the Elements by a judicious
use of some or all of the three Principles, which he named Sulphur,
Salt, and Mercury. He could not state in definite language what he
meant by these Principles; they were states, conditions, or qualities,
of classes of substances, which could not be defined. The directions
the alchemist was able to give to those who sought to effect the
change of one thing into another were these. Firstly, to remove those
properties which characterised the thing to be changed, and leave only
the properties which it shared with other things like it; secondly, to
destroy the properties which the thing to be changed possessed in
common with certain other things; thirdly, to commingle the Essence of
the thing with the Essence of something else, in due proportion and
under proper conditions; and, finally, to hope for the best, keep a
clear head, and maintain a sense of virtue.
If he who was about to attempt the transmutation inquired how he was
to destroy the specific properties, and the class properties, of the
thing he proposed to change, and by what methods he was to obtain its
Essence, and cause that Essence to produce the new thing, he would be
told to travel along "the road which was followed by the Great
Architect of the Universe in the creation of the world." And if he
demanded more detailed directions, he would be informed that the
substance wherewith his experiments began must first be mortified,
then dissolved, then conjoined, then putrefied, then congealed, then
cibated, then sublimed, and fermented, and, finally, exalted. He
would, moreover, be warned that in all these operations he must use,
not things which he could touch, handle, and weigh, but the _virtues_,
the _lives_, the _souls_, of such things.
When the student of chemistry desires to effect the transformation of
one definite substance into another, he is told to determine, by
quantitative experiments, what are the elements, and what the
quantities of these elements, which compose the compound which he
proposes to change, and the compound into which he proposes to change
it; and he is given working definitions of the words _element_ and
_compound_. If the compound he desires to produce is found to be
composed of elements different from those which form the compound
wherewith his operations begin, he is directed to bring about a
reaction, or a series of reactions, between the compound which is to
be changed, and some other collocation of elements the composition of
which is known to be such that it can supply the new elements which
are needed for the production of the new compound.
Since Lavoisier realised, for himself, and those who were to come
after him, the meaning of the terms _element_ and _compound_, we may
say that chemists have been able to form a mental picture of the
change from one definite substance to another, which is clear,
suggestive, and consistent, because it is an approximately accurate
description of the facts discovered by careful and penetrative
investigations. This presentment of the change has been substituted
for the alchemical conception, which was an attempt to express what
introspection and reasoning on the results of superficial
investigations, guided by specious analogies, suggested ought to be
the facts.
Lavoisier was the man who made possible the more accurate, and more
far-reaching, description of the changes which result in the
production of substances very unlike those which are changed; and he
did this by experimentally analysing the conceptions of the element
and the compound, giving definite and workable meanings to these
conceptions, and establishing, on an experimental foundation, the
generalisation that the sum of the quantities of the substances which
take part in any change is itself unchanged.
A chemical element was thought of by Lavoisier as "the actual term
whereat analysis has arrived," a definite substance "which we cannot
subdivide with our present knowledge," but not necessarily a substance
which will never be divided. A compound was thought of by him as a
definite substance which is always produced by the union of the same
quantities of the same elements, and can be separated into the same
quantities of the same elements.
These conceptions were amplified and made more full of meaning by the
work of many who came after Lavoisier, notably by John Dalton, who was
born in 1766 and died in 1844.
In Chapter I., I gave a sketch of the atomic theory of the Greek
thinkers. The founder of that theory, who flourished about 500 B.C.,
said that every substance is a collocation of a vast number of minute
particles, which are unchangeable, indestructible, and impenetrable,
and are therefore properly called _atoms_; that the differences which
are observed between the qualities of things are due to differences in
the numbers, sizes, shapes, positions, and movements of atoms, and
that the process which occurs when one substance is apparently
destroyed and another is produced in its place, is nothing more than a
rearrangement of atoms.
The supposition that changes in the properties of substances are
connected with changes in the numbers, movements, and arrangements of
different kinds of minute particles, was used in a general way by many
naturalists of the 17th and 18th centuries; but Dalton was the first
to show that the data obtained by the analyses of compounds make it
possible to determine the relative weights of the atoms of the
elements.
Dalton used the word _atom_ to denote the smallest particle of an
element, or a compound, which exhibits the properties characteristic
of that element or compound. He supposed that the atoms of an element
are never divided in any of the reactions of that element, but the
atoms of a compound are often separated into the atoms of the elements
whereof the compound is composed. Apparently without knowing that the
supposition had been made more than two thousand years before his
time, Dalton was led by his study of the composition and properties of
the atmosphere to assume that the atoms of different substances,
whether elements or compounds, are of different sizes and have
different weights. He assumed that when two elements unite to form
only one compound, the atom of that compound has the simplest
possible composition, is formed by the union of a single atom of each
element. Dalton knew only one compound of hydrogen and nitrogen,
namely, ammonia. Analyses of this compound show that it is composed of
one part by weight of hydrogen and 4.66 parts by weight of nitrogen.
Dalton said one atom of hydrogen combines with one atom of nitrogen to
form an atom of ammonia; hence an atom of nitrogen is 4.66 times
heavier than an atom of hydrogen; in other words, if the _atomic
weight_ of hydrogen is taken as unity, the _atomic weight_ of nitrogen
is expressed by the number 4.66. Dalton referred the atomic weights of
the elements to the atomic weight of hydrogen as unity, because
hydrogen is lighter than any other substance; hence the numbers which
tell how much heavier the atoms of the elements are than an atom of
hydrogen are always greater than one, are always positive numbers.
When two elements unite in different proportions, by weight, to form
more than one compound, Dalton supposed that (in most cases at any
rate) one of the compounds is formed by the union of a single atom of
each element; the next compound is formed by the union of one atom of
the element which is present in smaller quantity with two, three, or
more, atoms of the other element, and the next compound is formed by
the union of one atom of the first element with a larger number
(always, necessarily, a whole number) of atoms of the other element
than is contained in the second compound; and so on. From this
assumption, and the Daltonian conception of the atom, it follows that
the quantities by weight of one element which are found to unite with
one and the same weight of another element must always be expressible
as whole multiples of one number. For if two elements, A and B, form a
compound, that compound is formed, by supposition, of one atom of A
and one atom of B; if more of B is added, at least one atom of B must
be added; however much of B is added the quantity must be a whole
number of atoms; and as every atom of B is the same in all respects as
every other atom of B, the weights of B added to a constant weight of
A must be whole multiples of the atomic weight of B.
The facts which were available in Dalton's time confirmed this
deduction from the atomic theory within the limits of experimental
errors; and the facts which have been established since Dalton's time
are completely in keeping with the deduction. Take, for instance,
three compounds of the elements nitrogen and oxygen. That one of the
three which contains least oxygen is composed of 63.64 _per cent._ of
nitrogen, and 36.36 _per cent._ of oxygen; if the atomic weight of
nitrogen is taken to be 4.66, which is the weight of nitrogen that
combines with one part by weight of hydrogen, then the weight of
oxygen combined with 4.66 of nitrogen is 2.66 (63.64:36.36 =
4.66:2.66). The weights of oxygen which combine with 4.66 parts by
weight of nitrogen to form the second and third compounds,
respectively, must be whole multiples of 2.66; these weights are 5.32
and 10.64. Now 5.32 = 2.66 x 2, and 10.64 = 2.66 x 4. Hence, the
quantities by weight of oxygen which combine with one and the same
weight of nitrogen are such that two of these quantities are whole
multiples of the third quantity.
Dalton's application of the Greek atomic theory to the facts
established by the analyses of compounds enabled him to attach to each
element a number which he called the atomic weight of the element, and
to summarise all the facts concerning the compositions of compounds in
the statement, that the elements combine in the ratios of their atomic
weights, or in the ratios of whole multiples of their atomic weights.
All the investigations which have been made into the compositions of
compounds, since Dalton's time, have confirmed the generalisation
which followed from Dalton's application of the atomic theory.
Even if the theory of atoms were abandoned, the generalisation would
remain, as an accurate and exact statement of facts which hold good in
every chemical change, that a number can be attached to each element,
and the weights of the elements which combine are in the ratios of
these numbers, or whole multiples of these numbers.
Since chemists realised the meaning of Dalton's book, published in
1808, and entitled, _A New System of Chemical Philosophy_, elements
have been regarded as distinct and definite substances, which have not
been divided into parts different from themselves, and unite with each
other in definite quantities by weight which can be accurately
expressed as whole multiples of certain fixed quantities; and
compounds have been regarded as distinct and definite substances
which are formed by the union of, and can be separated into,
quantities of various elements which are expressible by certain fixed
numbers or whole multiples thereof. These descriptions of elements and
compounds are expressions of actual facts. They enable chemists to
state the compositions of all the compounds which are, or can be,
formed by the union of any elements. For example, let A, B, C, and D
represent four elements, and also certain definite weights of these
elements, then the compositions of all the compounds which can be
formed by the union of these elements are expressed by the scheme
A_{_n_} B_{_m_} C_{_p_} D_{_q_}, where _m_ _n_ _p_ and _q_ are whole
numbers.
These descriptions of elements and compounds also enable chemists to
form a clear picture to themselves of any chemical change. They think
of a chemical change as being; (1) a union of those weights of two, or
more, elements which are expressed by the numbers attached to these
elements, or by whole multiples of these numbers; or (2) a union of
such weights of two, or more, compounds as can be expressed by certain
numbers or by whole multiples of these numbers; or (3) a reaction
between elements and compounds, or between compounds and compounds,
resulting in the redistribution of the elements concerned, in such a
way that the complete change of composition can be expressed by using
the numbers, or whole multiples of the numbers, attached to the
elements.
How different is this conception of a change wherein substances are
formed, entirely unlike those things which react to form them, from
the alchemical presentment of such a process! The alchemist spoke of
stripping off the outer properties of the thing to be changed, and, by
operating spiritually on the soul which was thus laid bare, inducing
the essential virtue of the substance to exhibit its powers of
transmutation. But he was unable to give definite meanings to the
expressions which he used, he was unable to think clearly about the
transformations which he tried to accomplish. The chemist discards the
machinery of virtues, souls, and powers. It is true that he
substitutes a machinery of minute particles; but this machinery is
merely a means of thinking clearly and consistently about the changes
which he studies. The alchemist thought, vaguely, of substance as
something underlying, and independent of, properties; the chemist uses
the expression, this or that substance, as a convenient way of
presenting and reasoning about certain groups of properties. It seems
to me that if we think of _matter_ as something more than properties
recognised by the senses, we are going back on the road which leads to
the confusion of the alchemical times.
The alchemists expressed their conceptions in what seems to us a
crude, inconsistent, and very undescriptive language. Chemists use a
language which is certainly symbolical, but also intelligible, and on
the whole fairly descriptive of the facts.
A name is given to each elementary substance, that is, each substance
which has not been decomposed; the name generally expresses some
characteristic property of the substance, or tells something about
its origin or the place of its discovery. The names of compounds are
formed by putting together the names of the elements which combine to
produce them; and the relative quantities of these elements are
indicated either by the use of Latin or Greek prefixes, or by
variations in the terminal syllables of the names of the elements.