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ESSAYS

Al HlOAL

AND
CHEMICAL

BY

SIR WILLIAM RAMSAY, K.C.B.

COMMANDEUK DE LA LEGION D'HONNEUB

COMMENDATORE BELLA CORONA D'lTALIA

FELLOW OF THE ROYAL SOCIETY, ETC.

LONDON
ARCHIBALD CONSTABLE & CO. LTD.

10 ORANGE ST., LEICESTER SQUARE
1908

PREFACE

THESE Essays on Chemical History and Biography, and on
chemical topics, have been delivered as lectures, or pub-
lished as magazine articles at various times in the course
of the last twenty-five years. A little alteration has been
necessary to avoid undue repetition, and in some cases
footnotes have been added, to correct statements which
have been rendered inaccurate by the progress of dis-
covery.

I have to thank the University of Glasgow for permis-
sion to reprint the oration on Black ; the editor of the
Youth's Companion for permission to reprint the sketch
of Lord Kelvin, ' What is an Element ? ' ' On the Periodic
Arrangement of the Elements,' ' Radium and its Pro-
ducts,' ' What is Electricity ? ' and ' How Discoveries are
Made ' ; the editor of the Contemporary Review for
permission to reprint the article on ' The Becquerel Rays ' ;
and the Royal Society, which has kindly granted similar
permission to republish the life of M. Berthelot.

WILLIAM RAMSAY.

October 1908.

CONTENTS

I. HISTORICAL ESSAYS

PAOB

THE EARLY DAYS OF CHEMISTRY , . 1
THE GREAT LONDON CHEMISTS —

I. BOYLE AND CAVENDISH . . .. . 19

II. DAVY AND GRAHAM . , . .41

JOSEPH BLACK: HIS LIFE AND WORK . . .67

LORD KELVIN . . » . .89

PIERRE EUGENE MARCELLIN BERTHELOT . . 101

II. CHEMICAL ESSAYS

HOW DISCOVERIES ARE MADE . . . .115

THE BECQUEREL RAYS . . . . . 129

WHAT IS AN ELEMENT ? . . . • . .147
ON THE PERIODIC ARRANGEMENT OF THE ELEMENTS . 161

RADIUM AND ITS PRODUCTS . . . .179

WHAT IS ELECTRICITY 1 , . . . .193

THE AURORA BOREALIS . ... . 205

THE FUNCTIONS OF A UNIVERSITY . 227

I. HISTORICAL ESSAYS

THE EARLY DAYS OF CHEMISTRY

IN the early days of the world's history, the study of
science was unknown. The state of society was insecure ;
nation was constantly invading nation, and men had
little leisure for other pursuits save war and the chase.
Yet we find, among those nations which were sufficiently
powerful to resist the attacks of their neighbours, and
sufficiently prosperous to dispense with invasions of the
territory of others in quest of plunder, some attempts to
inquire into the mysteries of nature. In some countries,
as in Egypt, a leisured class of persons, the priests, urged
no doubt partly by a desire for knowledge, partly by a
wish to impress the people with a sense of their superior
powers, made some progress in what may be called
'natural philosophy,' understanding by that term
elementary physics and chemistry. To these they added
a considerable acquaintance with astronomy and mathe-
matics.

For practical purposes of life, too, certain of the arts,
notably metallurgy and dyeing, which are based on
chemical principles, were cultivated. But these were
carried on by rule of thumb, and their development was
slow. Indeed, they were for the most part in the hands
of slaves, the freemen finding it more profitable to
engage in commerce, or in administration. The state of
Turkey or Morocco, in the present day, gives a good
A

2 ESSAYS BIOGRAPHICAL AND CHEMICAL

idea of the condition of life in the centuries before the
Christian era, in so far as pursuit of science is concerned.
Even with the example of adjoining nations, whose
prosperity is in great part due to the attention they
have paid to the cultivation of scientific knowledge, the
Turks and the Moors display a total lack of interest.
Much less, then, could people such as those be expected
to show any eagerness in the discovery of Nature's
secrets.

Yet from time to time there have been minds who
refused to accept the daily drudgery of life as sufficient
for their needs. Questions such as : Whence did this
world arise ? What does it consist of ? What will be its
ultimate fate ? perplexed them, as they perplex us ; and
in an endeavour to answer questions like these, scientific
discovery was begun. Many nations, however, were
instructed by the priests of their religion that it is
impious to make such inquiries ; and it is not until the
era of the early Greek civilisation, when the current
mythology had ceased to retain its hold on abler minds,
that we find any serious attempt to grapple with funda-
mental problems like those stated. But even among the
Greeks we meet with a disinclination to take trouble
about matters which were imagined to have little if any
relation to human affairs ; even Socrates, one of their
greatest thinkers, taught that it was foolish to abandon
those things which more nearly concern man for
things external to him. Plato, who chronicled the sayings
of Socrates, wrote in the seventh book of the Republic :
' We shall pursue astronomy with the help of problems,
just as we pursue geometry; but if it is our desire to
become acquainted with the true nature of astronomy,
we shall let the heavenly bodies alone.' And he states
in another place, that even if we were to ascertain these
things, we could neither alter the course of the stars,

THE EARLY DAYS OF CHEMISTRY 3

nor apply our knowledge so as to benefit mankind. And
in Timaeus, Plato remarks, ' God only has the knowledge
and the power which are able to combine many things
into one, and to dissolve the one into the many. But
no man either is, or ever will be, able to accomplish either
the one or the other operation.'

Even in the middle ages, the same spirit of content
with insufficient observation, and the same disposition
to draw conclusions from insufficient premises, is to be
noticed. It is difficult for us, in this age when a certain
acquaintance with scientific methods of thought, if not
with scientific facts, is common to almost every one, to
imagine the kind of reply to elementary questions which
satisfied our predecessors, even those who devoted time
and, one would hope, some powers of mind to a con-
sideration of the subject. Let us take a few examples.

The answer which one of the schoolmen would give
to the question : ' Of what are bodies composed ? ' is thus
paraphrased by Le Febure, apothecary to His Majesty
Charles the Second : ' If the substance is a body, it must
possess quantity ; and of necessity, it must be divisible ;
now, bodies must be composed either of things divisible,
or indivisible, that is, either of points, or of parts : a body,
however, cannot be composed of points, for a point is
indivisible, possessing no quantity, and, consequently,
it cannot communicate quantity to a body, since it does
not itself possess it. Hence it must be concluded that
a body must be composed of divisible parts; to this,
however, it may be said that such parts must either be
divisible or indivisible; if the former, then the part
cannot be the smallest possible, since it may itself be
divided into others still more minute ; and if this smallest
part is indivisible, the same difficulty confronts us, for
it will be without quantity, which, therefore, it cannot
communicate to a body, for it itself does not possess it,

4 ESSAYS BIOGRAPHICAL AND CHEMICAL

seeing that divisibility is the essential property of
quantity.' The logic is unanswerable, but we are left
where we were.

Let us next see what ideas were held by Du Clos,
physician to Louis xiv., on the cause of the solidification
of liquids. These are his memorable words :

'The reason of the concretion of liquids is obviously
dryness ; for this quality, being the opposite of moistness,
which renders bodies liquid, may well produce an effect
opposite to that produced by the latter, to wit, the
concretion of liquids.' Again, we have not gained much
information by the profound utterance.

One more quotation. It is from a work by Jean Rey,
Doctor of Medicine, published in 1630, entitled, ' On an
Inquiry wherefore Tin and Lead increase in Weight on
Calcination.' He is arguing that ' Nature abhors a
vacuum,' a favourite thesis in former days. ' It is quite
certain that in the bounds of nature, a vacuum, which
is nothing, can find no place. There is no power in
Nature from which nothing could have made the universe,
and none which could reduce the universe to nothing :
that requires the same virtue. Now the matter would
be otherwise if there could be a vacuum. For if it could
be here, it could also be there ; and being here and there,
why not elsewhere ? and why not everywhere ? Thus the
universe could reach annihilation by its own forces ; but
to Him alone who could make it is due the glory of
compassing its destruction.'

We must remember, therefore, in studying the early
history of chemistry, that not only were facts, familiar to
many of us now, wholly unknown ; but we must also bear
in mind that the point of view from which the early
chemists surveyed the phenomena of nature was entirely
different from that to which we are now accustomed.
It is evident, from the examples quoted, which are not

THE EARLY DAYS OF CHEMISTRY 5

taken from the writings of those who lived at a very
remote time from the present day, but only six or seven
generations ago, that our great-great-great-grandfathers
differed from ourselves not merely in lack of knowledge,
but in the way they regarded the facts which they
observed. And it is consequently somewhat difficult for
us to adopt their point of view, and to think their
thoughts. But we must attempt to do so, if we are to
realise the progress of our science.

The progress of the science of Chemistry, indeed, forms
one phase of the progress of human thought. The ideas
which have been held, however, run in certain channels.
They may all be referred to speculations on the nature
of matter ; but the speculations take different forms.
For it may be inquired : What forms is matter capable of
assuming ? Or, what is the minute structure of matter ?
Or, what changes does matter undergo ? These three
questions were for the ancients, as they are still for us,
fundamental; and it will be the aim of these essays to
endeavour to give the reader some idea of the history
of these three lines of thought. We shall see that
our present knowledge enables us in some measure
to connect these three lines of inquiry by virtue of
certain hypotheses ; but it will be convenient to treat
of each separately, at least up to a certain stage.

THE ELEMENTS

The word 'Element,' in the old days, had a meaning
different from that which we now ascribe to it ; or, to be
more exact, it had two meanings, which were frequently
confounded with one another. The suggested derivation
of the word indicates one of these meanings ; it is that
which we usually give it ; for, just as ' 1,' ' m,' and ' n ' are

6 ESSAYS BIOGRAPHICAL AND CHEMICAL

constituents of the alphabet, so an ' element ' was regarded
as a constituent of substances. From the use of the
word by ancient authors, however, it would appear that
an element was often regarded as a property of matter ;
and it was evidently supposed that by changing the
properties, or in the words of the old writers adding more
or less of one or other element to a substance, the
substance itself could be transmuted into another wholly
different. We shall see examples of the two meanings
illustrated later on.

It is probable that the original ideas of elements
reached Greece from India. The Buddhistic teaching
was that the elements are six in number, namely, Earth,
Water, Air, Fire, Ether, and Consciousness. But they are
given by Empedocles of Agrigent, who lived about 440
B.C., without the two last; and many disputes arose as
to which was to be regarded as the primary one, from
which all the others were derived ; for even at that
remote date, speculation was rife as to the unity of
matter. While Thales contended that the original
element was water, Anaximenes believed it to be air or
fire; and Aristotle did not regard elements as different
kinds of matter, but as different properties appertaining
to one original matter. Plato, however, evidently con-
sidered elements to be different kinds of matter, for he
puts these words into the mouth of Timaeus : ' In the
first place, that which we are now calling water, when
congealed, becomes stone and earth, as our sight seems
to show us [here he refers probably to rock-crystal, then
supposed to be petrified ice] ; and this same element,
when melted and dispersed, passes into vapour and fire.
Air, again, when burnt up, becomes fire, and again fire,
when condensed and extinguished, passes once more
into the form of air ; and once more air, when collected
and condensed, produces cloud and vapour; and from

THE EARLY DAYS OF CHEMISTRY 7

these, when still more compressed, comes flowing water ;
and from water come earth and stones once more ; and
thus generation seems to be transmitted from one to the
other in a circle.'

Aristotle attributed to these elements four properties, of
which each possessed two. Thus, Earth was cold and
dry ; Water, cold and moist ; Air, hot and moist ; and
Fire, hot and dry. A fifth element was also conceived by
Aristotle to accompany these four; he termed it v\rj,
translated into the Latin Quinta Essentia ; and this was
regarded by alchemists of a later date as of the utmost
importance, for it was supposed to penetrate the whole
world. The ceaseless strivings of the alchemists after
the 'quintessence' were due to the notion that, were it
discovered, all transmutations would then be possible.
Yet the word ' Chemistry' was not, so far as we know, in use
in Aristotle's time. It is said to occur in a Greek manu-
script of Zosimus, a resident in Panapolis, a city in Egypt,
who wrote in the fifth century. It appeared to mean the
art of making gold and silver ; for the title of his Avork is
given by Scaliger as ' A faithful Description of the sacred
and divine Art of making gold and silver.' M. Berthelot,
who has made a detailed study of ancient Greek, Arabic,
Syriac, and Latin manuscripts relating to early chemistry,
believes that the attempts to transmute metals arose, not
from any philosophical notions regarding the nature of
elements, but from fraudulent attempts of goldsmiths to
pass off base metals on their customers for silver and
gold. One of the earliest manuscripts on record dates
from the third century, and is preserved at Leiden in
Holland. It was found in a tomb in Thebes in 1828.
It is a rough and ill-spelt collection of workman's receipts
for working in metals, in which frequent reference is
made to an alloy of copper and tin — an alloy which in
many respects resembles gold. It is apparently a manu-

8 ESSAYS BIOGRAPHICAL AND CHEMICAL

script which escaped the fate of most of the Egyptian MSS.
of that date ; for about the year 290, the Emperor
Diocletian commanded that all works on alchemy should
be burnt, ' in order that the Egyptians might not become
rich by the art [of making gold and silver] and use their
wealth to revolt against the Romans.'

But although the idea of transmutation did not arise
from such theoretical speculations as Aristotle's on the
unity of matter, and on the possibility of converting one
kind of matter into another by altering its properties,
or in the language of the time, adding or removing more
or less of one or other element, yet the later workers did
not scruple to use Aristotle's theory in order to make
good their case. And for many centuries — indeed until
our own time — there have always existed men who
devoted their lives to this object.

There was, at the same time, a supposed mystical
connection, of Chaldean origin, between the metals and
the planets. Thus gold was the sun ; silver, the moon ;
copper, Venus ; tin, and afterwards mercury, was associ-
ated with the planet of that name ; iron, used in battle,
had affinity with ruddy Mars ; electron, an alloy of gold
and silver, and subsequently tin, was Jupiter ; and sluggish
and heavy lead was the slow-moving Saturn. These
analogies were used in casting horoscopes, or predicting
the future of those rich and credulous enough to consult
astrologers.

At the same time as these fantastic notions were held,
many processes of manufacture, involving a knowledge
of chemical reactions, were carried on. These will be
alluded to later ; but it may be noted here that speculation
did not take the course of attempting to devise explana-
tions of chemical changes, but was indulged in, as
before remarked, with little reference to experimental
methods.

THE EARLY DAYS OF CHEMISTRY 9

The conquest of Egypt by the Arabians in the seventh
century put an end for a time to the school of learning
of Alexandria, where citizens of all nations met and dis-
cussed problems of all kinds. But the spirit of the Grseco-
Egyptians was too strong even for the fanaticism of the
Arabians ; the conquered became the conqueror ; and an
Arabian school of philosophy arose, which carried on the
traditions acquired from the Greeks. It has been be-
lieved, until M. Berthelot showed the belief to be erro-
neous, that Latin works which professed to be translations
from the Arabic of the eighth and succeeding centuries
were really renderings of the ancient Arabian authors.
It appears, however, that they are for the most part
forgeries, having little if any resemblance to the originals.
Thus Geber, said to have been translated into Latin in
1529, is entirely different from the Arabic writings of the
real Geber. The historical Geber lived in the ninth cen-
tury. His comment on alchemy is characterised by
strong common sense. It is : 'I saw that persons em-
ployed in attempts to fabricate gold and silver were
working in ignorance, and by false methods ; I then per-
ceived that they belonged to two classes, the dupers and
the duped. I pitied both of them.'

About this time, however, an addition to Aristotle's
classification of elements was made ; and it endured until
within the last two hundred years. It evidently arose
from attempts to account for the properties of the metals,
and the changes which they undergo by heat. These
additional 'principles,' as they were termed, were salt,
sulphur, and mercury. We read that the noble metals
contain ' a very pure mercury,' the meaning being, pro-
bably, that they possess a high metallic lustre ; while the
common metals, such as copper and iron, contain ' a base
sulphur,' implying that these metals are easily altered by
fire, losing their metallic appearance and changing into

10 ESSAYS BIOGRAPHICAL AND CHEMICAL

black scales. These principles were later increased to
five, by the addition of ' phlegm ' and of ' earth.' Fanci-
ful analogies were drawn between the Divine Trinity of
Father, Son, and Holy Spirit, the human Body, Soul,
and Spirit, and the three principles above-named. At-
tempts were incessantly made to draw inspiration from
such impossible fancies. Thus the volatilisation of mer-
cury, or ' Spirit ' as it was sometimes called, was deemed
analogous to the ascension of Christ! In fact, there is
no limit to the absurdity and folly of the endeavours of
the alchemists. Let us hear a list of their processes, as
told by Sir George Ripley, who lived and wrote in 1471.

' The fyrst Chapter shalbe of natural 1 Calcination ;
The second of Dyssolution secret and phylosopliycall ;
The third of our Elemental Separation ;
The fourth of Conjunction matrymonyall ;
The fifth of Putrefaction then f ollowe shall ;
Of Congelatyon, albyfycative shall be the Syxt,
Then of Cybation the seaventh shall follow next.
The secret of our Sublymation the eyght shall show ;
The nynth shall be of Fermentation ;
The tenth of our Exaltation I trow ;
The eleventh of our mervelose Multyplycatyon ;
The twelfth of Projectyon, then Recapytulatyon ;
And so thys treatise shall take an end,
By the help of God, as I entend.'

These chapters are wearisome and rambling ; and it is
impossible to gain a single clear idea from their perusal.
Indeed it was part of the creed of the alchemists that
their secrets were too precious to be revealed to the baser
sort of men.

' The Philosophers were y-sworne eche one
That they shulde discover it unto none,
He in no boke it write in no manere
For unto Christ it is so lefe and deare :

THE EARLY DAYS OF CHEMISTRY 11

That he wol not that it discovered be,
But where it liketh to his deite :
Man to inspire and eke for to defend
Whan that him liketh : in this is his end ' —

sang Chaucer, and he told a true tale, for the meanings of
alchemical expressions are often undecipherable.

The green lion, the basilisk, the cockatrice, the sala-
mander, the flying eagle, the toad, the dragon's tail and
blood, the spotted panther, the crow's bill, blue as lead,
kings and queens, red bridegrooms and lily brides, and
many more mystical terms which had no doubt some
meaning to adepts, were mingled in inextricable con-
fusion.

Moreover, the alchemists made use, not only of fantastic
expressions, in order to preserve their supposed secrets
from the common people, but they had also a set of
symbols, possibly originating from the Chaldean or Egyp-
tian alphabets, by which the substances and many of the
processes used were symbolised. While the chief aim of
modern science is perspicuity, that of the alchemists was
ambiguity and mystery. In many cases they were so
successful in preserving their secrets that even modern
investigation has failed to reveal them. But there is one
grain of comfort, albeit it savours of sour grapes, it is
perfectly certain that there was nothing worth revealing ;
at least nothing which it could profit a modern student
of science to know. Where the descriptions have been
interpreted, they refer to imperfect methods of doing
what we are now able to do with much greater economy
and rapidity. As already pointed out, their theory of
elements was erroneous ; they were, moreover, acquainted
with very few pure substances, and had no criterion of
the purity of those they possessed ; and they failed to
realise the existence of gases as forms of matter.

12 ESSAYS BIOGRAPHICAL AND CHEMICAL

Yet the interminable experiments which were con-
ducted with a view of discovering the ' Philosopher's
Stone,' which should convert the baser metals into gold,
and the elixir viice, which should convey undying youth
on its happy possessor, led to the discovery of many
chemical compounds. The writings of Basil Valentine,
reputed to have been a Benedictine monk living in South
Germany during the latter half of the fifteenth century,
contain a description of many substances, now known
as chemical entities, together with the methods of pre-
paring them. In a tract entitled ' The Great Stone of the
Ancients/ he gives in detail the properties of ordinary
sulphur; of mercury, alluding to the medicinal uses of
its compounds ; of antimony oxide or ' Spiessglas,' which
he conjectures to consist of 'much mercury, also much
sulphur, though little salt ' ; of copper- water, or a solution
of copper sulphate ; of lima potabilis or solution of silver
nitrate; of quick-lime; of arsenious oxide; of saltpetre.
The last he makes tell its own story : ' Two elements are
found in me, in quantity — fire and air ; I contain water and
earth in less amount ; therefore am I fiery, burning, and
volatile. For a subtle spirit resides in me ; I am likest to
mercury — inwardly hot but outwardly cold. My chief
enemy is common sulphur; and yet he is my greatest
friend, for I am purified and refined through him.' Sal-
ammoniac, tartar, vinegar, and above all, numerous com-
pounds of antimony were also described by Basil Valen-
tine, the last in his celebrated work entitled, The Trium-
phal Chariot of Antimony. In his writings, however,
he points out that many of the substances he describes
have medicinal properties ; and his successors, of whom
perhaps the best known was Paracelsus, developed this
part of his teaching. Yet in spite of his considerable
knowledge, he retained belief in transmutation : he also
added one to the previously received two principles of

THE EARLY DAYS OF CHEMISTRY 13

Geber and his disciples, namely salt, or, as he terms it,
' salt of the philosophers ' ; it is the constituent of matter,
which confers solidity, and which remains after the volatile
mercury and sulphur have been removed by heat.

In the first half of the sixteenth century Paracelsus
extended and applied the suggestion of Basil Valentine,
and founded what became known as the school of ' iatro-
chemists' — a body of men who taught that the chief
object of chemistry is not the transmutation of metals,
but the application of chemical substances to medical
uses. He adhered, however, to Valentine's theory of the
three principles ; but he applied them to the human
body, teaching that the organism itself consists of these
principles, and that disease, owing its origin to a deficiency
of one of them, is to be combated by its being restored
to the system. Increase of sulphur, he taught, gives rise
to fever and the plague ; increase of mercury to paralysis
and depression ; and of salt, to diarrhcea and dropsy. Too
little sulphur in the organism produces gout ; delirium is
caused by distilling it from one organ to another, and so
on in fanciful theorisings. One of the most fantastic is his
attributing the nutrition of the body to a beneficent spirit,
named the ' Archseus,' who resided in the stomach, and
presided over the function of digestion. But these
curious notions have little bearing on the development
of chemistry. The teaching of Paracelsus, however, had
the good effect of directing attention to an important
branch of chemistry— its use in pharmacy. And from
his time onwards, indeed, up to the middle of last cen-
tury, many of the best-known chemists had received a
medical training, and the ranks of chemical investigators
were largely recruited from the medical profession.

Although the alchemists, after the beginning of the
seventeenth century, exercised little influence on the
progress of chemistry, they continued their fruitless

14 ESSAYS BIOGRAPHICAL AND CHEMICAL

quest. The possibility of transmutation has always been
associated with speculations concerning the unity of
matter. And although there is little evidence as yet to
justify the supposition that all substances are ultimately
composed of matter of one kind, still the history of our
science contains many accounts of attempts to effect
transmutation. One such attempt, in modern times, was
made by Dr. Samuel Brown, who claimed to have obtained
silicon from paracyanogen, a compound consisting of car-
bon and nitrogen alone ; but subsequent Avorkers failed
to substantiate his results. There is, however, no ques-
tion as regards the honesty of Dr. Brown's work; the
only conclusion is that he must have omitted to take
sufficient precautions against contamination of his carbon
compounds with silicon. There exist at present in France
also secret societies, with such titles as ' L'Ordre de la
Rose-Croix,' and ' L' Association alchimique de France,'
the latter the successor of one named ' La Societe Her-
metique.' One of the latest of their 'researches' was
carried out by ' Maitre ' Theodore Tiffereau ; he professed
in 1896 to have obtained compounds of carbon — ether
and acetic acid — from the metal aluminium, sealed up
with nitric acid in a glass tube, and exposed to the sun's
rays for two months. But the attempt to transmute
baser materials into gold still holds the field. August
Strindberg claims to . have produced ' incomplete ' gold
from ferrous ammonium sulphate ; and still more recently
Emmens, who, however, disclaims the name of alchemist,
states that he has converted Mexican silver dollars into
gold, or more correctly, increased the small amount of
gold actually present in such coins, by hammering the
metal exposed to an extremely low temperature. There
is reason to suspect the existence of an element which
should resemble both gold and silver ; Emmens pro-
fesses to have made this element, which he names

THE EARLY DAYS OF CHEMISTRY 15

argentaurum, by hammering silver, and to have trans-
muted it, by a further process, into gold. He claims,
too, that Sir William Crookes has obtained proof, slight
it is true, though decisive, of an increase in the quantity
of gold in a Mexican dollar, after treating the latter by
his process.

We have seen from what precedes that the doctrine
concerning elements, held from remote times, was that
they were four in number, earth, water, air, and fire.
That besides these, there exist three chemical or ' hypo-
static ' principles, to wit, sulphur, mercury, and salt. In
spite of the refutation of such views by the Honourable
Robert Boyle, which we shall consider later, they lingered
on until the middle of last century, being quoted in
almost all treatises on chemistry. Macquer's Chemistry,
a text-book which obtained a wide circulation in its day,
gives the following description of the ancient elements
(1768): 'Air is the fluid which we constantly breathe,
and which surrounds the whole surface of the terrestrial
globe. Being heavy, like all other bodies, it penetrates
into all places that are not either absolutely inaccessible
or filled with some other body heavier than itself. Its
principal property is to be susceptible of condensation
and rarefaction; so that the very same quantity of Air
may occupy a much greater or a much smaller space,
according to the different state it is in. Heat and cold, or,
if you will, the presence or absence of the particles of Fire,
are the most usual causes, and indeed, the measure of its
condensation and rarefaction : for, if a certain quantity of
air be heated, its bulk increases proportionately to the
degree of heat applied to it ; the consequence of which is,
that the same space now contains fewer particles than
it did before.' ' Air enters into the composition of many
substances, especially vegetable and animal bodies ; fully
analysing most of them, such a considerable quantity

16 ESSAYS BIOGRAPHICAL AND CHEMICAL

thereof is extricated, that some naturalists have suspected
it to be altogether destitute of elasticity, when thus
combined with other principles in the composition of
bodies.'

After describing some of the physical properties of
water, Macquer continues : ' Water enters into the texture
of many bodies, both compounds and secondary principles ;
but, like air, it seems to be excluded from the composi-
tion of all metals and most minerals. For although an
immense quantity of water exists in the bowels of the
earth, moistening all its contents, it cannot be thence
inferred that it is one of the principles of minerals. It
is only interposed between their parts ; for they may be
entirely divested of it, without any sign of decomposition :
indeed, it is not capable of an intimate connection with
them.'

Of earth he says : ' We observed that the two principles
above treated of are volatile ; that is, the action of fire
separates them from the bodies they help to compose,
carrying them quite off and dissipating them. That of
which we are now to speak, namely earth, is fixed, and
when it is absolutely pure, resists the utmost force of fire.
So that, whatever remains of a body, after it has been
exposed to the power of the fiercest fire, must be con-
sidered as containing nearly all earthy principle, and
consisting chiefly thereof.' ' Earth, therefore, properly so
called, is a fixed principle which is permanent in the fire.'
He then goes on to distinguish between fusible or vitrifi-
able earths, and infusible or unvitrifiable earths, the latter
of which are also called absorbent earths, from their pro-
perty of imbibing water.

Maquer's views regarding fire are as follows : ' The matter
of the sun, or of light, the Phlogiston, fire, the sulphureous
principle, the inflammable matter, are all of them names
by which the element of fire is usually denoted. But it

THE EARLY DAYS OF CHEMISTRY 17

should seem that an accurate distinction has not been
made between the different states in which it exists ; that
is, between the phenomena of fire actually existing as a
principle in the composition of bodies, and those which
it exhibits when existing separately, and in its natural
state : nor have proper distinct appellations been assigned
to it in these different circumstances. In the latter state,
we may properly give it the names of fire, matter of the
sun, of light, and of heat ; and may consider it as a sub-
stance composed of infinitely small particles, continually
agitated by a most rapid motion, and of consequence essen-
tially fluid.' ' The greatest change produced on bodies,
by its presence or its absence, is the rendering them
fluid or solid; so that all other bodies may be deemed
essentially solid ; fire alone essentially fluid, and the
principle of fluidity in others. This being presupposed,
air itself might become solid, if it could be entirely de-
prived of the fire it contains ; as bodies of most difficult
fusion become fluid, when penetrated by a sufficient
quantity of the particles of fire.'

An attempt has been made in the preceding pages to
show the manner in which the world around us was
regarded. People were content to take as true what they
were told ; in fact, it was regarded as unfitting that the
' mysteries ' with which we are surrounded should be too
minutely inquired into. Great reverence was paid to
tradition ; and more attention to the celebrity and per-
sonal character of those who advocated certain dogmas
than to the evidence in favour of their intrinsic probability.

This spirit is by no means extinct; the vast majority
of the human race are content to gain knowledge at
second hand. Whether such knowledge is worth having
may well be questioned ; it is of course impossible that
every man should investigate natural phenomena for
himself ; but it is at least possible to place every child in

B

18 ESSAYS BIOGRAPHICAL AND CHEMICAL

the position of knowing, in however elementary a way,
how useful deductions have been drawn from observa-
tion and experiment, and of emancipating himself, to
some extent at least, from the thraldom of intellectual
authority.

THE GREAT LONDON CHEMISTS

I. BOYLE AND CAVENDISH

THE country which is in advance of the rest of the world
in Chemistry will also be foremost in wealth and in
general prosperity. For the study of Chemistry is so
closely bound up with our development in all kinds of
industry, with the arrestment of disease, and with our
success in war, that it is essential to a wealthy, healthy,
and peaceful nation. The electrician is dependent on
the chemist for the iron suitable for his dynamos; the
engineer, for the materials which he uses in his con-
struction ; and the scouring, bleaching, and dyeing of the
fabrics with which we are clothed, the manufacture of
the paper on which we write, and the ink with which we
soil the paper ; the provision of our food-supply, and
the removal of effete matter from our houses; the
preparation of our medicines; and the synthesis of the
high explosives with which warfare is now conducted ;
all these belong to the domain of the chemist, and
without them we should lapse into the semi-barbarism
of our ancestors.

Still, it must be borne in mind that we are far from
perfection. No process is so perfect that there is not
plenty of room for improvement. There is no finality
in science. And that which to-day is a scientific toy
may be to-morrow the essential part of an important
industry. This is one, though not in my view the most
important, inducement to study the science of Chemistry.

20 ESSAYS BIOGRAPHICAL AND CHEMICAL

To extend the bounds of human knowledge, and in so
doing to glorify our Creator, is surely still more an end
to be striven after. To quote from the words of Francis
Bacon, prefixed by Charles Darwin to his Origin of
Species: 'To conclude, therefore, let no man, out of a
weak conceit of sobriety or an ill-applied moderation,
think or maintain that a man can search too far, or be
too well studied in the book of God's words, or in the
book of God's works, divinity, or philosophy ; but rather
let men endeavour an endless progress or proficience in
both/ Yet the acquisition of wealth and fame will pro-
bably now, as it has in the past, appeal more forcibly to
the mind of the ordinary man ; and we must not despise
any inducement, which will lead to the furtherance of
the object to be gained, provided the motives are not in
themselves sordid.

The study of science, with the express object of securing
wealth and fame, is not likely to secure either. The old
story of the desire of King Solomon is often fulfilled in
our day. Solomon's request was, ' Give me now wisdom
and knowledge ' ; and he was answered, ' Wisdom and
knowledge is granted unto thee, and I will give thee
riches and wealth and honour.' The reason why an
attempt to utilise science for the attainment of wealth
often fails is a simple one. It is due to the unfortunate
circumstance that the human mind is not omniscient.
No man, beginning a research, can know to what it will
ultimately lead. It will certainly, if rightly pursued,
lead to knowledge ; but whether it will bring riches and
fame is beyond his ken. There have been, however,
researches expressly directed to some specific object,
which have succeeded in their purpose ; and we shall
see later how the discovery of principles which led to
the invention of the safety-lamp by Sir Humphry Davy
illustrates this. But as a rule, those chemists who have

THE GREAT LONDON CHEMISTS 21

achieved for themselves immortal fame have striven
after the nobler goal — the increase of the sum of human
knowledge. It is to the lives of some of those, who have
been more or less connected with London, that I ask your
attention. May those of us who follow, at however far a
distance, profit by their example !

In the olden days, science, as we know it now, was
non-existent. The minds of most men who were free
from the thraldom of incessant labour were occupied
with war or statecraft as a business, and with the chase
as a recreation. Those to whom such pursuits, from
circumstances or mental habit, were repugnant, found
occupation in history, poetry, philosophical discussion,
or religion. It is true, speculation on the nature of the
world around them was indulged in by some; but they
were guided in their views by their opinion rather of what
ought to be, than what is. The attitude of the modern
mind is more humble. We no longer believe that we
share enough of the creative power to enable us to
construct a system of the universe; we are content if
we are able, in however modest a way, to interpret
nature, and we call to our aid experiment, as a means of
questioning nature. We are prompt in communicating
our knowledge to others, and we expect their aid and
look for their criticism. In former days, the language
of mystery was employed. It concealed secrets too
precious to be laid bare to the vulgar crowd. ' In those
days,' to quote the words of Dr. Samuel Brown,1 'the
metals were suns and moons, kings and queens, red
bridegrooms and lily brides. Gold was Apollo, " sun of
the lofty dome " ; silver, Diana, the fair moon of his
unresting career, and chased him meekly through the
celestial grove ; quicksilver was the wing-footed Mercury,

1 Dr. Samuel Brown's Essays.

22 ESSAYS BIOGRAPHICAL AND CHEMICAL

Herald of the Gods, " new-lighted on a heaven-kissing
hill " ; iron was the ruddy-eyed Mars, in panoply complete ;
lead was heavy-lidded Saturn, " quiet as a stone," within
the tangled forest of material forms ; tin was the Diabolus
Metallorum, a very devil among the metals, and so forth
in not unmeaning mystery.

' There were flying birds, green dragons, and red lions.
There were virginal fountains, royal baths, and waters of
life. There were salts of wisdom, and essential spirits so
fine and volatile, that drop after drop, let fall from the
lip of the wonderful phial that contained them, could
never reach the ground. There was the powder of
attraction which drew all men and women after its
fortunate possessor ; and the alcahest, or universal solvent
and noli-me-tangere of essences. There was the grand
elixir that conferred undying youth on the glorious
mortal who was pure and brave enough to kiss and
quaff the golden wavelet as it mantled o'er the cup of
life — the fortunate Endymion of a new mythology. There
were the Philosophical stone, and the Philosopher's stone ;
the former the art and practice, the latter the theory
and idea, of turning baser natures into nobler ; the theory
and practice of exaltation. The Philosophical stone was
younger than the elements, yet at her virgin touch the
grossest calx among them all would blush before her into
perfect gold. The Philosopher's stone was the first-born
of all things, and older than the king of metals. — In a
word, there was an interminable imbroglio of a few of
the hard-won facts of nature, a multitude of traditionary
processes and results, several very just analogies, some
most fantastical notions, one or two profound, but intract-
able ideas, a haze of philosophical mysticism, and an
under- current of fervid religiosity.'

Such conceptions ruled the minds of philosophers, as
they loved to call themselves, until the middle of the

THE GREAT LONDON CHEMISTS 23

seventeenth century. But the practice of interrogating
nature by experiment had sprung up, and was soon
destined to bear good fruit. Although these notions of
matter and its elementary forms lingered on until a much
later date, and indeed are not wholly extinct at the present
day, they received their first great blow about this time ;
the first brunt of an attack which was destined ultimately
to overthrow them.

This attack was made by Boyle. The spirit in which
he approached the hostile ranks is best given in his own
words: 'For I am wont to judge of opinions, as of coins;
I consider much less in any one that I am to receive
whose inscription it bears, than what metal 'tis made of.
'Tis indifferent enough to me whether 'twas stamped
many years or ages since, or came but yesterday from
the mint. Nor do I regard how many or how few hands
it has passed through, provided I know by the touchstone
whether or no it be genuine, and does or does not deserve
to have been current. For if, upon due proof, it appears
to be good, its having been long and by many received
for such will not tempt me to refuse it ; but if I find it
counterfeit, neither the Prince's image nor superscription,
nor its date, nor the multitude of hands it has passed
through, will engage me to receive it. And one dis-
favouring trial, well made, will much more discredit it
with me, than all those spurious things I have named
can recommend it.'

In this spirit the ' Sceptical Chymist, or considerations
upon the experiments usually produced in favour of
the four elements, and of the three chymical principles
of the mixed bodies' was written. In it, the various
theories of matter, which, like a river rising in the
remotest recesses of time had gathered tributaries as it
flowed and presented a formidable flood in Boyle's days,
were searchingly criticised. Every postulate was ex amined ;

24 ESSAYS BIOGRAPHICAL AND CHEMICAL

if possible, experimentally tested; if true, kept; if false,
rejected.

Thus, early in the book, we meet with the phrase, long
accepted as true, Homogenea conyregare ; that is, 'Like
draws to like.' This Boyle disproved by showing that
liquids, like alcohol and water, alike in being colourless
and transparent, although they mix with each other, may
be easily separated by freezing; for, when cooled, the
water freezes, leaving the alcohol unfrozen. Here we find
the first record of experiments on a subject which, in
Raoult's hands, yielded such extraordinarily important
results. Another of Boyle's arguments is, that although
liquids and gases mix respectively with each other, yet
solids show no such tendency, and do not even cohere,
except in cases where the cohesion can be explained
by the form of the solid, and the consequent exertion of
atmospheric pressure.

After making a number of such attacks, Boyle proceeds
to consider the hypothesis at that time all-prevalent and
universally accepted, of the elements salt, sulphur, and
mercury. He opens two distinct lines of attack. His
first may be stated thus : If all substances are composed
of salt, sulphur, and mercury, and if vegetable and animal
substances contain, as is stated, much mercury, little
sulphur, and less salt, then it is desirable to show that a
vegetable may be constructed of a substance containing
none of these principles, but only of water, which was
then sometimes termed ' phlegm,' and was ranked among
the elements. This he attempted by growing a ' pompion '
in a weighed quantity of earth, and after the pumpkin
had grown, he showed it to consist of water, by distilling
it ; and by weighing the earth, he proved that it had not
lost weight. He then turns to the ' vulgar spagyrist,' and
triumphantly challenges the truth of his theory. It is
now known that the elements carbon and nitrogen, and

THE GREAT LONDON CHEMISTS 25

others in small quantity, must be added to those contained
in water to produce a ' pompion ' ; but it was a great step
to show that no salt, sulphur, or mercury were necessary.
Boyle viewed the ' pompion ' as simply transmuted water.
He quotes from M. de Roche, who stated that he had
transmuted earth into water, and vice versa. Of the
correctness of M. de Roche's opinion, he is not quite
sure, but he attaches a certain amount of weight to it.

His second line of attack is to prove that the so-called
elements are themselves further resolvable. And begin-
ning with sulphur, he points out that what the chymists
understand by sulphur has not always the same properties.
It is, however, always inflammable. Sulphur, in the then
accepted meaning of the word, was the inflammable
portion obtained on distilling an animal or vegetable
substance; mercury, another portion, not miscible with
the sulphur; but uninflammable, and having taste; the
residue on incineration, or, as it was termed, the caput
mortuum, was salt. In an old writing on the subject,
salt is said to be the basis of solidity and permanency
in compound bodies ; oil or sulphur (the two words came
to have nearly the same meaning) serves the purpose of
making the mass more tenacious ; mercury is to leaven
and to promote the ingredients, and earth is to soak and
dry up the water in which the salt is dissolved.

We note here a change in the manner of regarding
elements. They are no longer principles, or abstract
qualities of matter, but they exist in the matter, and can
be extracted from it by suitable processes. Their number
varied ; and phlegm or water was now accepted as elemen-
tary, now rejected, as suited the purpose of the theorist.
Boyle clearly showed that these elements had not always
the same properties; that the sulphur and mercury not
only differed in every respect from brimstone and quick-
silver, but that one variety, obtained by distilling wood,

26 ESSAYS BIOGRAPHICAL AND CHEMICAL

differed from that obtained by submitting bones to the
same process. He clinched his point by distilling the
distillates themselves in turn — in fact by performing what
we now call a ' fractional distillation ' — and showed that
it was possible to divide them in turn into several liquids,
differing from each other in properties. In this he antici-
pated a process now practised on a very large scale, namely
the manufacture of vinegar from wood, which he success-
fully separated from wood-spirit and tar.

Almost all research, before Boyle's time, employed two
processes, ignition or heating in contact with air, and dis-
tillation, or heating in a vessel of irregular shape, named
an alembic, leading the vapours through a cooled tube,
still called a worm, and collecting the liquefied product in
a pear-shaped vessel, named a receiver. Heat was assumed
to be the universal resolver of bodies ; and the products
of the action of heat on compounds were accepted as
elements. Boyle doubted this; he questioned whether
the products obtained on distillation were pre-existent in
the substances distilled, as the theory of elements would
require. He found that on distillation the same substances
are not always produced, nor the same number ; and he
demonstrated that these products themselves are not pure
or elementary bodies, but ' inixts.' He says : ' It is to be
doubted whether or no there be any determinate number
of elements, or if you please, whether all compound bodies
do consist of the same number of elementary principles
or ingredients.'

But Boyle was not merely a destroyer; he also, if not
in so orderly a manner, attempted to construct a theory
of his own. He appears to have held the notion of a
universal matter, and to have conceived the different
varieties to be due, not to the presence of separable pro-
perties, but to the form and motion of its minute portions.
In supporting this doctrine against the theories prevalent

THE GREAT LONDON CHEMISTS 27

in his time, he says : ' I demand also, from which of the
chymical principles motion flows, which yet is an affection
of matter much more general than can be deduced from
any of the three chymical principles.' In an essay entitled
' The history of Fluidity and Firmness,' he endeavours with
some success to show that all bodies, even those which
appear most rigid, are in motion. For example, he points
out that the diamond when rubbed shines in the dark,
and in conformity with our present views, attributes that
to molecular motion. He also notices that all bodies ex-
pand by heat, and is inclined to ascribe the magnetisation
of steel to the motion of its minute particles. He attri-
butes the varying properties of matter to motion and
rest. In yet another passage, he supposes the action of
acids on metals to be due to the pointed shape of their
atoms, which, by inserting themselves between the more
rounded particles of the metal, wedge them asunder, and
themselves become blunt during the process.

It is difficult to overestimate the value of Boyle's
labours in the field of chemistry. Although he was the
first to proclaim that chemistry is independent of any art,
and must be regarded as part of the great field of nature,
yet the practical benefit which has accrued to mankind
through Boyle's theoretical as well as his practical work
is incalculable. It was not until after his time that it
was possible to construct a theory explaining the rule-of-
thumb methods of manufacture which were formerly
employed, and to render improvement and discovery no
longer a matter of chance, but of reasoning. The whole
progress of modern manufacture due to the elaboration
of scientific discoveries, themselves the result, not of hap-
hazard trial, but of careful and systematic investigation,
sufficiently attests the benefit conferred by him in the
practical application of scientific principles.

Time would fail to tell of Boyle's well-known memoir

28 ESSAYS BIOGRAPHICAL AND CHEMICAL

' Touching the Spring of the Air,' in which he describes
experiments proving that a volume of air under a pressure
of two pounds occupies exactly half the volume that it
does under a pressure of one pound. This, although not
absolutely true, is yet sufficiently exact to be generalised
into a law, which is known by Boyle's name. He finds a
reason for this ' spring ' in premising that ' the air abounds
in elastic particles, which being pressed together by their
own weight constantly endeavour to expand and free
themselves from that force ; as wool, for example, resists
the hand that squeezes it, and contracts its dimensions ;
but recovers them when the hand opens, and endeavours
at it even while that is shut.'

In truth Boyle delighted in mechanical explanations.
The titles of his papers attest this. We find, ' The
Mechanical Production of Magnetism ' ; ' The Mechanical
Production of Electricity'; 'The Mechanical Causes of
Precipitation ' ; ' The Mechanical Origin of Corrosiveness
and Corrosibility ' ; and even, ' The Mechanical Produc-
tion of Tastes and Colours.' The series finishes with ' The
Mechanical Origin of Heat and Cold.' To produce heat
it is necessary ' that the moving particles should be small' ;
and ' agitation is requisite to heat ' ; — in fact, a statement,
in language of the time, of modern views. In accounting
for the decomposition of bodies by heat, his words are :
' It rather seems that the true and genuine property of
heat is to set amoving and thereby dissociate the particles
of matter.'

In spite of Boyle's numerous attempts to account for
natural phenomena in terms of matter and motion, his
modesty led him to make this statement : ' Having met
with many things of which I could give myself no probable
cause, and some things to which several causes may be
assigned, so differing as not to be able to agree in anything
unless in their all being probable enough; I have often

THE GREAT LONDON CHEMISTS 29

found such difficulty in searching into the cause and
manner of things, and I am so sensible of my own disability
to surmount these difficulties, that I dare speak posi-
tively of very few things except of matters of fact.' This,
I think, is in the main still our position.

Boyle's claim to rank as a ' Great London Chemist '
rests upon his having taken up his residence here from
the year 1668, until his death, which took place on the
last day of the year 1691, in the sixty-fifth year of his
age. But he was not a Londoner by birth. He was an
Irishman, born at Lismore in County Waterford, and of
noble parentage, for he was the seventh son, and the
fourteenth child, of the Earl of Cork. He was educated as
a child at home ; but at the age of eight he was sent to
Eton, where, as he says, ' he lost much of that Latin he
had got ; for he was so addicted to the more solid parts of
knowledge, that he hated the study of bare words natur-
ally.' At the age of eleven (they were precocious in those
days) his career at Eton was over ; and he was sent with
a French tutor, along with his brother, to Geneva, where
he pursued his studies for twenty-one months, and then
went to Italy. There he stayed until 1642; when his
father's finances having become embarrassed, owing to the
breaking out of the great Irish rebellion, Boyle returned
home, to find his father dead. Two estates had been left
to him ; one at Stalbridge, in Dorsetshire, where he pro-
ceeded to reside. In 1654, when twenty-seven years of
age, he removed to Oxford, in order to associate himself
with a number of men who had united themselves into a
society, under the name of the ' Philosophical College.'
This society afterwards moved its headquarters to London ;
and in 1663 it was incorporated by Charles IL, under the
name of the ' Royal Society of London,' its object being
the ' Promotion of Natural Knowledge.'

Boyle's name is frequently mentioned in the first few

30 ESSAYS BIOGRAPHICAL AND CHEMICAL

volumes of ' The Transactions.' Thus we find on January 2,
1601, that 'Mr. Boyle was requested to bring in his
cylinder, and to show at his best convenience the experi-
ment of the air ' ; but his convenience was long in arriv-
ing, for on March the 20th ' Mr. Boyle was requested to
remember his experiment of the air/ and on April 1 ' he
was desired to hasten his intended alteration of his air-
pump.' On May 15, 'Mr. Boyle presented the Society
with his engine,' and with it numerous experiments
were made in the presence of members of the Society.
In such ' philosophical ' pursuits he spent his uneventful
life ; and, to quote his own words, from a biographical
sketch drawn up by himself at an advanced period of his
life, he says: 'To be such parents' son, and not their
eldest, was a happiness that our Philarethes [a lover of
virtue — himself] would mention with great expressions of
gratitude ; his birth so suiting his inclinations and designs,
that had he been permitted an election, his choice would
scarce have altered God's discernment.'

Cavendish, like Boyle, was also of noble birth. He was
the son of Lord Charles Cavendish, himself the third son
of the second Duke of Devonshire. His mother was Lady
Anne Grey, fourth daughter of Henry, Duke of Kent.
But except in the fact of their both being of the higher
rank of society, and in their both being addicted to the
pursuit of science, they have little in common. Boyle's
mind roamed over the whole domain of nature ; his writ-
ings treat of religious, philosophical, and scientific subjects
with a fulness and lack of mental reserve which testify
to his frank, transparent character. His motto was Nihil
humanum, a me alienum puto ; and he carried this motto
into his life and work. Cavendish, on the other hand,
was by nature very shy and reserved ; he had no friends,
and few acquaintances; and instead of discussing the
whole of nature, as did Boyle, he limited himself to the

THE GREAT LONDON CHEMISTS 31

investigation of a few problems of first-rate importance.
His work is characterised by the utmost accuracy and
elegance ; and he was cautious to an extreme in announc-
ing his conclusions. Both types of mind have their good
side ; but in their case one might have wished for a little
more moderation. Had Boyle not been so many-sided, he
might have advanced science more by accurate experi-
mental work ; and had Cavendish not been so reserved,
he would have done more good to his contemporaries, and
he would certainly have been a happier man. Neither
was married ; and it is perhaps legitimate to draw the
conclusion that man's nature does not culminate in its
best without the influence of a helpmeet.

Like Boyle's, Henry Cavendish's life was an uneventful
one, and may be told in a few words. He was born on the
10th October 1731, at Nice, where his mother had gone
for her health. She died when he was two years old. In
1742, he became a pupil of Dr. Newcome, at Hackney
School, where he stayed until 1749 ; in that year, he
matriculated at Cambridge, and entered as a student at
Peterhouse. In 1753, he left without taking his degree;
he probably went to London ; but all details of his life are
lacking for the next ten years, though it is probable that
he spent the major part of his time in mathematical and
physical studies, and in research in the stables belonging
to his father's town house, which he had fitted up as a
laboratory. It was not until 1766 that he summoned up
resolution enough to publish ; although his note-books
show that in 1764 he had begun to make experiments
which would have been well worth recording. From that
time forward, until 1809, the year before his death, his
papers appeared in constant succession. There was little
interruption to this incessant work, unless we consider a
series of journeys made through various parts of England
and Wales with the object of studying the geology of the

32 ESSAYS BIOGRAPHICAL AND CHEMICAL

country, and the manufactures carried on in the various
industrial centres, as a species of holiday. There was
no weekly interruptions to his labours; Sunday as well
as weekday was devoted to research, and so the years
glided past. During his father's lifetime, he is said to
have had an income of £500 a year ; but at his father's
death in 1783, and afterwards, owing to the legacy of an
aunt, he became possessed of enormous riches. Indeed,
M. Biot, in pronouncing a biographical oration on Caven-
dish, used the phrase : ' II etait le plus riche de tons les
savants, et probablement aussi, le plus savant de tous les
riches.'

His town house was at the corner of Montague Place
and Gower Street ; visitors, however, were rarely ad-
mitted ; and Cavendish kept his library for his own use
and for that of the scientific public in a separate house in
Dean Street, Soho. To this library he went for his own
books, signing a formal receipt, as one would do at a
public library, for each one borrowed.

His laboratory was a villa at Clapham. The upper
rooms were an astronomical observatory. Here he
occasionally entertained friends, but in an unostentatious
way. His standing dish was a leg of mutton. It is
related that on one occasion, when the unprecedented
number of five guests had been invited, his housekeeper
ventured to point out that one leg of mutton would be
insufficient fare for so many ; his answer was, ' Well, then,
get two.' Several of his contemporaries have left a
record of their personal impressions of him. Professor
Playfair described him as of an awkward appearance,
without the look of a man of rank. He spoke very
seldom, and then with great difficulty and hesitation, but
exceedingly to the purpose, his remarks either displaying
some excellent information, or drawing some important
conclusion. An Austrian gentleman to whom he had

THE GREAT LONDON CHEMISTS 33

been introduced, after the fashion of his country, assured
him that his principal reason for coming to London was
to see and converse with one of the greatest ornaments of
his age, and one of the most illustrious philosophers that
ever existed. To all these high-flown speeches Mr. Caven-
dish answered not a word, but stood with his eyes cast
down, quite abashed and confounded. At last, spying an
opening in the crowd, he darted through it with all the
speed he could muster, nor did he stop until he reached
his carriage, which drove him directly home. Sir Hum-
phry Davy said of him : ' His voice was squeaking, his
manner nervous ; he was afraid of strangers, and seemed,
when embarrassed, even to articulate with difficulty. He
wore the costume of our grandfathers ; was enormously
rich, but made no use of his wealth.' And Lord
Brougham's recollection was that he would often leave
the place where he was addressed, and leave it abruptly,
with a kind of cry or ejaculation, as if scared and dis-
turbed. ' I recollect,' said Lord Brougham, ' the shrill cry
he uttered, as he shuffled quickly from room to room,
seeming to be annoyed if looked at, but sometimes
approaching to hear what was passing among others.'

On occasion, he was not ungenerous, although the
thought of giving did not occur to him. When dining
one evening at the Royal Society Club, some one present
mentioned the name of a gentleman who had previously
acted as a temporary librarian in his library. Mr. Caven-
dish said, ' Ah ! poor fellow, how does he do ? How does
he get on ? ' 'I fear very indifferently,' said this person.
' I am sorry for it,' said Mr. Cavendish. ' We had hopes
that you would have done something for him, sir.' ' Me,
me, me, what could I do ? ' 'A little annuity for his life ;
he is not in the best of health.' 'Well, well, well, a
cheque for £10,000, would that do ? ' '0 sir, more
than sufficient, more than sufficient.'
c

34 ESSAYS BIOGRAPHICAL AND CHEMICAL

Solitary he lived, and solitary was his death. Having
been ill for several days, his valet was called to his bed-
side, and told to summon Lord George Cavendish, as soon
as he should be dead. In about half an hour he again
summoned the servant, and made him repeat the
message. He then said, 'Right. Give me the lavender
water. Go.' Half an hour later the servant returned to
his room, and found that he had expired.

If Boyle found interest in all things human, Cavendish
appeared to take no thought of anything, except
phenomena. As his biographer, Dr. George Wilson, said,
his motto was Panta metro, kai arithmo, kai stathmo
(Hdvra peTpa), Kai apiO/up, Kai a-rafffjiw). This we shall
now learn, from a short consideration of his work.

Cavendish's earlier work is only to be found in his un-
published papers. It appeared to have been his habit,
for some time, to write an account of his experiments,
without any intention of bringing them to the notice of
the public. An account of two long investigations was
found among his papers, after his death, of a date con-
siderably prior to that on which his first memoir
appeared in the Philosophical Transactions. The first
of these deals with the differences between 'regulus of
arsenic' (metallic arsenic) and its two oxides. He con-
cluded that arsenic oxide was ' more thoroughly deprived
of its phlogiston ' (in modern language, more thoroughly
oxidised) than arsenious oxide; and the latter, than
arsenic itself. The paper also contains speculations on
the nature of the red fumes obtained in the conversion
of arsenious to arsenic oxide by means of nitric acid ;
speculations which were afterwards to bear rich fruit, in
his work on the composition of air.

Another of his unpublished researches deals with heat.
Cavendish discovered independently the laws of specific
heat ; and he collected tables of the specific heats of many

THE GREAT LONDON CHEMISTS 35

substances. He also was acquainted with what Black
termed ' latent heat,' that is, the heat absorbed during the
evaporation of liquids, or which is evolved during the
condensation of gases or vapours, or the solidification of
liquids.

As this essay deals with Cavendish as a chemist, I shall
treat very shortly of his physical work. One of the most
important of his investigations has reference to the
cause of the shock given by that curious fish the
torpedo. By constructing a species of artificial torpedo,
he proved that the shock was due to an electric discharge ;
and what is more, he was the first to distinguish between
electric quantity and electric intensity. Indeed, these
terms are due to him, as Faraday has acknowledged.

In 1783, 1786, and 1788, he published three papers on
freezing, in which his views on the nature of heat were
expounded. The first of these deals with the freezing of
mercury ; the second and third, with the congelation of
the mineral acids, and of alcohol. He objected to Black's
expression, ' the evolution, or setting free of latent heat/
as involving an hypothesis that the heat of bodies is
owing to their containing more or less of a substance
called the matter of heat. He preferred to adopt Boyle's
and Sir Isaac Newton's supposition that heat consists in
the internal motion of the particles of bodies. And he
therefore uses the expression ' heat is generated.'

An interesting part of the last of these papers is a
passage in which he anticipates Richter's tables of the
equivalents of the acids and bases, not by any elaborate
disquisition, but as a device for estimating the strength of
sulphuric acid. In 1788 he wrote: 'The method 1 used
was to find the weight of the plumbum vitriolatum formed
by the addition of sugar of lead, and from thence to com-
pute the strength, on the supposition that a quantity of
oil of vitriol, sufficient to produce 100 parts of plumbum

36 ESSAYS BIOGRAPHICAL AND CHEMICAL

vitriolatum, will dissolve 33 of marble; as I found by
experiment that so much oil of vitriol would saturate as
much fixed alkali as a quantity of nitrous acid sufficient
to dissolve 33 of marble.' Richter's tables were published
in 1792. Cavendish's remarks involve a knowledge of
fixity of proportion, and also of reciprocal proportions;
doctrines which were after nearly twenty years pro-
pounded by Dalton.

Perhaps the most important piece of physical work
ever performed was Cavendish's determination of the
constant of gravitation, or as it is often called, ' the weight
of the earth.' The experiment is usually spoken of as
the 'Cavendish experiment,' although the method of
executing it was first suggested by the Rev. John Mitchell.
A delicate torsion balance, suspended by a wire, had
leaden balls suspended at each end. Two heavy spherical
masses of metal were brought near the balls, so that their
attraction tended to draw the two balls aside. The de-
viation of the arms was observed, or calculated from the
time of vibration ; and from the data found, it is easy to
calculate the attraction of a sphere of water, equal in
mass to the ball or a similar ball resting on its surface ;
and so to determine the density of the earth, knowing the
attraction which it exerts on the ball. The results
obtained compared very favourably with the best results
obtained by other observers, using the utmost precau-
tions ; and it is a very remarkable instance of Cavendish's
experimental skill and ingenuity.

We have here to consider more particularly Caven-
dish's chemical work. It was of the highest order, and
bears the imprint of a master mind, guiding a master
hand.

Before Black's time, the word ' gas ' had no plural.
Indeed, what we now know as a gas was set down as a
modification of ordinary air. Black, however, proved that

THE GREAT LONDON CHEMISTS 37

a gas could be contained in a solid state, as for instance
in carbonate of lirne or of magnesia, or in what were then
known as the ' mild alkalies ' ; and that it could possess
weight. He termed carbonic anhydride ' fixed air.'
Cavendish's first published paper deals with 'Factitious
Air'; it appeared in 1766, seven years after the publica-
tion of Black's memoir on ' Magnesia alba, Quick-lime, and
other Alkaline Substances.' ' Factitious air ' was defined
by Cavendish as ' any kind of air which is contained in
other bodies in an unelastic state, and is produced from
thence by art.' He first treats of hydrogen, next of
carbon dioxide, and lastly of gases evolved during fermen-
tation and putrefaction. Although not the first to prepare
hydrogen (for it must have been known for centuries that
an inflammable gas was evolved on bringing metals into
contact with certain dilute acids), yet he was the first to
characterise hydrogen as a definite substance, and not a
mere variety of common air. He prepared this gas from
zinc, iron, or tin, and weak sulphuric or hydrochloric acid.
He found that the substance was identical in each case,
by weighing a known volume ; which he did with no great
accuracy in a bladder, but with considerable exactitude
by weighing a flask containing, for example, zinc and
acid, unmixed ; and after mixture, weighing again ; a
further experiment served to determine the volume of gas
obtainable from a known weight of zinc. Another method
of establishing their identity, curious to our notions, was
to mix the sample with a known volume of air, and
estimate the loudness of the explosion which took place
on applying a flame. Cavendish also prepared 'the
volatile sulphurous acid,' by substituting concentrated
sulphuric acid for dilute; and a non-inflammable air
(nitric oxide), by the action of nitric acid.

Cavendish did not suppose that the ' air ' came from
the acid, but from the metal. It must be remembered

38 ESSAYS BIOGRAPHICAL AND CHEMICAL

that at that time, the current doctrine was that when
substances burn, they lost a principle, to which the name
' phlogiston ' had been applied by Stahl, the propounder of
the doctrine. The hydrogen evolved was at first sup-
posed by Cavendish to be the long-sought phlogiston
itself. But fuller consideration induced him to change
his view ; and he subsequently held that hydrogen was a
hydrate of phlogiston, or a compound of that hypothetical
substance with water. In this paper, too, as well as in
one which followed, Cavendish added many facts to those
which had been published by Black on the properties of
carbonic acid ; but as these contain little of theoretical
interest, they need not detain us.

Seventeen years later, the next of his ' pneumatic '
papers was published. It was entitled, ' An Account of a
New Eudiometer.' The eudiometer, which in no way
resembled the picture of the instrument usually ascribed
to him, was designed, not for the explosion of a mixture
of two gases, but for the removal of oxygen from air, by
means of nitric oxide. With its aid, he determined the
composition of many samples of air, and his final result,
translated into our method of statement, gave for the
proportion of oxygen in air the extraordinarily accurate
number, 20'83 per cent.

Cavendish's next paper in order of publication (1784)
gave the results of experiments begun in 1781. Its title
is ' Experiments on Air.' The object of these experiments
was to ' find out the cause of the diminution which com-
mon air is well known to suffer by all the various ways
in which it is phlogisticated, and to discover what becomes
of the air thus lost or condensed.' His first idea was that
this treatment might result in the formation of ' fixed
air.' But having disproved this, he proceeded to try
whether, as some of Priestley's experiments appeared to
show, ' the dephlogisticated part of common air might

THE GREAT LONDON CHEMISTS 39

not by phlogistication be changed into nitrous or vitri-
olic acid ' ; i.e. whether oxygen, by reduction, might not
be converted into nitric or sulphuric acid. Absorbing
the oxygen by burning sulphur, he failed to find nitric
acid; and using nitric oxide as the absorbent, the re-
sulting nitrate and nitrite contained no sulphate. He
therefore tried firing a mixture of hydrogen and air by
means of an electric spark ; an experiment which led to
the discovery of the composition of water. Having
burned 500,000 grain measures of inflammable air (hydro-
gen) with two and a half times its volume of common
air, he collected upwards of 135 grains of water, ' which
had no taste nor smell, and which left no sensible sedi-
ment when evaporated to dryness.'

It is impossible in a short sketch like the present to
enter into a description of the exceedingly ingenious
experiments devised to show whence the acid was derived
which is formed when the hydrogen is present in insuf-
ficient amount ; we must be content to remember that in
default of hydrogen with which to combine, some of the
oxygen unites with the nitrogen, yielding nitrous and
nitric acids.

Although Cavendish employs the language of the
phlogistic theory in stating his conclusions, yet it must
not be supposed that he was ignorant of the newer views,
propounded by Lavoisier. In the memoir which we have
been considering, he states his conclusions in the new
phraseology ; but he concludes as follows : ' It seems,
therefore, from what has been said, as if the phenomena
of nature might be explained very well on this principle
without the help of phlogiston ; and indeed, as adding
dephlogisticated air to a body comes to the same thing
as depriving it of its phlogiston, and adding water to it,
and as there are perhaps no bodies entirely destitute of
water, and as I know no way by which phlogiston can be

40 ESSAYS BIOGRAPHICAL AND CHEMICAL

transferred from one body to another without leaving it
uncertain whether water is not at the same time trans-
ferred, it will be very difficult to determine by experiment
which of these opinions is the truest; but as the com-
monly received principle of phlogiston explains all
phenomena, at least as well as Mr. Lavoisier's, I have
adhered to that.' We shall meet with this same difficulty
again, when we consider Davy's experiments, which led
to true views concerning the nature of chlorine.

Cavendish's aim in these experiments, stated in modern
language, was to find out what becomes of the oxygen,
when substances burn in air ; whether the production of
carbon dioxide is a constant accompaniment of com-
bustion. He mentions five ways in which air may be
deprived of oxygen, namely, by the calcination of metals ;
by burning in it sulphur or phosphorus; by mixing it
with nitric oxide; by exploding it with hydrogen; and
lastly by submitting it to the action of electric sparks.
In the second series of his experiments on air, he ex-
amines in detail the action of a continued rain of sparks
on air ; and this led to the discovery of the composition
of nitric acid ; for the ' caustic lees ' on evaporation to
dryness ' left a small quantity of salt, which was evidently
nitre, as appeared by the manner in which paper im-
pregnated with a solution of it burned.' But he doubted
whether 'there are not, in reality, many different sub-
stances confounded by us under the name of phlogisticated
air.' He ' therefore made an experiment to determine
whether the whole of a given portion of the phlogisticated
air of the atmosphere could be reduced to nitrous acid,
or whether there was not a part of a different nature
from the rest, which would refuse to undergo that change.'
On experiment, he found that ' if there is any part of the
phlogisticated air of our atmosphere which differs from
the rest, and cannot be reduced to nitrous acid, we may

THE GREAT LONDON CHEMISTS 41

safely conclude that it is not more than Tf-g- part of the
whole.' Here he was nearly right; about one per cent,
is actually left ; and it has been recently recognised as a
separate element, and named Argon. And still more
recently, the argon has been shown to contain a small
proportion of other gases, also elements, to which the names
helium, neon, krypton and xenon have been given. This
paper was the last on chemical subjects published by
Cavendish.

These two men, Boyle and Cavendish, both rank as
great men. The first has been termed with justice ' the
father of modern chemistry ' ; the second by ' weighing the
earth/ and by establishing the composition of water and
of air, has even more decided claims to that title. Each
was in advance of his age : Boyle by reason of his calm
philosophical spirit, and clear judgment; Cavendish in
the power he possessed, in an age of qualitative en-
deavours, of carrying out quantitative experiments with
the most refined accuracy, and of drawing from them
correct conclusions.

II. DAVY AND GEAHAM

Between a prospect over an extensive landscape, and a
retrospect in history, an instructive analogy may be
drawn. It is true that when the spectator is removed
from the object by a great distance, whether of time or
space, its appearance is ill-defined and hazy, as are to us
the personalities of the ancient Egyptians, Greeks, and
Arabians ; and just as the imagination supplies details to
the distant features of a landscape, details which may or
may not be in consonance with fact, so through the mists
of time we are apt to read into the writings of the

42 ESSAYS BIOGRAPHICAL AND CHEMICAL

ancients ideas which have their origin rather in our
own brains than in their works. Objects in the middle
distance are perhaps most truthfully interpreted. They
are not obscured by the haze of perspective nor by the
multitudinous aggregations of propinquity. So it is with
Boyle and with Cavendish. But with Davy, and with
Graham, whose lives and works are to form the subject
of this essay, it is difficult to select from their writings
those salient features which will, in the course of another
half-century, stand out clearly and luminously among
the labours of their contemporaries. In chemical and
physical work, as in life, safety lies in a happy mean ; and
it shall be my endeavour to avoid unimportant details,
while presenting the main characteristics of the work of
these two remarkable men. The difficulty is to know
what to omit ; for that which appears unimportant to-day
may to-morrow turn out to be essential to the fundamental
doctrines of our science.

At the time when Cavendish was beginning his splendid
series of experiments on gases, Humphry Davy, an infant
of two, was beginning to show signs of that ability which
so remarkably distinguished him in after life. At that
age, he could speak fluently ; a year or two later, he was
sent to school, where he learned to read and write before
he was six ; and in his seventh year he was sent to the
Grammar School at Truro, his native place. Looking
back on his experiences there, from the standpoint of a
young man of twenty-two, he wrote : ' I consider it fortu-
nate that I was left much to myself when a child, and
put upon no particular plan of study, and that I enjoyed
much idleness at Mr. Coryton's school.' Do not we err
in insisting too much on the systematic employment of
time by the boys of our modern schools ? For, be it re-
membered, the compulsory cricket and football, so com-
mon in our schools, is to some boys the hardest task

THE GREAT LONDON CHEMISTS 43

they have to master, and leaves no time for salutary
idleness.

Like many boys, Davy entered the study of chemistry
through the doorway of fireworks. His favourite amuse-
ments were fishing, and the art of rhyming. During his
whole life, he never lost the taste for these two pursuits ;
and though it must be confessed that he was a more
successful fisher than poet, still his verses have a certain
amount of merit, and betoken a considerable gift of
imagination, necessary to the higher achievements in
science, as he indicates in the two stanzas which I venture
to quote : —

While superstition rules the vulgar soul,

Forbids the energies of man to rise,
'Raised far above her low, her mean control,
Aspiring genius seeks her native skies.

She loves the silent, solitary hours ;

She loves the stillness of the starry night,
When o'er the bright'ning view Selene pours

The soft effulgence of her pensive light.

In his later efforts he preferred decasyllabics ; and
though his sentiments thus expressed are praiseworthy,
his execution rarely exceeds the level demanded from a
poet laureate.

At the early age of fifteen, his school education was at
an end. For the next year he continued in the ' enjoy-
ment of much idleness.' But in the beginning of the
year 1795 he was apprenticed to Mr. Borlase, surgeon and

t apothecary, in his native town. Then the demon of work
seized on him, and he threw himself into the task of self-
improvement with irresistible ardour. His scheme of
study is so remarkable, and so extensive, that I cannot

44 ESSAYS BIOGRAPHICAL AND CHEMICAL

resist the temptation to quote it at full length. Here
it is : —

1. THEOLOGY OR EELIGION, taught by Nature.

ETHICS, or moral virtues, by Revelation.

2. GEOGRAPHY.

3. MY PROFESSION — 4. LANGUAGE —

1. Botany. 1. English.

2. Pharmacy. 2. French.

3. Nosology. 3. Latin.

4. Anatomy. 4. Greek.

5. Surgery. 5. Italian.

6. Chemistry. 6. Spanish.

5. LOGIC. 7- Hebrew-

6. PHYSICS.

1. The doctrines and properties of natural bodies.

2. Of the operations of nature.

3. Of the doctrines of fluids.

4. Of the properties of organised matter.

5. Of the organisation of matter.

6. Simple astronomy.

7. MECHANICS. 8. HISTORY AND CHRONOLOGY.
9. RHETORIC AND ORATORY. 10. MATHEMATICS.

Which of us has undertaken a course of study so exten-
sive, and so inclusive ?

Following out this course, not quite in the prescribed
order, however, he reached the subject of chemistry in
January 1798. His textbooks were Lavoisier's Chemistry
and Nicholson's Dictionary of Chemistry. He kept up
the study of mathematics during the whole course, having
begun in 1796: for he remarks on its usefulness as a
preliminary to the study of chemistry and physics. In
his self-imposed task of mastering chemistry, he at once
began practical work, having fitted up a small laboratory,
furnished with the very simplest and most inexpensive

THE GREAT LONDON CHEMISTS 45

apparatus, in Mr. Tonkins's house. About four months
after beginning his chemical studies he was in corre-
spondence with Dr. Beddoes, a medical man residing at
Clifton, on the subject of heat and light. This corre-
spondence was fraught with momentous consequences for
Davy; for it led to his being offered the position of
superintendent of the ' Pneumatic Institution/ founded
by the doctor, with the help of Josiah Wedgwood and Mr.
Gregory Watt, youngest son of James Watt, with the
object of experimenting with the gases, at that time
recently discovered, in order to ascertain whether they
would prove suitable as remedial agents.

In reviewing the career of a man, it is interesting to
note the motives which underlie his actions. The latter,
indeed, may not always be worthy of the sentiments which
give them birth, but it is just to give credit for pure
intentions, and to form an estimate of character by taking
both motive and action into consideration. In one of the
earliest of Davy's notebooks, intended for no eye but his
own, there is this entry: 'I have neither riches, nor
power, nor birth to recommend me ; yet, if I live, I trust
I shall not be of less service to mankind and to my
friends than if I had been born with these advantages.'
And again, in 1821, nearly twenty-five years later, .his
diary contains the aspiration, ' May every year make me
better — more useful, less selfish, and more devoted to the
cause of humanity and science.' These are noble words,
and they lead one to form a high estimate of the charac-
ter of Humphry Davy.

In January 1799 he went to the Pneumatic Institute,
and worked under the patronage of Dr. Beddoes. By the
following year he had finished his classical research on
nitrous oxide, and had discovered and investigated its
remarkable anesthetic properties. He also discovered
the composition of nitric acid, nitric oxide, nitric peroxide,

46 ESSAYS BIOGRAPHICAL AND CHEMICAL

and ammonia. By 1801 he had begun his experiments
with the ' galvanic battery,' which was to be so fruitful of
important results in his hands. During these two years,
he published no fewer than nine papers in the scientific
journal of his time, Nicholson's Journal, the predecessor
of the Philosophical Magazine, — the result of astonishing
industry.

At this period of his life, Davy's acumen led him to
avoid undue theorising, and to endeavour to accumulate
facts. His own words are : ' When I consider the variety
of theories that may be formed on the slender foundation
of one or two facts, I am convinced that it is the business
of the true philosopher to avoid them altogether. It is
more laborious to accumulate facts than to reason con-
cerning them ; but one good experiment is of more value
than the ingenuity of a brain like Newton's.' In the light
of this opinion, it is interesting to examine the programme
which he laid down for himself at the time. It was
written in the spring of 1799, and is as follows : —

' To decompose the muriatic, boracic, and fluoric acids ;
to try triple affinities, and the contact with heated com-
bustible bodies at a high temperature.

' To ascertain all the phenomena of oxydation.

' To discover with accuracy the vegetable process.'

The decomposition of the muriatic and the boracic
acids was successfully accomplished at a much later date.
But the ' phenomena of oxydation ' are even now known
only imperfectly. He contributed useful facts, however,
as we shall see, to our knowledge of ' the vegetable
process.'

Consistently with these ideas regarding the relative
merits of theory and practice, Davy made his greatest
successes in the realm of facts. Where he attempts
theorising, the results are not happy. It is true that he
did not risk the publication of his theories ; but those

THE GREAT LONDON CHEMISTS 47

revealed by his notebooks have not much to recommend
them. He allowed his imagination, of which he possessed
a rich share, full scope in other directions. Many of his
imaginative projects were, however, not realised. Among
them may be mentioned an epic poem, in six books,
entitled The Epic of Moses, written, what there is of it, in
decasyllabics. He possessed a deeply religious nature;
and Jie regarded ' this little earth as but the point from
which we start towards a perfection bounded only by
infinity.'

In 1801 Davy was recommended by Professor Hope of
Edinburgh for the lectureship at the Royal Institution,
which had been founded a few years previously by Count
Rumford, on the resignation of Dr. Garnet, the first
Professor of Chemistry there. He delivered his first
lecture in April 1801, and he at once achieved a great
success. To quote from an account by a contemporary
witness : ' The sensation created by his first course of
lectures at the institution, and the enthusiastic admira-
tion which they obtained, is at this period hardly to be
imagined. Men of the first rank and talent — the literary
and the scientific, the practical and the theoretical — blue-
stockings and women of fashion, the old and the young, all
crowded, eagerly crowded, the lecture-room. His youth, his
simplicity, his natural eloquence, his chemical knowledge,
his happy illustrations and well-conducted experiments, ex-
cited universal attention and unbounded applause. Com-
pliments, invitations, and presents were showered on him in
abundance from all quarters ; his society was courted by
all, and all appeared proud of his acquaintance.' With
all these temptations to neglect his work, he remained
faithful to his charge. In 1803 he wrote : ' My real, my
waking existence is among the objects of scientific
research. Common amusements and enjoyments are
necessary to me only as dreams to interrupt the flow of

48 ESSAYS BIOGRAPHICAL AND CHEMICAL

thoughts too nearly analogous to enlighten and vivify.'
Still many of our scientific workers of to-day would be
glad if they could extract as much leisure time from
amidst their daily employments. Davy generally entered
the laboratory about ten or eleven o'clock, and if uninter-
rupted, remained there till about three or four. His
evenings were almost invariably spent in dining out, and at
evening parties afterwards. ' To the frequenters of these
parties he must have appeared a votary of fashion, rather
than of science,' as his brother remarked.

Yet, during the years which followed, he accomplished
an immense amount of very remarkable work. Besides
investigating, by the request of the managers of the Royal
Institution, the chemistry of tanning, an investigation
which led to the use of catechu as a substitute for the
old-fashioned oak-bark, he lectured, by the request of the
Board of Agriculture, on ' The Connection of Chemistry
with Vegetable Physiology.' These lectures were given
every year, and in them were incorporated the results of a
considerable number of experiments made by him, or
under his direction, on the chemistry of plants. In 1813,
when he ceased to lecture on the subject, he published his
lectures, under the title The Elements of Agricultural
Chemistry. For the copyright of this work he received
one thousand guineas, and fifty guineas for each subse-
quent edition. Truly he was a fortunate man !

Between January 1801 and April 1812 he accomplished
two of his most remarkable pieces of work ; first, on the
decomposition of the alkalies ; and second, on the nature
of chlorine. As his name lives chiefly in connection with
these two investigations, and in his research on the
nature of flame, which culminated in the invention of the
safety-lamp, I shall give some account of them in
minuter detail.

The Swedish chemist, Scheele, had discovered in 1774,

THE GREAT LONDON CHEMISTS 49

that on treating manganese dioxide with hydrochloric
acid, or as it was then called ' spiritus salis,' in a flask to
which a bladder had been attached, a ' yellow air ' filled
the bladder, which possessed a suffocating smell, which
bleached litmus paper and flowers, and which attacked
metals, even gold. He named this new gas ' dephlogisti-
cated marine acid,' imagining that the manganese had
deprived the marine acid of its ' phlogiston,' and that it
had consequently been converted into the yellow gas.
Count Berthollet, in 1788, prepared this gas, and on
saturating with it water cooled with ice, he discovered
that a solid crystalline hydrate separated from the water.
Having exposed a solution, thus obtained, to sunlight, he
noticed the evolution of oxygen, and he, therefore, con-
cluded that the dephlogisticated marine acid was in
reality a compound of marine acid with oxygen, since,
under the action of sunlight, oxygen was evolved, and
marine acid left. This idea, according to Berthollet,
readily explained the action of the solution of the yellow
gas on metals; for it might be supposed to give up to
metals its oxygen, and the metallic oxide would then, as
usual, dissolve in the marine acid. In consequence of
this observation, M. de Morveau, in conjunction with
Lavoisier, Berthollet, and de Fourcroy, in drawing up
their Meihode de nomenclature chimique, proposed for
the gas the name 'Oxymuriatic acid.' To follow the
further history of chlorine, it will be advisable to pause,
and consider Davy's researches on the alkali metals.

Before leaving Bristol, Davy had begun experiments
with the galvanic battery. On reaching London, he con-
tinued his electrical work; and in 1807 he published a
remarkable paper on the 'Chemical Agencies of Elec-
tricity.' It had been shown that when the two poles of a
battery with platinum terminals were plunged into two
vessels of water, connected together by wet asbestos, or

50 ESSAYS BIOGRAPHICAL AND CHEMICAL

cotton wick, an acid appeared round the positive wire, and
an alkali round the negative wire. Davy showed by a
series of convincing experiments that the alkali is usually
potash or soda derived from the glass, and the acid
usually hydrochloric acid from the common salt present
as an impurity in the water. From experiments such as
these he evolved a theory that all substances which have
a chemical affinity for each other are in opposite states of
electrification, and that the positive pole attracts those
constituents of the solution which possess a negative
charge, while the negative pole attracts the positively
charged component. The more powerful the battery,
the greater the force of these attractions and repulsions.
For example, oxygen and acids are negative bodies, for
they are attracted by the positive pole, and liberated
there ; whereas metals and their oxides, and hydrogen,
nitrogen, carbon, and selenium are positive, because they
separate at the negative pole. It ought, therefore, to be
possible, by help of a sufficiently strong electric current,
to decompose any compound whatsoever. Davy carried
his inference farther, and suggested that the reason of
chemical attraction is the oppositely charged state of the
components of a compound. A compound is an elec-
trically neutral body, for the constituents of the com-
pound, in uniting, have respectively equal and opposite
charges, which neutralise each other by the act of com-
bination. But a current of electricity, passing through
such a compound, might neutralise the electricity in each,
and so, by overcoming their attractions, decompose the
compound.

By applying these ideas, he succeeded in decomposing
the ' fixed alkalies,' as caustic soda and potash used to be
called, into oxygen, hydrogen, and the metals sodium and
potassium. Having failed to obtain any products from
aqueous solutions of these compounds, except oxygen and

THE GREAT LONDON CHEMISTS 51

hydrogen, he next attempted to pass a very powerful
current through the fused alkalies. Potash was fused in
a platinum spoon, connected with the positive side of a
battery ; and a platinum wire, connected with the negative
pole of the battery, was dipped into the fused alkali. The
result was an intense light at the negative wire, and a
column of flame from the point of contact. On reversing
the current, 'aeriform globules, which inflamed in the
atmosphere, rose through the potash.' The substance
produced was evidently inflammable, and was destroyed
at the moment of liberation. Better results were obtained
by the use of slightly moist potash ; and small metallic
globules were collected, ' precisely similar in visible char-
acteristics to quicksilver.' ' These globules numerous ex-
periments soon showed to be the substance I was in search
of, and a peculiar inflammable substance, the basis of
potash.' Soda gave an analogous result; and thus the
metals of the alkalies were discovered.

These new metals burned in oxygen, forming the
alkalies from which they had been obtained; they also
burned in ' oxymuriatic acid/ forming ' muriates ' of potash
or soda. They decompose water with evolution of hydro-
gen, giving solutions of the respective alkalies ; and they
form compounds with sulphur and with phosphorus.
They reduce metals such as copper, iron, lead, and tin
from their oxides ; and they attack glass, apparently
liberating the ' basis of the silex.'

Fairly accurate estimations were made of the proportion
of these new metals in the alkalies, which were believed
by Davy to be oxides ; and thus the approximate composi-
tion of these compounds, which at one time were believed
to be elements, was definitely established.

Although similar phenomena were seen with the alka-
line earths 'barytes' and ' strontites,' it was not found
possible to isolate the metals ; but on electrolysing with a

52 ESSAYS BIOGRAPHICAL AND CHEMICAL

negative pole of mercury, amalgams were obtained, con-
taining the new metals barium and strontium ; while
from lime and magnesia, evidence was similarly obtained
that they consisted of metals, named by Davy calcium
and ' magniuin.' On removing the mercury by distilla-
tion, white metallic residues were obtained, still containing
mercury, but oxidising rapidly in the air, to the respective
oxides. An account of these results was published in
1807 and 1808, in the Philosophical Transactions.

In December 1808, the celebrated paper on the elemen-
tary nature of chlorine was read. Having failed to obtain
any other products than hydrogen and oxygen on passing
a current through an aqueous solution of muriatic acid
gas in water (why, is not so apparent, unless only dilute
solutions had been employed), Davy treated dry muriatic
acid gas with potassium. The gas was absorbed, yielding
-^ of its volume of hydrogen. He concluded from this
that dry muriatic acid gas contained at least one-third
of its weight of water, and that it had not been ' decom-
pounded ' by the potassium. His first attempt, therefore,
was directed to obtaining really dry muriatic gas. For
this object, he heated dry muriate of lime with dry sul-
phate of iron, with phosphoric glass, and with dry boracic
acid ; but without any evolution of gas, although when
water was added to the ignited mass, quantities of
muriatic gas were liberated. After numerous attempts of
the same kind, during which the chlorides of sulphur and
phosphorus were discovered, these substances were them-
selves submitted to the action of potassium, but without
the formation of any gaseous product.

In an appendix to these observations, which were pub-
lished as the Bakerian Lecture, Davy announces the view
that 'muriatic acid gas is a compound of a substance,
which as yet has never been procured in an uncombined
state, and from one-third to one-fourth of water, and that

THE GREAT LONDON CHEMISTS 53

oxymuriatic acid is composed of the same substance (free
from water), united to oxygen.' His idea then was that
' when bodies are oxidated in muriatic acid gas, it is by a
decomposition of the water contained in that substance,
and when they are oxidated in oxymuriatic acid, it is by
combination with the oxygen in that body.' Davy believed
that the chlorides all contained oxygen.

In a later paper, read in November 1809, he arrived at
the true explanation of these facts. It was based on
experiments on the ignition of charcoal to whiteness in
muriatic and oxymuriatic gases. No action occurred ;
and Davy began to doubt whether, as universally sup-
posed, these bodies contain any oxygen. He therefore
tried whether compounds produced by the action of oxy-
muriatic acid on tin, phosphorus, and sulphur would give
with ammonia precipitates of the oxides of these elements,
or any compounds containing oxygen ; and his experi-
ments were attended with negative results. He next con-
sidered one argument that the so-called ' oxymuriatic acid '
contained oxygen, viz. the fact that on treatment with
metals, hydrogen is evolved ; and in a further paper, read
in November 1810, he proved that on heating barium or
strontium in the gas, one volume of oxygen is liberated
for every two volumes of oxymuriatic acid absorbed. This
is exactly the amount of oxygen contained in the oxide ;
and experiments with other oxides of metals resulted in
similar liberation of all the oxygen previously combined
with the metal. From these facts, Davy concluded that
' to call a body which is not known to contain oxygen, and
which cannot contain muriatic acid, oxymuriatic acid, is
contrary to the principles of that nomenclature in which
it is adopted ' ; and he therefore proposed for the gas the
name chlorine.

Many derivatives of chlorine were made by Davy for
the first time ; among them were the oxygen compounds

54 ESSAYS BIOGRAPHICAL AND CHEMICAL

of chlorine. But he did not commit himself to the dog-
matic assertion that this gas is an element; on the con-
trary, he writes : ' In the views that I have ventured to
develop, neither oxygen, chlorine, nor fluorine are asserted
to be elements ; it is only asserted that, as yet, they have
not been decomposed.' It would be well, were all chemists
to imitate Davy's caution.

These views were combated by Gay-Lussac and The-
nard; but it would take too much time to follow the
contest. Suffice it to say, that Davy came off with flying
colours.

During all these years, honours were being showered on
Davy. In 1803, he was made a Fellow of the Royal
Society ; in 1807, he was chosen for its secretary, an office
which he held until 1812 ; and in the latter year he was
knighted. In his private diary, in which he transcribed
his inmost thoughts, there is a pleasant little sentence,
recording sentiments on the subject of honours : ' A man
should be proud of honours, not vain of them.' But
besides honours, wealth was also his portion; for two
courses of lectures in Dublin, he was paid no less a sum
than £11 70!

In 1812, his Elements of Chemistry was published. It
was dedicated to his wife ; for in that year he married
Mrs. Apreece.

In the same year, he nearly lost his sight by experi-
menting with chloride of nitrogen, which had recently
deprived its discoverer, Dulong, of a finger. In 1813, he
established the true nature of fluorine, and demonstrated
its analogy with chlorine; and towards the end of the
same year, he paid a visit to Paris, conveying with him a
portable laboratory, by help of which he proved the simi-
larity of iodine to chlorine. That element, which had
been discovered about two years previously by Courtois,
was supposed by Gay-Lussac to yield an acid identical

THE GREAT LONDON CHEMISTS 55

with hydrochloric acid. Davy communicated his dis-
covery to Gay-Lussac, who by no means agreed with his
conclusions; and it was not until a considerable time
had elapsed, and the latter chemist had carried out his
masterly researches on iodine and its compounds, that he
became convinced of the correctness of Davy's views.

On his return from this Continental tour, he devoted
his time to the investigation of the nature of flame, with
the result that he discovered how to prevent flame from
spreading into the adjoining atmosphere, by surrounding
it with a sheath of wire-gauze ; the conducting power of
the gauze so cooling the explosive mixture of gases, that
they no longer inflame after traversing the gauze dia-
phragm. This invention was hailed with the greatest
satisfaction by the public, as well as by those whose
interest was bound up in mines; and in 1817, he was pre-
sented with a service of plate, valued at £2500, by the
owners of many important collieries. His services to
humanity were, indeed, valued so highly, that in the
following year a baronetcy was bestowed on him. And in
1820, on the death of Sir Joseph Banks, who had presided
over the meetings of the Royal Society for no less than
forty-one years, Sir Humphry Davy received the highest
honour which can be bestowed on a scientific man, in
being elected his successor. He resigned the presidency
in 1827. His own view regarding honours was : ' It is not
that honours are worth having, but it is painful not to
have them ' ; and again, ' It is better to deserve honours
and not to have them, than to have them and not deserve
them.' These sentiments remind one of Burns's rhyming
grace before meat :

Some hae meat, and canna eat,

And some wad eat that want it ;
But we hae meat, and we can eat,

And sae the Lord be thankit.

56 ESSAYS BIOGRAPHICAL AND CHEMICAL

During these years, Davy published many papers, having
relation to the preservation of inetals by electro-chemical
means, with special reference to the preservation of the
copper sheathing of ships. In 1826, these, and other
similar inquiries, were summed up in the ' Bakerian '
Lecture, on the Relation of Electrical and Chemical
Changes.

His scientific work, however, was nearly at an end ; for
in 1826 he had a slight shock of paralysis, and though he
lived until 1829, it was in a continual search for health.
He travelled much on the Continent, and made partial
recoveries ; but he was seized by a final stroke at Geneva
in May 1829, where he died, in his fifty-first year.

Sir Humphry Davy's work is well summed up in a
notice published in Silliman's American Journal of
Science and Arts : ' To conclude, we look upon Sir
Humphry Davy as having afforded a striking example of
what the Romans called a man of good fortune ; — Avhose
success, even in their view, was not however the result of
accident, but of ingenuity and wisdom to devise plans,
and of skill and industry to bring them to a successful
issue. He was fortunate in his theories, fortunate in his
discoveries, and fortunate in living in an age sufficiently
enlightened to appreciate his merits.' But let him speak
his own epitaph; it is: 'My sole object has been to serve
the cause of humanity; and if I have succeeded, I am
amply rewarded in the gratifying reflection of having
done so.'

Fortunately for your patience, my task to-day is limited
to sketching the lives of those chemists who have gone
from among us. And confining myself to the names of
those who must pass without cavil as 'great,' that of
Graham presents itself. There have been men of con-
siderable ability, who have in their day done good and

THE GREAT LONDON CHEMISTS 57

useful work ; such men as Turner, Graham's predecessor ;
Daniel, who gave us the battery known by his name;
Miller, to whose painstaking labours we owe the revision
of our standards of weight and measure ; and many others
of less eminence. But of these I can only mention the
names.

The city of Glasgow gave Graham to London ; Boyle
was an Irishman; Cavendish was born in France; and
Davy came from Cornwall. But London made some
return for depriving Glasgow of Graham ; for Penny was
a Londoner, who passed the major part of his life in
Glasgow, having been called thither as successor to
Graham. He, too, did good work in his day; he was
an extremely attractive lecturer, and may be said to have
brought the art of giving professional evidence to perfec-
tion. In the eyes of many, this last may prove no recom-
mendation ; but if it be regarded as unworthy of the
character of a true man of science, voluntarily to abandon
that most precious heritage of a genuine philosopher, an
open mind, Penny atoned for his sins by many beautiful
investigations, the most important of which are perhaps
his determinations of atomic weights, determinations
which even to-day rank among the most reliable.

Thomas Graham was the son of a Glasgow manu-
facturer, and was born towards the end of the year 1805.
He was educated in the Glasgow High School, and after-
wards at the university there. His university career lasted
an unusually long time ; for entering when he was four-
teen years of age, he did not graduate until he had reached
the mature age of twenty-one. I am well aware that to an
Oxford or Cambridge ' man/ the age of fourteen appears a
ridiculously early one at which to enter the university;
but in many cases, as for instance in that of a late
president of the Royal Society, Lord Kelvin, it is amply
justified in its results. There are many boys who

58 ESSAYS BIOGRAPHICAL AND CHEMICAL

develop early, and whom it is unfair to measure by the
uniform standard of a public school.

Graham's teacher of chemistry was Dr. Thomas
Thomson, a man of European reputation. It was in his
textbook of chemistry that Dalton's atomic theory was
published, before its author had committed his own ideas
to the press; and he was a man who maintained the
liveliest interest in his science, and whose teaching was
most stimulating. His teacher of physics, Professor
Meikleham, was also, I have heard, an attractive lecturer ;
and during his student career, Graham devoted much
attention to physics and to mathematics. At the end
of his student career, however, Graham had an unfortu-
nate difference of opinion with his father, who had
designed him for the Church; with that reserve which is
frequently a characteristic of the Scottish nature, neither
had made the other aware of his wishes in the choice of
a profession ; and having made the discovery, with that
' dourness,' also characteristic of the race, neither would
yield up his will to the other. Graham therefore left his
native city, and pursued his studies in Edinburgh, kept
from want by the self-sacrifice of his mother and his
sister Margaret, for his father had cut off supplies.
There he studied with Dr. Hope, the discoverer of stron-
tium, working diligently the while at mathematics and
physics, and so preparing himself for his life-work. Before
his student days were over, however, he had begun to
earn a little money ; and it is recorded that the first six
guineas which he earned were spent in presents for his
mother and sister.

Having returned to Glasgow, and started a small private
laboratory, it was not long before he was asked to become
lecturer in the Mechanics' Institute, taking the place of
Dr. Clark, the inventor of the process for softening water,
who had been appointed to the Chair of Chemistry at

THE GREAT LONDON CHEMISTS 59

Aberdeen. And in 1830, he succeeded Ure, the author
of the Dictionary of Chemistry, as professor in ' The
Andersonian University,' an institution which had been
founded in rivalry to the University of Glasgow, towards
the end of the eighteenth century.

In 1837, Edward Turner, the Professor of Chemistry
at the then newly founded University of London, now
University College, died ; and Graham was chosen from
among many candidates as his successor. He was much
elated at the change, and in a letter to my grandmother
(for he was an intimate friend of the family), he tells
her that he has suddenly risen to affluence, being in
receipt of the fees of no fewer than 400 students who
attended his lectures !

Graham was neither a fluent nor an elegant lecturer ;
but his accuracy, his conscientiousness, the philosophical
method in which he treated his subject, and his en-
thusiasm for his science are said to have proved very
attractive to his audience, and without doubt contributed
to fill his classroom. The same characteristics are to be
noted in his textbook, which I venture to think is the
best textbook on chemistry ever written, although it is
now completely out of date. No longer republished in
English, it still survives in Germany, under the name
of ' Graham-Otto.'

Until 1854, Graham retained his Chair at University
College ; but in that }7ear, Sir John Herschel resigned his
office as Master of the Mint, and Graham was chosen to
occupy that position, held by so many men of eminence,
foremost among whom was Sir Isaac Newton. During
his tenure of the office, Graham's conscientiousness proved
a sore thorn in the side of the minor officials ; and he had
a hard struggle to introduce necessary reforms. His
strength of character, however, stood him in good stead ;
and after some years of active combat, he left the field

60 ESSAYS BIOGRAPHICAL AND CHEMICAL

victorious, with leisure to resume the scientific work
which the state of warfare had interrupted. In this
office he remained until his death, which took place in
1869.

Unlike Davy, Graham was of a modest and retiring
disposition. His gentleness endeared him to all those
whom he admitted within the circle of his friends ; and
his calm judgment rendered him an invaluable counsellor.
Yet he received his full meed of honour ; he was the first
president of the Chemical Society ; a Fellow of the Royal
Society; the 'Keith' Medallist of the Royal Society of
Edinburgh; he twice received a Royal Medal of the
Royal Society of London, and in 1862 the Copley Medal,
given as the reward of a life successfully devoted to
scientific discovery ; he was a Corresponding Member of
the Institute of France ; and he received from that
august body the Prix Jecker.

Graham's scientific work admits of division into two
groups, one relating to the physical behaviour of gases
and liquids, and the other to the constitution of salts.
Besides papers on these subjects, he published a number
of miscellaneous papers.

In the second of these groups, his earliest communica-
tion was on the existence of compounds containing
alcohol of crystallisation, analogous to the well-known
water of crystallisation. The analogy between water and
alcohol was thus shown ; an analogy which, in the hands
of his successor Williamson, played an important part in
the development of modern views on the constitution of
the carbon compounds, and indirectly on the whole of
chemistry. In 1833, Graham published his remarkable
memoir on the phosphoric acids, in which he argued that
as alcohol could replace water in hydrated salts, so water
could replace bases, in such salts as the phosphates.
The acids of phosphorus had previously been a puzzle to

THE GREAT LONDON CHEMISTS 61

chemists. Graham proved that orthophosphoric acid
consists of a compound of the anhydride, P2^s> w^h
three molecules of water, and that each molecule is
capable of replacement by the oxide of such a metal as
sodium ; that pyrophosphoric acid may be regarded as
composed of a molecule of anhydrous phosphoric acid
with two molecules of water, each of which is replaceable
by an oxide; and that metaphosphoric acid is to be
represented as a compound of one molecule of anhydride
with one molecule of. water. The general term, which
came to be used for this behaviour of acids was basicity,
and an acid was termed monobasic, dibasic, or tribasic,
according as it was capable of uniting with one, two, or
three molecules of base; yet it might contain the same
anhydrous oxide in each case. These views of Graham's
made it possible to account for the fact, at that time most
mysterious, that on mixing nitrate of silver, with its
neutral reaction, with alkaline phosphate of sodium, an
acid liquid was the result. These experiments of Graham's
paved the way for the later theory, that acids are salts of
hydrogen. In Graham's language, the three phosphoric
acids were ' terphosphate, biphosphate, and phosphate of
water ' ; for he understood by the term ' phosphoric acid '
what we nowadays name phosphoric anhydride. The word
phosphate, however, is now applied to the group P04,
and hence the name phosphates of hydrogen. Graham
was the first to recognise that (to quote his own words)
'when one of these compounds (the phosphoric acids)
is treated with a strong base, the whole or a part of the
water is supplanted, but the amount of base in combina-
tion with the acid remains unaltered.' We should now
say, ' the whole or a part of the hydrogen of the acid is
supplanted, but the total number of atoms of hydrogen
plus metal in the salt remains unaltered.'
Continuing the train of ideas aroused by his researches

62 ESSAYS BIOGRAPHICAL AND CHEMICAL

on the phosphoric acids, Graham next advanced the sug-
gestion that certain salts may be substituted, molecule for
molecule, for water of crystallisation. Thus, sulphate of
zinc ordinarily crystallises with seven molecules of water,
forming the heptahydrate, ZnS04.7H20. It is possible to
replace one of these molecules of water with a mole-
cule of potassium sulphate, obtaining the double salt,
ZnS04.K2S04.6H20. It appeared, too, with this and
similar salts, that six molecules of water may be expelled
at a lower temperature than the seventh, which may be
supposed to be the one which is replaced by the potassium
sulphate in the double salt.

Experiments were also made on the heat evolved on
neutralising bases with acids, and on the solution of salts
in water. Such experiments on salt were carried on until
1843.

But Graham had all the while another set of re-
searches in progress, in which he attempted to arrive
at some definite knowledge regarding the constitution of
matter. Recognising that the gaseous state represents
matter in a simpler condition than that of liquid or solid,
his experiments were largely directed towards elucidating
the properties of gases. These experiments were started
in 1836. From an observation of Doebereiner's, that in a
cracked cylinder, containing hydrogen, and standing over
water, more gas escaped than entered, so that the level of
the water rose in the cylinder, Graham was led to make
his experiments on the diffusion of gases, and also on the
rate of the escape of gases through narrow openings.
Both sets of experiments led to the same law, viz. that
the rates of escape are inversely proportional to the square
roots of the densities of the gases. Under equal physical
conditions, hydrogen moves four times as quickly as
oxygen, which is sixteen times as heavy as the former.
And since the densities are proportional to the weights of

THE GREAT LONDON CHEMISTS 63

the molecules, it follows that a molecule of hydrogen
moves through space four times as rapidly as a molecule
of oxygen. This law was confirmed by measurements
made on many other gases. These experimental re-
searches of Graham's have been one of the chief supports
of the kinetic theory, devised long afterwards, on the
assumptions that the pressure of gases is due to the im-
pacts of their molecules on the walls of the containing
vessel, and that their temperature is to be ascribed to the
rate of motion of the molecules.

Much later, in 1849, Graham investigated the rate of
flow of gases through narrow tubes, and obtained results
which have also been found of incalculable service to the
theory of gaseous matter.

A few years later, in 1851 and 1852, Graham published
investigations on the diffusion of liquids, a subject follow-
ing close on the lines of his former work on the diffusion
of gases. His plan of experiment was as simple as it was
well adapted to furnish the information sought. A wide-
mouthed bottle was filled with the solution of a salt, and
placed inside a wider jar; the jar was then carefully filled
with water, care being taken not to disturb the level of
the solution in the bottle. The apparatus was then left
to itself for a considerable time. It was found that the
salt did not stay within the bottle, but gradually escaped
into the jar. The amount escaping in different times and
at different temperatures was measured.

Experiments made on a great variety of substances soon
revealed the fact that some substances escape much more
rapidly than others. For instance, Graham found that 69
parts of sulphuric acid, 58 of common salt, 26 of
sugar, 13 of gum-arabic, and only 3 of egg-albumen
escape in equal times, other circumstances being equal.
Some other substances, such as potassium and ammonium
chlorides, potassium and ammonium nitrates, magnesium

64 ESSAYS BIOGRAPHICAL AND CHEMICAL

and zinc sulphates, take equal times to diffuse. More-
over, some salts may be decomposed into their constitu-
ents by diffusion ; among these are ordinary alum, where
the more easily diffusible potassium sulphate passes away
from the less quickly diffusing aluminium sulphate.
And even potassium sulphate itself shows signs of
yielding potassium hydroxide and sulphuric acid on
diffusion.

It was known that a solution, placed on the outside of
a porous diaphragm, on the inside of which was pure
water, tended to pass through the septum; and if the
inner vessel, containing the water, were fitted with a
pressure-gauge, the pressure would rise in the interior.
This pressure had been named ' osmotic pressure.'
Graham attempted to connect this phenomenon with
diffusion, but found that ordinary salts, as well as sugar,
tannin, alcohol, urea, and similar bodies, had little effect
in raising pressure. On the other hand, osmotic pheno-
mena were well marked when strong acids, or tartaric,
citric, or acetic acids, were present in the cell. In all
cases of osmotic pressure, it was found that the porous cell
was strongly attacked, and Graham was inclined to ascribe
the phenomenon to chemical action. It is in all pro-
bability due to the fact that such diaphragms present
very little of what we now term 'semi-permeability' to
the salts in question.

From the year 1852 to the year 1861, Graham's duties
at the Mint absorbed nearly all his time, so that there is
a long gap in the series of his publications. But in the
latter years he published the results of experiments on
the transpiration of liquids, a subject which has lately
been successfully treated by numerous investigators.
And with his practical bias, Graham devised a plan of
applying osmotic phenomena to the separation of
crystalline substances, which easily pass through a

THE GREAT LONDON CHEMISTS 65

porous diaphragm, such as the common acids and salts,
from ' colloid ' or gum-like substances, the rate of passage
of which is much slower. Especially useful was this pro-
cess for the separation of poisons such as the alkaloids
and metallic salts from the contents of the stomach in
medico-legal inquiries.

Time allows me only to mention Graham's most in-
teresting experiments on the absorption of gases by
metals, and the passage of hydrogen through a thin sheet
of palladium; the retention of hydrogen by palladium
led him to surmise that the metallic substance was a
true alloy of palladium, with metallic hydrogen, and to
form the theory that hydrogen itself should be ranked
among the metals. He even tried to impress the view by
terming the element ' hydrogenium,' in consonance with
the nomenclature of most metals.

But I must conclude this imperfect sketch of Graham's
work, trusting that what I have said may induce some of
my readers to make acquaintance with it at first hand.
Graham's conscientiousness in all he did, his enthusiasm,
and his great ability render his style in writing a most
fascinating one ; and his papers will always remain a
model to those who publish on similar subjects. He
possessed a truly philosophical mind ; and in this he more
resembled Boyle, than Cavendish or Davy. Indeed, it
may be guessed that if Graham had lived in the seven-
teenth century, and Boyle in the nineteenth, the results of
their labours would not have differed very widely from
those which bear their respective names.

Contrasting Graham's character with those of Cavendish
and Davy, it may be said that Avhile Cavendish carried his
devotion to science to such a height that it deprived him of
the ordinary pleasures of a human being, and while Davy
took perhaps too prominent a part in the world of fashion

E

66 ESSAYS BIOGRAPHICAL AND CHEMICAL

to escape the accusation of 'playing to the gallery/
Graham pursued a happy mean, beloved by the few whom
he chose for his intimate friends, and esteemed and
respected by all. Of him, as of Faraday, it might have
been said with no shade of misgiving, ' He was a good and
a true man.'

JOSEPH BLACK: HIS LIFE AND WORK

THERE are some natures so happily constituted that they
escape many of the trials which beset most men. Marcus
Aurelius thanked his adopted father for having taught
him the advantages of ' a smooth and inoffensive temper ;
constancy to friends, without tiring or fondness ; being
always satisfied and cheerful ; reaching forward into the
future, and managing accordingly ; not neglecting the least
concerns, but all without hurry, or being embarrassed.'
Such a character had Joseph Black. Dr. Robison, the editor
of his lectures, his successor in Glasgow University, and his
biographer, wrote : ' As he advanced in years his coun-
tenance continued to preserve that pleasing expression of
inward satisfaction, which, by giving ease to the beholder,
never fails to please. His manner was perfectly easy and
unaffected and graceful. He was of most easy approach,
affable, and readily entered into conversation, whether
serious or trivial. His mind being abundantly furnished
with matter, his conversation was at all times pertinent
and agreeable. He was a stranger to none of the elegant
accomplishments of life.' His friend Dr. Ferguson said of
him : ' As Dr. Black had never anything for ostentation,
he was at all times precisely what the occasion required ,
and no more. Never did any one see Dr. Black hurried at
one time to recover matter which had been improperly
neglected on a former occasion. Everything being done in
its proper season and place, he ever seemed to have leisure
in store ; and he was ready to receive his friend or acquaint-
ance, and to take his part with cheerfulness in any con-

68 ESSAYS BIOGEAPHICAL AND CHEMICAL

versation that occurred.' His successor, Dr. Thomas
Thomson, found Dr. Robison's estimate of Black's char-
acter so just that he appropriated it almost verbatim in
his History of Chemistry without the formality of quota-
tion marks.

His pupil, Henry Brougham, one of the founders of the
college in which I have the honour to hold a chair, por-
trays him in his Philosophers of the time of George III.
as ' a person whose opinions on every subject were marked
by calmness and sagacity, wholly free from both passion
and prejudice, while affectation was only known to him
from the comedies he might have read. His temper in
all the circumstances of life was unruffled. . . . The sound-
ness of his judgment on all matters, whether of literature
or of a more ordinary description, was described by Adam
Smith, who said he " had less nonsense in his head than
any man living." ' Brougham, writing as an old man,
said : ' I love to linger over these recollections, and to
dwell on the delight which I well remember thrilled me
as I heard this illustrious sage detail the steps by which
he made his discoveries, illustrating them with anecdotes
sometimes recalled to his mind by the passages of the
moment, and giving them demonstration by performing
before us the many experiments which had revealed to
him first the most important secrets of nature. Next to
the delight of having actually stood by him when his
victory was gained, we found the exquisite gratification of
hearing him simply, most gracefully, in the calm spirit of
philosophy, with the most perfect modesty, recount his
difficulties, and how they were overcome ; open to us the
steps by which he had successfully advanced from one
part to another of his brilliant course ; go over the same
ground, as it were, in our presence, which he had for the
first time trod so many long years before ; hold up per-
haps the very instruments he had then used, and act over

JOSEPH BLACK: HIS LIFE AND WORK 69

again the same part before our eyes which had laid the
deep and broad foundations of his imperishable renown.
Not a little of this extreme interest certainly belonged to
the accident that he had so long survived the period of
his success — that we knew there sat in our presence the
man now in his old age reposing under the laurels won
in his early youth. But take it altogether, the effect was
such as cannot well be conceived. I have heard the
greatest understandings of the age giving forth their
efforts in its most eloquent tongues — have heard the com-
manding periods of Pitt's majestic oratory — the vehe-
mence of Fox's burning declamation — have followed the
close compacted chain of Grant's pure reasoning — been
carried away by the mingled fancy, epigram, and argu-
mentation of Plunket; but I should without hesitation
prefer, for mere intellectual gratification (though aware
how much of it is derived from association) to be once
more allowed the privilege which I in those days enjoyed
of being present while the first philosopher of his age was
the historian of his own discoveries, and be an eye-witness
of those experiments by which he had formerly made
them, once more performed with his own hands.'

Truly, Scotland in the last half of the eighteenth
century was the home of many great men. Adam Smith,
the first political economist ; David Hume, the historian ;
James Hutton, the geologist; and James Watt, the
engineer : all these were intimate friends of Black's, and
each in his way was an originator of the first order.
And it is my pleasant task to present to you an account
of Black's discoveries and their consequences, and to
attempt to show that his work began a new epoch for
chemistry and physics.

There is little to tell of Black's early history; nor,
indeed, was his life even remotely adventurous. His
career may be told in a few words.

70 ESSAYS BIOGRAPHICAL AND CHEMICAL

Joseph Black was born on the banks of the Garonne,
near Bordeaux, in 1728. His father, John Black, was a
native of Belfast, descended from a Scottish family which
had settled there; he resided at Bordeaux, where he
carried on a business in wine ; he was an intimate friend
of President Montesquieu. Joseph was one of thirteen
children, of whom eight were sons. In 1740, at the age
of twelve, he was sent to school in Belfast ; and like many
other boys of the north of Ireland, he crossed to Glasgow to
attend its University, for in those days, of course, Queen's
College, Belfast, had not been founded. This was in the
year 1746. Dr. Robison mentions letters from Mr. Black
to his son Joseph, from which it would appear that he was
in every respect a satisfactory son and a diligent student.
He received a general education ; we find, at least, that he
could write good Latin ; and he was taught ethics by
Adam Smith. His leanings for natural science, however,
were probably encouraged by his intimate friendship with
the son of the Professor of Natural Philosophy, Dr. Robert
Dick, later successor to his father in the chair, who, un-
fortunately, occupied it only a few years, for he was early
cut off by death. Black also owed much to Cullen, of whom
a very interesting account is given by Thomas Thomson
in his History. Cullen was Lecturer in Chemistry in
the University of Glasgow from 1746 to 1756; and in
1751 he was appointed Professor of Medicine; at that time,
and, indeed, until Thomas Thomson taught chemistry,
that subject was taught only by a lecturer. Thomson
attributes to Cullen a singular talent for arrangement, dis-
tinctness of enunciation, vivacity of manner, and profound
knowledge of his science — in short, enthusiasm — qualities
which made him adored by his students. He took
especial pains to gain their friendship by frequent social
intercourse with them, and no doubt early recognised
Black's great promise. Cullen's single contribution to

JOSEPH BLACK: HIS LIFE AND WORK 71

chemico-physical literature dealt with the boiling of ether
on the reduction of pressure, and its growing cold during
the process. The reason of this behaviour, however, was
later discovered by Black, for Cullen confined himself to
recording the observation. It was not long before Black
rendered help to Cullen as his assistant ; and Black's name
was frequently quoted by Cullen in his lectures as an
authority for certain facts.

Black's methodical habits led him to keep a sort of
commonplace book, in which not merely the results of
his experimental work was entered, but also notes on
medicine, jurisprudence, or matters of taste; and he
practised 'double entry,' for he also kept separate journals
in which these notes were distributed according to their
subjects. From these notebooks the dates of his most
important discoveries can be traced.

Chemistry, in these days, was handmaid to medicine ;
the influence of the iatro-chemists, founded by Paracelsus,
still held its sway, although certain bold investigators —
among them Boyle, Mayow, and Hales — a century before,
had shaken themselves free from its thraldom. And the
lectureship on chemistry in Glasgow was regarded as a
step to a more remunerative position, and was held, along
with the Crown professorship of medicine, by Cullen from
1751 to 1756. It was probably owing to Cullen's advice
that Black went to Edinburgh in 1750 or 1751 to finish
his medical studies ; perhaps another reason may be found
in his having had a cousin in the University, Mr. James
Russel, as Professor of Natural Philosophy, with whom he
lived. There he took the degree of doctor of medicine in
1754. It is true that he might have graduated in Glasgow
three years earlier ; but no doubt his thoroughness made
him wish to offer a thesis worthy of praise, and it was
this thesis which established his reputation. More of
this hereafter.

72 ESSAYS BIOGRAPHICAL AND CHEMICAL

In 1756 Dr. Cullen was called to fill the Chair of
Chemistry in Edinburgh, and Black, who had been prac-
tising as a physician since he had graduated, was called to
succeed him in the Chair of Anatomy and the lectureship
in Chemistry; for his reputation in the subject which he
had made his own was even then a high one. Black did
not retain the Chair of Anatomy for long, however ; his
tastes lay more in the direction of medicine ; and with the
concurrence of the University he and the professor of
medicine exchanged chairs. While he held these offices
he also engaged in medical practice ; and Robison says that
his countenance at that time of life — he was then about
thirty-two — was equally engaging as his manners were
attractive ; and in the general popularity of his character
he was in particular a favourite with the ladies. No one,
so far as we know, was singled out by his preference ; and
to the end of his days he remained unmarried. It appears
that the ladies regarded themselves as honoured by his
attentions, and we are told that these attentions were not
indiscriminately bestowed, but exclusively on those who
evinced a superiority in mental accomplishments or
propriety of demeanour, and in grace and elegance of
manners.

In 1766, Dr. Cullen exchanged the Chair of Chemistry
at Edinburgh for that of Medicine ; and with one accord
University and town united in calling Dr. Black to the
vacant chair. Indeed, in 1756, he had been recom-
mended for the chair by the University; but the Town
Councillors who were the electors did not agree with
the recommendation, and Cullen was appointed. Now,
however, unanimity prevailed, and Black removed to
Edinburgh, where he spent the rest of his days.

From this date, he devoted himself to tuition, and
spared no pains to make his lectures attractive and
useful. He illustrated them by numerous experiments.

JOSEPH BLACK-: HIS LIFE AND WORK 73

Robison tells us that, ' while he scorned the quackery of
a showman, the simplicity, neatness, and elegance with
which they were performed were truly admirable.' And
Brougham also praises his manipulation. 'I have seen
him/ he writes, 'pour boiling water or boiling acid from
one vessel to another, from a vessel that had no spout
into a tube, holding it at such a distance as made the
stream's diameter small, and so vertical that not a drop
was spilt. The long table on which the different pro-
cesses had been carried on was as clean at the end of the
lecture as it had been before the apparatus was planted
upon it. Not a drop of liquid, not a grain of dust
remained.'

Black had a profound influence on the attitude of the
Edinburgh public towards science. The reputation which
he established as a lecturer induced many to attend his
lectures without any particular wish to learn chemistry,
but merely to enjoy an intellectual treat ; and it became
the fashion to hear him.

The study of the chemistry of gases, after Black's dis-
covery of carbonic acid, made rapid progress ; but Black
did not take part in its advance. His health had never
been good; he was very subject to dyspepsia; and on
several occasions his lungs or his bronchia appear to have
narrowly escaped being affected, for he was troubled with
spitting of blood. But he had learned the lesson — yvwOe
a-eavrov — know thyself; and he regulated his exercise and
his diet with the result that he lived a quiet, and a fairly
long life. 'Happy is the nation that has no history';
and Dr. Black's uneventful life was passed in happiness.
He held his chair for more than thirty years, and grew
old gracefully, living amongst many intimate friends.
He at one time acqyired a reputation for parsimony ; but
Brougham, while suggesting a reason for this report,
namely that he kept a pair of scales on his study table

74 ESSAYS BIOGRAPHICAL AND CHEMICAL

with which he used to weigh the guineas paid in as fees,
defends this perhaps somewhat curious practice, and
refutes the imputation ; and Robison, who also alludes to
it, states in a footnote that he could give more than one
or two instances in which a great part of Black's fortune
was at risk for a friend.

As his strength decreased, the care of his health
occupied more and more of his attention ; he became
more and more abstemious in his diet. One of his
intimate friends, Dr. Ferguson, gives the following account
of his death, one worthy of such a calm and placid philo-
sopher: 'On the 26th November 1799, and in the
seventy-first year of his age, he expired, without any
convulsion, shock, or stupor to announce or retard the
approach of death. Being at table, with his usual fare,
some bread, a few prunes, and a measured quantity of
milk, diluted with water, and having the cup in his hand
when the last stroke of his pulse was to be given, he had
set it down on his knees, which were joined together, and
kept it steady with his hand in the manner of a person
perfectly at ease, and in this attitude expired, without
spilling a drop, and without a writhe in his countenance,
as if an experiment had been required to show his friends
the facility with which he departed.'

He left more money than any one thought he could
have acquired in the course of his career. His will was a
somewhat fantastic one ; he divided his property into ten
thousand shares ; and he distributed it among numerous
individuals in shares or in fractions of shares, according to
his conception of their needs or deserts.

A tale is told in Kay's Edinburgh Portraits of Black and
Hutton, who were almost inseparable cronies. Having had
a disquisition as to the waste of food, it occurred to them
that while testaceous marine animals were much esteemed
as an article of diet, those of the land were neglected ;

JOSEPH BLACK : HIS LIFE AND WORK Y5

they resolved to put their views in practice, and having
collected a number of snails, had them cooked, and sat
down to the banquet. Each began to eat very gingerly ;
neither liked to confess his true feelings to the other.
'Dr. Black at length broke the ice, but in a delicate
manner, as if to sound the opinion of his messmate:
"Doctor," he said, in his precise and quiet manner,
"Doctor, do you not think that they taste a little — a
very little queer ? " — " Queer, — queer indeed ! — tak them
awa', tak them awa' ! " vociferated Dr. Hutton, start-
ing up from table, and giving vent to his feelings of
abhorrence.'

The portraits of the subject of this biography reveal
Black as possessing a calm, contemplative nature; but
Kay's caricatures indicate that he could take a some-
what humorous view of life, and perhaps might even
display a vein of caustic sarcasm. A portrait of him
while lecturing may well have been sketched, we may
suppose, while he was making scathing comments on
the objections raised by a German chemist named Meyer
to his doctrine of causticity, which ' that person,' as
Brougham tells us, ' explained by supposing an acid, called
by him acidum pingue, to be the cause of alkaline mild-
ness. The unsparing severity of the lecture in which
Black exposed the ignorance and dogmatism of this
foolish reasoner cannot well be forgotten by his hearers.'
It appears to me, however, that Meyer's theory cannot
have been correctly stated by Brougham (for it is remark-
ably like Black's own explanation), or must have been
misunderstood by Black. Another of Kay's portraits
exhibits Black and Hutton, under the title of 'The
Philosophers ' ; and here again the caricaturist has made
it obvious that Black could appreciate a joke. A third
portrait represents him taking a gentle walk ; it conveys
an idea of his appearance in his fifty-ninth year.

76 ESSAYS BIOGRAPHICAL AND CHEMICAL

The portrait of Dr. Cullen, Black's predecessor both
in Glasgow and Edinburgh, and his life-long friend,
is also given by Kay. Cullen died in 1790, at the age
of eighty-one.

In the olden days it was considered quite as marvellous
that a gas could be made to occupy a small volume, or
that ' air ' could be produced in quantity from a stone, as
that an Arabian 'djinn' of enormous size and ferocious
mien could issue from a bottle, as related in the ' Tale of a
Fisherman,' one of the charming stories of the Arabian
Nights Entertainments. It is true that in the middle of
the seventeenth century Robert Boyle had enunciated his
famous discovery, 'Touching the Spring of the Air'; in
which he proved that the greater the pressure to which a
gas is exposed the smaller the volume it will occupy.
But however great the pressure, Boyle's air remained air.
It might have been thought that the boiling of water into
steam should have convinced men that a liquid, at least,
could be changed into a gas; but the fact that steam
changed back to water probably prevented attention being
paid to its comparative large volume while hot. It was
Black's discovery of the production of carbonic acid gas
from marble, or as he named it, 'fixed air,' which first
directed notice to this possibility of the production of a
gas from a solid; and further, the peculiar property of
this gas — its power of being fixed — was one which com-
pletely differentiated it from ordinary air. Stephen Hales
the botanist, it is true, had distilled many substances of
vegetable, animal, and mineral origin; among them he
treated many which must have produced impure hydrogen,
marsh-gas, carbonic acid gas, and oxygen; but Hales
contented himself with measuring the volume of gases
obtained from a known weight of material, without con-
cerning himself about their properties. And as the result
of many experiments, he concluded that ' our atmosphere

JOSEPH BLACK: HIS LIFE AND WORK 77

is a chaos, consisting not only of elastick, but also of
unelastick air-particles, which in plenty float in it, as well
as the sulphureous, saline, watry, and earthy particles,
which are. no ways capable of being thrown off into a
permanently elastick state, like those particles which
constitute true permanent air.' This was the current
belief as regards the nature of air.

The cause which gave rise to Black's famous research is
a curious one. Sir Robert Walpole, as well as his brother
Horace, afterwards Lord Walpole, were troubled with the
stone. They imagined that they had received benefit
from a medicine invented by a Mrs. Joanna Stephens;
and through their influence she received five thousand
pounds for revealing the secret, which was published in
the London Gazette on the 19th June 1739. It was
described as follows : —

'My medicines are a Powder, a Decoction, and Pills.
The powder consists of Egg-shells1 and Snails,2 both
calcined. The decoction is made by boiling some Herbs 3
(together with a Ball, which consists of Soap,4 Swines'-
Cresses, burnt to a Blackness, and Honey) in water. The
Pills consist of Snails calcined, Wild Carrot seeds, Burdock
seeds, Ashen Keys, Hips and Hawes, all burnt to a Black-
ness, Soap and Honey.'

Dr. Cullen and his colleagues held opposing views as to
the efficacy of such quaint and caustic remedies ; and it
was with the object of discovering a ' milder alkali,' and
bringing it into the service of medicine, that Black began

1 ' Egg-shells and Snails calcined in a crucible surrounded with coal for
8 hours. Then left in an earthenware pan to slake in a dry room for 2
months. The Shells thus become of a milder taste, and fall into powder.'

2 ' Snails left in a crucible until they have done smoaking, then rubbed
up in a mortar. Take 6 parts of Egg-shell to 1 of Snail-powder. Snails
ought only to be prepared in May, June, July, and August.'

3 ' Herbs of decoction : Green Chamomile, Sweet Fennel, Parsley, and
Burdock ; leaves or roots.'

4 'Soap: Best Alicant Soap.'

78 ESSAYS BIOGRAPHICAL AND CHEMICAL

his experiments on magnesia. They are described in a
paper entitled ' Experiments upon Magnesia Alba, Quick-
lime, and some other Alcaline Substances'; it was the
chemical contents of his thesis for the degree of M.D.,
which he took at Edinburgh in 1754 ; he had been making
the experiments since 1752. The actual thesis was in
Latin : ' De Humore Acido a Cibis orto, et Magnesia Alba ' ;
the pamphlet was published in the following year.

The medicines in vogue as solvents of the urinary cal-
culus were all caustic ; the lapis infernalis, or caustic
potash, and the ley of the soap-boilers, or caustic soda.
These substances are made from mild alkali, or carbonates,
by boiling their solutions with slaked lime, itself produced
by slaking quicklime with water. Now quicklime is
formed by heating lime-stone in the fire; it thereby
acquires its burning properties, or causticity ; and this it
was supposed to derive from the fire, of which it absorbed,
as it were, the essence. The act of boiling the mild
alkalies with lime was supposed to result in a transference
of this educt of fire to the alkalies, which themselves
became caustic. Lime-water, or a solution of caustic lime
was used as a solvent for the calculus; and it was an
attempt to produce a less caustic solvent from Epsom salts
that induced Black to begin his researches.

As his notes show, Black began by holding the old view.
He attempted to catch the igneous matter as it escaped
from lime, as it becomes ' mild ' on exposure to the air :
he appears to have made some experiment with this view;
but his comment was, 'Nothing escapes — the cup rises
considerably by absorbing air.' Two pages further on in
his notebook he records an experiment to compare the
loss of weight sustained by an ounce of chalk when it is
calcined with its loss when dissolved in ' spirit of salt,' or
hydrochloric acid ; and he then evidently began to suspect
the reason of ' mildness ' and ' causticity.'

JOSEPH BLACK : HIS LIFE AND WORK 79

Another memorandum, a few pages later, shows that he
had solved the mystery. ' When I precipitate lime by a
common alkali there is no effervescence. The air quits
the alkali for the lime, but it is not lime any longer, but
c.c.c. It now effervesces, which good lime will not.'

But we must trace the chain of reasoning which led him
to come to this conclusion.

Having prepared 'mild' magnesia by mixing Epsom
salt or sulphate of magnesia with carbonate of potash, or
' pearl-ashes,' he found that it is ' quickly dissolved with
violent effervescence or explosion of air by the acids of
vitriol, nitre, and of common salt, and by distilled vinegar ' ;
that the properties of these salts — the sulphate, nitrate,
chloride, and acetate of magnesium — differ greatly from
those of the common alkaline earths; that when boiled
with 'salt-ammoniac,' or chloride of ammonium, volatile
crystals of smelling-salts were deposited on the neck of
the retort, which, on mixing with the chloride of mag-
nesium remaining in the retort, reproduced the 'mild'
magnesia; that a similar effect is produced by boiling
' mild ' magnesia with ' any calcareous substance ' ; while
the acid quits the calcareous salt to unite with the mag-
nesia, ' mild ' magnesia is again precipitated on addition of
a dissolved alkali.

On igniting ' mild ' magnesia, it changed into a white
powder, which dissolved in acids without effervescence.
And the process of ignition had deprived it of seven-
twelfths of its weight. Black next turned his attention to
the volatile part ; he attempted to restore it by dissolving
the magnesia in a sufficient quantity of ' spirit of vitriol '
or dilute sulphuric acid, and separated it again by the
addition of alkali. The resulting white powder now effer-
vesced violently with acids, and ' recovered all those
properties which it had lost by calcination. It had
acquired besides an addition of weight nearly equal to

80 ESSAYS BIOGRAPHICAL AND CHEMICAL

what had been lost in the fire; and as it is found to
effervesce with acids, part of the addition must certainly
be air.'

Black here made an enormous stride ; he had weighed
a gas in combination. He argues further : ' It seems there-
fore evident that the air was forced from the alkali by the
acid, and lodged itself in the magnesia.' We may repre-
sent the change diagrammatically thus :

Magnesia \ y( Alkali->-Vitriolated alkali.
Spirit of vitriol X Air->Mild magnesia.

The next step was to try whether mild magnesia lost
the same weight on being mixed with acid as it did when
heated in the fire. But owing probably to the solubility
of the fixed air in the water, a much less loss was found
on dissolving the magnesia (35 grains out of 120) than by
heating it (78 grains out of 120). The amount of acid
required to expel the fixed air was, however, practically
the same as that required to dissolve the magnesia usta,
or heated magnesia (267 and 262 grains).

Turning his attention next to chalk, he dissolved some
in muriatic acid, and having precipitated with fixed alkali
no difference could be detected between the recovered and
the original chalk. He had thus first separated the fixed
air from the chalk, and then recombined the two. These
experiments led Black to conclude that fixed air must be
of the nature of an acid, for it converts quick-lime — the
acrid earth, as he termed it — into crude lime, or mild
earth, the mildness being due to its union with fixed air.

The explanation is thus given of the curious fact that
mild magnesia, mixed with lime-water, gives pure water ;
for the fixed air leaves the magnesia and unites itself to
the lime, and both the magnesia usta and the chalk
which are formed are insoluble in water. And the action

JOSEPH BLACK: HIS LIFE AND WORK 81

of quick-lime in causticising alkali is similarly explained
by its removing the fixed air from the alkali, thus render-
ing the latter caustic, while itself becoming mild.

Reasoning further, Black foresaw that caustic alkali,
added to Epsom salt or vitriolated magnesia, should give
a precipitate of magnesia which should not effervesce with
acids, for here fixed air is excluded ; and, also, that caustic
alkali should separate from acids lime in the quick state,
only united with water.

Similar experiments of treating chalk with acids and
heating it, which had been performed with magnesia,
showed similar results.

But it had yet to be demonstrated that fixed air did not
share the properties of ordinary atmospheric air. So
Black placed four fluid ounces of lime-water, as well as
four ounces of common water, under the receiver of an
air-pump, and exhausted the air; air rose from each in
about the same quantity ; it therefore appeared that the
air which quick-lime attracts is of a different kind from
that which is mixed with water. Quick-lime does not
attract air when in its most ordinary form, but is capable
of being joined to one particular species only, 'which is
dispersed through the atmosphere, either in the state of a
very subtle powder, or, more probably, in that of an elastic
fluid. To this I have given the name of fixed air, and
perhaps very improperly ; but I thought it better to use a
word already familiar in philosophy than to invent a new
name, before we be more fully acquainted with the nature
and properties of this substance.'

The next step was to examine the nature of caustic
alkali, and to prove whether it gained weight on being
made ' mild.' This was achieved indirectly, by finding the
amount of acid required to neutralise the same weight of
caustic alkali, and 'salt of tartar' — what we know as
potassium carbonate. Six measures of acid were required
F

82 ESSAYS BIOGRAPHICAL AND CHEMICAL

to saturate the former, and five the latter ; and Black was
very near the truth ; indeed his error was only about four
per cent. He proved, by addition of sulphuric acid, that
the caustic alkali contained no lime, and therefore that
its causticity was not due to an admixture of that
substance.

To prove that lime-stone, or magnesia, 'loses its air'
when dissolved in an acid, but regains it on addition of a
mild alkali, the acid in which the lime was dissolved
passing to the alkali, Black added caustic ley to a solution
of Epsom salt, the result being a precipitate of magnesia ;
this dissolved in vitriol without effervescence, showing
that no fixed air had taken part in the change. He also,
on adding caustic alkali to a solution of chalk in spirit of
salt (or hydrochloric acid), produced lime, which on being
dissolved in water produced lime-water, indistinguishable
from that produced from quick-lime and water. He goes
on to say that ' had we a method of separating the fixed
alkali from an acid, without at the same time saturating
it with " air " we should then obtain it in a caustic form.'
It can be done, it is true, by heating nitre with charcoal,
but the alkali is then found saturated with air; and
again, by heating the alkali-salts of vegetable acids, the
same occurs. Black conjectures that the fixed air must
be derived either from the nitre or the charcoal in the
first case (indeed it is derived from both, the nitre supply-
ing the oxygen to the carbon); and in the second, he
remarks that the vegetable acid is not really separated,
but rather destroyed by the fire. How nearly he came
to the discovery that fixed air is produced from carbon !

Such was Black's research on fixed air. And now
having shown that a gas can be retained by a solid, and
can be made to escape by treatment with acid or by heat,
he attacked somewhat later the problem of the cause of
this fixation. He discovered it to be due to what he

JOSEPH BLACK: HIS LIFE AND WORK 83

termed ' latent ' or hidden heat. But his research was not
made with this object; the connection of the two was
fortuitous, although of a fundamental nature.

Between the years 1759 and 1763, he formed opinions
regarding the quantity of heat necessary to raise equally
the temperatures of different substances. Boerhaave
imagined that all equal portions of space contain equal
amounts of heat, irrespective of the nature of the matter
with which they are filled ; and his reason for this state-
ment was that the thermometer stands at the same
height if placed in contact with objects near each other.
Here we have a confusion between heat and temperature ;
and this was perceived by Black, for he pointed out that
a distinction must be drawn between quantity and inten-
sity of heat : the latter being what we now call tempera-
ture. He quotes Fahrenheit to show that while equal
measures of water at different temperatures acquire a
mean temperature when mixed, it requires three measures
of quicksilver at a high temperature to convert two
measures of water at a low temperature to the mean of
the two temperatures ; and this corresponds to twenty
times the weight of the water. Black expressed this by
the statement that the capacity for heat of quicksilver is
much less than that of water.

But before this, in 1757, Black had made experiments
leading up to these views. He had noticed that when ice
or any solid substance is changing into a fluid, it receives
a much greater amount of heat than what is perceptible
in it immediately afterwards by the thermometer. A
great quantity of heat enters into it without making it
perceptibly warmer. Conversely, in freezing water or any
liquid, a large amount of heat comes out of it, which again
is not revealed by a thermometer.

He then proceeded to estimate the quantity of heat
which had to be absorbed by a known weight of ice in

84 ESSAYS BIOGRAPHICAL AND CHEMICAL

order to melt it. He hung up two globes side by side,
about 18 inches apart, in a large empty hall, in which the
temperature remained practically constant ; each globe
contained 5 ounces ; one of ice at 32° F., the other water
at 33°. The latter had a delicate thermometer suspended
in it. The temperature of the hall was 47° F. In half an
h our, the water had attained the temperature 40° F. ;
and the ice took ten hours and a half to attain the same
temperature, that is, twenty-one times as long as the
water. The heat, which the ice absorbed during melting
was (40 — 33) x 21 or 147 units; that is, had it been
absorbed by the five ounces of water it would have made
it warmer by 147°. The temperature of the ice, however,
was 8° warmer than its melting-point, after the 21 half-
hours ; hence 139 or 140 ' degrees had been absorbed
by the melting ice, and were concealed in the water into
which it had changed.'

The method of experiment was next varied. Black
weighed a lump of ice, and added it to a weighed quantity
of warm water of which the temperature was known.
The warm water was cooled to a much lower degree by
the melting of the ice, than if it had been mixed with a
quantity of water of 32° F., equal in weight to the ice.
The quantity of heat absorbed by the ice in melting ap-
peared from this second experiment to have been capable
of heating an equal quantity of water through 143° F.

A third experiment was made, in which it was proved
that a lump of ice, placed in an equal weight of water at
176°, lowered the temperature of the water to 32°. Now
176 — 32 = 144° — again a similar result. The latent heat
of water is therefore about 142 or 143, in Fahrenheit
units. The result of the most careful measurements give
79'5° centigrade units, which corresponds with 143° units
of Fahrenheit's scale. Curiously enough, this fundamental
datum has not yet been determined with the accuracy

JOSEPH BLACK : HIS LIFE AND WORK 85

which is customary nowadays, and it is still uncertain to
one seven-hundredth of its value. Black's determination
was a remarkably good one, especially if we consider the
crude appliances which he used.

The substance of this research was communicated to
the ' Philosophical Club,' or Society of Professors and
others in the University of Glasgow in the year 1762, and
was expounded yearly by Black in his lectures to his
students.

Black suggested to Irvin, his pupil, and afterwards his
successor in the Glasgow chair, to determine the latent
heat of fusion of spermaceti and bees'-wax ; and he found
that these substances, too, absorb heat, insensible to the
thermometer, on assuming the liquid state. In this
manner, he made his thesis general. But in attempting
to extend it beyond the case of liquids and solids, he went
astray. For example, he imagined that the great rise of
temperature, which may even reach redness, caused by the
hammering of iron by a skilled smith, was due to the
' extrication of the latent heat of the iron by hammering.'
He did not realise that heat can be produced from
mechanical work ; that work can be quantitatively trans-
formed into heat ; a discovery made more than eighty
years later, by Joule, although it had been anticipated by
Count Rumford, and by Sir Humphry Davy, in the begin-
ning of last century.

Similar experiments were made by Black on the latent
heat of steam, in which he compared the time required for
a known weight of water to rise through a definite interval
of temperature when exposed to a constant supply of heat
with that required to dissipate the water into steam. But
his estimate of 830 units required to evaporate one part of
water was not so accurate ; the actual figure is 967 units on
the Fahrenheit scale. Black cited experiments by Boyle,
by Robison, his successor in the Glasgow chair, and by

86 ESSAYS BIOGRAPHICAL AND CHEMICAL

Cullen, his predecessor, in which the boiling-point of
liquids had been found to be lowered by reduction of
pressure; he rightly ascribes this to the freer escape of
the vapour, and to the absorption of heat by the vapour,
and the consequent cooling of the liquid from which it is
escaping.

These conceptions of Black's were utilised by his friend
James Watt in his work on condensers, and, as every one
knows, effected a revolution in the structure of steam-
engines, and as a consequence in the whole of our indus-
trial and social life ; and further, they were developed by
many men of science, until in the hands of the masters —
Joule, Clerk-Maxwell, Rankine, James Thomson, and
Kelvin, on the physical side, and of Wlllard Gibbs, the
American, on the chemical side— they form the very
groundwork of the sister sciences, physics and chemistry.

Black's great chemical discovery that a gas exists which
is clearly not a modification of atmospheric air, seeing it
can be ' fixed ' by alkalies and alkaline earths, led the way
to ' pneumatic chemistry,' as it was called, and was followed
by the discovery of oxygen by Priestley, of nitrogen by
Rutherford, of hydrogen by Cavendish and Watt, and of
the more recent discoveries of argon and its congeners, all
of them constituents of the atmosphere. In fact, the gases
of the atmosphere have been discovered entirely by Scots-
men and Englishmen.1

And Black's proof, that the change of a complex com-
pound to simpler compounds, and the building up of a
complex compound from simpler ones, can be followed
successfully by the use of the balance, has had for its
consequence the whole development of chemistry. It is
only in the most recent years, since Becquerel observed
the effect of uranium ores and salts in discharging an

1 In justice to the Swede Scheele, it should be said that his discovery
of oxygen was contemporaneous with Priestley's.

JOSEPH BLACK: HIS LIFE AND WORK 87

electroscope, and since Madame Curie discerned one of
the causes of the discharge by uranium ore, namely, the
existence in it of a new element, radium, and since Ruther-
ford and Soddy's isolation of the gases evolved from
radium and from thorium, that a new and more sensi-
tive instrument has been placed at the disposal of
chemists in the electroscope. We are at the beginning of
a new era. Every discovery of a new principle of research
heralds a new departure; and the compound nature of
many of the so-called elements begins to appear from
their electrical behaviour, in much the same manner as
Black demonstrated the decomposability of compounds in
the year 1752.

LORD KELVIN

ON June 16, 1896, there took place in the University of
Glasgow an almost unique ceremony. On that day
the jubilee of Lord Kelvin was celebrated ; he had been
Professor of Natural Philosophy at Glasgow University
for fifty years. The Prince of Wales, now King Edward,
sent him a letter of congratulation ; twenty-eight univer-
sities, twelve colleges, and fifty- one learned societies
sent delegates with addresses, wishing Lord Kelvin many
more years of health and happiness, and mentioning in
terms of profound admiration his magnificent achieve-
ments in the domain of physics. What were these, and
why did they deserve and obtain such universal admira-
tion ? To answer that question fully would require a
much longer space than is at my disposal; but I shall
try to give a short sketch of William Thomson's life and
work.

In 1812, James Thomson, William's father, was a teacher
in the Royal Academic Institute of Belfast. He was one
of the descendants of a number of Scotsmen who emigrated
to North Ireland in the seventeenth and eighteenth
centuries. He had two sons, James and William, both of
whom were born in Ireland, and both of whom became
illustrious. When William was eight years old, his father
was appointed to the Chair of Mathematics in the Uni-
versity of Glasgow. My father was one of his students ;
and I remember well his allusions to Professor Thomson's
kindliness and sense of humour.

90 ESSAYS BIOGRAPHICAL AND CHEMICAL

It was his habit to cross-examine his students, at the
beginning of each lecture, on the subject of the preceding
day's work ; and it was customary in his junior class to
begin with very elementary questions. One day he asked
a certain Highlander : ' Mr. M'Tavish, what do you under-
stand by a " point " ? ' The answer was, ' It 's just a dab ! '
Again, Mr. M'Tavish was asked, in the course of the con-
struction of some diagram : ' What should I do, Mr.
M'Tavish ? ' ' Tak a chalk in your hand.' ' And next ? '
' Draw a line.' Professor Thomson complied, and pausing,
said : ' How far shall I produce the line, Mr. M'Tavish ? '
' Ad infinitum ! ' was the astounding reply.

At the mature age of ten William entered the university.
His training had been wholly in his father's hands ; Pro-
fessor Thomson was clear-sighted enough to recognise that
he had two very remarkable sons. They were brought up
on Classics and Mathematics, Logic and Philosophy.

In May 1907, at the annual dinner of the London
' Glasgow University Club/ I had the good fortune to hear
Lord Kelvin express his views on education. His theme
was the ' University of Glasgow ' ; and he commended the
universality of the training which it used to give. By the
age of twelve, said he, a boy should have learned to write
his own language with accuracy and some elegance; he
should have a reading knowledge of French, should be
able to translate Latin and easy Greek authors, and should
have some acquaintance with German. ' Having learned
thus the meaning of words,' continued Lord Kelvin, ' a boy
should study Logic.' In his charming discursive style, he
went on to descant on the advantages of a knowledge of
Greek. ' I never found/ he said, ' that the small amount
of Greek I learned was a hindrance to my acquiring some
knowledge of Natural Philosophy.' It certainly was not
in his case. And it may here be remarked that it is surely
a mistake to lay down a hard and fast rule that no youth

LORD KELVIN 91

should enter a college until he has reached the age of
fifteen or sixteen; William Thomson took the highest
prizes in Mathematics and Physics before he reached that
age. It may be said that his precocity was phenomenal ;
no doubt it was; but it is precisely those boys who are
unique and unlike their fellows who are of value to the
race, and every chance should be given to exceptional
talent.

Although William Thomson spent six years at Glasgow
University, he did not graduate : in those days the aim of
a student's ambition was not a degree, but the acquisition
of knowledge. Before he had reached the age of seventeen,
he went to Cambridge, where he passed four years. There
the examination system was in full swing; and to the
disgrace of the examiners, Thomson was not the ' Senior
Wrangler '; he was not regarded as the best mathematician
of his year ; and this, in spite of the remark made by one
of his examiners, that ' the Senior Wrangler was not fit
to cut pencils for Thomson.' It is known that success in
this examination depends largely on rapidity in writing
and on accuracy of memory, rather than on originality ;
and the tale is told that on Thomson's ' coach,' or tutor,
asking him why he had spent so much time in answering a
particular question, he replied that he had to think it all
out from first principles. ' But it is a problem of your own
discovery,' said the coach. Thomson had to confess that
he had quite forgotten his own handiwork, and that while his
competitor had learned the answer by heart, Thomson had
had to rediscover the solution. However, he was successful
in gaining the ' Smith's Prize,' a reward for inventiveness
rather than memory. That same year, he was elected
Fellow of his College, and had an income of about £200,
which enabled him to continue his studies in France.

While at Cambridge, Thomson was not only a student ;
he always took a keen interest in music, and was president

92 ESSAYS BIOGRAPHICAL AND CHEMICAL

of the Musical Society ; he also carried off the ' Colquhoun
sculls ' for his excellence as an oarsman. In those days
the science of Cambridge was fettered by the bonds which
Newton had imposed. It is unfortunate, though perhaps
natural, that to the advent of a great man a period of
stagnation succeeds. It was thus with the Schoolmen,
who subsisted for many centuries on the philosophy of
Aristotle; and the science of Cambridge, in 1845, was
based on the work of Newton, nearly a century and a half
old. Indeed, the spirit was that of Timseus, in Plato's
dialogue, who said: 'If we wish to acquire any real
acquaintance with astronomy, we shall let the heavenly
bodies alone.' In fact, Bacon's advice to proceed by way
of experiment and induction had been forgotten. Needless
to say, this reproach has long been removed, by the labours
of Clerk-Maxwell, Rayleigh, Stokes, and J. J. Thomson.
In the 'forties Paris was the home of Fourier, Fresnel,
Ampere, Arago, Biot, and Regnault, all physicists and
mathematicians of the highest rank ; and Thomson spent
a year working in Regnault's laboratory, where experiments
on water and steam, their densities, pressure, and specific
heats, were being carried on with the utmost refinement.
During the next year, 1846, the Chair of Natural Philosophy
in Glasgow fell vacant, and, to their credit, the Senate of
the day advised Queen Victoria to appoint William
Thomson, then a youth of twenty- two, as professor.
Never was a choice better justified in its results. For
Thomson, by example and by precept, trained many
students to be a credit to their old university, and carried
out in cellars, which served as laboratories, and which
were situated almost next door to that in which James
Watt invented the condensing engine, almost all his
numerous and important investigations.

Thomson was not what would be called a good lecturer ;
he was too discursive. I doubt whether any man with a

LORD KELVIN 93

brain so much above the ordinary, so much more rapid in
action than the average, can be a first-rate teacher.
Certainly, in my own case, I gained much more in my
second than in my first year's attendance. But Thomson
never allowed the interest of his students to flag; his
aptness in illustration and his vigour of language prevented
that. Lecturing one day on ' Couples,' he explained how
forces must be applied to constitute a couple, and illus-
trated the direction of the forces by turning round the
gas-bracket. This led to a discussion on the miserable
quality of Glasgow coal-gas, and how it might be improved.
Following again the main idea, he caught hold of the
door, and swung it to and fro ; but, again, his mind
diverged to the difference in the structure of English and
Scottish doors. We never forgot what a couple was ; but
— the idea might have been conveyed more succinctly.
He held strong views on the 'absurd, ridiculous, time-
wasting, soul-destroying system of British weights and
measures ' ; and in spite of all the efforts of the ' Decimal
Association,' we, the Americans, and the Russians remain
examples of irrational conservatism in respect of the
awkwardness of our systems.

The Cartesian method of locating a point was indelibly
impressed on my memory by the following incident: A
student, whose position was roughly about the centre of
the lecture-room, made that noise so disturbing to a
lecturer, yet so difficult to locate, caused by gently rubbing
the sole of his foot on the floor. ' Mr. Macfarlane ! ' said
Sir William. Mr. Macfarlane, the fides Achates, came,
received a whispered communication, and went out of the
room. In about ten minutes he returned with a tape-line,
and proceeded to measure a length along one wall, on
which he made a pencil-mark. He then measured out at
right angles another length, and made a chalk-mark on
the floor, erecting on it a pointer. ' Mr. Smith, it was you

94 ESSAYS BIOGRAPHICAL AND CHEMICAL

who made that noise : be so good as to leave the room,'
said Sir William. Mr. Smith blushed and retired. Then
came the explanation. Mr. Macfarlane had gone below
the sloping tier of seats ; had accurately diagnosed the
precise position of Mr. Smith's erring foot, and had
accurately measured the distance from the two walls.
These measurements were reproduced in full view of the
students, and the advantages of the system of Cartesian
co-ordinates were experimentally demonstrated, while
justice was satisfied.

Owing to an accident, Sir William was lame ; but it did
not interfere with his activity of body. Indeed, it lent
emphasis to his amusing class demonstration of ' uniform
velocity,' when he inarched backwards and forwards
behind his lecture-bench, with as even a movement as his
lameness would permit ; and the class generally burst into
enthusiastic applause when he altered his pace, and intro-
duced us to the meaning of the word ' acceleration.'

In his laboratory Sir William was a most stimulating
teacher, though his methods were not those which have
since been introduced into physical laboratories. I re-
member that my first exercise, which occupied over a
week, was to take the kinks out of a bundle of copper
wire. Having achieved this with some success, I was
placed opposite a quadrant electrometer and made to
study its construction and use. I was made to determine
the potential difference between all kinds of materials,
charged and uncharged ; and among others between the
external and internal coatings of a child's balloon, black-
leaded externally and internally, and filled with hydrogen.
Nor was the Professor always prescient. On one occasion
I turned the handle of a large electrical machine, while
he held a two-gallon Leiden jar by its knob, and charged
the outside coating. It was not until it was fully charged
that it occurred to one of us that while the jar was quite

LORD KELVIN 95

safe as long as it was in his hands, it was impossible for
him to deposit it on the table without running the risk of
an inconveniently heavy shock. Finally, after rapid de-
liberation, two of us held a towel by its corners, and Sir
William dropped the jar safely into the middle ; it was
then possible to touch the outside without mishap. In
short we had little systematic teaching, but were at once
launched into knowledge that there is an unknown region
where much is to be discovered ; and we were made to
feel that we too might help to fathom its depths.
Although this method is not without its disadvantages —
for systematic instruction is of much value — there is much
to be said for it. On the one hand, too long a course of
experimenting on old and well-known lines, as is now
the practice among teachers of science, is likely to imbue
the young student with the idea that all physics consists
in learning the use of apparatus, and in repeating
measurements which have already been made. On the
other hand, too early attempts to investigate the unknown
are likely to prove fruitless for want of manipulative skill,
and for want of knowledge of what has already been
done. The best of all possible training, however, is to
serve as hands for a fertile brain — the brain of one who
knows what he wishes to discover, who is familiar with all
that has already been attempted, and who gradually trains
his assistant to take part in the thinking as well as in the
manipulation. If at the same time the student is made
to read, not merely concerning the problem on which he
is immediately engaged, but on all branches of his sub-
ject, nothing can be better than such stimulating inter-
course with an inventive teacher for those who have ability
to profit by it.

It is extremely difficult to explain Lord Kelvin's contri-
butions to knowledge to those who have not themselves
some acquaintance with its problems. Let me begin by a

96 ESSAYS BIOGRAPHICAL AND CHEMICAL

quotation from Helmholtz, late Professor of Physics in
Berlin, an old and intimate friend of Lord Kelvin :
' His peculiar merit consists in his method of treating
problems of mathematical physics. He has striven with
great consistency to purify the mathematical theory from
hypothetical assumptions, which were not a pure expres-
sion of the facts. In this way he has done very much to
destroy the old unnatural separation between experimental
and mathematical physics, and to reduce the latter to a
precise and pure expression of the laws of the phenomena.
He is an eminent mathematician, but the gift to translate
real facts into mathematical equations, and vice versa, is
by far more rare than that to find a solution of a given
mathematical problem, and in this direction Sir William
Thomson is most eminent and original.' When Lord
Kelvin began his work, the equivalence of heat and
energy was unrecognised ; forces were distinguished as
' conservative ' and ' unconservative ' ; the world was sup-
posed to be filled with subtle fluids and effluvia ; and it
must have seemed almost hopeless to seek any general
explanation of material phenomena. Light, heat, elec-
tricity, magnetism, and chemical action were all regarded
as distinct 'forces,' each a cause of change. Thomson,
and his collaborator Tait, the late Professor of Physics in
Edinburgh, in their Treatise on Natural Philosophy, did
much to emphasise the view that Physics deals with
things, not theories ; with relations, not with their mathe-
matical expression, equations ; and they tried successfully
to free the science from the bonds of formal mathematics.
They demonstrated that the principle of ' Least Action '
is universal ; that by its help it is possible to explain the
motions of the planets and their satellites, of wheels,
lathes, machines of all kinds, of every system of which
we can define the moving parts and the forces which act
on them.

LORD KELVIN 97

In 1893 Lord Kelvin gave a discourse on 'Isoperi-
metric Problems ' at the Royal Institution, in which he
attempted to describe the nature of this general problem ;
it is that technically called 'Determining a minimum';
and he began with the task which faced Dido of old — to
surround the most valuable piece of land with a cowhide,
i.e. to draw the shortest possible line around it. A
similar problem is, to build a railway-line through
undulating country at the smallest possible cost ; and one
very different in appearance, but related to those already
cited, owing to Lord Kelvin's consummate power of dis-
covering analogies between phenomena apparently uncon-
nected, is the condition of stability of water rotating in
an ellipsoidal vessel, and a number of similar problems.
Kelvin's work on Elasticity is no less far-reaching ; in
Karl Pearson's great treatise on that subject, no less
than one hundred pages are filled with Kelvin's con-
tributions.

Lord Kelvin was also the author of a theory of the
nature of the ultimate particles of matter — the atoms.
He imagined them to consist of 'vortex rings in the
ether,' the ether being conceived as a frictionless fluid, all-
present, even filling the interstices between the atoms, or
ultimate particles of matter. Vortex rings in air, some-
times made by smokers, are elastic ; they cannot be cut
without being destroyed ; and, in a frictionless fluid, their
rotatory motion would be eternal, if once impressed.
Recent discoveries may lead to the modification of this
theory of the nature of matter ; but it has much in its
favour.

Kelvin was a strong partisan of Joule's work on the
equivalence of heat and work. It was believed up to
1850 that the heat developed on compressing a gas was
'caloric,' squeezed out of the gas, as one might squeeze
water out of a sponge ; but Kelvin taught that heat must
G

98 ESSAYS BIOGRAPHICAL AND CHEMICAL

be due to the motions of the molecules of a gas; and
that when the gas is compressed, the impacts of its mole-
cules on the walls of the containing vessel are more
numerous, and that the work done in compressing a gas
appears as heat, owing to the more numerous impacts of
its molecules. Following on this, it was necessary to
devise an absolute scale of temperature, and that we also
owe to Lord Kelvin. It is based on what is known as the
' Second Law of Thermodynamics ' — that heat cannot be
transferred from a cold to a hot body without expending
work. Following these ideas, Lord Kelvin was led to
consider the probable age of the earth, based on an
estimate of its original temperature, and the rate at which
heat would be lost by radiation. His opinion is that the
earth may have been habitable twenty million years ago,
but could not have been habitable as long ago as four
hundred million years.

The province of electro-magnetism owes very much to
Lord Kelvin. It was he who developed the medium sug-
gested by Faraday into a means of representing electro-
magnetic forces by analogy with the distortion of an elastic
solid. After he had worked out in this manner the con-
nection between energy and electro-magnetism, he devised
our present system of electrical units — volts, amperes,
farads, coulombs, etc., and invented machines to deter-
mine their numerical values. If it be permitted to assign
their relative importance to his contributions to practical
science, this must be pronounced the greatest. Without
it the science of electricity would be helpless as commerce
without a monetary system, and without weights and
measures. His work is the foundation of wireless tele-
graphy, and of many applications of the electric current.
It was he who taught the world how to transmit rapid
and trustworthy signals through cables; and he was a
pioneer of cable telegraphy. In the old days of cables

LORD KELVIN 99

attempts were made to ensure rapid signalling by heavy
currents; but Kelvin showed that feeble currents, com-
bined with delicate instruments, made the difficulty dis-
appear. His 'siphon recorder' is still used, and cannot
well be improved on. A great social and commercial
revolution dates from August 1858, when the message
was signalled under the ocean, ' Europe and America are
united by telegraphic communication. " Glory to God in
the highest, and on earth peace, goodwill toward men." '
This revolution owed much to Sir William Thomson, who
never lost heart and never faltered in the belief that all
difficulties would be overcome. His presence on board
ship during the laying of the first Atlantic cable directed
his attention towards nautical matters; and to him we
owe a deep-sea sounding apparatus, and a compass easily
corrected for the magnetic deviations produced by the
iron or steel used in the construction of ships.

We must not estimate Lord Kelvin's greatness, how-
ever, merely by his own discoveries and inventions, great
as these are ; he has served as a model for many disciples.
His sincere and single-minded devotion to truth; his
interest in the work of others, and his sympathy with
their efforts; his fairness of mind and absence of pre-
judice ; and his straightforward and loving character have
raised the ideals of the whole scientific world, and have
deeply influenced the best minds in all countries. His
idea of ' a treasure of which no words can adequately
describe the value ' is : ' Goodwill, kindness, friendship,
sympathy, encouragement for more work.' Jt is to such
a man that the world owes an eternal debt of gratitude,
and he it was for whom no honour that men have it in their
power to bestow could be too great. It is pleasant to be
able to state that Lord Kelvin's mental energy was unim-
paired by his burden of more than eighty years. He was
present at the meeting of the British Association at

100 ESSAYS BIOGRAPHICAL AND CHEMICAL

Leicester in August 1907, and took part in the discussions
on the ' Nature of the Atom.' The minds of most men,
like their bodies, grow stiff with age and unreceptive of
new impressions ; but Lord Kelvin's until his latest days
had all the vigour and elasticity of a young man's. We
may well rejoice that he was spared so long to enrich the
world with his wisdom and his inimitable example.

PIERRE EUGENE MARCELLIN BERTHELOT

1827-1907 J

MARCELLIN BERTHELOT was a native of Paris, born on
October 25, 1827, in a flat looking on to the Rue du
Mouton, situated in the Place de Greve, now, owing to the
activity of Baron Haussinann, the Place de l'H6tel-de-
Ville. His father, a doctor of medicine, was a member of
the sect of the Jansenists, a small branch of the Gallic
Catholic Church. He was a serious man, impatient with
the folly of his concitoyens, and somewhat depressed by
the poverty and sufferings of his patients. The ' Church
of Faith ' had its own Liturgy, and the congregation joined
in singing psalms and hymns. Many of the prttres
were among Dr. Berthelot's patients, and young Berthelot
must often have listened to discussions on the attempts,
ultimately successful, to substitute the Roman for the
Gallic liturgy. Dr. Berthelot was married in 1826, shortly
after starting practice. His wife was a lively, bright
woman, who transmitted her features to her son.

At that time, Charles the Tenth was on the throne.
The allied powers had involved France in a Gouverne-
ment de Cures ; and it was part of the State Ceremonial
to form a procession, which was headed by the Holy
Sacrament and the Papal Nuncio, a cardinal in red, from
the Tuileries, to Notre Dame and back, and in which the
King, the Queen, the Dauphin (who, according to Madame

1 A notice which appeared in the Proceedings of the Royal Society for
1907.

101

102 ESSAYS BIOGRAPHICAL AND CHEMICAL

Berthelot mere, was able to look behind him without turn-
ing his head), and the Court took part. The spectators,
under the penalty of sacrilege, were obliged to kneel as
the Corpus Christi procession passed. Those who refused
were prosecuted and severely punished.

Such a travesty of religion was not to Dr. Berthelot's
taste ; the bourgeoisie was liberal and imbued with the
sentiments of Voltaire ; and the Berthelot family was of
the bourgeois class. During the revolutions of 1830 and
1848, their house commanded a full view of one of the
chief scenes of operation, and young Berthelot must have
often been a spectator of many a scene of disturbance and
violence. Highly developed intellectually, and mentally
impressionable, his later convictions were doubtless largely
owing to his early surroundings.

That Marcellin resembled his mother in features has
already been mentioned. But the resemblance was not
merely external ; there existed between them the most
intimate sympathy. Their favourite promenade was in
the Bishop's garden behind Notre Dame, along the Quays
with their stalls of flowers, and in the Jardin des Plantes.
Their minds were both quick and versatile; they were
eagerly interested in all that passed around them, and, as
Madame Berthelot used to say (borrowing the simile from
one of the invasions which she witnessed), they could both
' drive a Russian team with a sure hand and at a full
gallop.' The writer, who knew Berthelot only during his
later years — since 1878 — never conversed with any one
who possessed such rapidity of thought. Given an idea,
with his quick discursive mind he would follow out all
possible paths and by-ways, seeing the consequences of
this assumption and of that, interposing occasionally a
quaint remark, not exactly humorous, but de plaisanterie.
He was a delightful conversationalist, interested and in-
tensely interesting, willing to discuss all possible subjects,

PIERRE EUGENE MARCELLIN BERTHELOT 103

and willing, too, to hear all varieties of view, even those
contrary to his own opinion.

His persistence, energy of character, and devotion to
duty were inherited from his father. Berthelot used to
regret that he had not inherited his mother's optimism.
He used to say that when a misfortune overtook her, she
had what the French call a crise de larmes, soon over
and followed by her usual optimistic cheerfulness ; that a
rainbow generally rose through her tears, and that she
became gaily resigned to the incurable evil.

After the demolition of the Rue du Mouton, the family
moved to Neuilly, then quite in the country. Renan often
looked in on Sundays as a guest at their midday meal.
In one of his private letters he tells how Berthelot and
he became friends. He had just renounced his clerical
orders, and was maitre-repetiteur in a school, where he
led a lonely and melancholy existence, depressed by the
mental struggles which he had come through, and far
from his family and his native Brittany. One day, a
pupil about four years younger than himself accosted
him; the talk became intimate, and a friendship with
Berthelot was soon formed, destined to endure for life.
Their intercourse was frequent ; begun early, when both
were slender youths, never a year, hardly a month, passed
without their seeing each other. Renan used sometimes
to poke fun at Berthelot ; the tale is told that, passing a
cemetery, Renan said to him : ' La, voici la seule place que
tu n'as jamais convoitee.' Such sallies were always received
with amusement and good temper. On another occasion,
provoked by the remark that his coat was worn with the
air of a cassock, Renan retorted : ' What is there in you,
Marcellin, that gives you the air of just having left off
fighting behind a barricade ? ' While Berthelot retained
his slender form, Renan became very corpulent ; Berthelot,
nervous and active, maintained to the last his almost

104 ESSAYS BIOGRAPHICAL AND CHEMICAL

feverish love of work ; Renan was meditative — almost a
dreamer. It was Berthelot's sad duty to speak of his
lost friend when the monument at Treguier was raised to
his memory. He emphasised Renan's lucidity even to
the end, his power of work, his great mental activity ; the
words were applicable with equal force to himself.

Never was there a more devoted couple than Monsieur
and Madame Berthelot. After he had ended his brilliant
career at the Lycee Henri iv., Berthelot gained the prize
of honour at the open competition in 1846. Without any
coaching, he passed successively all his degrees — Bachelier,
Licencie, and Docteur-es-Sciences ; for the doctorate he
presented a somewhat sensational thesis, entitled, ' The
Compounds of Glycerine with Acids, and the Artificial
Production of the Natural Fats.' While working at this
research, he was lecture-assistant (preparateur) to Balard,
at the College de France. In 1861, largely through the
influence of Duruy, then . Minister of Public Instruction,
Berthelot was promoted to the Chair of Organic Chemistry
in that institution ; and there he remained all his life.
In that year he was awarded by the Academy of Sciences
the Jecker Prize for his remarkable researches on the
artificial production of organic compounds by synthesis,
and at the same time the Academy recommended the
creation of the special chair which Berthelot filled so long
and so illustriously. In his own words: 'Adonne, des
mes debuts dans la vie, au culte de la verite pure, je ne
me suis jamais mele a la lutte des interets pratiques qui
divisent les hommes. J'ai vecu dans mon laboratoire
solitaire, entoure de quelques eleves, mes amis.'

When he won the Jecker Prize, he was in his thirty-
fifth year. The appointment to the Chair at the College
de France made it possible for him to marry Mademoiselle
Breguet, the daughter of a French Swiss, whose family
had made money by manufacturing watches, famed since

PIERRE EUGENE MARCELLIN BERTHELOT 105

the middle of last century. Monsieur Breguet was a
constructeur industriel, or builder of factories. He lived
near the Place de THotel-de-Ville, on the Quai de
1'Horloge, and the families were acquainted from early
days. Mademoiselle was a desirable partie, well-dowered,
and of great beauty, which she retained up to the end of
her life. She was placid in manner, with lovely eyes, and
a brilliant complexion, rendered even more striking, when,
at an advanced age, her hair was silver ; and in the church
of Saint-Etienne du Mont there is a picture of Sainte-
Helene, the lovely face of which is taken from a portrait
of Madame Berthelot as a girl The meeting of the young
couple was somewhat romantic ; Mademoiselle Breguet,
no doubt, must have appeared to Marcellin to be beyond
his reach, and besides, his attention was otherwise occupied.
But one day, on the Porit Neuf, Mademoiselle was crossing
the longest bridge in Paris in the face of a strong wind,
wearing a charming Tuscan hat, then the mode. Behind
her walked her future husband; suddenly she turned
round, to avoid having her hat blown off, and practically
ran into his arms. If not exactly love at first sight, it
was a case of love at first touch. Their married life was
of the happiest ; indeed, it may be said that they were in
love with each other till the end. One of the sons
wrote: ' Mon pere et ma mere s'adoraient; jamais le
moindre nuage n'avait trouble leur bonheur. Us s'etaient
coinpris des le premier jour. 11s etaient si bien faits pour
se completer ! Bien que tres lettree et fort intelligente,
maman s'etait toujours effacee devant son mari, se bornant
a s'efforcer de le rendre parfaitement heureux. C'etait,
a son avis, la seule fa^on de collaborer a son ceuvre.'
Another intimate friend added: 'Monsieur et Madame
Berthelot s'adoraient; tous deux etaient de la nature
d'elites ; sa compagne n'avait cesse de 1'encourager et de
le soutenir.' No one visiting their house could fail to

106 ESSAYS BIOGRAPHICAL AND CHEMICAL

remark this absolute devotion to each other ; never was
there a happier family. Although not a conversationalist,
Madame Berthelot, by her perfect tact, her serene manner,
and her charming sympathetic face, knew how to make
each guest appear at his best; the ball of conversation
was lightly tossed round the table, Berthelot himself, by
his quaint and paradoxical remarks, contributing his
share. A dinner at Berthelot's, in his old house in the
Palais Mazarin, the home of the Institute, was a thing to
be remembered. Always charitably disposed, Madame
Berthelot used to send all the cast-off clothes of the
family to the cleaners, and after they had been carefully
mended, they were distributed to poor friends.

In 1881, Berthelot was elected a 'Permanent Senator';
he thought it incumbent on him to bear his share in the
government of his country. With his wife's help, he
managed to carry on his two functions at the same time.
Iri his place in the Senate, Berthelot used to sit buried in
his arm-chair, his head thrown back, and his eyes closed,
apparently inattentive to all that passed ; but nothing of
importance escaped him. He took a leading and active
part as member of various Committees dealing with
education, and in 1886, as Minister of Education in the
Goblet Cabinet, he busied himself with the reform of
educational methods in such a manner as to acquire
a wide popularity; the Bills introduced by him dealt
with primary and with higher instruction, with universi-
ties, and with technical schools; in the last he was no
believer, except in so far as manual training was given.
Later, in 1895, he was for a short time Foreign Minister
in the Bourgeois Cabinet ; but the delays of parliamentary
procedure were not to his mind. It was with difficulty
that he was persuaded to sign the Anglo-French Treaty
defining the position of Siam ; and, almost immediately
after, he resigned office.

PIERRE EUGENE MARCELLIN BERTHELOT 107

Berthelot's career is easily told ; it consisted of honour
after honour. He was elected a Member of the Academic
de Medecine in 1863, and in 1867 he collaborated in the
foundation of the Ecole des Hautes Etudes, and in the
reorganisation of scientific teaching. Membership of the
Academic des Sciences followed in 1873, and in 1889 he
became its Secretaire Perpetuel.

In 1900, he had the rare honour of being elected among
the immortal forty in the Academie Fran9aise, succeeding
to the Chair of Joseph Bertrand. Of 28 voters, 19 voted
for him, 9 abstaining. Four years later, in 1904, he
delivered the statutory discourse. He was a Member of
the Conseil Superieur des Beaux-Arts, of the Conseil
Superieur de V Instruction Publique, and in 1886 he was
created a Grand Officier of the Legion of Honour. He
was Foreign Member of almost every scientific society
in the world, including our own Royal Society.

On November 24, 1901, the Berthelot jubilee celebration,
the anniversary of his seventy-fifth birthday, was held in
Paris, M. Loubet, President of the Republic, in the chair.
It took place in the great hall of the Sorbonne ; all the
Cabinet, the ambassadors of all countries, and delegates
from universities and scientific societies from all over the
world were present. Madame Berthelot with her children
and grandchildren occupied a conspicuous place, beaming
over with unaffected pleasure ; Berthelot had declined the
State offer to make a triumphal procession in the carriage
of the President with a military escort ; he went on foot
from the Quai Voltaire to the Sorbonne, his greatcoat
buttoned so as to hide the grand-cordon of the Legion
of Honour, and his head down so as to avoid recognition.
He was embraced by the President of the Republic, and
amid the enthusiastic applause of the spectators, address
after address was delivered, each delegate conveying the
congratulations of the body which he represented. It

108 ESSAYS BIOGRAPHICAL AND CHEMICAL

was a national fete. Thus did the French honour science
and its doyen.

On March 18, 1907, the end came. Madame Berthelot
had been ailing for about three months ; it turned out to
be an attack of heart-disease, dangerous at the age of
seventy. After she was confined to bed, Berthelot watched
by her each night, seated in a deep arm-chair, only leaving
her when she was asleep. He himself suffered from the
same disease, and it was accelerated by his want of rest.
His family noticed his feverish appearance in the morn-
ings ; he excused himself by saying that he was finishing
a memoir for publication. On Passion Sunday there was
a slight improvement, and Berthelot passed the afternoon
in his laboratory at Meudon. That night, however,
Madame Berthelot became comatose, and her husband
never left her bedside until Monday at four, when the end
came. Berthelot suddenly rose from the arm-chair in
which he was seated, threw his arms in the air, uttered a
cry, and fell back dead. They died, as they had lived,
together.

It now remains to give a sketch of Berthelot's scientific
work. The ' Prix- Jecker ' has already been alluded to.
This was the reward of his labours on the synthesis of
carbon compounds. He began in 1851 by investigating
the action of a red-heat on alcohol, acetic acid, naphtha-
lene, and benzene ; this led him in 1860 to the rediscovery
of acetylene, a compound originally obtained by Edmund
Davy, Sir Humphry's brother. In 1856 he synthesised
methane by the action of a mixture of sulphuretted
hydrogen with carbon disulphide on copper; and in 1862
he obtained ethylene and acetylene by heating marsh-gas
to redness. His condensation of acetylene to benzene in
1866 established the first link between the fatty and the
aromatic series. His direct synthesis of acetylene from
carbon and hydrogen in 1862, and the formation of alcohol

PIERRE EUGENE MARCELLIN BERTHELOT 109

by hydrolysing ethyl-sulphuric acid, obtained by absorbing
ethylene in sulphuric acid, taken in conjunction with his
synthesis of hydrocyanic acid in 1868, pointed the way to
the formation from the elements of innumerable com-
plicated compounds of carbon.

Much light has also been thrown by Berthelot on the
alcohols. In 1857 he produced methyl alcohol from
marsh-gas by chlorination and hydrolysis; in 1858 he
recognised cholesterine, trehalose, meconine, and camphol
as alcohols ; in 1863 he added thymol, phenol, and cresol
to the same class ; and he showed how to diagnose alcohols
by acetylation.

Turning to the esters, the nature of glycerine occupied
his attention in 1853 ; in that year he succeeded in syn-
thesising some animal fats, and showing their analogy
with esters, as has already been mentioned ; and he pre-
pared other salts of glyceryl by submitting it to the action
of acids. The action of hydriodic acid was, however,
found to yield two substances of a different nature, namely
isopropyl iodide, and allyl iodide ; and from the latter he
prepared, for the first time, artificial oil of mustard. The
analogy of sugars with glycerine led him to investigate
the action of acids on sugars, and this resulted in the
synthesis of many of their esters. The fermentation of
mannite and other polyhydric alcohols was also studied
in 1856 and 1857, also the conversion of mannite and
glycerine into sugars, properly so called. The esters of
pinite, etc., with tartaric acid, were also studied, and in
1858, trehalose and melezitose were discovered. In 1859,
Berthelot maintained that the action of yeast is not a vital,
but a chemical phenomenon ; and he returned again and
again to the study of fermentation.

These and other similar investigations on esters led him,
in conjunction with Pean de Saint- Gilles, to investigate
the rate of esterification ; and the experiments, begun in

110 ESSAYS BIOGRAPHICAL AND CHEMICAL

1861, led to a long piece of work on chemical equilibrium,
and on ' affinity.' In 1869 he attempted to limit the
action of hydrochloric acid on zinc by pressure, but unsuc-
cessfully; and in the same year he investigated the
equilibrium between carbon and hydrogen, in sparking
acetylene under pressure. And later in that year he
announced laws, describing the partition of bodies between
two solvents, and he investigated the state of equilibrium
in solution. In the same year appeared the first of the
long series of researches on thermal chemistry. In 1875
he returned to the subject of chemical equilibrium, deal-
ing with the partition of acids between several bases in
solution.

Among other syntheses was that of formic acid from
caustic soda and carbon monoxide ; oxalic acid was pro-
duced by the oxidation of acetylene ; and acetates, by the
slow oxidation of acetylene, in contact with air and
caustic potash, in diffuse daylight.

In 1857 the combination of unsaturated hydrocarbons
with the halogen acids was studied, as well as the conver-
sion of chloro- and bromo-hydrocarbons into hydrocarbons
by reduction. In 1860 ethyl iodide was synthesised by
the union of ethylene with hydriodic acid; and in 1867
the use of a concentrated solution of hydriodic acid as a
universal reducing agent at high temperatures was dis-
covered.

Berth elot's numerous and important researches on the
acetylides of silver and copper doubtless led him to pay
attention to explosives. Begun in 1862, they were con-
tinued until 1866 ; and in that year he enunciated the
theory that the production of mineral oils may conceivably
have been due to the action of water and carbonic acid on
acetylides of the alkaline metals, and to the subsequent
resolutions of acetylene at a high temperature into other
hydrocarbons. These researches on the acetylides were

PIERRE ETJG&NE MARCELLIN BERTHELOT 111

followed in 1870 by investigations on the explosive force
of powders, the explosions being carried out in a calori-
meter.

In 1871 Berthelot proceeded to investigate the detona-
tion of mixtures of gases, and he made measurements of
the heat of formation of nitro-glycerine. In 1874 and
1876 the work was continued ; and in 1877 it was extended
to the temperatures of explosive mixtures, and to the
velocity of combustion. In 1878 explosive mixtures of
dust with air, and in 1880 fulminating mercury, were
examined. A research on the velocity of the explosive
wave in gases followed in 1882; and in 1884 measure-
ments of the specific heats of gases at high temperatures
were made. In the same year the calorimetric bomb was
invented ; and in 1892 it was adapted to the requirements
of organic analysis.

Allotropic varieties of the elements also claimed Ber-
thelot's attention. In 1857 he commenced with a study
of allotropic varieties of sulphur ; and in 1870 he investi-
gated these varieties thermally. In 1869 he examined
the allotropic varieties of carbon, and this led him to the
preparation of various forms of graphitic oxides. Allo-
tropic silver and other allotropic forms were also the
subject of his research.

Berthelot also did much work by help of the ' silent
discharge.' Attracted to it in 1876, when he submitted
mixtures of organic substances with nitrogen to its
influence, and succeeded in causing the nitrogen to enter
into combination, he repeated Brodie's experiments, and
reproduced the oxide C404. In 1878 he produced by the
same means the higher oxide of sulphur, S2O7, in needles
often a centimetre in length, and in 1881 pernitric
anhydride. In 1895 he carried out similar work with
argon, and later with helium.

From an early date Berthelot interested himself in

112 ESSAYS BIOGRAPHICAL AND CHEMICAL

agricultural chemistry. From his laboratory at Meudon,
assisted by his colleague, Andre, have appeared a succes-
sion of memoirs, chiefly relating to the absorption of
nitrogen by plants, and to their behaviour under the
influence of electric energy. To the very end his interest
was kept up in these experiments ; and he was hopeful of
increasing by electrical means the productiveness of
cereals, and of adding to the world's food-supply.

Though so keenly alive to the present, the past had for
Berthelot a great attraction. In 1877 he analysed a
sample of Roman wine, which had been preserved in a
sealed flask ; and he has contributed to the Journals many
notices of the composition of ancient objects of metal.
His works on Les Origines de I'Alchimie, and on a Collec-
tion des anciens Alchimistes grecs, texte et traduction, and
his Introduction a V etude de la Chimie des Anciens et du
moyen dge,' involved long research of ancient manuscripts ;
he acquired facility in reading ancient Greek, though for
Arabian sources he was dependent on others.

Berthelot was the author of numerous works besides
those on Alchemy. In 1872 he published a Treatise on
Organic Chemistry; a fourth edition appeared in 1899.
This was followed by La Syntkese chimique; Essai de
Chimie mechanique (1879), in which he announced the
principle of ' maximum work,' a doctrine afterwards with-
drawn, or, at least, greatly modified in 1894; Traite
jrratique de Calorimetrie chimique (1893); Thermochimie :
Donnees et lois numeriques (1898), in which an account
of his long series of calorimetrical measurements is
given ; this work and that of Julius Thomson on Tkcr-
mochimie are the standard books on the subject, and
each contains the results of the individual researches of
its author.

Berthelot's mind was one which interested itself greatly,
not merely with things, but with their origins; and in

PIERRE EUGENE MARCELLTN BERTHELOT 113

Science et Philosophic and Science et Morale he treats of
the relation of science to human thought. The same
critical spirit manifests itself in his Histoire des Sciences :
La Chimie au moyen age, in which Syrian and Arabian
Alchemy is treated of.

A partisan of Lavoisier, La Revolution chimique de
Lavoisier presents that point of view strongly. He also
published in 1898 his correspondence with Renan.

The lectures which he delivered at the College de
France were published under the titles Lemons sur les
Methodes generates de Synthese en Chimie organique ;
Lecons sur la thermochimie ; Lecons sur les principes
sucres; and Lecons sur I'isomerie. The application of
thermal chemistry to problems of life was treated of in
his Chaleur anil/note, and in 1901 he published three
volumes on Les Carbures d'Hydrogene.

One point remains to be mentioned. It has sometimes
been objected that Berthelot kept science on a wrong
path by persistently retaining the old system of represent-
ing formulae, after all the rest of the world had aban-
doned it. The writer remembers well a conversation in
the late '80's, in which Berthelot defended his views. He
thought the position of those who employed the customary
notation (and, of course, they comprised practically the
whole chemical world) not unlike that of the defenders of
the phlogiston theory ! The retort was obvious, but not
made. Berthelot had not even the excuse of Cavendish,
who, after a calm, deliberate statement of the results of
his research in terms of the then new hypothesis of
Lavoisier, restated it in terms of the phlogistic method,
saying that he preferred to make use of the older and
better known language, rather than of the newer modes
of expression. For in 1890 Berthelot was, perhaps, the
only survivor of the older chemists. Professor Guye, who
attended his lectures in 1890-91, tells that the session was

114 ESSAYS BIOGRAPHICAL AND CHEMICAL

begun, as usual, with the special notation of which Ber-
thelot was the sole defender ('equivalents based on two
volumes of vapour '), and that, without the slightest warn-
ing in the middle of&ckapitre, to the great astonishment of
his audience, he effected the change, dealing with a subject
of which the first portion had been expounded in the
' equivalent ' notation, and continuing in the newer nota-
tion of which he had so long been the opponent.

No one is more conscious than the Avriter that he has
failed to do justice to this remarkable personality. His
only excuse is that he has done his best. He wishes that
it were possible to convey to the reader a sense of the
brilliancy, the vivacity, the power, the ability, the talent,
and the high character of the great chemist. In the life-
like plaquette by Chaplain, his features and his attitude
have been admirably reproduced. Truly he was one of
the most remarkable of the eminent men of whom France
may be proud. He and his wife lie in the vaults of the
Pantheon, in life united, in death not put asunder.

IF. CHEMICAL ESSAYS

HOW DISCOVERIES ARE MADE

THERE is a difference between discovery and invention.
A discovery brings to light what existed before, but what
was not known ; an invention is the contrivance of some-
thing that did not exist before. I suppose, however, that
inventions and discoveries are made in much the same
manner ; though I have no claim to speak as an inventor,
except in a very small way.

Many people, probably most people, think that when a
discovery is made, it comes all in a flash, as it were — that
a new idea suddenly crops up, and its conception is a dis-
covery. That may sometimes be the case.

We have all heard of the puzzle given to Archimedes ;
how he was asked to find out, without injuring it in the
least, whether a certain crown consisted of silver or of
gold ; and by weighing it in air and in water, he invented
the method of taking specific gravity: for the crown when
weighed in water lost weight equal to that of the water
which it displaced. And he ran through the streets of
Alexandria, crying, ' Heureka ! I have found it ! '

His finding that the crown was of gold was a discovery ;
but he invented the method of determining the density of
solids. Indeed, discoverers must generally be inventors ;
though inventors are not necessarily discoverers.

116 ESSAYS BIOGRAPHICAL AND CHEMICAL

It is too often supposed that, like the poet, discoverers
are ' born, not made ' ; but I think I shall be able to show
that many people, though not all, have in them the power
of making discoveries ; and if this short article can give
to any one the hope of making discoveries, and prompt
him to try, it will have more than achieved its object.

Like every other endeavour, the beginning is in small
things. Any one who tries to look into anything with
sufficient care will find something new. A drop of water ;
a grain of sand ; an insect ; a blade of grass ; we know in-
deed little about them when all is told. First, of course,
we must learn what others have done ; and for that pur-
pose we go to school and to college, and read books and
hear lectures. Before beginning, we should at least have
an idea of what has been achieved by our predecessors.
After that there is nothing for it but to try.

But there are two ways of trying : and what I wish to
convey is best told in an allegory.

There are two kinds of fishers : those who fish for
sprats and those who angle for salmon. I do not say
there are not others ; but these two kinds are at the
extremes of the fishing world. The fishers for sprats are
sure of a large catch, or at least of catching something ;
but the fish are small, not particularly attractive as food,
and of no great value ; they are, however, numerous and
easily caught. But the salmon fisher hunts a very dif-
ferent prey ; if there is any special quality about a salmon,
it is his power of motion and his fickleness of taste ; so
that the angler, when he casts his line, is by no means
sure that a fish is within reach of his cast, nor, if he is,
whether he will rise to the fly. If fate is propitious, how-
ever, his prize is a great one; his pleasure consists not
merely in catching the fish, but in struggling with him,
possibly for an hour or more ; wading after him in alter-
nate hope and fear — hope that his line may stand the

HOW DISCOVERIES ARE MADE 117

strain, fear that it may part, or that some hasty move-
ment may lose him his fish.

Most discoverers are like fishers for sprats : they go
where they are sure of a reward ; but the gain is not
great, at least as regards sport. It is much more fun to
fish for salmon ; but then there is a great chance that the
angler has mistaken the place to fish, or that he has used
the wrong fly ; or that the weather is unfavourable ; or
that a hundred things, impossible to foresee, will prevent
the salmon taking the hook.

We may not pursue the allegory further: salmon are
now not nearly so plentiful at they used to be; sprats,
perhaps even more numerous. And it requires training
and a good eye to know where the salmon lie and in what
pools to fish.

But let us dismiss this image and become historical.

One of the first puzzles which awaited solution was the
nature of flame. The ancients believed it to be an ele-
ment— that is, a property, or perhaps a constituent of
most, or of all, other things. Flame, said they, is hot;
and everything which is hot partakes of the nature of
flame.

Robert Boyle guessed that it was a sign of the rapid
movement of the minute particles of which he supposed
everything to be composed ; but this, although very near
Avhat we now suppose to be the truth, was merely a lucky
guess ; for he had no real ground for making the sugges-
tion. It was noticed that flame appears when anything
burns ; and the reason for combustion, or burning, had
first to be sought.

The real step towards this was made by Joseph Priestley,
an English dissenting minister, and by Karl Scheele, a
Swedish apothecary, almost at the same time. Priestley
was a fisher for salmon, to revert to our old image ; he
fished everywhere and caught many large fish. And so

118 ESSAYS BIOGRAPHICAL AND CHEMICAL

was Scheele. They noticed that when certain substances
were heated, gases — or, as they termed them, 'airs' — escape.
For it had been supposed that all gases, as we now name
them, were merely modifications of ordinary air ; just as
we sometimes notice a pleasant or a disagreeable smell,
and attribute it to the ' goodness ' or ' badness ' of the air, so
it was generally thought that gases, such as coal-gas, were
a sort of air with an unpleasant odour and the curious
property of catching fire.

About fifteen years before Priestley and Scheele made
their great discovery of oxygen, the constituent of air
which supports combustion, a Scottish professor, Joseph
Black, investigated the particular kind of 'air' which
escapes when chalk or limestone is heated. And he made
the great discovery that this ' air ' can be reabsorbed by
lime — the residue left after chalk is heated — so that
chalk is again formed.

Moreover, he weighed the chalk before it was heated,
he measured the gas, and he weighed the lime left after
the gas had been driven off' from the chalk. And lastly
he weighed the chalk which was re-formed after the lime
had absorbed the gas.

He found that the lime was lighter by just as much
as the gas weighed ; and he called this gas ' fixed air,' to
emphasise the fact that it could be ' fixed ' or absorbed by
lime and similar substances.

This first opened the way for the investigation of gases ;
it was a great discovery — perhaps one of the most fertile
which has ever been made. It is to be noted that Black
was not content with this, however ; for he recognised
that the fixed air from chalk was of the same nature as
steam from water. And just as it was necessary to heat
water so as to drive it into steam, so it appeared to him
that carbonic acid gas, to give ' fixed air ' a more modern
name, was a gas by virtue of the heat or ' caloric ' which it

HOW DISCOVERIES ARE MADE 119

contained. He went on to discover how much heat is
required to convert a known weight of water into steam.
He found that about fifty-four times as much heat is
required as is necessary to heat the same weight of water
from the freezing-point to the boiling-point. But the
steam is no hotter than the boiling water ; hence Black
called this heat the ' latent heat ' of steam, because it lies
hidden in the steam and does not affect a thermometer.
Black made quantitative experiments — that is, he not
merely made discoveries, but found the quantities in
which the changes took place.

The way was now plain for Priestley and Scheele. They
heated all kinds of substances : if they evolved gas, that
gas was collected and examined ; but neither Priestley nor
Scheele paid much attention to quantities. The methods
of dealing with gases had to be invented, moreover. And
while Scheele caught his gases in bladders, Priestley in-
vented, or rather reinvented, what he called a ' pneumatic
trough,' a vessel filled with water containing jars and
bottles standing inverted full of water. If the tube lead-
ing from the retort in which the substance evolving the
gas was heated was directed so that its open end was
directly under the mouth of the bottle, the escaping gas
entered the bottle and displaced the water; and when the
bottle was full, it could be corked, still under water, and
removed so that the gas could be examined.

It is usually the case that discoveries have to be accom-
panied by inventions ; the sequence is that to try any
new thing, a piece of apparatus has to be devised which
will effect the purpose — or perhaps an apparatus already
known has to be altered — so that it may almost be said
that invention and discovery go hand in hand.

For this reason it is very important that the discoverer
should be a good worker in all kinds of materials — in glass,
for most small pieces of apparatus can best be constructed

120 ESSAYS BIOGRAPHICAL AND CHEMICAL

of glass : in brass, for if anything of the nature of machinery,
such as pumps, stirrers, etc., is required, brass is perhaps
the most convenient material; in clay, for vessels are
wanted which will withstand a high temperature ; and of
recent years silica glass, made from fused rock-crystal, has
proved of great use, for it can be worked before a blow-pipe
fed with coal-gas and oxygen.

But to return to the discovery of oxygen. Priestley
heated oxide of mercury, or, as he called it, ' red precipi-
tate,' in a retort, and collected the escaping gas ; and he
found that a candle burned in it much more brightly than
in air; and, moreover, after having found that a mouse
could live in it longer than in the same volume of air,
confined in a bottle, he breathed it himself and found
that its effect was pleasant and exhilarating.

Similar experiments were made by Scheele with the
same result; but Scheele went much further. Having
noticed that a number of substances had the property of
making combustible bodies, such as wood, flour, and
charcoal, deflagrate, or burn more brilliantly when mixed
with them, he heated these substances, and found that
they too evolved oxygen gas. Among the substances
were red-lead, black oxide of manganese, nitre, and many
others ; so he established a general rule that those sub-
stances which can be mixed with charcoal to make a kind
of gunpowder will evolve oxygen when heated.

It thus became known that air contained a gas, amount-
ing to about a fifth — Scheele says a sixth — of its bulk,
possessing the property of making combustible objects
burn with greater vigour. Flame, therefore, was caused
by the action of oxygen, as the new gas was called later,
with combustible bodies.

It would take too long to consider the curious doctrine
of ' phlogiston,' an immaterial effluvium which was sup-
posed to escape when bodies burn ; I can merely mention

HOW DISCOVERIES ARE MADE 121

that Lavoisier, a celebrated French chemist, gave the
correct explanation of combustion — namely, that it is
caused by the union of oxygen with the substance burning.
Lavoisier, however, cannot be ranked as a great discoverer,
though he shone as an interpreter of the discoveries of
others.

Henry Cavendish, who did his best work between 1770
and 1790, discovered the composition of water; that it is
produced when oxygen and hydrogen unite; and he
determined with great accuracy the proportions by volume
in which the union of the two gases is completed. He
also attempted to show, by passing electric sparks through
a mixture of the inert gas of the atmosphere, nitrogen,
mixed with oxygen, that nitrogen was a single substance
and not a mixture ; nearly all the nitrogen disappeared
under this treatment, only about one hundred-and-
twenty-fifth of the whole being left. It would hardly
have been possible for him, in the existing state of know-
ledge, with the imperfect appliances which alone were
available at that time, to have identified his inactive
residue with 'argon,' a gas discovered more than a
century later ; for the spectroscope was then unknown,
and it is the chief means of identifying and characterising
gases, and indeed elements of every kind. This is an
example of how discovery has sometimes to wait on in-
vention ; for, until the instruments of research are invented,
it is almost impossible to confirm a discovery, even
although it may be genuine.

The true nature of flame, which, as before remarked,
has been a puzzle since the remotest ages, has had to
wait on invention for its discovery. When a current of
electricity of high tension, such as is produced by an
induction-coil or by an electric machine, is passed through
any rarefied gas, it gives out a peculiar and often a very
beautiful coloured light : sometimes red, as in the case of

122 ESSAYS BIOGRAPHICAL AND CHEMICAL

hydrogen or neon; sometimes bluish-white, as with
carbonic acid or krypton ; sometimes purple-red, as with
argon or nitrogen. When examined through a prism or
a spectroscope, this light is seen to consist of a number of
colours, which blend to give the colour seen with the
naked eye.

Thus the brilliantly red spectrum of hydrogen is easily
shown to be a compound impression ; the red light, which
is the brightest, is mixed with and slightly modified by
a blue-green and a violet light. Tubes which are well
adapted to show this light were invented by a German
physicist named Pliicker in the 'fifties. Twenty-five
years later, Sir William Crookes, with the aid of his
skilful assistant, Mr. Gimingham, improved the then
existing form of air-pump, invented by Dr. Hermann
Sprengel, so that it became capable of exhausting the
air much more completely than was previously pos-
sible.

He found that, at a much greater exhaustion than that
which causes gases to glow and give out their spectrum, a
current of high-tension electricity produced in the tube a
violet or a green phosphorescence, according as the glass
of which it was made contained lead and potash, or lime
and soda, combined with the silica, or sand.

Moreover, the position of this curious phosphorescent
glow depended on the shape and direction of the wire or
plate from which the negative electricity passed into the
tube. From a wire the glow proceeded in all directions
perpendicular with its length, so as to colour the tubes
immediately surrounding the wire with phosphorescent
light. If the wire, however, were terminated with a plate,
then the phosphorescent light appeared mostly between
the front of the plate and the positive wire of the vacuum-
tube. Supposing the plate were curved, so as to form a
concave metallic reflector, the light of what was evidently

HOW DISCOVERIES ARE MADE 123

a discharge was concentrated on a point at the focus of
the metallic mirror.

Moreover, if an object of any kind were placed at the
focus, and submitted to the discharge, it became intensely
hot ; or if it could move— if, for instance, it formed the
vanes of a little wheel or windmill — the wheel revolved
rapidly as if it were being bombarded by infinitesimally
small bullets. Crookes imagined that by being thus
highly rarefied, the gaseous matter changed so as to
become ' ultra-gaseous,' that it changed its state in some-
what the same manner as ice becomes water or as water
becomes steam.

It is interesting here to recall how Sir William Crookes
came to make these most remarkable discoveries. He
began by using a spectroscope to investigate the spectrum
or coloured light given out by the various constituents
into which he had analysed the dust which deposits in
the flues used to convey the sulphurous acid produced by
the burning of pyrites (a compound of sulphur and iron),
then (in the 'sixties) recently introduced as a source of
sulphur for the manufacture of sulphuric acid or oil of
vitriol. One of his precipitates, when examined with the
spectroscope, showed the presence of a bright green light;
and this was traced to the presence of a new element, to
which he gave the name ' thallium,' from the Greek
thallos, a green twig.

One of the first things done with a new element is to
try to discover its ' equivalent ' — that is, the proportion by
weight of the element which will combine with 8 parts
by weight of oxygen. (The number 8 is chosen, because
8 parts by weight of oxygen combine with 1 part of
hydrogen to form water.) The weighings require to be
very accurately made ; and a peculiarity which affects all
attempts to weigh very accurately must now be told of.
The question is often asked as a catch : — ' Which weighs

124 ESSAYS BIOGRAPHICAL AND CHEMICAL

most: a pound of feathers or a pound of lead?' The
usual answer is, ' They weigh the same.'

Although this is strictly true (for a pound is a pound,
whether of lead or feathers), a little consideration will
show that when the feathers are placed on one pan of a
pair of scales and the lead on the other, the lead takes up
far less room than the feathers; in other words, the
feathers displace much air, while the lead displaces little.
That is, the air which the feathers displace no longer
rests on the pan ; and if it were still there, the feathers
would weigh more. Hence a so-called pound of feathers
weighs less than it ought to by the weight of the air
displaced.

Now to overcome this difficulty and to avoid the some-
what complicated and uncertain calculations necessary to
ascertain the true weight of the things weighed, Sir
William Crookes devised a balance closed in by a case in
which a vacuum could be made. And it was while
obtaining this vacuum that he discovered that light
apparently (but really heat) appears to repel certain
objects more than others. Thus he was led to experi-
ment on vacuum-tubes and to perform all the beautiful
experiments which have made his name so famous. At
the same time he invented the ' radiometer,' a pretty little
toy for showing the repelling action of heat.

Here again we see the advantage of following up small
trails; they may widen to great and most important
roads. If Sir William had been content to weigh his
compounds of thallium in his vacuum-balance, as most
others would have done, and had not had the genius to
follow this side-track, he would have missed many of his
greatest discoveries.

A further great step was made when the German
physicist Lenard found that Crookes's ' rays ' — the ' fourth
form of matter' which he supposed to be repelled from

HOW DISCOVERIES ARE MADE 125

the negative pole of the Pllicker tube when very highly
exhausted — could pass out of the tube through a thin
' window ' of the very light and strong metal aluminium.
It is true they could not pass very far ; they soon became
scattered. Here was a discovery made with a set purpose.
Professor Lenard wished to decide the question whether
Crookes's ' rays ' were really due to a stream of corpuscles
or whether they were vibrations like those of light.

Sir William had previously found that if a magnet were
placed near the tube the path of the rays was no longer
straight, but curved. And Lenard observed that if the
aluminium window were placed so that a ' vacuum ' (not
a complete, but a nearly complete one) were on both sides of
the aluminium window, the 'rays' could be bent out of their
course by the magnet after passing through the window.

It must be remembered that these rays are not them-
selves visible ; it is only possible to see where they strike
by their causing phosphorescence. Professor Rontgen,
the celebrated German physicist, discovered in his turn
that if these rays be suddenly stopped — say by falling on
glass or metal — rays of another kind are sent on, which
have the power of affecting a photographic plate and of
rendering certain substances exposed to them phosphores-
cent; so that, as different kinds of matter have very
different powers of stopping Rontgen rays, it is possible to
photograph the bones of the body, although the flesh is
comparatively transparent to them. The bones, as it
were, cast their shadow ; or the shadow of the bones can
be thrown on a piece of card, painted with material which
phosphoresces and shines when exposed to the impact of
the rays.

I believe that Rontgen's discovery arose from an acci-
dental observation that a box of photographic plates left
near a Crookes's tube became 'fogged,' and he too had
genius to follow up this clue.

126 ESSAYS BIOGRAPHICAL AND CHEMICAL

We are getting on rather slowly, however, in the hunt
for an explanation of flame. A great step in advance was
made by the discovery of radium by Madame Curie.

Radium is a metal, the salts of which continually give
out ' Lenard rays,' or ' Crookes's rays.' And it is certain
that it is losing" substance during their emission.

Mr. Soddy and I have actually trapped and measured
one of the products which is being thrown off by radium
while these rays are being shot out; it is a gas called
' radium emanation.' And it in its turn decomposes and is
changed to some extent into the gaseous element helium,
which I discovered in 1895.

All the while that these changes are taking place, what
are called ' yS-rays ' (beta-rays) are being evolved, and the
opinion is now generally held that these so-called rays are
really negative electricity, and are identical with the
' cathode-rays ' of Lenard.

I have been frequently asked : ' But is not electricity a
vibration ? How can wireless telegraphy be explained by
the passage of little particles or corpuscles ? ' The answer
is 'Electricity is a thing; it is these minute corpuscles,
but when they leave any object, a wave, like a wave of
light, spreads through the ether, and this wave is used for
wireless telegraphy.'

It has been found that flames are capable of conducting
electricity, while gases, under the usual atmospheric
pressure, are very good insulators, and sparks can pass
through air only when the current is one of very high
tension. Now, in flames rapid chemical action is taking
place; compounds are burning— that is, their constituents
are in the act of uniting with oxygen.

Although it is not certain that /3-rays — or, to give their
other name, corpuscles of electricity — are being shot out
during such changes, it is not improbable that they are.
No doubt they impinge on the neighbouring atoms and

HOW DISCOVERIES ARE MADE 127

set them in rapid vibration ; and they may even break up
molecules and cause them to assume other forms of
combination. And in doing so, very short electric waves
are sent out through the ether, and these are what we
term ' light,' and ' radiant ' heat.

There are several other lines of evidence which support
this notion. For example, a pure gas cannot be heated
red-hot or made to glow by heat alone. There must be a
chemical change of some kind at the same time. Again,
a Welsbach incandescent gas mantle, if made of pure
thoria (and that means ' nearly pure,' because we are not
acquainted with really pure substances), does not give out
much light when heated, but if some other earth, such as
oxide of cerium, is mixed with the thoria, the familiar
brilliant incandescence is produced when it is heated by a
Bunsen burner. The ' pencil ' of a Nernst lamp is made
chiefly of zirconia, another earth ; and here, again, unless
the zirconia is mixed with a trace of some other oxide, it
will not glow very brightly when a current of electricity
is passed through it. In all these cases there is almost
certainly chemical change, and also, no doubt, evolution of
corpuscles of electricity which set the ether vibrating and
so produce light and heat.

It may be asked : ' Do substances not lose weight when
corpuscles are being shot out ? ' Professor Landolt, of
Berlin, has been making experiments on the gain or loss
of weight when a weighed quantity of substances capable
of chemical change are mixed in a closed vessel ; and he
finds that in many cases there is a minute loss of weight.
Perhaps that is due to the escape of corpuscles ; but too few
experiments have been made to allow of a definite answer.1

Perhaps, too, the corpuscles when expelled are not
moving very rapidly, and are thus absorbed by the sides
of the vessel in which the reaction takes place ; and this

1 He has since shown that there is no change of weight.

128 ESSAYS BIOGRAPHICAL AND CHEMICAL

may also be the case with flames. A flame, however, if
brought near an object containing an electric discharge
will discharge it; and this may possibly be due to the
action of electric corpuscles on the charged object.

It will be seen, then, that we do not know yet with
certainty what flame is, but we are getting on the track.
And the direction in which to make experiments is clear.
Whosoever asks shall receive, but he must ask sensible
questions in definite order, so that the answer to the first
suggests a second, and the reply to the second suggests a
third, and so on. If that course be followed, it will
certainly result in discoveries, many of which may be
important and lead to inventions of great practical value.
For, indeed, an invention is often definable as a method
for utilising a discovery.

THE BECQUEREL RAYS1

IT is remarkable how the writings of ancient authors often
contain a forecast of subsequent discoveries. Puck's pro-
jected girdle round the earth, which was promised com-
pletion in forty minutes, has been surpassed many hundred
times by the rate of the electric current in a telegraph-
wire ; and Robert Boyle's suggestions regarding the nature
of the air are on the high-road towards verification. He
wrote, about the year 1670: 'Our atmosphere, in my
opinion, consists not wholly of purer aether, or subtile
matter which is diffused thro' the universe, but in
great number of numberless exhalations of the terr-
aqueous globe; and the various materials which go to
compose it, with perhaps some substantial emanations from
the celestial bodies, make up together, not a bare indeter-
mined feculancy, but a confused aggregate of different
effluvia.'

Up to 1894, it was supposed that our atmosphere con-
sisted mainly of the two gases, nitrogen and oxygen, together
with minute quantities of carbonic acid, water-vapour,
ammonia, peroxide of hydrogen, and ozone ; but in that
year it was shown to contain a not inconsiderable amount
of an inactive gas, argon ; and crude argon has since been
found to contain minute quantities of no fewer than four
other similar gases. Small traces of hydrogen have also
been discovered in air; although a large percentage of

1 An article which appeared in the Contemporary Review, 1902.

I

130 ESSAYS BIOGRAPHICAL AND CHEMICAL

hydrogen would render air explosive (for water is formed
with explosive violence when hydrogen and oxygen com-
bine), yet traces of hydrogen may coexist with oxygen
without combination, except when the mixture is actually
in contact with a flame.

These, however, are not the only constituents of the
atmosphere; and in the following pages an account will
be given of certain phenomena which render it* exceed-
ingly probable that still more ' subtile matter ' is on the
eve of discovery.

In order to follow the course of events, it is first neces-
sary to devote some attention to the supposed nature of
light. Owing to its being perceived by our special organ
of sense, the eye, it early attracted attention. At first
believed to consist of corpuscles, shot out from the lumin-
ous body, it is now recognised as arising from the vibra-
tions of a medium pervading all space, termed ether ; and
the propagation of light takes place much as waves spread
in a pond, except in this : the particles of ether, unlike
the waves of water, are not restricted in their motion to
one plane, but the oscillations may take place in all direc-
tions at right angles to the direction of propagation.
There appears, however, to be no limit to the mode or
magnitude of the ethereal waves ; and though it cannot be
positively stated that the wave-motion ever takes place,
like sound waves, in the direction of propagation, still that
mode of propagation of waves is not excluded. It is cer-
tain, however, that such a mode of transmission does not
correspond with the nature of light, which consists wholly
of transverse vibrations.

Just as it is possible to measure the distance between
the crests of the waves of the sea, so it is possible to deter-
mine the distance between the crests of the waves of light,
or in other words, to measure the wave-length of light.
And it has been discovered that all the visible rays of

THE BECQUEREL RAYS 131

light are comprised in less than an octave; that is, the
longest visible waves are not twice as long as the shortest
visible. Their length, moreover, is not inconceivably
minute. The twenty-fifth part of an inch, or a millimetre,
although a small distance, is easily seen with the naked
eye ; indeed, the twentieth part of that length can still be
estimated without the aid of a lens. The average length
of a light- wave is about the hundredth part of that dis-
tance, or about the two-thousandth of a millimetre. The
thousandth part of a millimetre is termed a micron, the
symbol for which is the Greek letter p ; the wave-length
of deep red light is f p, and of violet light fyu,.

There are, however, ethereal waves which cannot be
seen. Those of greater wave-length give rise to the sensa-
tion of heat ; they are termed ' infra-red ' waves ; while
those of shorter period are accessible to photography, for
they change the nature of the compounds of silver which
form the sensitive coating of a photographic plate, and
can thus be recognised; they are termed 'ultra-violet'
waves. One of the difficulties of tracing the existence of
the short wave-lengths by photography consists in the
absorptive power which glass and air have for such waves.
A pane of glass, though transparent to ordinary light
waves, is nearly opaque to ultra-violet waves. Quartz or
crystal, of which spectacle-lenses are generally made, is
much more transparent to vibrations of short wave-
lengths ; but even quartz has its limits. By an ingenious
contrivance for exposing a sensitive plate in a vacuum, so
that the absorption of the air did not influence the result,
Schumann succeeded in chronicling the existence of waves
only -J^/JL in length. On the other hand, Langley, by
means of an exceedingly delicate apparatus for detecting
heat-vibrations, termed a bolometer, has detected waves
as long as 30 p. Between that wave-length and one two
hundred times as great, six millimetres, there is a gap in

132 ESSAYS BIOGRAPHICAL AND CHEMICAL

our knowledge ; the longer waves are the vibrations the
discovery of which was due to Hertz, which are produced
electric oscillations, and which are now being utilised
for telegraphy without wires.

It is, however, with the shorter, and not with the longer
vibrations, that we have to do. These are not incom-
mensurable with the dimensions of a molecule, for the
larger molecules are believed to be about the millionth
of a millimetre in diameter, or about one hundredth of
the shortest wave-length which has been measured. And
just as an interposed grating offers little opposition to the
course of a large wave of water, while it will stop ripples,
so matter is sufficiently fine-grained not to oppose the
spread of a Hertzian wave of great wave-length, although
it may stop light and other vibrations of shorter wave-
length. It is known, indeed, that the signals of wireless
telegraphy are not blocked by material obstacles such as
houses, or even hills, while a very thin slice of brick or
stone is opaque to light.

When two thin strips of gold-leaf are suspended from a
glass support, and given an electric charge, they diverge,
owing to the repulsive force between the charges of elec-
tricity which they contain. They will remain apart for
an indefinite time, provided the charge cannot escape
through the support. But on exposure to ultra-violet
rays, the electroscope, if charged with negative electricity,
is at once discharged, and the leaves fall together. The
electricity finds some means of leaving the leaves of gold
and they drop, under the action of gravity. The rays do
not, however, discharge a positively charged electroscope.
This is one of the most characteristic properties of the
ultra-violet rays, and, as will shortly be seen, of rays from
sources other than luminous bodies. This fact was dis-
covered by Hertz.

The Becquerel family has contributed much to our

THE BECQUEREL RAYS 133

knowledge of the phenomena of radiation, and furnishes
as conspicuous an example as the Herschels of the her-
edity of a scientific faculty. Antoine Charles, born in
1788, was famous for his electric researches; Edmond, his
son, born in 1820, was author, with his father, of a treatise
on Electricity and Magnetism, and investigated the phe-
nomenon of phosphorescence, of which more anon ; and
Henri Becquerel, born in 1852, while engaged in extend-
ing his father's work, made the wonderful discovery of
the emission of rays from certain minerals containing
the rare metals uranium and thorium. We must first,
however, consider Edmond Becquerel's work.

Certain substances, after illumination, do not at once
cease to give back light, but continue to glow, even after
the source of light has been removed. Such substances,
one of the best known of which is fluor-spar, are called
phosphorescent. Some years ago, an attempt was made to
utilise one of such substances — a carbonate of lime con-
taining traces of sulphide of manganese — under the name
of ' luminous paint.' Another class of substances has the
property of transforming the vibrations they receive when
illuminated into vibrations of a different period; among
these are extract of horse-chestnut, and many artificial
colouring-matters, one of the most striking being the
lovely pink dye, eosin. Such bodies do not continue to
emit light after excitation ; they were differentiated from
the former by Edmond Becquerel, and are termed fluor-
escent. The tendency of these substances is to convert
short wave-lengths into longer ones. Thus a solution of
acid sulphate of quinine, which is perfectly colourless by
transmitted light, is opaque to ultra-violet rays. It reflects
them, and at the same time increases the wave-length ;
hence by reflected light the solution appears to possess a
violet shimmer.

It was in 1838 that Faraday investigated the luminous

134 ESSAYS BIOGRAPHICAL AND CHEMICAL

appearance which accompanies the passage of a high-
tension electric current through rarefied gases. Each gas
gives out a soft, coloured light, totally different from the
lightning-like sparks which pass between the positive and
negative poles through gases at ordinary atmospheric
pressure. The pressure must be reduced to about one-
hundredth of its normal amount before such phenomena
begin to appear; but the actual reduction of pressure
depends on the particular gas submitted to the dis-
charge. Under such conditions hydrogen glows with a
red light ; air with a pale violet glow ; and carbonic acid
has a steel blue appearance. The resistance of such
rarefied gases to the passage of the electric current is
much less than of gases at atmospheric pressure. As with
solid conductors, it depends on the distance between the
poles and the particular kind of matter employed.
Hittorf, the eminent electrician, Professor in Mtinster,
was the first to conduct experiments at still lower
pressures, on still more rarefied gases, and he noted an
increase in the resistance of the gas to the passage of
electricity. Further, he observed that from the negative
electrode, or cathode, the glow proceeded in straight lines,
so as to cast the shadow of an interposed object on the
opposite wall of the tube. He discovered, too, that such
rays can be deviated by a magnet, a discovery made for
the electric arc by Sir Humphry Davy in 1821. Sir
William, then Mr., Crookes took up this subject in 1878,
simultaneously with M. Goldstein, and has made it
popular, by reason of the ingenious experiments which he
devised to exhibit the rectilinear course of these rays.
He devised a theory, moreover, to account for the recti-
linear path, namely, that the electric current when it
leaves the negative pole attaches itself to the molecules of
gas, which, projected with great velocity, will pursue a
parallel path, if the cathode is a flat piece of metal, or can

THE BECQUEREL RAYS 135

be focussed to a point, if the cathode be given the form of
a concave mirror. Objects placed in the focus of such a
mirror are bombarded, according to Sir William, and may
be heated to whiteness by the impacts they receive from
the prodigious number of moving molecules. Goldstein,
on the other hand, conceived the phenomena to be due to
a transmission of energy, apart from the conveyance of
material particles ; but he gave no precise definition of the
nature of this transmitted energy. In 1883, however,
Professor Wiedemann of Leipzig made the suggestion
that possibly such ' cathode rays,' as the rectilinear dis-
charges have since been termed, are composed of radia-
tions of very short wave-length, shorter even than those
of the most ultra-violet light. The same conception was
held by Lenard. But while the cathode rays are deviated
by a magnet, light waves are uninfluenced ; and this forms
an argument in favour of the former being due to pro-
jected particles. The suggestion has also been made, but
on no sufficient grounds, that these phenomena are attri-
butable to a longitudinal vibration of the ether, the waves
being thus analogous to sound-waves in air — alternate
condensations and rarefactions; or to choose a visible
analogy, the longitudinal vibrations of a spiral spring, in
which the coils periodically come closer together at one
point of space, and then recede and become wider apart.
A fourth hypothesis, similar to, yet differing from that of
Crookes, is held by Professor J. J. Thomson of the
Cavendish Laboratory, Cambridge. His view, which
appears to be well supported by experimental evidence,
is that each molecule of gas, in absorbing its electric
charge, dissociates, or splits up, into two or more charged
atoms or groups of atoms. Such charged portions of
matter have long been taken for granted as existing
during the passage of an electric current through a con-
ducting liquid, and were named by Faraday, ions, or

136 ESSAYS BIOGRAPHICAL AND CHEMICAL

travellers. An important argument in favour of this
contention is, that the heat developed in such tubes is
proportional to the intensity of the current, and not to the
square of the intensity, as would be the case were the
passage of electricity one of ordinary conduction. Thomson
attributes the heat to the recombination of the ions to
molecules, after discharge ; and the number of ions would
obviously be proportional to the intensity of the current
and not to its square.

Goldstein and Crookes both thought that ordinary
matter, such as glass or metal, was opaque to such
cathode-discharges ; but Lenard, following a suggestion of
Hertz's, carried out at Bonn a beautiful series of experi-
ments, which showed that the cathode rays could pass
through a thin piece of aluminium foil, and be prolonged
outside of the exhausted tube. Not only could they pass
through ordinary air, although not to such a distance as
through rarefied gases, but they also passed through a
vacuum as perfect as could be produced by a mercury-
pump, aided by intense cold to condense mercury- vapour
out of the empty space. It appeared that the absorbing
power of different gases is proportional to their specific
mass.

The velocity of propagation of such cathode rays has
been measured by an ingenious process by Professor J. J.
Thomson. It is found to be approximately 200 kilo-
metres, or about 124 miles a second. This, however, is
enormously less than the velocity of light or of electric
waves through the ether, which approximates to 180,000
miles a second. The accidental discovery by Professor
Rb'ntgen in 1896 that some flakes of platinocyanide of
barium, placed near a Hittorf tube which was wrapped up
in black paper, emitted a phosphorescent light, led to a
great development of the subject. It was soon discovered
that even behind a book of 1000 pages, or a plate of

THE BECQUEREL RAYS 137

aluminium half an inch thick, or a wooden board, lumin-
escence was still produced. Rontgen investigated the
transparency of various objects, and soon discovered that
while skin and flesh are nearly transparent to these
radiations, bone is comparatively opaque, and may be
made to throw its shadow on a photographic plate or on a
screen covered by phosphorescent material. The surgical
bearing of this discovery was at once evident ; and by help
of ' skiographs ' or shadow-writing the presence of a bullet
embedded in the tissue can be recognised, and its exact
situation localised ; and in cases of fractures of bones,
their exact shape can be made out, and they can be
successfully set, for it is always possible to examine the
position of the fractured ends through envelopes of
bandages, which themselves are nearly transparent to
Rontgen or X-rays.

One of the most remarkable properties of these rays is
that they cannot be refracted by passage through a prism,
nor apparently reflected from any object, however smooth
and well-polished, nor can they be polarised. They are,
however, absorbed by different substances unequally, and
apparently the denser the substance the greater its absorb-
ing power.

It might be supposed at first blush that the X-rays of
Rontgen were identical with cathode rays. But if this
were the case the X-rays should pass straight from the
cathode through the walls of the tube, and proceed in a
straight line ; as a matter of fact, their point of origin can
be displaced with a magnet, and if a spherical bulb be
used to contain the cathode, each point on the bulb is a
centre of emission, sending its radiations in all directions.
Now Lenard had recognised that cathode rays could be
differentiated into two distinct kinds. Suppose that they
were made to pass through a hole in a block of lead, and to
impinge on a photographic plate, if a magnet were placed

138 ESSAYS BIOGRAPHICAL AND CHEMICAL

at one side, not only was there the image of a circle
exactly opposite the hole, but also, at some distance from
the circular spot, a diffused drawn-out impression, as if
some of the rays had been unequally deviated by the
magnet, and had impressed the plate separately. It is
therefore probable that cathode rays contain some
X-rays.

The wave-length of light can be measured by reflection
from a metal plate on which from 14,000 to 25,000 parallel
lines are ruled in each inch ; such a prepared plate is
termed a 'grating'; the modern gratings, which are
wonderfully accurately ruled, are made by Mr. Brashier
of Alleghany, New York State, by means of apparatus
devised by the late Professor Rowland of Baltimore.
Careful measurements by M. Perrin have proved that if the
X-rays are due to ethereal vibrations at all, these cannot
possess a wave-length greater than 0*04 p, that is, less than
half the shortest- waved ultra-violet vibrations which have
ever been photographed.

Again, when light is passed through a slice cut from
a crystal of tourmaline it is said to be polarised ; it can
pass through a second plate of tourmaline if held in a
particular position, but if the second plate be rotated so
that its second position is at right angles to its first, the
light is cut off, and fails to pass through the second plate.
M. Becquerel found that X-rays cannot be polarised ; they
pass easily through plates of tourmaline in whatever
position relatively to each other they be placed. On the
other hand, the rays emitted by phosphorescent bodies,
which may be termed the Becquerel rays, are capable of
polarisation. Hence they cannot be identical with X- or
with cathode rays.

Lastly, it will be remembered that ultra-violet rays
discharge negatively electrified bodies; they are without
rapid action on bodies possessing a positive charge. But

THE BECQUEREL RAYS 139

X-rays discharge electrified bodies equally well, whether
they be charged positively or negatively.

There is accordingly a certain degree of probability in
favour of the view that cathode rays are due to molecular
or ionic bombardment ; but they are generally mixed with
X-rays, which are apparently independent of matter for
their propagation, and are therefore to be considered as
due to disturbances of the ether. Ultra-violet rays, on
the other hand, must be ethereal waves of very short
wave-length ; but they have the power of splitting gaseous
molecules into charged atoms or groups of atoms, termed
ions. It may be calculated, too, that the atoms conveying
cathode-rays have a velocity of 124 miles a second; it
would follow that of such atoms a single gram, or about
one-thirtieth of an ounce, must have the same energy as
a locomotive of 80 tons weight rushing at the rate of
50 miles an hour ! No wonder, then, that they penetrate
thin sheets of metal and embed themselves in glass.

In 1896 M. Poincare, the well-known mathematician,
suggested that all fluorescent substances might emit
Rontgen rays ; being guided to this guess by the hypo-
thesis that it is the glass, against which the Rontgen rays
strike, which phosphoresces and emits the rays. This
suggestion was almost at once verified by M. Charles
Henry, when he discovered that sulphide of zinc, a sub-
stance which shows marked phosphorescence, greatly
increases the effect of X-rays when placed in their path.
M. Henri Becquerel, too, in the same year, found that rays
were emitted from a compound of the metal uranium,
which affected a photographic plate wrapped in black
paper, sufficient to exclude rays of direct sunlight. This
power to affect a sensitised plate persists long after all
visible phosphorescence ceases. Moreover, it is unneces-
sary to expose uranium salts to light before they are
capable of producing a photographic image, for these

140 ESSAYS BIOGRAPHICAL AND CHEMICAL

compounds may be prepared in the dark and still possess
actinic power. And the rays emitted from them have the
power of discharging both positively and negatively
electrified bodies. Not merely salts of uranium possess
this property, but even metallic uranium itself, a dark-
coloured, brittle metal, which emits sparks of fire when
shaken in a bottle, a phenomenon due probably to
oxidation.

Shortly after this discovery of Becquerel's, Madame
Curie, a Polish lady working in Paris, discovered that a
certain specimen of pitchblende, the common ore of
uranium, possesses the properties of uranium, and in
greater measure. Pitchblende, though consisting mainly
of an oxide of uranium of the formula U308, contains
small amounts of other elements. On separating these,
Monsieur and Madame Curie found that the bismuth
obtained from this source is particularly radio-active,
while ordinary bismuth shows no trace of that property.
Attributing this behaviour to its containing a new element,
they patriotically named it 'polonium,' in allusion to
Madame Curie's nationality. But it was not long before
they discovered that it was not only the bismuth which
exhibited radio-activity, but also the barium; and they
inferred the presence of a second element, naming it
'radium.' A third substance has also been separated
from the same uranium ores by Debierne, who, following
precedent, has termed it ' actinium.' It appears to be
associated with another element, titanium, contained in
pitchblende ; and thorium, an element whose compounds
were discovered to possess radio-activity by G. C. Schmidt,
must be added to the list. We have therefore at present
no fewer than four radio-active substances: polonium,
associated with bismuth ; radium, with barium ; actinium,
with titanium ; and thorium. Associated with thorium is
a much more powerfully radio-active material, to which

THE BECQUEREL RAYS 141

the name radio-thorium was applied by its discoverer,
Otto Hahn.

Besides the properties already mentioned, radium, and
presumably the others, have the curious property of
changing a spark-discharge from an electric machine or
a RuhmkoriFs coil into a violet glow-discharge; the
interposition of a piece of lead, however, re-establishes
the spark-discharge ; and if barium bromide containing
radium be held on the forehead between the closed eyes
in a dark room, a distinct luminous haze is visible after
a few seconds. The actinium rays, indeed, are said to be
100,000 times as powerful as those of uranium. Very
powerfully radio-active preparations of barium chloride
and bromide are now manufactured by various firms by
processes devised by Madame Curie and by Professor
Giesel.

A new light has been thrown on all these phenomena
by Professor Rutherford, who has found that thorium
compounds give out an ' emanation,' which may be likened
to one of Boyle's ' exhalations of the terraqueous globe.'
Dr. Russell had previously discovered that photographic
plates are affected by hydrogen dioxide vapour, which
appears to be produced in small amount under the most
varying conditions ; but Rutherford's exhalations persisted
under treatment which would have been fatal to hydrogen
dioxide ; moreover, these emanations rapidly discharge
electrified bodies, a property which hydrogen dioxide does
not possess. The existence of such emanations (of which
more hereafter) must be borne in mind in forming a
judgment of the statements made about these various
radiations.

Radio-active substances can communicate transitory
radio-activity to all kinds of matter, metals, glass, paper,
etc., which then for a short time possess radio-activity
equal to ninety times that of uranium. They lose the

142 ESSAYS BIOGRAPHICAL AND CHEMICAL

property more rapidly, however, when heated or washed.
Even distilled water acquires radio-activity, when placed
near radium chloride under a glass bell-jar ; the water
rapidly loses its power in an open vessel after removing
it from the proximity of the radium; and even when
sealed into a glass tube it loses power after a few days.
On the other hand, a solution of a radium salt (e.g. radio-
active barium bromide) loses activity on exposure to air,
but regains it on being kept in a sealed tube.

MM. Curie and Debierne find that this induced radio-
activity is greatly increased when the radium compound
is placed in a small open vessel under a bell-jar, and sheets
of various materials are exposed under the same cover.
Even behind leaden screens the activity is induced. If
they are in contact with the vessel containing the radium,
or with the walls of the enclosed space, only the exposed
surfaces are rendered radio-active. The activity of such
sheets of material induced by a specimen of barium
bromide containing radium, and of which the mean atomic
weight of the mixture of metals is 174 instead of 137 (that
of barium), is 8000 times that of a piece of uranium of the
same dimensions. As long as the sheets are left in the
enclosure, the activity persists ; if removed, it disappears
in a few days. This conveyance of induced radio-activity
is equally brought about if the radium compound is
placed in one vessel, and the sheets in another, connected
with the former by means of a capillary tube ; but if
communication between the vessels is cut off, the trans-
mission of activity ceases.

It is very remarkable that this transference of radio-
activity is confined to radium and actinium; polonium
compounds do not appear to possess the property of
giving off emanations. It may be that this difference
is connected with the fact discovered by Becquerel that
while his rays (those of radium and actinium, probably),

THE BECQUEREL RAYS 143

like cathode rays, are deviable by a magnet, those of
polonium resemble X-rays in being unaffected. Curie,
on the other hand, states that both deviable and undevi-
able rays are emitted from radium as well as from
polonium, and that the non- deviable rays are stopped by
a piece of thin aluminium foil. None of these rays appear
to be polarisable, nor do they show refraction when passed
through a prism.

Becquerel also discovered that air, left in contact with
some radio-active substances, discharges electrified bodies ;
indeed, it is impossible to charge an insulated conductor
in a room in which any such preparations have been
exposed. This power of inducing air to discharge electri-
fied bodies persists for at least a year, even although the
preparation has been kept in the dark all the time; it
cannot therefore be supposed that light-energy is in any
way transformed into such radiations.

In Curie's experiments on induction it was found that
provided the vessel containing radium was kept vacuous,
the emanations had no longer the property of inducing
radio-activity in sheets of metal, etc., exposed in the same
vessel. It appears possible, therefore, to pump off the
radio-active matter; and the natural conclusion is that
it is a gas. The gaseous matter has been collected, or at
least air charged with it, and it displays marked chemical
action, as well as high radio-activity. It converts oxygen
into ozone, and the glass vessels which contain it, if
formed of soda-glass, turn violet, and then black, owing
to some change. Becquerel, too, remarks on the destruc-
tive action of radium rays on the skin; they discolour
rock-salt, change yellow phosphorus to red, and destroy
the germinating power of mustard and cress seeds.

On the hypothesis that the radiation of radium is
produced by the escape of material particles which
bombard the walls of the containing vessel, the velocity

144 ESSAYS BIOGRAPHICAL AND CHEMICAL

of such particles can be determined by a device which
may be illustrated thus : Imagine a bullet fired from a
rifle placed horizontally, at some little distance above the
ground ; the bullet will be attracted to the earth, and will
fall to the ground after it has gone a certain distance.
The factors which determine the spot at which it will
strike the ground (excluding the retarding influence of
air) are its speed, and the attraction of the earth. If the
attraction is known, the speed can be calculated. This
analogy illustrates, although imperfectly, the method of
arriving at the speed of these impelled particles. They
are deviated by a magnetic field, and have a trajectory
just as a rifle-bullet has; and their speed has been cal-
culated by Becquerel at 160,000 kilometres or 100,000
miles per second. This estimate differs greatly from the
one previously mentioned for cathode rays.

In conclusion, it has been suggested that the existence
of such radiations and emanations may be attributed to
the existence of ' electrons ' in the free state. An electron,
it may be explained, is an electric charge which attaches
itself to an atom of an element, thereby converting it into
an ion. The act of solution in water of such a substance
as common salt is now currently held to cause the atom
of sodium to separate from the chlorine atom, while each
acquires an electric charge, the sodium combining with a
positive electron, the chlorine with a negative one, thus :
NaCl + water + ®0 = Na® + water + C10 +
water; the neutral molecule of electricity, consisting of
two oppositely charged electrons being thus dissociated.
Now it is conceivable that such a substance as pitchblende
or its radio-active constituents may combine with one of
the electrons, liberating the other. It has, indeed, been
shown by the Curies that radium rays charge negatively
the bodies which receive them, while the radium prepara-
tion acquires a positive charge.

THE BECQUEREL RAYS 145

Whatever be the true explanation of these mysteries,
it cannot be denied that they form the beginnings of
what may, and almost certainly will, affect the material
future of the human race. When we consider the begin-
nings made by Gilbert, by Franklin, by Volta, and by
Faraday, and contrast them with the outcome of these
discoveries, the electric telegraph, and the dynamo
machine, we cannot avoid the inference that the future
has in store even greater developments than these. It
is true that investigators like Hertz, Lenard, Becquerel,
and the Curies do not make practical application of their
discoveries ; but there is never any lack of men who
discover their practical value, and apply them to ends
useful to mankind. All the more reason, therefore, that
every encouragement should be given to the investigator,
for it is to him that all our advances in physical and
material well-being are ultimately due.

WHAT IS AN ELEMENT?

IT was for long held that things around us, animals,
vegetables, stones, or liquids, partook of the properties of
one or more of the elements — Fire, Air, Earth, or Water.
The doctrine was a very ancient one; it probably
originated in India; it reached our forefathers through
the Greeks. Fire was supposed to be ' hot and dry ' ; air,
' hot and moist ' ; water, ' cold and moist ' ; and earth,
' cold and dry.' And substances which partook of such
qualities were supposed to contain appropriate amounts
of the elements, which conferred on them these pro-
perties.

But in the reign of Charles n. of England, about the
year 1660, Robert Boyle, an English philosopher and
chemist, restored to the word element the meaning which
its derivation implies. ' Element,' or elemens in Latin, is
supposed to be derived from the three letters L M N ; and
to denote that, as a word is composed of letters, so a com-
pound is composed of elements. Boyle, in his celebrated
work The Sceptical Chymist, restricted the use of the
word element to the constituent of a compound ; and
that is the meaning which is still attached to the
term.

It has often been asked : Does a compound contain an
element ? Are the elements actually in the compound ?
If this means, for example, that iron is present as iron in

148 ESSAYS BIOGRAPHICAL AND CHEMICAL

iron-rust, the answer must be : No. The properties of
rust are wholly different from those of iron; no iron
particle can be detected in the rust by any tests which are
suitable for the recognition of the metal as such. But if
it is meant that iron if exposed to damp air changes into
rust, and that by suitable treatment metallic iron can be
extracted from rust, then the answer must be in the
affirmative.

The fact that an element, when it combines with other
elements, entirely loses its original properties, led to the
not unnatural supposition that it should be possible to
change an element into another, or to transmute it. Long
before the notion of ' element ' was formulated by Boyle,
innumerable attempts had been made to convert one
metal into another ; and, indeed, it would appear on the
face of it to be much easier to transmute lead into silver
or gold than to convert it into the yellow earthy powder
which it becomes when heated in air. For on the old
doctrines, the properties of gold — its lustre, its ductility,
its melting in the fire — were much more similar to those
of lead than the properties of litharge or oxide of lead,
produced by heating lead to redness in air. After Boyle's
day, however, it gradually came to be seen that certain
substances resisted all such attempts to change them into
others without increasing their weight. For example, all
changes in nature not of a temporary and evanescent charac-
ter which iron can be made to undergo, are accompanied
by an increase in the weight of the iron ; they are produced
by the combination of iron with other elements, and the
addition of another element to iron invariably increases
the weight, for the weight of the combining element is
added to that of the iron, and the result is a compound
differing in properties from iron. It was slowly discovered
that about seventy substances must be classed as elements
— the minimum number of the present day is seventy-

WHAT IS AN ELEMENT ? 149

four — and of these ten are gases, two are liquids, eight
elements are usually classed as non-metals, since they do
not possess the lustre and some of the other properties of
metals ; and the remainder are metals. These substances
are classified as elements solely because no attempts to
convert one into another have up till now been successful ;
not because such change is in the nature of things im-
possible. But inasmuch as the properties of these
elements, and the changes which they undergo on
being brought together with other elements or compounds,
have been the subject of an enormous number of experi-
ments, and because no hint of transmutation has been
found, the conclusion as regards the immutability of
elements has been arrived at. Hence the ' transmutation
of elements ' has generally been regarded as impossible,
and as unattainable as perpetual motion, or as the ' quad-
rature of the circle.'

Speculation, however, has a deep fascination for many
minds ; and it has been often held that it is not im-
possible that all elements may consist of a primal
substance — 'protyle,1 as it has been called— in different
states of condensation. It will be worth while to spend
a few minutes in considering the reasons for this
opinion.

About the beginning of last century, John Dalton
revived the old Greek hypothesis that all matter, elements
included, consists of atoms or minute invisible particles ;
these, of course, like the matter which is formed of them,
possess weight. Although they are so minute that any
attempt to determine their individual weight would be
out of the question, Dalton conceived the idea that at
least their relative weights could be determined, by ascer-
taining the proportions by weight in which they are pre-
sent in their compounds. The compound of hydrogen
and chlorine, for example, commonly known as muriatic

150 ESSAYS BIOGRAPHICAL AND CHEMICAL

or hydrochloric acid, consists of one part by weight of
hydrogen combined with 35J parts by weight of chlorine ;
and as it is believed to contain one atom of each element,
it follows that an atom of chlorine is 35i times as heavy
as an atom of hydrogen. On the same principle, the
relative weights of the atoms of other elements were
determined. And so, taking the weight of the lightest
atom, hydrogen, as unity, the atom of nitrogen weighs
14 times as much, of oxygen 16, of iron 56, of lead 207,
and so on.

Attempts to classify elements according to their proper-
ties soon followed ; and at first the divisions were some-
what arbitrary. The non-metals were distinguished from
the metals by their lack of lustre, their feeble power of
conducting heat, and the fact that their oxides when
mixed with water generally formed acid substances, while
those of the metals were earthy, insoluble powders. Cer-
tain of the metals, which either do not unite with or are
difficult to unite with oxygen at a red heat, were called
' noble ' metals ; others, which are at once attacked by
water, such as sodium and potassium, and which give
soapy liquids with a harsh taste, were named 'metals
of the alkalies/ and so with the rest. In 1863, however,
Mr. John Newlands, a London analyst, was successful in
arranging the elements in groups, so that each element
in a horizontal column showed analogy with others in the
same column. He found that by writing the names of
the elements in horizontal rows, beginning with the one
of lowest atomic weight, each eighth element possessed
properties similar to those of the elements which pre-
ceded or followed it in the vertical columns. And in
general the composition of the compounds of such
similar elements was similar. The first two lines of
such a table are reproduced here, so as to show what is
meant : —

WHAT IS AN ELEMENT? 151

Name . . Lithium. Beryllium. Boron. Carbon. Nitrogen. Oxygen. Fluorine.
Atomic Weight .7 9'1 11 12 14 16 19

Name . . Sodium. Magnesium. Aluminium. Silicon. Phosphorus. Sulphur. Chlorine.
Atomic Weight . 23 24'4 27'1 28"4 31 32 35'5

If one were to proceed further in the same manner, we
should find five elements in the first vertical column —
namely lithium, sodium, potassium, rubidium, and
caesium. All of these are soft metals, easily cut with a
knife, white in colour like silver, rapidly tarnishing in air,
attacked violently by water so that they either catch fire
or run about on the surface of the water and rapidly dis-
appear. Their compounds with chlorine each consist of
one atom of each element : for example, using Na
(natrium) as the symbol for one atom of sodium, and Cl
for one atom of chlorine, the composition of the com-
pound of chlorine with sodium (common salt) is expressed
by the formula NaCl, implying that the compound is
formed of one atom of each element. So with the
others: the chloride of lithium is LiCl, of potassium
KC1, of rubidium RbCl, and of csesium CsCl. They all
resemble common salt ; the taste is similar in all cases,
the salts dissolve in water, they are all white in colour,
they all crystallise in cubes, and possess many other pro-
perties in common. The oxides, too, are all powders,
which dissolve in water and give liquids with a soapy
feel and a burning taste. For these and other similar
reasons, all these elements are believed to belong to the
one class.

Let us take an example, too, from the other end of the
table. Fluorine, the first of the column, is a pale yellow
gas, with a suffocating odour. It combines instantly with
hydrogen, yielding a colourless gas, soluble in water, and
giving an acid liquid, which corrodes many metals.
Chlorine, the second member, is a greenish yellow gas,
very similar in properties to fluorine. The third member,

152 ESSAYS BIOGRAPHICAL AND CHEMICAL

bromine, is a dark red liquid, but at a somewhat lower
temperature than that of boiling water it changes into a
red gas, with a smell similar to that of chlorine ; iodine,
though a black solid at the ordinary temperature, be-
comes, when heated, a violet gas. Like fluorine, they all
form compounds with hydrogen, of the formulae HF, HC1,
HBr, and HI ; these are colourless gases, soluble in water.

Enough has been said to show that Newlands' method
of classifying the elements brings together in vertical
columns those that have similar properties. This method
was developed by a German chemist named Lothar
Meyer, and by a Russian named Mendeleeff, and it is now
universally acknowledged to be the only rational way of
classifying the elements.

If we consider one of the horizontal rows, we shall also
discover a peculiarity. The number of atoms of the
elements which combine with an atom of oxygen gradually
alters ; and if they form compounds with hydrogen, the
same kind of regularity can be observed. For instance,
the elements of the first horizontal row given above form
the following compounds with oxygen and hydrogen :

Name . . Lithium. Beryllium. Boron. Carbon. Nitrogen. Oxygen. Fluorine.

Formula of

Oxide . . Li20 BeO B203 C02 N205 — -
Formula of

Hydride . LiH unknown BH3 CH4 NH3 OH2 FH

The elements of the subsequent rows show similar
regularity.

Up till recently, no elements were known which refused
to combine with other elements. In 1894, however, Lord
Rayleigh and Sir William Ramsay discovered that
ordinary air contained such a gas, and they named it
'argon,' a Greek word which signifies inactive or lazy.
This gas had been overlooked because of its resemblance
to another constituent of the atmosphere, present in
nearly one hundred times greater amount — nitrogen.

WHAT IS AN ELEMENT? 153

Argon cannot be made to combine, and hence it is left
behind when the nitrogen and oxygen have been removed
from the atmosphere.

Shortly after the discovery of argon, Ramsay found
that certain minerals when heated give off a gas similar
to argon, inasmuch as it forms no compounds, but with
a much lower atomic weight; for while argon possesses
the atomic weight forty, the atomic weight of helium (the
name given to this new gas) is only four. Now these
elements evidently belong to one series, for they are both
colourless gases, incapable of combining with other
elements. And it appeared almost certain that other
gases, similar in properties to these two, should be capable
of existence. And Ramsay, in conjunction with Travers,
spent several years in a hunt for the missing elements.
They heated upwards of a hundred minerals, to see
whether they evolved gas, and, if so, whether the gas
obtained was new; but although they discovered that
many minerals give off helium when heated, no new gas
was found. Mineral waters were boiled, so as to expel
dissolved gases; again only argon and helium were
obtained. Even meteorites, or ' falling stars,' were
heated ; only one was found to give off gas incapable of
combination, and that gas consisted of a mixture of the
two which were already known.

As a last attempt, Ramsay and Travers prepared a large
quantity of argon, by removing the oxygen and the
nitrogen from air, and then forced the gas into a bulb,
dipping in a vessel immersed in a tube full of liquid air,
which is so cold that the argon changed to liquid. It
forms a colourless, mobile liquid, just like water. When
the liquid air is removed, the argon begins to boil.

It was hoped that the distillation of crude liquid argon
might separate from it other gases boiling at a lower or a
higher temperature ; that if it contained any other liquids
of lower boiling-point, these would distil over first, and

154 ESSAYS BIOGRAPHICAL AND CHEMICAL

could be collected separately; while any 'heavier' gases
would be the last to distil over. The hope was not dis-
appointed— at all events as regards the first expectation ;
for the first part of the gas which evaporated was consider-
ably lighter than argon and had a much lower boiling-
point. After a few redistillations, however, it was found
that liquid air was not sufficiently cold to condense this
light gas to liquid. But Dr. Travers was equal to the
emergency. He constructed an apparatus by help of
which hydrogen gas was condensed to liquid ; and the
boiling-point of liquid hydrogen is much lower than that
of liquid air; it is — 252'5° C. On cooling the mixture
of gases which had been separated from the argon, a
portion only condensed, while about one- third still remained
as a gas ; the gaseous portion was helium, and the liquid (or
solid) portion evaporated into a gas which was named
' neon,' the Greek word for ' new.'

It was also found that two other gases could be sepa-
rated from air by allowing a large quantity of liquid air
to boil away. These gases have a much higher boiling-
point than oxygen, nitrogen, or argon, and therefore they
remain mixed with the last drops of liquid after most of
the air has evaporated. They were separated from each
other by ' fractionation ' ; one was named 'krypton,' the
Greek for ' hidden ' : and the other ' xenon,' or ' strange.'

Five new gases were thus obtained ; they are given with
their atomic weight in the following line :

Helium, 4 ; Neon, 20 ; Argon, 40 ; Krypton, 81 '6 ; Xenon, 128.

Their position among other elements is well seen from the
following extract from the whole table of the elements:

Hydrogen, 1 Helium, 4 Lithium, 7 Berylium, 9'1, etc.

Fluorine, 10 Neon, 20 Sodium, 23 Magnesium, 24 "3, etc.

Chlorine, 35 '5 Argon, 40 Potassium, 39'1 Calcium, 40, etc.

Bromine, 80 Krypton, 81 Rubidium, 85'4 Strontium, 87'6, etc.

Iodine, 127 Xenon, 128 Caesium, 133 Barium, 137'4, etc.

WHAT IS AN ELEMENT ? 155

It will be noticed that their atomic weights lie between
those of the elements in the vertical rows ; and that they
separate the active elements of the fluorine group from
the equally active elements of the sodium group.

The discovery of these elements, however, has added
little to our knowledge as regards the nature of elements in
general, except in so far as to show that elements which
form no compounds can exist. It might be supposed that
the same agencies which are successful in splitting up
compounds into the elements of which they consist might
decompose elements into some still simpler substances ;
of course the elements thus decomposed could no longer
be called elements. And it appeared not impossible that
in a series of elements closely resembling each other, like
those of the sodium column, or the chlorine column, it
might be impossible to decompose those of higher atomic
weight into those of lower atomic weight, and perhaps
something else. Such agencies are : a high temperature
or an electric current. Water, for instance, can be decom-
posed into hydrogen and oxygen either by heating steam
to whiteness or by passing an electric current through
water. But it is needless to say that the elements have
been repeatedly exposed to the highest temperature and
to the strongest electric currents and yet have remained
elements. There are, indeed, reasons for supposing that
at the enormously high temperatures of the sun and of
the fixed stars some of our elements are decomposed ; but
it has hitherto been impossible to reproduce such extreme
conditions on the earth.

The element carbon is characterised by the enormous
number of compounds which it forms, chiefly with hydrogen
and oxygen, although many other elements can be in-
duced to combine with it. And one instructive fact is
to be noticed as regards such compounds : the greater the
number of atoms they contain the more easily they are

156 ESSAYS BIOGRAPHICAL AND CHEMICAL

decomposed by heat. Indeed, some compounds are so un-
stable that they decompose at the ordinary temperature,
not into their elements, it is true, but into other com-
pounds of carbon, hydrogen and oxygen. Such compounds
are stable only at a low temperature, and the higher the
temperature the more readily they decompose. Judging
by analogy, we should expect elements of high atomic
weight to show tendency to decomposition, granting, of
course, that any element at all is capable of decomposing.
Now among the three elements of highest atomic weight
known is radium, an element belonging to the barium
column, of which the atomic weight is 226. This remark-
able substance exists in a mineral named pitchblende,
an oxide of uranium ; its discovery by Madame Curie, of
Paris, is one of the most remarkable of recent events in
chemical history.

The second element of high atomic weight is thorium
(232'5). It was noticed by Dr. Schmidt, and indepen-
dently by Professor Rutherford, of Montreal, that if air
was passed over a salt of thorium, or bubbled through its
solution, it carried with it an ' emanation ' which possessed
for a short time the power of discharging an electroscope.
Radium salts also give off such an emanation, or gas,
which, however, retains its properties for more days than
the thorium gas does for minutes. Uranium, the chief
constituent of pitchblende, too, has also the power of
discharging an electroscope, but it gives off no emana-
tion. Its atomic weight is 239'5 : it is the highest
known.

The gases evolved from compounds of thorium and
radium can be condensed to solid or liquid by passing
them through a tube cooled with liquid air. But they
are present in such excessively minute quantity that they
have never been seen, even as a minute drop. They are
as inert as argon, and they are members of that group of

WHAT IS AN ELEMENT ? 157

elements ; and the radium gas shines in the dark, so that
a tube containing it gives off a whitish phosphorescent
light like that given off by stale fish, or like the luminosity
of the sea on calm summer evenings, or like the head of a
lucifer match if it is gently rubbed in the dark. If the
gas from radium is mixed with air, it is possible to see it
passing through a tube in the dark, and to recognise it by
its faint shining when it is transferred from one glass tube
to another.

It is very easy to remove oxygen from a mixture of
gases ; if a piece of the element phosphorus be heated in
oxygen, a solid compound of the two is formed, and all
oxygen can then be got rid of; or oxygen may be ab-
sorbed by passing the mixed gases over red-hot copper.
Hence it is convenient to allow the emanation from
radium salts to mix with oxygen rather than with air;
for nitrogen, the other constituent of air, is more diffi-
cult to remove. And it is then possible to collect the
radium emanation, mixed with oxygen, in a glass tube,
and then to absorb the oxygen, leaving only the emana-
tion present.

Now, as has been said, the emanation gradually loses its
power of discharging an electroscope. After four days it
requires twice as much emanation to produce the same
discharging effect as would be required if the emanation
were freshly prepared from radium salts. And the ques-
tion suggested itself to Mr. Soddy and Sir William Ramsay :
What becomes of the emanation ? Does it merely lose its
luminosity and discharging power, or is it changed into
something else ?

Chemists have long had at their disposal a means of
recognising almost inconceivably minute quantities of
matter. All substances, when made into a gas by intense
heat, give out light; and that light, if passed through a
prism, is seen not often to be all of one kind. For example,

158 ESSAYS BIOGRAPHICAL AND CHEMICAL

the light given out by sodium gas at a red heat is yellow ;
and if passed through a slit, and then through a prism,
two yellow lines are seen — the spectrum of sodium.
Similarly, potassium salts, in a spirit-lamp flame, gives
out a violet light ; and the prism shows us that the light
consists of two kinds — one red and one violet. And so
for other elements. If the spectra of gases have to be
examined, they can be made to glow by passing an electric
discharge through a very narrow tube containing a minute
trace of the gas. Helium, for example, if examined in
this way, gives out light consisting of many colours : red,
yellow — the most intense — green, green-blue, blue and
violet. Hence it is easy to recognise the presence of
helium in such a capillary tube, by passing an electric
discharge through it, for the exact position of the lines
in its spectrum is easily recognised.

Now Ramsay and Soddy found that the emanation from
radium salts, though it gave out a special light of its own
when made luminous by an electric discharge, showed
none of the lines characteristic of helium. But after
standing for three days the yellow line of helium began to
be visible, and that is the one most easily seen. As time
went on, and as the emanation lost its self-luminosity, the
other lines denoting the presence of helium became dis-
tinctly visible. The conclusion was forced upon them,
therefore, that, as the emanation disappears, helium is
formed, or, in other words, the emanation is changing
slowly into helium.

Professor J. J. Thomson, of Cambridge, has of recent
years been investigating the motion of particles which are
shot off from the negative pole when an electric discharge
is passed through gases ; and he has succeeded in showing
that some of the particles move with enormous rapidity,
and that they possess a weight which cannot be much
more than one seven-hundredth of that of a hydrogen

WHAT IS AN ELEMENT? 159

atom. It is almost certain that radium salts continually
emit such rapidly moving particles, and it is known that
while doing so the temperature of the radium salt is some
degrees higher than that of the surrounding atmosphere ;
radium, therefore, is continually giving off heat. We are
wholly unacquainted with any similar change; these
properties are new. But we do know of compound sub-
stances which decompose with slight provocation, give off
a great amount of heat in doing so, and at the same time
are wholly converted into a large quantity of gases ; per-
haps the most familiar example is gun-cotton, of which
most of the high explosives used for blasting and in the
manufacture of modern gunpowder are made. The dif-
ferences between the two phenomena, moreover, are
sufficiently pronounced: gun-cotton decomposes almost
instantaneously, with explosive violence; radium salts
slowly ; gun-cotton requires to be started by the explosion
of a percussion-cap ; radium salts decompose spontaneously,
and the rate of decomposition, so far as is known, appears
to be independent of temperature; the amount of heat
evolved when gun-cotton explodes, though great in itself,
is small in comparison with that evolved during the de-
composition of an equal weight of radium salt ; and it is
not known that any electrical phenomena accompany the
decomposition of gun-cotton. Still, it appears reasonable
to suspect that the two kinds of change may, after all, be
similar, and that the heavy atom of radium is decompos-
ing into the lighter helium atom. It is pretty certain
that helium is not the only substance produced when the
emanation from radium decomposes ; and it is not known
whether radium, when it gives off its emanation, produces
at the same time any other decomposition product. Much
has yet to be discovered. Yet it must be acknowledged
that a distinct advance has been made, and that at least
one so-called element can no longer be regarded as ulti-

160 ESSAYS BIOGRAPHICAL AND CHEMICAL

mate matter, but is itself undergoing change into a simpler
form of matter.

The young student, when he learns what is known, is
too apt to think that little is left to be discovered ; yet all
our progress since the time of Sir Isaac Newton has not
falsified the saying of that great man — that we are but
children picking up here and there a pebble from the
shore of knowledge, while a whole unknown ocean stretches
before our eyes. Nothing can be more certain than this :
that we are just beginning to learn something of the
wonders of the world on which we live and move and
have our being.

ON THE PERIODIC ARRANGEMENT OF
THE ELEMENTS

AT the end of the eighteenth century, after the investiga-
tions of Black, Scheele, Priestley, Cavendish, and Lavoisier
began to crystallise the previous arbitrary collections of
chemical facts into more or less of a system, it became
evident that the distinguishing feature of a ' compound,'
as contrasted with a ' mixture,' was the invariability of its
composition. Early in the nineteenth century, Dalton
formulated his celebrated hypothesis, by means of which
a concrete view was gained regarding the cause of this
constancy and invariability of composition. Every one
knows that this ' explanation ' consisted in the supposition
that the combination of two substances, one with another,
in definite proportions, involves the union either of one
atom of the one with one atom of the other, or of certain
small but simple numbers of atoms of the two substances.
The atom was regarded, not necessarily as indivisible, but
as not having been divided into any smaller particles.
The advance made by Dalton consisted chiefly in ascribing
to each atom a definite weight ; but as he had no data for
determining the absolute weight of any one atom, he was
obliged to content himself with relative weights, and chose
the smallest known to him, that of hydrogen, as an arbi-
trary unit. This choice has proved to be a just one, for
as yet no element has been discovered possessing a lower
atomic weight than hydrogen, although it is by no means
impossible that such an element may exist.
L

162 ESSAYS BIOGRAPHICAL AND CHEMICAL

After the convenience of Dal ton's hypothesis had been
acknowledged, the labour of chemists was for many years
devoted to the determination of the relative values of the
' atomic weights ' of the elements ; or, expressed in a
manner independent of hypothesis, of their combining
proportions. The name of the Swedish chemist, Berzelius,
is prominent in this connection. By the analysis of an
almost incredibly large number of compounds, he estab-
lished on a firm basis the constancy of composition of
compounds, and the law of multiple proportions. Towards
the 'forties, therefore, a set of numbers had been col-
lected, which invited an attempt to place them in order,
with the view of seeing whether some still more profound
law could not be discovered connecting the combining
numbers attached to them. Dobereiner, as early as 1817,
and again in 1829, pointed out that certain elements had
atomic weights which were nearly the mean of those of
others which were closely related to them ; thus, the mean
of the atomic weights of calcium and barium gives a close
approximation to the atomic weight of strontium ; that of
sodium lies near the mean of those of lithium and potassium ;
and sulphur and tellurium similarly indicate selenium
as a middle element. In 1843 Gmelin, who published
a Handbook of Chemistry, which is still a classic, attempted
a classification based, not upon numerical relations, but
on similarity of properties. For instance, we find the
groups— F, 01, Br, I; S, Se, Te; P, As, Sb; 0, B, Si; Li,
Na, K ; Mg, Ca, Sr, Ba ; and so on. In 1851 Dumas gave
a lecture before the British Association, in which he
showed that not merely is the atomic weight of bromine
the mean of those of chlorine and iodine, but that its
physical properties, such as its colour, its density in the
gaseous and in the liquid state, etc., are also half-way
between those of the allied elements. In 1852 Faraday
criticised Dumas' attempts as 'speculations which have

PERIODIC ARRANGEMENT OF ELEMENTS 163

scarcely yet assumed the consistence of a theory, and
which are only at the present time to be ranked among
the poetic day-dreams of a philosopher'; and he pro-
ceeded : ' We seem here to have the dawning of a new
light indicative of the mutual convertibility of certain
groups of elements, although under conditions which are
as yet hidden from our scrutiny.'

Passing over attempts by Gladstone, Cooke, Odling,
and Strecker, we come to the years 1863 and 1864, when
John Newlands, in a series of letters to the Chemical
News, announced what he termed the ' Law of Octaves.'
His actual words were : ' If the elements are arranged in
the order of their equivalents, with a few slight trans-
positions, it will be observed that elements belonging to
the same group usually appear on the same horizontal
line. It will also be seen that the numbers of analogous
elements generally differ, either by 7 or by some multiple
of 7 ; in other words, members of the same group stand
to each other in the same relation as the extremities of
one or more octaves in music. Thus in the nitrogen
group, between nitrogen and phosphorus there are 7
elements; between phosphorus and arsenic, 14; between
arsenic and antimony, 14 ; and lastly, between antimony
and bismuth, 14 also. This peculiar relationship I propose
provisionally to term the " Law of Octaves." '

In 1869 and 1870, Lothar Meyer and Dmitri Mendeleeff,
independently of Newlands, and also of each other,
published papers in which they maintained that the
properties of the elements are periodic functions of their
atomic weights. This discovery goes by the name of the
'Periodic Law,' or better, the 'Periodic System.' The
arrangement of Meyer (p. 164), which differs but little
from that of Mendeleeff, is the one generally adopted.

If this diagram is rolled round a cylinder, it will form a
continuous spiral, beginning with lithium and ending with

164 ESSAYS BIOGRAPHICAL AND CHEMICAL

I.

II.

III.

IV.

V.

VI.

VII.

VIII.

Li

He

7-03

Be

U

9-1

B

11-0

C

12-0

N.

14-04

O

16-00

P

Na

19

Ne

2305

Mg

SO

2436

Al

27-1

Si

28-4

P

31-0

8

32-06

Cl

K

35-45

A

39-14

Ca

39-9

40'0

Sc

44

Ti

48-1

V

51-2

Cr

52-1

Mil

Cu

55-0

Pe

63-6

Zn

56-0

Co

Ni

65-4

Ga

59-0

58-7

70

Ge

74

As

75

Se

79-1

Br

Rb

79-96

Kr

85-4

Sr

Si -5

87'6

Y

89

Zr

90-6

Nb

94

Mo

90-0

V

Ag

99

Ru

Rh

Pd

107-95

Cd

101-7

103-0

106

112

In

144

Sn

119-0

Sb

120

Te

127-6

j

Cs

126-85

X

133-0

Ba

1SS

137-16

La

138

Ce

140

Prd

141

Nd

143-5

7

?

152

165

7

170

Yb

173

9

176

Ta

w

184

|

An

185

Os

Ir

Pt

197-2

^00 "3

Tl

191

193

195-2

204.1

Pb

206-9

Bi

208-5

?

210

f

7

211

?

222

Ra

226

7

230

Th

232

^

234

U

240

7

242

PERIODIC ARRANGEMENT OF ELEMENTS 165

uranium ; but there are certain gaps unfilled, denoted by
the sign ?, which, it is believed, represent the places of
still undiscovered elements. Indeed, Meyer's original
diagram contained a larger number of these; and Men-
deleeff, averaging the properties of the elements surround-
ing such gaps, prophesied the discovery of scandium,
gallium, and germanium, made at a much later date by
Cleve, by Lecoq de Boisbaudran, and by Winckler.

There are many other ways of representing these rela-
tions; but except perhaps in convenience (and questionably
even in that), they present no particular advantage, and
convey no new knowledge. Only one point must be
emphasised. The elements, as arranged above, divide
themselves into two 'periods' — long periods and short
periods. Thus the seventh member after lithium, sodium,
is hi its character very like lithium; and, again, potassium,
the seventh after sodium, presents strong analogies with
the two elements named ; but it is then necessary to pass
over fifteen elements before rubidium is reached, which
again closely resembles lithium, sodium, and potassium ;
and caesium, the seventeenth element after rubidium, forms
the first term of another long period. Copper, silver, and
gold are also separated by long periods ; and so with the
elements in the other columns. To distinguish these in
the table, the symbols of the elements in the middle of
the long periods are printed towards the left, and those at
the beginning towards the right, of the figures denoting
the atomic weights.

One other point requires mention. Several instances
occur in which the elements appear to occupy a reversed
position. Thus, nickel, with the atomic weight 58'7,
follows cobalt, to which a higher atomic weight is ascribed;
tellurium precedes, instead of following iodine ; and it will
be seen that argon precedes potassium. The differences
between the various consecutive atomic weights are

166 ESSAYS BIOGRAPHICAL AND CHEMICAL

irregular, and vary between fairly wide limits ; and it is
quite probable that these differences may occasionally be
negative.

In 1894 a new constituent of the atmosphere, which
was named ' argon,' was discovered by Lord Rayleigh and
Ramsay; this was followed in 1895 by the discovery by
Ramsay of helium in certain minerals. This gas gives a
spectrum in which a brilliant yellow line is conspicuous.
So long ago as 1868 this line had been observed in the
solar spectrum by Jansen ; it was attributed by Frank-
land and Lockyer to the presence of a new element in
the sun, and they named the then unknown element
' helium.' These discoveries were followed by that of three
other gaseous elements in atmospheric air, by Ramsay and
Travers in 1898 ; thus five elements were added to the
list. All these elements are distinguished by their inert-
ness, for none of them forms compounds with other
elements.

The Roman figures at the head of the columns of the
periodic table have a certain significance. They show the
maximum number of atoms of hydrogen which the ele-
ments in each column can combine with or replace, or, as
it is termed, their ' valency.' Thus an atom of lithium
combines with one atom of hydrogen ; it can also replace
one atom, as when it forms lithium hydroxide, LiOH, in
which it has replaced one atom of hydrogen in water,
H20. So also magnesium can replace two atoms of
hydrogen, for it forms the hydroxide Mg(OH)2. Boron
combines with three atoms of hydrogen; carbon with
four ; phosphorus, although it can combine with only
three atoms of hydrogen, can replace five ; for it forms a
chloride PC15, in which it has replaced the five atoms of
hydrogen in five molecules of hydrogen chloride, 5HC1.
Sulphur forms a hexafluoride, and iodine a pentafluoride,
in which they replace six and five atoms of hydrogen

PERIODIC ARRANGEMENT OF ELEMENTS 167

respectively, in 6HF, and in 5HF. Only one of the ele-
ments of the eighth group appears to be able to replace
eight atoms of hydrogen, namely, osmium; it forms a
tetroxide, Os04, thus replacing the eight atoms of hydrogen
in four molecules of water, 4H20. But the new gaseous
elements of the atmosphere form no compounds, and have
no valency, as the power of replacing or combining with
hydrogen is termed. They thus form a column by them-
selves ; and it was interesting to ascertain whether their
atomic weights would form a series like those in the other
columns. In this case, the atomic weight could not be
determined by the usual process of determining the ratio
in which the elements combine with hydrogen ; hence a
different method was adopted, depending on the known
fact that equal numbers of molecules of gases occupy
equal volumes under the same conditions of temperature
and pressure ; and making use of an argument relating to
the number of atoms in such molecules. The atomic
weights were : —

Helium
4

Neon
20

Argon
39-9

Krypton
81-5

Xenon

128

These numbers, as will be seen on reference to the table,
fit in the eighth column ; the symbols and atomic weights
of these gases are printed in italics. They form the initial
members of the first and second short series, and of the
first, second, and third long series.

Some doubt exists as to the place to be assigned to
hydrogen, the element with lowest atomic weight. Both
Mendeleeff and Meyer shirked placing it. It may be that
it should be placed at the head of the fluorine column ;
but there are equally good, or perhaps better, reasons for
believing that it is the first member of the lithium
column.

168 ESSAYS BIOGRAPHICAL AND CHEMICAL

Many attempts have been made to devise some mathe-
matical relation between these atomic weights. So long
as there was reason to doubt the accuracy of the experi-
ments by means of which the atomic weights have been
determined, some such relation as the following had
considerable probability in its favour : — Taking the
differences between the atomic weights of the elements
in the first column, lithium, sodium, potassium, rubidium,
and caesium, they are —

K-Na = 39-23 = 16;

Rb-K = 85-39 = 46 = (3x 16) nearly;

Cs-Rb = 133-85 = 48 = (3xl6).

The differences are 16, 16, 3x16, and 3x16. Now
there are compounds of carbon and hydrogen which
possess the formulae, CH4, C2H6, C3H8, C4H10, C5H12, C6H14,
etc. ; and as the atomic weight of carbon is 12, and that of
hydrogen 1, the sum of the atomic weights, or, as they are
called, the molecular weights, are respectively 16, 30, 44,
58, 72, 86, etc., with a common difference of 14. We see,
therefore, that a set of compounds may so differ in mole-
cular weight as to present a regular series, with a common
difference. Nothing was more likely, then, than that
sodium should be regarded as a compound of one atom of
lithium with one atom of an unknown element of atomic
weight 16, or with two atoms of an unknown element of
atomic weight 8 ; while potassium might be looked upon
as a compound of an atom of lithium, with four atoms of
the element of atomic weight 8 ; and so on. But, unfor-
tunately for this simple theory, the differences between
the atomic weights of the elements are not exactly equal.
Instead of 16, the real difference between the atomic
weights of lithium and sodium is 16'02; between potassium

PERIODIC ARRANGEMENT OF ELEMENTS 169

and sodium, 16'09; and so on. In other groups the
divergences are still more striking.

The cause of this irregularity has, therefore, to be
sought. In seeking for a clue, the first question is : Are
the atomic weights invariable ? A further question is : Is
weight invariable ? Does a body always possess the same
weight under all conditions ? For example, would the
weight of a body remain the same if it were to be weighed
at different temperatures? Or, if electrically charged,
would its weight remain unaltered ?

It is a very difficult problem to weigh an object at a
high temperature. If the balance, as is usual, contains
air, convection currents are produced by the ascent of air
heated by the warm body, and the body apparently weighs
too little. If the whole balance were uniformly heated,
the weights would be at the same temperature as the
substance weighed ; and it is to be presumed that both
they and the substance would alter in weight equally, and
still remain in counterpoise. And if the balance case be
pumped empty of air, as was done by Crookes in deter-
mining the atomic weight of thallium, other phenomena
intervene, which, however interesting in themselves (they
led Crookes to the invention of the radiometer), are very
disconcerting ; for attractions and repulsions, which com-
pletely disturb equilibrium, are produced by the slightest
variations of temperature. However, some curious calcula-
tions have been made by Hicks in dealing with Baily's
experiments on the attraction of leaden balls by masses
of lead — experiments which afford data for calculating the
density of the earth. At a high temperature the attraction
appeared to be less than at a low one ; and as the attrac-
tion of the earth is the cause of weight, supposing these
experiments to be correct, and the deductions legitimate,
it would follow that weight is altered by temperature.
The subject is well worthy of further experiment.

170 ESSAYS BIOGRAPHICAL AND CHEMICAL

Again, interesting experiments have been made by
Landolt as regards constancy of weight. Having sealed
up in an inverted U-tube two substances capable of acting
on each other, such as silver nitrate and sodium chloride,
each substance in solution occupying one limb of the
tube, he weighed the tube with the utmost accuracy ; the
possible error might be one part in a million. On inverting
the tube, the two solutions mixed, and the reaction took
place. It was again weighed. For long, Landolt supposed
that he had detected small changes in weight, sometimes
negative, sometimes positive; but he was able to trace
these changes to the porous nature of glass. On employ-
ing tubes made of fused quartz, no change of weight could
be detected after the reaction was over. Apparently,
therefore, no change of weight takes place as the result of
a chemical reaction, provided nothing leaves or enters the
vessel in which the reaction goes on.

A very ingenious experiment of Joly's deserves mention.
It was designed to try whether any change of mass occurs
on mixing two reacting bodies, and the disposition of the
apparatus was somewhat like that devised by Landolt.
But instead of utilising the attraction of the earth in order
to estimate whether the mass had changed or not, the
inertia of the substances and of their mixture was deter-
mined. The vessel containing the substances to be mixed
was suspended to the arm of a torsion-balance, the arm of
which was at right angles to the direction of motion of the
earth, which is known to be at the rate of about 30 miles
a second through space. If matter had been created
during the chemical change, then the created matter
would not partake of the earth's velocity, and a retarda-
tion, made manifest by the rotation of the arms of the
torsion-balance in one direction, would have been observed ;
and if, on the other hand, matter had been destroyed, an
acceleration would have shown itself. The experiments

PERIODIC ARRANGEMENT OF ELEMENTS 171

were entirely negative ; hence it may be concluded, con-
firmatory of the experiments of Landolt, that no change
in mass is produced by a chemical reaction. A variation
in weight or in inertia has not been observed.

There is one curious discrepancy which still remains
unexplained. The density of nitrogen gas has been very
accurately determined by two very competent observers —
Lord Rayleigh and Leduc. They both agree in their
results to one part in 10,000. Now it is known, for reasons
into which we cannot enter here, that the molecules of
both nitrogen and oxygen consist each of two atoms ; and
as it is also certain that equal volumes of gases contain
nearly equal numbers of molecules, when measured under
similar conditions of temperature and pressure, the rela-
tive weights of these gases correspond to the relative
weights of the atoms. The word ' nearly ' has been used ;
for a slight correction must be introduced in order to
secure exact correspondence. Hence the atomic weight
of nitrogen, referred to that of oxygen taken as 16, as is
now customary, must be 14'008, since that is the density of
nitrogen referred to oxygen as 16, after the necessary cor-
rection has been made. But this number does not corre-
spond with the atomic weight of nitrogen obtained by the
celebrated chemist Stas, as the result of the analysis of such
compounds as potassium nitrate, when he determined the
ratio between the quantities of nitrogen and oxygen in
the molecule KNO3. Both he and, quite recently, one
of the most skilful of analysts, to whom we owe in recent
years many exact determinations of atomic weights,
Theodore Richards, agreed in ascribing the number 14-04
to nitrogen as its atomic weight. The difference does not
appear very great ; but yet it amounts to one part in 370 :
and the error of experiment is not likely to be greater
than one part in 10,000. This discrepancy is one of the
most curious of chemical facts, and it would well repay

172 ESSAYS BIOGRAPHICAL AND CHEMICAL

further investigation. It may be added that the deter-
mination by Gray of the density of nitric oxide, a com-
pound containing one atom of nitrogen in combination
with one atom of oxygen, entirely corroborates the results
of Lord Rayleigh and Leduc. Experiments are now in
progress to combine a weighed quantity of nitric oxide
with oxygen, so as to cause it to take up one other atom
of oxygen, and to find the increase in weight ; and also
to remove from it the atom of oxygen, and to find the
weight of the oxygen removed ; we may, therefore, hope
for some explanation of the above discrepancy at no dis-
tant date.1

The writer of this article was so much impressed by the
consideration of this discrepancy, that some years ago, in
conjunction with Miss Aston, an attempt was made to
find whether the fact of a compound having been formed
with absorption, instead of, as is commoner, with evolu-
tion of heat, had any influence on the proportions of the
elements which it contained. For this purpose the salts
of a curious acid derivative of nitrogen named hydrazoic
acid, HN3, were analysed ; but there is reason to distrust
the results, for it is possible that decomposition occurred
during the preparation to some small extent, and so may
not have led to trustworthy conclusions. But such as
they were, they were in favour of the supposition that the
atomic weight of nitrogen in such compounds is less than
in those formed with evolution of heat, like the nitre
analysed by Stas and by Richards. -

An entirely new light has been thrown on the numerical
relations of the atoms by the remarkable discovery of
radium by the Curies, and by the discovery by Rutherford
and Soddy, that what are termed the ' rays ' from its salts,

1 Such investigations have since been carried out by Dr. R. Gray and
by Professor Philippe Guye, with the result that the true atomic weight
of nitrogen has been lixed as 14*01.

PERIODIC ARRANGEMENT OF ELEMENTS 173

as well as from those of thorium, are produced by gases
resembling in their inertness the gases of the argon group.
These gases, moreover, have the extraordinary property
that they are transient, although they change in very
different intervals of time. Whereas the gas from thorium
is half gone in about a minute (that is, has changed to
the extent of one-half into some other substance or sub-
stances), that from radium requires about four days before
it has undergone half the change of which it is capable.
A third gas has been obtained from a radio-active element
to which the name ' actinium ' has been given by its dis-
coverer, Debierne; this gas has an extraordinarily short
life, for the total duration of its existence is only a few
seconds. The spectrum of the gas from radium has been
mapped by Ramsay and Collie ; the amount of gas pro-
duced from a known weight of radium bromide has been
measured by Ramsay and Soddy ; and they, too, proved
that one of its products of decomposition is the lightest
gas of the argon group, helium. At first, the spectrum of
the emanation from radium shows none of the character-
istic lines of helium ; but in the course of a few days the
helium spectrum appears in full brilliancy. Here, evi-
dently, is a case of the transformation of one element into
another ; no doubt there are other products than helium,
but what they are remains for the present unknown. If
they were elements like iron, for example, there are at
present no known means delicate enough to detect the
extremely minute amount which would be produced.
These gases from radium, thorium, and actinium are self-
luminous, and shine brilliantly in the dark ; and they also
possess the power of altering air and other gases with
which they are mixed, so that they acquire the property
of discharging an electrified body; the air is said to be
' ionised.' But a still more remarkable property is their
giving off heat during their change into other elements,

174 ESSAYS BIOGKAPHICAL AND CHEMICAL

the amount of heat being enormous when their extremely
small quantity is considered. Thus the radium emana-
tion (the name applied to the gas which is continuously
evolved from salts of radium), during its decomposition
gives off no less than three million times the heat which
would be evolved during the explosion of an equal volume
of a mixture of oxygen and hydrogen in the proportion
requisite to form water. Now if radium is disappearing,
it must be continually in process of formation, else there
would be none on the surface of the earth ; it would all
have disappeared and have been changed into other
bodies during the lapse of time since the minerals con-
taining it were formed. As radium is always associated
with uranium, it appears not unreasonable to suppose that
uranium, too, which is a radio-active element, is slowly
changing into radium; and there appears to be definite
ground for the surmise that polonium, the first of the
radio-active elements, also discovered by Madame Curie,
which has a half-life period of about one year, is a product
of the decomposition of radium, with which it is always
associated. It may be mentioned, too, that all minerals
containing uranium contain more or less helium.

It will be noticed, on referring to the periodic table,
that all the radio-active elements, that is, all those which
are undergoing change of the nature described, have very
high atomic weights. That of uranium is 240; that of
thorium, 232 ; and that of radium, 226. Now it is a com-
monplace of the organic chemist that it is not possible to
build up compounds of carbon and hydrogen of unlimited
complexity; indeed, it is doubtful if any compound has
been prepared containing more than 100 atoms of carbon.
Attempts to prepare them lead to failure, owing to their
decomposing at the ordinary temperature into compounds
containing a smaller number of atoms. And it is pro-
bable that more complex hydrocarbons, as such com-

PERIODIC ARRANGEMENT OF ELEMENTS 175

pounds are termed, would, if they could exist, decompose
with evolution of heat. Such a decomposition appears to
present analogy with the change which an element like
radium is undergoing. It is in process of change into
other elements of lower atomic weight ; and in changing,
it evolves heat, in amount enormously greater than that
produced by any change of a compound into a mixture of
simpler compounds. But the matter is complicated by
another phenomenon — that of discharging with almost
inconceivable velocity particles which appear, according
to J. J. Thomson, to be identical with negative electricity.
These ' corpuscles,' as they have been termed, embed them-
selves in the vessel in which the radio-active body is
confined ; and, owing to their extreme minuteness, they
may even pass through the walls of the containing vessel.
Indeed the opposition of their passage has been shown to
depend merely on the density of the matter of which the
confining walls are composed ; gold, which is denser than
lead, stops their passage better than lead; for a similar
reason lead is better than iron, iron better than glass, and
so on. Thomson has calculated that the mass of one such
particle is approximately one- thousandth of that of an
atom of hydrogen.

This new chemistry is just at its commencement. It
dates from 1896, when Becquerel showed that compounds
of uranium evolved some sort of radiation which would
impress a photographic plate. It is still too early to
formulate any definite statement relating to its connection
with the irregularity in the numerical sequence of the
atomic weights ; yet it may be permissible to speculate,
aided by the recent discoveries. When two elements
combine, heat is generally evolved ; now heat is only one
form of energy, and the combination of elements may be
so carried out as to be accompanied by other kinds of
energy — for instance, by the production of an electric

176 ESSAYS BIOGRAPHICAL AND CHEMICAL

current. Conversely, when a compound is resolved into
its elements, it is generally necessary to impart energy to
it ; and the element may, therefore, be said to ' contain '
more energy than its compounds. Now, as Ostwald has
pointed out in his 'Faraday' lecture, the progress of
discovery has kept pace with the amount of energy with
which it was possible at the time to load a compound;
and he cited the discovery of the metals of the alkalies,
sodium and potassium, by Davy. It was because Davy
had at his disposal the powerful battery of the Royal
Institution, that he was able to convey enough energy
into caustic potash to isolate from it potassium, hydrogen,
and oxygen. If we assume that radium, as may be
possible, is produced by a spontaneous change in uranium ;
and if we also assume that radium contains more energy
than uranium ; then as such a spontaneous change must
be accompanied, on the whole, by a loss of energy, there
must be formed other bodies from the uranium which
contain less energy than it does. Such a substance may
be iron, which is generally found in company with uranium.
If we could concentrate energy into iron, it might be
possible to convert it into uranium.

But there is another side to this question. The nature
of the energy required appears to be electric in character.
Now it is almost certain that negative electricity is a
particular form of matter; and positive electricity is
matter deprived of negative electricity — that is, minus this
electric matter. The addition of matter in any form would,
according to all experience, increase mass ; it would also in-
crease weight. It is, therefore, conceivable that an element
may consist of a compound of two or more elements of
lower atomic weight, plus a certain quantity of negative
electricity. This might account for the approximate
numerical relations which subsist between the atomic
weights of the nearly related elements ; and also for the fact

PERIODIC ARRANGEMENT OF ELEMENTS 177

that the relation is not an exact one, but only approximate ;
for the difference between the actual atomic weight, and
that which would follow if one element were a compound
of other elements of lower atomic weights, would be caused
by the addition of a certain number of electric atoms to
the molecule.

It must be confessed, however, that the basis for specu-
lations like these is a slender one ; the sole ground is the
undoubted fact that radium produces an emanation
which spontaneously changes into helium ; and also that,
in doing so, the emanation parts with a large number
of corpuscles carrying negative charges. Nevertheless,
enough is known to prove that there is a wide field for
experiment, and that the harvest will be a rich one;
further, the reapers' task will be one of extraordinary
interest.

RADIUM AND ITS PRODUCTS

CHEMISTRY and physics are experimental sciences ; and
those who are engaged in attempting to enlarge the
boundaries of science by experiment are generally un-
willing to publish speculations ; for they have learned, by
long experience, that it is unsafe to anticipate events. It
is true they must make certain theories and hypotheses.
They must form some kind of mental picture of the
relations between the phenomena which they are trying
to investigate, else their experiments would be made at
random and without connection. Progress is made by
trial and failure; the failures are generally a hundred
times more numerous than the successes ; yet they
are usually left unchronicled. The reason is that the
investigator feels that even though he has failed in
achieving an expected result, some other more fortunate
experimenter may succeed, and it would be unwise to
discourage his attempts.

In framing his suppositions, the investigator has a
choice of five kinds; they have been classified by Dr.
Johnstone Stoney. ' A theory is a supposition which we
hope to be true, a hypothesis is a supposition which we
expect to be useful ; fictions belong to the realm of art ; if
made to intrude elsewhere, they become either make-
believes or mistakes.' Now the ' man in the street/ when
he thinks of science at all, hopes for a theory ; whereas
the investigator is generally contented with a hypothesis,
and it is only after forming and rejecting numerous hypo-

180 ESSAYS BIOGRAPHICAL AND CHEMICAL

theses that he ventures to construct a theory. He has a
rooted horror of fiction in the wrong place, and he dreads
lest his hypothesis should turn out to be misplaced
fiction.

I have thought it better to begin by these somewhat
abtruse remarks, in order to place what I propose to
discuss on a true basis. It is to be understood that any
suppositions which I shall make use of are of the nature
of hypotheses, devised solely because they may prove
useful. Events are not yet ripe for a theory.

It will be remembered that Professor Rutherford and
Mr. Soddy announced a ' view ' that certain elements
which possess the power of discharging an electroscope,
and which are therefore called ' radioactive,' are suffering
disintegration — that is, they are splitting up into other
elements, only one of which has as yet been identified.
Three of these elements, namely, radium, thorium, and
actinium, early in the process of disintegration give off an
' emanation,' or supposed gas; the proof of the gaseous nature
of these emanations is that they can be confined by glass
or metal, like gases, and that they can be liquefied or
solidified when cooled to a sufficiently low temperature.
It is necessary to pay attention to this peculiarity; for
these radioactive elements, and two others, uranium and
polonium, also give off so-called /3-rays, which penetrate
glass and metal, and which are believed from the dis-
coveries of Professor J. J. Thomson and others to be
identical with negative electricity.

Now Rutherford and Soddy, reasoning on the premises
that radium was always found associated with uranium
and thorium, and also that the ores of these metals,
pitchblende and thorite, had been found to contain the
gas helium, made the bold suggestion, 'The speculation
naturally arises whether the presence of helium in minerals
and its invariable association with thorium and uranium

RADIUM AND ITS PRODUCTS 181

may not be connected with their radioactivity.' Besides
the premises already mentioned, they had evidence of
the probable mass of the ' a-particles/ which appeared to
be about twice that of an atom of hydrogen. Now
helium is the lightest gas next to hydrogen; and its
atoms are four times as heavy as atoms of hydrogen. It
was, therefore, a striking confirmation of the accuracy of
this view when Ramsay and Soddy discovered that helium
can actually be obtained from radium.

Before giving an account of that discovery, a short
description of the nature and properties of helium may
not be out of place. When light passes through a prism,
it is refracted or bent ; and Newton discovered that white
light, such as is emitted from the sun or the stars, after
passing through a prism, gives a spectrum consisting of
coloured images of the hole in the window-shutter through
which the sunlight fell on his prism. Fraunhofer, a
Berlin optician, conceived the idea of causing the light to
pass through a narrow slit, instead of a round hole ; and
the spectrum then consisted of a number of images of the
narrow slit, instead of the round hole. He was struck by
one peculiarity shown by sunlight when thus examined,
namely, that the coloured band, rainbowlike, and exhibit-
ing a regular gradation of colour from red at the one end,
through orange, yellow, green, and blue, to violet at the
other end, was interspersed by very numerous thin black
lines. The nature of these lines was discovered by
Kirchoff. The light emitted by a white-hot body shows
a continuous spectrum ; but if such white light be passed
through the vapours of a metal, such as sodium, a portion
is absorbed. For example, glowing sodium gas shows two
yellow lines, very close together ; but if this light is passed
through the vapour of sodium, these lines are extinguished
if the correct amount of vapour be interposed. Now it
was found that the position of the two dark lines in the

182 ESSAYS BIOGRAPHICAL AND CHEMICAL

sun's spectrum, discovered by Fraunhofer, is identical
with that of the two yellow lines visible in the spectrum
of glowing sodium vapour ; and Kirchoff concluded that
this coincidence furnished a proof of the presence of
sodium in the sun. Fraunhofer had named these lines
Dx and D2. Similar conclusions were drawn from obser-
vations of the coincidence of other black solar lines with
those of elements found on the earth ; and the presence
of iron, lead, copper, and a host of elements in the sun
was proved.

In 1868 a total eclipse of the sun took place; an
expedition was sent to India, from which a good view was
to be obtained. Monsieur Janssen, the distinguished
French astronomer, observed a yellow line, not a dark, but
a bright one, in the light which reached the earth from
the edge or ' limb ' of the sun, and which proceeded from
its coloured atmosphere or chromosphere. It was for
some time suspected that this line, which was almost
identical in position with the yellow lines of sodium, Dj
and D2, and which Janssen named D3, was due to
hydrogen. But ordinary hydrogen had never been found
to show such a line ; and after Sir Edward Frankland and
Sir Norman Lockyer had convinced themselves by
numerous experiments that D3 had nothing to do with
hydrogen, they ascribed it to a new element, the exist-
ence of which on the sun they regarded as probable;
and for convenience, they named this undiscovered
element 'helium/ from the Greek word for the sun,
^Xio?.

It was not until the year 1895 that helium was found
on the earth. After the discovery of argon in 1894,
Ramsay repeated some experiments which had previously
been made by Dr. Hillebrand, of the United States Geo-
logical Survey. HiDebrand had found that certain
minerals, especially those containing the somewhat rare

RADIUM AND ITS PRODUCTS 183

elements uranium and thorium, when heated, or when
treated with acids, gave off a gas which he took for
nitrogen. But the discovery of argon had taught Ramsay
how to deal with such a gas. He examined it in the hope
that it might lead to the discovery of a compound of
argon ; but its spectrum turned out to be identical with
that of solar helium, and terrestrial helium was discovered.
It proved to be a very light gas, only twice as heavy as
hydrogen, the lightest substance known ; its spectrum con-
sists chiefly of nine very brilliant lines, of which D3 is the
most brilliant ; it has never been condensed to the liquid
state, and is the only gas of which that can now be said
(for hydrogen has been liquefied within the last few years1),
and, like argon, it has not been induced to form any
chemical compound. That it is an element is shown by
the relation of its atomic weight, 4, to that of other
elements, as well as by certain of its properties, the most
important of which is the ratio between its specific heat
at constant volume and constant pressure ; but to explain
the bearing of this property on the reasoning which proves
it to be an element would be foreign to the subject of this
article.

This then was the elementary substance that Ruther-
ford and Soddy suspected to be one of the decomposition
products of radium. The word ' decomposition/ however,
implies the disruption of a compound, and the change
which takes place when radium produces helium is of
such a striking nature that it is perhaps preferable to use
the term ' disintegration.'

Having procured fifty milligrammes (about three-
quarters of a grain) of radium bromide, Ramsay and
Soddy placed the greyish-brown crystalline powder in a
small glass bulb about an inch in diameter. This bulb
was connected by means of a capillary tube with another

1 It has since been liquefied by Kammerlingh Onnes of Leiden.

184 ESSAYS BIOGRAPHICAL AND CHEMICAL

bulb of about the same size ; on each side of the second
bulb there was a stop-cock, as shown in the sketch. To
begin with, the bulb A was pumped empty of air; it
contained the dry bromide of radium. The
stop-cock B was then shut. Next, some
water was placed in bulb C, and it too was
pumped free from air, and the stop-cock D
was closed. B was then opened, so that
the water in C flowed into A, and dissolved
up the bromide of radium. As it was
dissolving, gas bubbles were evolved with
effervescence, and that gas collected in the
two bulbs, A and B. The sketch shows the
state of matters after the water had been
added and the gas evolved. The apparatus
was then permanently sealed on to a tube
connected with a mercury-pump, so con-
EXTRACTION OP trived that gas could be collected. The stop-
GASESFROM opened, the gas passed

RADIUM BROMIDE

into the pump, and was received in a small
test-tube. From the test-tube it was passed into a reservoir,
where it was mixed with pure oxygen, and electric sparks
were then passed through it for some hours, a little caustic
soda being present. This process has the result of causing
all gases except those like argon to combine, and they are
therefore removed. It was easy to withdraw oxygen by
heating a little phosphorus in the gas ; and it was then
passed into a small narrow glass tube, which had a platinum
wire sealed in at each end — a so-called Plucker's vacuum-
tube. On passing an electric discharge from a Ruhmkorff
induction-coil through the gas in the tube, the well-known
spectrum of helium was seen.

Thus helium was proved to be contained in radium
bromide which had stood for some time. The specimen
used was said to be about three months old, and the

RADIUM AND ITS PRODUCTS 185

helium had accumulated. But whence came the helium ?
That was the next question to be settled.

A solution of radium bromide gives off gas continuously.
That gas, on investigation, is found to be a mixture of
oxygen and hydrogen, the constituents of the water in
which the bromide is dissolved. It contains, however, a
small excess of hydrogen, which implies that some oxygen
has been absorbed, probably by the radium bromide,
although what becomes of that excess has not yet been
determined.

When an electric spark is passed through a mixture of
oxygen and hydrogen, an explosion takes place; the
gases combine, and water is formed. Any excess of
hydrogen is, however, unaffected. Now the gases evolved
from a solution of radium bromide make glass luminous in
the dark, and possess the power of discharging an electro-
scope, like radium bromide itself. Rutherford and Soddy
discovered that when this mixture of gases is led through
a tube shaped like a U, cooled to — 185° C. by dipping in
liquid air, the luminous gas condenses, and the gases
which pass on have nearly ceased to be luminous in
the dark, and no longer discharge an electroscope. To
such condensable gases Rutherford applied the term
' emanation ' ; this one is known as the ' radium emana-
tion.'

The next question to be answered was : Is the helium
evolved from the radium bromide directly, or is it a pro-
duct of the emanation ? It was necessary, therefore, to
collect the emanation and to examine its spectrum. This
was managed, after many unsuccessful trials, by exploding
the mixture of oxygen and hydrogen containing the
emanation, allowing the remaining hydrogen to pass into
a tube containing a thin spiral of slightly oxidised copper
wire kept at a red heat by an electric current: the
hydrogen combined with the oxygen of the oxide of

186 ESSAYS BIOGRAPHICAL AND CHEMICAL

copper, and formed water. The apparatus was so arranged
that mercury could be allowed to enter the tube from
below, so as to sweep before it any remaining gas ; and
the water was removed from the gas by making it pass
through a tube filled with a suitable absorbing agent,
followed up by mercury. The gas finally entered a very
small spectrum-tube, entirely made of capillary tubing,
like the stem of a thermometer. On passing a discharge
from a coil through the spectrum-tube after the emanation
had been thus introduced, a spectrum was seen, consisting
of some bright green lines ; but it was extremely difficult
to prevent the presence of traces of carbon compounds,
and at this stage their spectrum was always seen. But
the D3 line of helium was absent. After a couple of days,
however, a faint yellow hue began to appear, identical in
position with D3 ; and as time went on, that line became
more distinct, and was followed by the other lines charac-
teristic of helium, until, after a week, the whole helium
spectrum was visible. It was thus proved that the radium
emanation spontaneously changes into helium. Of course
other substances might have been, and undoubtedly were,
formed ; but these it was not possible to detect.

The next problem was to measure the amount of
emanation, resulting from a given weight of radium, in a
given time. The method of procedure was similar to that
already described, except in one respect : the spiral of
oxidised copper wire was omitted, and the excess of
hydrogen, mixed with the emanation, was cooled in a small
bulb by help of liquid air. This condensed the emanation;
and the hydrogen, which of course is not liquefied at the
temperature of liquid air, was pumped away. On removal
of the liquid air, the emanation became gaseous, and it
was forced by means of mercury into a minute measuring
tube, like the very narrow stem of a thermometer. It
was thus possible to measure its volume. It is a well-

RADIUM AND ITS PRODUCTS 187

known law that gases decrease in volume proportionally
to increase of pressure ; if the pressure is doubled, the
volume of the gas is halved, and so on. Now this was found
to be the case with the emanation ; hence the conclusion
that it is a gas, in the ordinary meaning of the word.
But it is a very unusual gas ; for not only is it luminous
in the dark, but it slowly contracts, day by day, until it
practically all disappears. It does not lose its luminosity,
however ; what remains, day by day, is as luminous as
ever ; but its volume decreased, until after about twenty-
five days the gas had contracted to a mere luminous
point. What had become of the helium ? That was dis-
covered on heating the tube. It is well known that glass,
exposed to the radium emanation, turns purple, if it is
soda glass; brown, if it is potash glass. This is due to
the penetration of the glass by the electrons, which are
exceedingly minute particles, moving with enormous
velocity. When the emanation changes into helium,
the molecules of that gas are also shot off with enormous
velocity, although they move much more slowly than the
electrons. It is sufficient, however, to cause them to
penetrate the glass ; but on heating they are evolved, and
collect in the tube, and the volume of the helium can be
measured. It turned out to be three and a half times
that of the emanation. But as the emanation is probably
fifty times as heavy as hydrogen, all the emanation is
not accounted for by the volume of helium found; it is
almost certain that solid products are formed, which are
deposited on the glass, and which are radioactive. Up to
the present these products have not been investigated
chemically.

It was possible, knowing the volume of the emanation,
and knowing also the volume which the radium would
have occupied had it, too, been gaseous (for a simple rule
enables chemists to know the volume which a given

188 ESSAYS BIOGRAPHICAL AND CHEMICAL

weight of any element would occupy in the state of gas),
to calculate how long it would take for the radium to be
converted into emanation, supposing that to be its only
product. This gives for half of the radium to be decom-
posed about 1150 years. But there is a good deal of
conjecture about the calculation; for many unproved
assumptions have to be made.

A further experiment, conducted in a somewhat similar
manner, but with the utmost precaution to exclude every
trace of foreign gas, made it possible to measure the
position of the lines of the spectrum of the emanation.
In general it may be said that the spectrum has a similar
character to those of argon and helium ; it consists of a
number of bright lines, chiefly green, appearing distinctly
on a black background. It confirms the supposition,
made after examination of the chemical properties of the
emanation, that it is a gas belonging to the argon group,
with a very heavy atomic weight. Some of the lines of
the spectrum appear to be identical with lines observed in
the spectra of the stars ; and it may perhaps be inferred
that such heavenly bodies are rich in radium.

In the diagram on page 184, the bulb containing radium
bromide there shown was surrounded by a small glass
beaker, as a precautionary measure. As a matter of
fact, there were three such bulbs and three such beakers,
on the principle of not putting all one's eggs in
one basket. These beakers had never been in contact
with the radium bromide, nor with the emanation ; but
they had been bombarded for months by /3-rays, or
electrons, which are so minute, and move so rapidly, that
they penetrate thin glass with ease. It was found that
these beakers were radioactive ; and it is very remarkable
that after washing with water, the beakers lost their radio-
activity, which was transferred to the water. Evidently,
then, some radioactive matter had been produced by the

RADIUM AND ITS PRODUCTS 189

influence of the /3-rays. On investigation, it was proved
that more than one substance had been produced. For
on bubbling air through the water, a radioactive gas
passed away along with the air ; it had the power of dis-
charging an electroscope, but its life lasted only a few
seconds. It was only while the current of air was passing
through the electroscope that the gold-leaves fell together;
on ceasing the current, the leaves remained practically
stationary. Now had radium emanation been introduced
into the electroscope, its effect would have lasted twenty-
eight days ; had the emanation from thorium been intro-
duced, it would have taken about a minute before it ceased
to cause the gold-leaves to fall in. There is an emanation,
however, that from actinium, which is very short-lived,
and it looks probable that one of the substances produced
from the /3-rays is actinium. But it is not the only one.
For the water with which the glass was washed gives a
radioactive residue after evaporation to dryness; and it
contains a substance which forms an insoluble chloride,
sulphide, and sulphate, though the hydroxide is soluble in
ammonia. Either, then, the /3-rays have so altered the
constituents of the glass that new radioactive elements are
formed ; or perhaps it is the air which surrounds the glass
which has yielded these new elements ; or it may be,
though this appears less probable, that the /3-rays them-
selves, which are identical with electrons, or 'atoms' of
negative electricity, have condensed to form matter.

Such are some of the results which have been obtained
in a chemical examination of the products of change of
radium. The work is merely begun, but it leads to a
hypothesis as regards the constitution of radium and
similar elements, which was first put forward by Ruther-
ford and Soddy. It is that atoms of elements of high
atomic weight, such as radium, uranium, thorium, and the
suspected elements polonium and actinium, are unstable ;

190 ESSAYS BIOGRAPHICAL AND CHEMICAL

that they undergo spontaneous change into other forms of
matter, themselves radioactive, and themselves unstable ;
and that finally elements are produced which, on account
of their non-radioactivity, are, as a rule, impossible to
recognise, for their minute amount precludes the applica-
tion of any ordinary test with success. The recognition of
helium, however, which is comparatively easy of detection,
lends great support to this hypothesis.

The natural question which suggests itself is : Are other
elements undergoing similar change ? Can it be that
their rate of change is so slow that it cannot be detected ?
Professor J. J. Thomson has attempted to answer this
question, and he has found that many ordinary elements
are faintly radioactive ; but the answer is still incomplete,
for, first, radium is so enormously radioactive that the
merest trace of one of its salts in the salt of another
element would produce such radioactivity ; and, second, it
is not proved that radioactivity is an invariable accompani-
ment of such change ; or, again, it may be evolved so
slowly as to escape detection. A lump of coal, for
example, is slowly being oxidised by the oxygen of the
air; oxidation is attended by a rise of temperature, but
the most delicate thermometer would detect no difference
between the temperature of a lump of coal and that
of the surrounding air, for the rate of oxidation is so
slow.

Another question which arises is : Seeing that an element
like radium is changing into other substances, and that its
life is a comparatively short one, it must be in course of
formation, else its amount would be exhausted in several
thousand years. An attempt has been made by Soddy to
see if uranium salts, carefully purified from radium, have
reproduced radium after an interval of a year; but his
result was a negative one. Possibly some other form of
matter besides uranium contributes to the synthesis of

RADIUM AND ITS PRODUCTS 191

radium, and further experiments in this direction will be
eagerly welcomed.1

Lastly, the experiments of Ramsay and Cook, of
which an account has been given, on the action of the
/3-rays appear to foreshadow results of importance.
For while radium, during its spontaneous change, parts
with a relatively enormous amount of energy, largely
in the form of heat, it is a legitimate inference that
if the atoms of ordinary elements could be made to
absorb energy, they would undergo change of a con-
structive and not of a disruptive, nature. If, as looks
probable, the action of /3-rays, themselves the con-
veyers of enormous energy, on such matter as glass,
is to build up atoms which are radioactive, and con-
sequently of high atomic weight ; and if it be found that
the particular matter produced depends on the element
on which the /3-rays fall, and to which they impart their
energy : — if these hypotheses are just, then the transmuta-
tion of elements no longer appears an idle dream. The
philosopher's stone will have been discovered, and it is
not beyond the bounds of possibility that it may lead to
that other goal of the philosophers of the dark ages — the
elixir vitce. For the action of living cells is also dependent
on the nature and direction of the energy which they
contain; and who can say that it will be impossible to
control their action, when the means of imparting and
controlling energy shall have been investigated ?

1 There appears to be an intermediate product to which the name
' ionium ' has been given by Boltwood, its discoverer.

WHAT IS ELECTRICITY ?

AN old friend of mine, by profession a banker, who
spent a large portion of his life of eighty-nine years in
studying geology and astronomy, once put to me the
question : ' Whence comes the motive power of electricity ?
I can understand the motive power of steam, but not of
electricity.'

This led me to think on the subject ; and although there
is not much new in my reply, it contains, nevertheless, one
novel point, which contributes, I think, to clearness of
thought.

The answer refers only to electricity generated by a
battery ; not to a current made by means of a dynamo
machine. The answer to the question, What generates a
current in a dynamo ? must be left till a later oppor-
tunity.

The simplest form of a battery consists of a vessel
containing dilute hydrochloric acid, into which dip a
copper and zinc plate, connected by a wire. A current
flows through the wire ; its presence can be demonstrated
by a galvanometer, or by dipping the wire from the copper
plate and the wire from the zinc plate into a solution of
iodide of potassium ; a brown stain begins to appear at
the end of the wire connected with the zinc plate ; it is
caused by the iodine being set free, which dissolves in the
liquid with a brown colour.

If it is desired to make the test more striking a little
starch may be added to the solution of iodide of potassium.

N

194 ESSAYS BIOGRAPHICAL AND CHEMICAL

The colour will then be blue, for iodine and starch give a
blue colour. Now why does the current pass ?

To explain this, let us consider what happens to a
lump of sugar lying at the bottom of a cup of water.
After a few minutes the sugar will melt, or, more cor-
rectly, dissolve in the water. But the water at the top
will not be sweet for a long time ; the sugar takes a good
many minutes before it spreads up into the water. Why ?
It is believed that sugar consists of minute invisible
particles called molecules ; and they are in motion.

Although we cannot see molecules move, we may
nevertheless make an experiment which will prove to us
that particles of matter, easily visible under a fairly
powerful microscope, are always in rapid motion.

An ordinary water-colour paint, rubbed with water,
gives particles of a convenient size ; gamboge is perhaps
the best colour to take. These particles are always
'jigging' to and fro; their motion is not regular, but
spasmodic; and they spread, in virtue of that motion;
so that they move from one part of the water to
another.

So it is with the sugar molecules ; that they do spread
is proved by the water becoming sweet, even at the
surface. In fact the sugar particles try to move from
where they are to where they are not. If one felt inclined
to moralise on the subject, one might ask, Is not that
what we all try to do ? Is not an attempt at motion what
makes for progress of all kinds in the world ?

If such motion could be hindered, say by a screen which
would block the passage of the sugar molecules, while
allowing the water molecules to pass, the sugar molecules
would bombard the screen, giving it innumerable blows,
and these blows would make themselves evident as a kind
of pressure on the screen.

This pressure has been measured ; a partition has been

WHAT IS ELECTRICITY? 195

found which allows the water to pass, while blocking the
way for sugar. It is as if gravel of two sizes were being
shaken on a sieve; the stones which pass through the
meshes do not press on the sieve, while those which are
stopped by the sieve may be recognised by their
pressure.

Substances other than sugar, too, can be stopped by the
same screen ; for example, tartaric acid can. And it has
been found that the pressure produced by equal numbers
of molecules or particles of sugar and of tartaric acid,
contained in equal volumes of water, is equal.

Common salt is a compound of a metal named sodium
and a yellow-green gas called chlorine. Each molecule or
particle of salt must therefore contain these two elements ;
that is, each particle must be made up of at least two
smaller particles, and these smaller particles are called
' atoms.' If a spoonful of salt be placed at the bottom of
a glass of water, like the sugar, its particles will wander
through the water, so that, after some time, the water will
become salt all through.

Just as with sugar, it is possible to find a membrane
which will allow water to pass through it, while it stops
the passage of salt; and it is possible to measure the
pressure of molecules of salt on the membrane.

Now here a very curious thing has been found ; mole-
cules of salt give twice as great a pressure as an equal
number of particles of sugar, spread through the same
volume of water ; it looks as if there were twice as many
particles of salt present. And it is supposed that there
really are twice as many. To account for this, it is
believed that each molecule of salt splits up into two
atoms, one of sodium and one of chlorine, and that each
atom plays the part of a molecule, in so far as it is able to
raise pressure. Owing to the habit which such minute
particles as the atoms of sodium and chlorine have of

196 ESSAYS BIOGRAPHICAL AND CHEMICAL

moving about in a watery solution, they are named ' ions,'
a Greek word, which means ' wanderers.'

But an ion is not merely a wandering particle; the
moving particles of sugar are not called ions. The ions
contained in a solution of salt have another peculiarity ;
one has gained, and the other has lost, what we may term
an atom of electricity. Now what is electricity ?

It used to be believed, formerly, that there were two
kinds of electricity, one called positive and the other
negative. At that time it would not have been possible
to answer the question. But recent researches make it
probable that what used to be called negative electricity
is really a substance. Indeed the relative weight of its
particles has been measured ; each is about one seven-
hundredth of the mass of an atom of hydrogen : and the
mass of an atom of hydrogen is the smallest of all
masses of what we have been used to call matter.

Atoms of electricity are named ' electrons ' ; they appear
to be all of one kind. The metal sodium, and indeed all
other metals, may be regarded as compound of electrons
with a stuff which may be named ' sodion ' for sodium,
' cuprion ' for copper, ' ferrion ' for iron, and so on. When
sodium loses an electron it becomes ' sodion ' ; when iron
loses three electrons it becomes ' ferrion,' and similarly
with the rest.

How can sodium be made to lose its electron ? This
happens when it enters into combination. When sodium
is heated in air, which contains oxygen gas, it burns, and
is said to unite or combine with oxygen ; burning appears
to be accompanied by a transference of an electron from
the sodium to the oxygen. Common salt may be made
by heating sodium in chlorine gas ; it takes fire, burns
and is changed into white ordinary salt. It has lost an
electron ; chlorine has gained one.

When dissolved in water, the sodium exists in the water

WHAT IS ELECTRICITY ? 197

as sodion ; that is, sodium less an electron. The chlorine
is in the water, not as chlorine ; by gaining an electron, it
has been converted into chlorion. We see, therefore, that
those elements which we call metals become ions by
losing electrons; while those which we call non-metals
become ions by gaining electrons.

Let us now consider the simple battery or cell, consist-
ing of a plate of copper and a plate of zinc, dipping in a
jar half full of dilute hydrochloric acid. This hydro-
chloric acid consists of a number of ions of hydrogen;
and ions of hydrogen differ from ordinary hydrogen gas
in the same way as ions of sodium differ from metallic
sodium, namely, by each atom having parted with an
electron. The electron which each atom has lost has
attached itself to an atom of chlorine, and the chlorine
atom is thereby converted into an ion.

The plate of zinc cannot dissolve in the water, until its
atoms have been converted into ions. They would then
each have to part with two electrons. But the attraction
of an atom of zinc for these two electrons is so great that
the zinc does not dissolve, unless, indeed, the electrons
can be conveyed elsewhere.

Now electrons have the power of travelling through
metal; this point will be considered later; it must be
accepted for the present. When an atom of zinc gives up
its two electrons to the zinc plate, the atom of zinc which
lies nearest to that which has parted with these two elec-
trons will be overloaded ; it already is in combination with
its own two, and cannot unite with two additional ones ;
or, if it does, it must pass on its own electrons to the
neighbouring atom.

These two electrons, therefore, displace others, or, it may
be, are themselves transmitted through the zinc, until
they reach the copper wire. Copper, in the metallic
state, is also a compound of copper ions with two elec-

198 ESSAYS BIOGRAPHICAL AND CHEMICAL

trons ; and the copper, like the zinc, is overloaded by the
electrons from the zinc. Hence it transmits them to the
copper plate, and they find their way to the surface of the
plate.

There they find hydrogen ions, which are ready to com-
bine each with one electron in order to form hydrogen
atoms ; and having combined, the atoms of hydrogen
unite in couples, bubbles of hydrogen are formed, and
float up to the surface and burst. In short, the zinc
passes on its electrons through the copper wire to the
copper plate, when they are transmitted to the ions of
hydrogen in solution, and these first become atoms and
then molecules.

These conceptions, which are rather intricate, may be
rendered clearer by means of a diagram, a is the solu-
tion of hydrochloric acid in water ; b is the zinc plate ;
c is the copper plate, and d the connecting wire. H H, on
the left of the diagram, are two atoms of hydrogen, each

c b

EXPLANATION OF A GALVANIC CELL

of which has gained an electron ; they will unite together
to a molecule, and escape in a bubble up through the

WHAT IS ELECTRICITY? 199

liquid. The electrons which they have gained have
followed the arrows from the zinc plate, along the copper
wire and down the copper plate.

A zinc atom minus its two electrons has left the zinc
plate ; it is now a zinc ion. These two electrons have dis-
placed other electrons from their combination with zinc
and copper ; and it is these electrons, or their substitutes,
which have attached themselves to the hydrogen ions.
There are hydrogen and chlorine ions in the liquid. The
hydrogen ions move toward the copper plate, and the
chlorine ions toward the zinc plate, but less rapidly.

Some of these will touch the zinc plate ; and if they
could pass round the circuit, through the wire, there
would be no electric pressure ; but it is because the plates
and the connecting wire are impervious to matter, while
they are pervious to electrons, that electric pressure — or
to give it the usual name, electromotive force or potential
— is developed. In fact, the metals and the wire are semi-
permeable membranes ; they allow electrons to pass, while
they block the passage of matter.

Perhaps the idea may be somewhat more easily grasped
if it is put in another form. Electrons do not pass
through water; probably because the treble combination
of electrons, hydrogen, and oxygen is too firm to allow
of the transference of electrons from one molecule to
another. But when a salt is dissolved in the water elec-
trons can pass, for they easily transfer themselves from one
place to another, carrying along with them atoms such as
chlorine. Their progress is much impeded thereby ; but,
as explained before, they are easily transmitted through
metals, and thus, again, electric pressure is developed.

The analogy with ' osmotic pressure,' as the pressure of
the sugar molecules dissolved in water against a semi-
permeable membrane is called, is obvious; just as the
water in which the sugar is dissolved can pass in and out

200 ESSAYS BIOGRAPHICAL AND CHEMICAL

through the semi-permeable screen or partition, so the
electrons can pass backwards and forwards through the
metallic plates and wire; and just as the sugar molecules
are unable to traverse the membrane, so the matter with
which the electrons are in combination is unable to pass
through the metal. The metal is thus a semi-permeable
membrane, and electric pressure is developed in con-
sequence, in the same way as osmotic pressure is developed
by the sugar in solution.

If a weak solution of common salt be boiled down, after
sufficient water has been evaporated away, crystals of salt
separate out and deposit. Now the weak solution con-
tains the constituents of the salt almost entirely in the
state of ions ; that is, the sodion is without an electron,
which, if added, would convert it into the metal sodium ;
and the chlorion would be the element chlorine, if it
could part with its electron.

During concentration, as the water evaporates, the ions
of sodium and chlorine are brought nearer each other,
and they combine to form solid salt when enough water
has been removed. But even when combined to form
salt in the solid state, the electron does not leave the
chlorion and attach itself to the sodion ; if that happened
the result would be metallic sodium and chlorine gas;
and they are certainly not formed. A crystal of salt
differs from a solution of salt in much the same respects
as a piece of ice differs from water ; the one is solid and
the other is liquid ; but evidently the same stuff is there ;
the only difference is in the solidification.

It must therefore be supposed as a legitimate inference
that when a lump of sodium unites with chlorine and
burns in it as a lump of coal burns in air, the act of
combination consists of the transference of an electron
from the sodium metal to the chlorine ; the result of this
transference is to convert the sodium metal into sodions

WHAT IS ELECTRICITY? 201

and the chlorine gas into chlorions. These are substances
with quite different physical and chemical properties from
the metal sodium and the gas chlorine.

On dissolving in a little water, some of the chlorions
and sodions, but only a few, become separated ; however,
if water be added so as to dilute the solution, a larger and
larger number separate, until at a sufficient dilution all
are separated. In fact, if this conception be extended,
all chemical combinations should be regarded as the
transference of electrons from one set of elements to
another.

But not all compounds are split into ions when they
are dissolved ; it may be conjectured that in the case for
instance of such a compound as sugar, which dissolves in
water as such, the atoms of carbon, hydrogen, and oxygen,
of which it consists, have interchanged electrons, otherwise
chemical combination would not exist ; but that the ions
do not part from each other, even when opportunity is
given by dissolving the sugar in water.

Although facilities for motion in many cases lead to
separation of ions, it does not follow that when facilities
are present separation will always take place.

When common salt is melted, which takes place if it be
heated to redness, the ions separate ; that this is the case
is proved by its being then able to conduct electricity.
Melted glass is also a conductor, although solid glass is
not ; and the reason again is probably in the fact that the
ions have no freedom of motion in the solid.

These considerations, however, though closely connected
with the nature of ions, are not in such close touch with
the subject of this essay, the motive power of electricity.
Perhaps a last analogy may make the explanation which
I have tried to give somewhat clearer ; it is this :

Place a dilute solution of salt in one vessel and a
concentrated solution in another ; cover both vessels with

202 ESSAYS BIOGRAPHICAL AND CHEMICAL

a bell jar; pump out all air, so that the bell jar is filled
only with vapour of water, and leave the whole standing
for a long time. The weak solution will grow stronger,
for it will evaporate; and the strong solution will grow
weaker, for the vapour of water will condense in it. Now
imagine that the two salt solutions are placed, not under
the same bell jar, but under two separate bell jars, and
that these bell jars are connected by a pipe. In the
middle of this pipe is a little engine ; the pipe from the
weak solution enters the steam pipe of the cylinder, and
the pipe leading from the cylinder, which would in an
ordinary engine lead to the exhaust, is connected with the
bell jar containing the stronger salt solution; then, if the
engine is delicate enough, it will be driven by the current
of vapour passing from the weak salt solution to the strong
one.

Why? Because although steam can pass away from
the surface of the water, salt cannot; the surface of the
water is a diaphragm which will allow steam to pass, but
which is impenetrable for salt.

The analogy with a battery is this: The zinc plate is
like the weak solution of salt ; when it dissolves, it gives
up electrons at its surface ; these electrons can pass along
the wire, which is the analogue of the steam-pipe; if
required, a small magneto-electric engine could be inter-
posed so that it would be driven by the current passing
through the wire, that is, by the stream of electrons,
just as the steam-engine is driven by the current of
steam.

On arriving at the copper plate the electrons combine
with hydrogen ions and escape ; and in this respect the
battery described resembles rather a high pressure engine.
But if desired the electrons may be kept in the system ; it
is only necessary to surround the copper plate with some
substance such as sulphate of copper, and the electrons

WHAT IS ELECTRICITY? 203

are retained by uniting with the copper ions, when copper
atoms will be deposited on the copper plate.

Just as the surface of the water forms a diaphragm
through which salt cannot pass, while steam can, so the
surface of the zinc plate forms a diaphragm through
which matter such as zinc, hydrogen, or chlorine ions
cannot pass, while electrons can, and they are also able to
be conveyed by the wire, as steam is conveyed through
the pipe. The motive power both of steam and electricity,
in a word, is due to their passing from a region where
their pressure is high to where it is low.

THE AUKORA BOREALIS

THE Northern Lights, or the Merry Dancers, as they are
often called, must have attracted attention in our country
ever since it was inhabited. But whether owing to their
frequent appearance they escaped chronicling, or whether
records of natural phenomena were regarded as unim-
portant, I can find no mention of them in Scottish records.
South of the border and across the English Channel
mention is occasionally made of them ; for in these more
southern regions their occurrence was sufficiently un-
common for the display to attract attention. They were
often supposed to portend disaster. An account of an aurora
seen in London in 1560 likens it to ' burning spears' : —

' Fierce fiery warriors fight upon the clouds,
In ranks and squadrons and right form of war.'

An aurora was described by Cornelius Genune, Professor
at Louvain, in 1575 ; several were seen by Michael Mestlin,
tutor to the famous Kepler, in 1580; and in April and
September 1581, and in September 1621, brilliant auroras
were chronicled. From that date until 1707 there is no
mention of an aurora having been seen.

It has long been known that the compass-needle, which
usually points northward, and is inclined at an angle to
the horizon (or is said to ' dip '), becomes disturbed and
oscillates when an aurora is seen in the sky. It was the
celebrated Halley l who, in 1714, hazarded the bold con-
jecture that the aurora was therefore a magnetic pheno-

1 Philosophical Transactions, xxix. No. 341.

205

206 ESSAYS BIOGRAPHICAL AND CHEMICAL

menon ; the oscillations of the compass may even exceed
ten minutes of arc, as observed by Mr. James Glaisher l in
1847. And many hypotheses have been brought forward
to account for the connection between the two simul-
taneous phenomena. The last few years have seen the
equipment of expeditions to Iceland, Finland, and Northern
America, which have had for their principal object the
observation of the earth's magnetic disturbances and the
corresponding auroral displays. Many theories have been
advanced, and it will be my task to try to bring them
before you, and to supplement them where they appear to
be wanting.

Let us first, however, listen to an eloquent description
of the Northern Lights from the pen of the celebrated
Alexander von Humboldt : 2 —

* Low down in the distant horizon, about the part of the
heavens which is intersected by the magnetic meridian
(i.e. the point to which the compass-needle is directed),
the sky, which was previously clear, is at once overcast.
A dense wall or bank of cloud seems to rise higher and
higher, until it attains an elevation of 8 or 10 degrees.
The colour of the dark segment passes into brown or
violet, and stars are visible through the smoky stratum,
as when a dense smoke darkens the sky. A broad,
brightly luminous arch, first white, then yellow, encircles
the dark segment. . . . The luminous arch remains some-
times for hours together, flashing and kindling in ever-
varying undulations before rays and streamers emanate
from it and shoot up to the zenith. The more intense
the discharge of the northern light, the more bright is the
play of colours, through all the varying gradations from
violet and bluish-white to green and crimson. The mag-
netic columns of flame rise either singly from the luminous

1 Philosophical Transactions, Iviii.

2 Cosmos (Bohn's edit.), vol. i. p. 189.

THE AUROKA BOREALIS 207

arch, blended with black rays similar to thick smoke, or
simultaneously in many opposite points of the horizon,
uniting together to form a nickering sea of flame, whose
brilliant beauty admits of no adequate description, as the
luminous waves are every moment assuming new and
varying forms. Round the point in the vault of heaven
which corresponds to the direction of the inclination of
the needle, the beams unite together to form the corona —
the crown of the northern light — which encircles the
summit of the heavenly canopy with a milder radiance
and unflickering emanations of light. It is only in rare
instances that a perfect crown or circle is formed; but,
on its completion, the phenomenon has invariably reached
its maximum, and the radiations become less frequent,
shorter, and more colourless. The crown and the luminous
arches break up, and the whole vault of heaven becomes
covered with irregularly scattered broad, faint, almost
ashy grey, luminous, immovable patches, which in their
turn disappear, leaving nothing but a trace of the dark
smoke-like segment on the horizon. There often remains
nothing of the whole spectacle but a white, delicate cloud,
with feathery edges, or divided at equal distances into
small roundish groups, like cirro-cumuli.'

These phenomena are also visible in the Southern
hemisphere, and are produced by the Aurora Australis.

The luminous arches were also well described by Mr.
William Key in a letter to Dr. Priestley, published in the
Philosophical Transactions for 1783. He noticed that
the summit of the arch passed near or through the pole-
star; the arches were not always accompanied by the
' dancers.' Key, following Canton unwittingly, connected
the aurora with discharges of electricity through rarefied
gases. His words are: 'Let me hazard a conjecture
respecting the white colour and stationary appearance of
some of these arches. Experiments in electricity, made

208 ESSAYS BIOGRAPHICAL AND CHEMICAL

with what is called an ' exhausted ' receiver, show that the
colour and motion of the electric spark vary in proportion
to the rarity of the air in the receiver. The more the air
is rarefied, the more movable and coloured is the electric
aura passing through it. On the contrary, the colour of
the spark approaches to whiteness, and moves with greater
difficulty, as the air is admitted. Will this observation
serve in any measure to account for the difference in
colour and motion of these electrical arches, for such I
presume to call them ? May we not suppose the more
coloured and brilliant portions of the aurora borealis to be
made in the rarer parts of the atmosphere, while the more
white and stationary ones possess the denser parts ? The
whitest arches which I saw were the most fixed.'

Repeated attempts have been made to ascertain the
height of an aurora. Henry Cavendish, the celebrated
chemist, calculated the height from the data furnished by
three observers of an aurora which was seen in 1784 — one
of whom was stationed at Cambridge, one at Kimbolton
in Huntingdonshire, and one at Blockley in Gloucester-
shire— by simple trigonometry, knowing the angle which
the summit of the arch appeared to subtend with the
horizon in each case ; the results are very reasonably con-
cordant, and give an altitude of 52 to 71 miles. Many
subsequent attempts have been made, and with similar
results. One of the latest writers, Professor Birkeland,
of Christiania, gives as limits 62 to 124 miles (100-200
kilometres). The difficulty in such observations is to
make sure that the observers in different places have
been measuring the same arch at the same moment. I
shall have occasion later to bring evidence of a totally
different character to confirm the general accuracy of such
measurements.

Between the years 1786 and 1793 John Dalton, who
was as indefatigable a meteorologist as he was a distin-

THE AURORA BOREALIS 209

guished chemist, observed, from Kendal and Keswick, in
Cumberland, no fewer than 250 displays of northern
lights ; he established the fact that the highest part of the
luminous arc lies exactly above the magnetic pole, and
that the streamers are parallel, at least ' over a moderate
extent of country,' with the compass-needle as it dips
towards the magnetic pole, which is believed to exist in
the north of Canada, within the Arctic circle.

The celebrated De la Rive, of Geneva, made an attempt
to reproduce the aurora in the interior of a glass vessel.1
He started from the fact that the atmosphere is always
charged with positive electricity, and that the earth is
negatively electrified ; he presumed, accordingly, that the
two kinds of electricity would neutralise one another, and
that currents would, as a rule, rise vertically to the earth's
surface. Neutralisation occurs slowly when rain or snow
falls, and suddenly when lightning flashes. De la Rive's
theory is that in the upper regions of the atmosphere
electric currents circulate from the equator to the two
poles ; and terrestrial currents, in the interior of the earth,
are continually flowing from the poles towards the
equator. Conduction, he thought, would be easier in the
higher than in the lower regions of the atmosphere, and
also better at the poles than near the equator, because of
the moisture and frequent mists in the polar atmosphere.
The discharge through the polar air would, he believed,
render the mist luminous, and thus produce the pheno-
mena already described.

His apparatus, which I had the good fortune to see in
September 1902 at Geneva, consisted of a globe with a
neck at each ' pole.' Through one of these necks passed
a copper rod A, one end of which was connected with the
positive discharge of an electrical machine ; at the other
end a ring of copper B was attached. G is an insulated

1 Mtmoires de la Soc. de Phys. et d 'His. Nat. de Geneve, vol. xiii.
O

210 ESSAYS BIOGRAPHICAL AND CHEMICAL

soft-iron bar covered with an insulating composition, and
projecting through the opposite neck of the flask. By
touching the exposed end of this rod with an electro-

DE LA RIVK'S APPARATUS FOR REPRODUCING THE AURORA

magnet D, it also became a magnet. The air in the globe
having been rarefied, a brush discharge took place between
the ring B and the end of the rod (7; on making C a
magnet, the discharge became more luminous and regular,
and revolved round the magnet, sending streamers towards
the end of the rod. In De la Rive's model the copper
ring represents the atmosphere, from which electricity
discharges to the rod C, representing the earth. He con-
cluded that the aurora forms a luminous ring round the
magnetic poles as centres, with a greater or less diameter,
the ring rotating on account of the earth's magnetism ;
that it is due to a discharge from the positively electrified
atmosphere to the negatively electrified earth, the separa-
tion of the two kinds of electricity being caused by the
action of the sun, chiefly in equatorial regions ; that
discharges are of constant occurrence, though with very
varying intensities, and that the cirro-cumulus clouds are
also illuminated by such discharges.

When the spectroscope was turned on the aurora the
presence of a green line of wave-length about 5570 units

THE AURORA BOREALIS 211

was noticed. Different observers gave : — Angstrom, 5568 ;
Vogel, 5572; Vijkander, 5573; Lemstrom, 5570; Huggins,
5570-4; Copeland, 5573; Gyllenskjold, 5569; Campbell,
557T6; Sykera, 5570; the Danish Mission to Iceland in
1899-1900, 5570. Many other lines have been photo-
graphed, of which more hereafter ; but this line is extra-
ordinarily intense, and, indeed, can often be seen when
there is no visible aurora by simply directing a pocket
spectroscope towards the north. The line when first
observed was not known to be characteristic of the
spectrum of any element.

In 1898 I had the honour to announce to the Royal
Society the discovery, in conjunction with my assistant,
Dr. M. W. Travers, of the existence of three new elemen-
tary substances in the atmosphere, to which we gave the
names — neon, or ' the new one ' ; krypton, or ' the hidden
one'; and xenon, or 'the stranger.'

The spectrum of neon is characterised by many lines
in the red, orange, and yellow ; while that of xenon
shows many green and blue lines. The light evolved
from tubes containing these gases under low pressure
when an electric current of high tension is passed through
them, is of a corresponding hue ; thus neon sends out a
splendid rose or flame-coloured light ; and xenon, a sky-
blue ; while the light of krypton is nearly white, although
seen by some of a pale lilac, and by others of a pale-green
colour.

The densities of the elements proved to be as had been
expected : that of neon, compared with hydrogen taken as
2, is 20 ; of krypton, 82 ; and of xenon, 128.

Shortly after the discovery of krypton, my assistant,
Mr. Baly, measured carefully the wave-lengths of its more
important lines ; and one of these, a very brilliant green
line, had the wave-length 5570'5. The day after this
was published, Sir William Huggins wrote me privately

212 ESSAYS BIOGRAPHICAL AND CHEMICAL

pointing out the identity of this wave-length with the
principal auroral line ; and a week later, Professor Arthur
Schuster, in a letter to Nature, called attention to the
same coincidence.

It therefore appeared probable that the aurora might
be produced by electric discharges in the upper atmo-
sphere, through a gas in which krypton was present in
considerable amount.

In the meantime Professor Paulsen, of Copenhagen,
has been examining the photographed spectra of the
aurora collected by the Icelandic and Finland expeditions;
and it appears probable that many of the lines seen in the
auroral spectrum are identical with those of the common
gas nitrogen, seen at the cathode terminal of a vacuum-
tube. Professor Paulsen has had the great kindness to
send me prints of two photographs, the lines of which are
numbered I. and II. in the following table. I have added
in a parallel column the corresponding wave-lengths of
krypton lines.

Lines of auroral and of cathode Lines of

nitrogen spectrum. krypton. Intensity.

I. II.

1 Absent. 3140

2 „ 3160

3 „ 3370

4 Absent. 3540

5 3580 3580 3590 7

c 3718 10

6 3710 Absent. < 3719 8

I 3721 7

7 3760 3760 3754 5

8 3800 3800 3805 4

9 3920 3920 3920 8
10 4000" 4000 {3995 6

THE AURORA BOREALIS 213

Lines of auroral and cathode Lines of

nitrogen spectrum. krypton. Intensity.

I. II.

11 4060 4060 4057 8

12 4260 4260 4274 8

13 5570 Absent. 5570 10

The last is the characteristic line of the aurora, and is one
of the two brilliant lines of the krypton spectrum; the
other brilliant krypton line is in the yellow, and cannot
be easily photographed when the light is not bright but
flickering, as the auroral light is.

I am not able to decide yet whether the lines are all
due to krypton or to the cathode spectrum of nitrogen.
Certainly there is a striking similarity between the
nitrogen spectrum and that of the aurora ; and, on the
other hand, the lines of krypton, though sufficiently
coincident with those of the aurora to satisfy criticism,
leave other bright lines of the krypton spectrum un-
accounted for. Yet the cathode spectrum of nitrogen
does not contain the line 5570, the most brilliant of the
auroral spectrum, and the one most easily discovered by
aid of a pocket spectroscope. Experiments on this matter
are not yet decisive.

Moreover, it appears improbable that the aurora should
always exhibit only one spectrum. The discharge of
electricity through a mixture of gases reveals more or less
completely the spectrum of each. Those gases which are
present in smallest amount have, as a rule, their spectra
proportionately enfeebled. But it does not always happen
that all the lines of the spectrum of any one gas are
proportionately enfeebled ; sometimes the character of the
spectrum itself is altered. The interposition of a Leiden
jar and a spark-gap often causes a radical alteration in
the spectrum of a gas. This can be well seen with argon ;
when the discharge is altered, many of the red lines of the

214 ESSAYS BIOGRAPHICAL AND CHEMICAL

spectrum disappear and blue lines become visible ; hence
the colour of the discharge changes from red to blue.
And other gases exhibit the same kind of change, though
not generally in so striking a manner. Further, it has
been shown by my colleague, Dr. Collie, that an element
may develop a new and strong line in its spectrum
on being mixed with a certain gas, which it does not
exhibit if another gas be substituted. All these questions
are very obscure, and have not as yet been investigated ;
only the fringe of the subject has been touched. As the
aurora, without doubt, is visible on different occasions at
very different altitudes, it is more than possible that the
spectra will differ. The appearance of red auroras would
imply a spectrum in which red lines predominate ; but I
am not aware of any observation having been made of the
spectrum of a red aurora. From the similarity of colour
it might well be conjectured that the red tint is due to
the discharge occurring through an atmosphere compara-
tively rich in neon.

Assuming for the moment the identity of the line of
wave-length 5570 with that of krypton, two questions at
once suggest themselves. First, why should this line be
so remarkably brilliant when krypton is present in the
atmosphere in comparatively very minute amount ?
What are the relative intensities of the spectra of krypton
and of other gases under similar circumstances ? And
second, is there any process which will tend to increase
the relative amount of krypton in the upper regions of
the atmosphere ? I have attempted to answer both these
questions.

Some years ago, in conjunction with Professor Collie,

experiments were made on the visibility of the spectrum

of one gas in presence of another with which it was

diluted.1 The results are given in the following table : —

1 Proc. Hoy. Soc., lix. 257.

THE AURORA BOREALIS 215

AMOUNT OF GAS DETECTABLE IN A MIXTURE

1. Helium in hydrogen, 10 per cent, of helium barely visible.

2. Hydrogen in helium, O'OOl „ of hydrogen visible.

3. Nitrogen in helium, O'Ol „ of nitrogen almost invisible.

4. Helium in nitrogen, 10 „ of helium difficult to detect.

5. Argon in helium, 0'06 „ still visible.

6. Helium in argon, 25 ,, invisible.

7. Nitrogen in argon, 0*08 „ just visible.

8. Argon in nitrogen, 37 „ barely visible.

9. Argon in oxygen, 2 '3 „ difficult to distinguish.

This table shows the enormous differences which exist
between the behaviour of different gases. To take the
extreme cases — while it is possible to detect 1 part of
hydrogen in 100,000 of helium, it is barely possible to
recognise 1 part of argon in 2 of nitrogen.

Similar experiments with krypton showed that
In air, 1 part of krypton is visible in 7,100 parts.

In oxygen, 1 „ „ „ 1,250,000 „

In hydrogen, 1 „ „ „ 67 „

In argon, 1 „ „ „ 7,150 „

In helium, 1 „ „ „ 2,860,000 „

The pressure of krypton, too, in the case of air is almost
inconceivably low ; it amounts to only one thirty-millionth
of the usual atmospheric pressure. This shows the enor-
mous persistency of the krypton spectrum — that is, of the
most conspicuous line, the auroral green, for that was the
one observed in all instances. If, then, an electric dis-
charge passes through the upper and rarefied strata of the
atmosphere, the probability of detecting the green line of
krypton will be much greater than that of detecting the
spectrum of any other element, even though the latter
be present in enormously greater proportion. Hydrogen
alone has any marked power of extinguishing the spectrum
of krypton.

It is possible to calculate the maximum height of the
aurora, on the supposition that the krypton line is no

216 ESSAYS BIOGRAPHICAL AND CHEMICAL

longer visible when the pressure falls below 0-000035
millimetre — the pressure observed when, in a mixture of
krypton and helium, the green line of krypton became
very faint and almost invisible. Neglecting the influence
of temperature, the pressure of the atmosphere can be
made to give its height by the formula —

H = 18-382 (log. B-log. b) kilometres.
Substituting for B (barometer) its normal height, 760
millimetres, and for b the pressure of the krypton, 0-000035
millimetre, we have height = 135 kilometres, or about 84
miles. This number is reasonably near the figures given
by Cavendish and others. Professor Birkeland, the latest
authority, it will be remembered, thinks the altitude is
from 100 to 200 kilometres,1 or from 62'5 to 125 miles.

We may next ask — Since the spectrum of krypton is
so persistent, why is it not visible in air ? The answer is
— Because the presence of nitrogen renders it invisible,
for it is not possible to distinguish less than one part of
krypton by volume in 7100 parts of air. But krypton
does not show its spectrum in argon, which may be said
to constitute about 1 per cent, of the volume of air. Now
7100 parts of air will yield about 70 parts of argon, and it
should be possible to distinguish the krypton line if the
amount of krypton present were 0-01 part, or 1 part in
7000. This would give, for the proportion of krypton
in air, 1 part in 700,000. Recent experiments, have
shown that it is possible to extract 1 part of krypton
from about 7,000,000 of air ; and of xenon, which, owing
to its lower vapour pressure, can be extracted from air
with more ease than krypton, there is only about 1 part
in 40,000,000 of air. It is therefore clear why the spec-
trum of krypton is not visible in that of crude argon.

We come next to the question — Is there any reason
to believe that krypton may concentrate in the higher

1 Expedition Norvtgienne, Christiania, 1901, p. 28.

THE AURORA BOREALIS 217

regions of the atmosphere, that is, that its proportion,
relatively to that of the more abundant gases oxygen and
nitrogen, may increase as the altitude grows greater ? To
this, I think, an affirmative answer may be given. Let us
consider the grounds for the supposition.

When a gas is compressed it turns warm, as every one
knows who has used a bicycle-pump. Conversely, when
it escapes from compression it cools itself. But all gases
do not heat or cool equally for equal amounts of compres-
sion or expansion ; for some gases are raised to a higher
temperature than others by absorbing the same quantity
of heat; and the same quantity of heat is, practically,
generated by the same degree of compression, or absorbed
by the same degree of expansion; for work is quanti-
tatively equivalent to heat, as was shown by Joule half a
century ago. Now 40 grams of argon should, if the
specific heat of that gas were the same as that of oxygen,
require the same amount of heat to raise its temperature
through 1 degree ; or put in another way, if each of these
gases were expanded to the same amount, they would be
equally cooled, if equal amounts of heat were requisite to
raise their temperatures through an equal number of
degrees. But this is not the case. Argon requires less
heat to raise its temperature than oxygen, in the ratio of
3 to 5 if it is not allowed to expand, or in the ratio
of 5 to 7 if expansion is possible under constant pressure.
If allowed to expand under circumstances in which volume
increases while pressure falls, some ratio intermediate
between these would show the difference in cooling ; the
exact amount depending on the degree of expansion in
question. Broadly stated, argon, in expanding will cool
itself considerably more than oxygen or nitrogen ; while its
congeners, helium, neon, krypton, and xenon, will exhibit
a degree of cooling practically identical with that of argon.

The next point to be considered is that gases diffuse

218 ESSAYS BIOGRAPHICAL AND CHEMICAL

freely into one another when left in contact; so that a
heavy gas will mix readily with a much lighter one, even
though the heavy one may be below and the lighter one
above. This diffusion results from the motion of the
molecules of gases ; and as the rate of motion depends on
the temperature of the gas, those molecules which happen
to have a high temperature move much more rapidly than
those with a lower. When two gases mix, however, or
when a hot gas mixes with a cold one, the more rapidly
moving, and therefore hot, molecules very rapidly com-
municate their motion to the colder gas, raising its
temperature until the temperatures of both sets of mole-
cules are equalised. This is due to the enormous number
of encounters which take place between the molecules,
partly on account of the minute size of each molecule,
and the consequent number in even a very small volume ;
and partly to the great rate at which they are moving.
For example, it can be calculated that in all probability
there are 50,000,000,000,000,000 or 50 quadrillion mole-
cules of hydrogen in a cubic millimetre of that gas (about
the volume of the head of a large pin) and that the
average velocity of each molecule is at the rate of 4| miles
per second. No wonder, therefore, that the exchange
between molecules of different temperature is almost
instantaneous. It must nevertheless be borne in mind
that hot gases diffuse much more rapidly than cold ones.
The densities of the gases constituting the atmosphere
are as follows, the standard being that of oxygen taken as
16:—

Water Vapour, 9 0'333 Neon, 10 0'316

Nitrogen, 14 0-287 Argon, 20 0'224

Oxygen, 16 0-250 Krypton, 41 0*156

Carbon Dioxide, 22 0-213 Xenon, 64 0-125

Helium, 2 0-707 -

THE AURORA BOREALIS 219

The relative rates of diffusion are inversely as the
square roots of the densities, and are given in the second
column. For example, oxygen escapes into a neighbour-
ing layer twice as quickly as xenon ; and helium nearly
three times as fast as oxygen. Now it is evident that the
gases which will escape most slowly are krypton and
xenon; carbon dioxide and argon come next in order;
while nitrogen, neon, water vapour, and helium escape
more rapidly in the order given. If then a jar with
porous walls were full of air, and were exposed to some
indifferent atmosphere, the gas remaining in the jar after
some time would contain more of the heavier and less of
thelighter gases proportionally to the original amounts
present.

The third premiss in the argument is that in equatorial
regions there is an upward current of air, due to the
warming of the earth by the nearly vertical rays of the
sun and the consequent expansion of the air in contact
with the soil or the sea ; while in the polar regions there
is a continual downward current, produced by the cooling
of the air in contact with the ice of the polar caps. This
circulation of the atmosphere was investigated by Professor
James Thomson in 1857, and his Bakerian lecture on the
subject appeared in the Philosophical Transactions for
1892, p. 653. The conclusion to which he came is that
the upward atmospheric current at the equator on reaching
the higher regions of the atmosphere, divides into two,
and while one part of the air travels in a north-easterly
direction, the other half travels in a south-easterly direction
towards the north and south poles respectively. Arrived
at the neighbourhood of the polar caps, the air descends
and, broadly stated, travels back near the surface of the
earth again towards the equator. We need not here regard
eddies which occur near the tropics of Cancer and Capri-
corn ; the main features are sufficient for our purpose.

220 ESSAYS BIOGRAPHICAL AND CHEMICAL

The air, then, as it ascends from equatorial latitudes
cools itself in the process ; and from what has been said,
it would seem that gases of the argon group would cool
more rapidly than the other atmospheric gases, oxygen
and nitrogen. Pour prdciser les iddes, as the French say,
let us confine our attention to the northern hemisphere,
and let us suppose that a vertical partition has been set
up in the neighbourhood of the equator, quite permeable
to gases, and surrounding the earth much as the wooden
frame of a terrestrial globe surrounds the globe. Indeed,
if we conceive of that frame as a double one, and the
ascending current rising between the walls, we shall
realise what is intended. As the upward current gains in
height, it falls in temperature ; and during the whole of
the ascent the nitrogen and oxygen are passing through
the porous diaphragm at a rate greater than that of the
argon gases. With increasing height the density of all
gases decreases ; their molecules are more widely separated
from each other, and interchange of velocity or, what is
equivalent, interchange of temperature becomes less rapid ;
hence the separation should be a more perfect one the
greater the altitude. But, at the same time, the argon
gases are not wholly left in the upward current; many
molecules will pass the barrier ; why should they not
return in as great number as they pass ? Because after
passing the partition they no longer move upwards with
the same velocity as before ; the farther they progress
towards the north the less inducement to rise, for the
temperature of the earth is lower.

This reasoning is equally applicable if we regard the
barrier as removed ; we may mentally surround the earth
with an infinity of such barrier rings, parallel to the plane
of the equator; and it will still remain true that the
warmer gases will tend to escape in the lower regions
of the atmosphere, leaving the cooler gases to ascend.

THE AURORA BOREALIS 221

At the poles the process is reversed. The argon gases
are more heated during their descent than the oxygen and
nitrogen, and will escape into neighbouring layers of
atmosphere at a greater altitude, on the average, than the
latter. The relative rates of diffusion of these gases, too,
may play an even more important part in effecting the
separation ; the heaviest — argon, carbon dioxide, krypton,
and xenon — will remain in the ascending layer in larger
relative proportion than the oxygen, nitrogen, and other
lighter gases, and will, therefore, be carried to the upper
regions of the atmosphere by the ascending equatorial
current ; but in the descending polar current the process
would be reversed, for the heavier gases would be carried
down in the current with less escape than the lighter
ones. The effect of diffusion alone, neglecting the heating
or cooling of the gases, would, therefore, be neutralised
during each complete circulation.

But the process of separation which depends on the
difference of temperature of the gases, were there only one
circulation, would in all probability be productive of very
small result ; it is to be observed, however, that the effect
is cumulative, that the process of concentration of the
argon gases in the higher regions of the atmosphere goes
on from age to age, and that there may now be an
apparently stationary state, when separation of argon
gases from oxygen and nitrogen balances mixture by
diffusion and the mixing which inevitably accompanies
winds. It may be suggested that the greater frequency
of auroras during years when the sunspots are large and
easily visible may be connected with the higher tempera-
ture of such years, as well as with the magnetic disturb-
ances which invariably accompany sunspots.

To sum up : — 1. The gases of the argon group are more
easily heated and cooled than are oxygen and nitrogen.
2. They are cooled more than the latter during their

222 ESSAYS BIOGRAPHICAL AND CHEMICAL

upward ascent at the equator, and therefore tend to con-
centrate in the ascending current as it reaches the con-
fines of the atmosphere, owing to the more rapid escape
of oxygen and nitrogen by diffusion. 3. The phenomena
are reversed in the descending currents at the poles, and
the argon gases tend to mix with neighbouring layers of
gas at high altitudes. 4. The higher strata of the atmo-
sphere are probably richer in the inactive gases than the
lower strata.

As electric discharges producing the aurora certainly
occur at great altitudes, the spectra seen are those of the
inactive gases; and owing to the fact that the krypton
green line, of wave-length 5570 units, is remarkably easily
visible, even in an admixture of other gases, it happens to
be the most conspicuous line in the auroral spectrum.

This leads us to consider, in the last place, the cause of
the electric current. And here we enter on a different
region of thought.

There are two theories on the subject, one due to Pro-
fessor Birkeland,1 of Christiania, the other to Professor
Arrhenius,2 of Stockholm. It has long been known that
violet light rays and the invisible rays of the spectrum
beyond the violet, which can be detected by photography,
have the property of discharging a negatively electrified
body. It is suggested by Professor Birkeland that the
spots on the sun are caused by solar eruptions, or, to use a
familiar word, volcanoes; and that the sun then emits
negatively charged corpuscles, similar to those which are
believed to constitute, partly at least, the cathode rays —
rays producing those utilised for surgical practice in taking
photographs of bones. Birkeland supposes that such
corpuscles are ' sucked in ' to the earth's magnetic poles,
giving rise to vortices of electric currents in the upper

1 Archives des Sciences Phys. et Nat. de Geneve, June 1896.
* Physikalische Zeituchrift, ii. Noa. 6 and 7.

THE AURORA BOREALIS 223

regions of the atmosphere. It is indeed known that such
rays are deviated by the neighbourhood of a magnet ; and
also that the presence of large solar spots is always
accompanied by magnetic ' storms ' on the earth and the
appearance of frequent and brilliant auroras.

The theory of Arrhenius is that the corpuscles emitted
by the sun are not inconceivably minute bodies, but have
an appreciable size ; that they are, say, the thousandth of
a millimetre, or the 25,000th of an inch in diameter, and
that they are expelled from the sun by the repulsive
action of light.

Whichever theory be correct, it is probable that nega-
tively electrified gaseous molecules are present in the
upper regions of the atmosphere, and it is also probable
that these molecules receive their charge most readily
where they are most exposed to a vertical sun, that is, at
and near the equator. We have seen that Professor James
Thomson's upper aerial currents would carry these and
other molecules towards the poles ; they would move
spirally northwards and southwards with an easterly
trend. As they approach the poles their number per unit
area will obviously increase ; for the terrestrial parallels of
latitude decrease in circumference the nearer they are to
the poles. It is to be expected that before the actual poles
are reached, the potential of the upper air should increase
to such an extent as to produce a luminous discharge, in
the form of a ring or halo, with the magnetic poles as
their centres. It is conceivably this ring which we see as
an arch in the sky ; it may not be so high as the coloured
streamers, and may well give the nitrogen spectrum. It
must be remembered, however, that the earth is a huge
magnet; and that lines of force connect the poles in a
fashion shown in the figure. The halo, exposed to these
magnetic forces, will send out streamers towards the poles
as well as towards the zenith ; as they approach the

224 ESSAYS BIOGRAPHICAL AND CHEMICAL

equator, however, the light will fade, owing to the spread-
ing and weakening of these lines.

An imperfect attempt has been made to imitate the
auroral phenomena, but it nevertheless shows in some
degree the appearance of the northern lights. A globe,
containing krypton at very low pressure, is suspended
between the poles of a powerful electro-magnet ; l a ring,
consisting of five or six coils of covered wire, is laid on
the top of the globe, and by help of an induction-coil and
a Leiden jar, strong induction discharges are made to
pass through the coil. Each discharge is accompanied by
a circular discharge in the interior of the globe. The
effect is that of a ring or halo near the upper side of the
jar. On 'making' the electro-magnet, the ring sends
out streamers, exactly similar in appearance to auroral
streamers, and like them they have a rotary motion and
flicker, shortening and lengthening, just as natural
streamers do. If it were possible to place a magnetic
model of the earth inside such a globe, I doubt not that
the streamers would follow directions similar to those in
the figure, and that the imitation would still more closely
resemble trie reality. The light evolved from pure
krypton, under the influence of such discharges, is of a
whitish steel-blue colour with occasional green and lilac
flickers, and it also recalls the appearance of the natural
aurora. But, as already remarked, it is more than
probable that the spectrum of the aurora, seen at different
times and in different altitudes, may show not only the
spectrum of krypton, but also those of the other atmo-
spheric gases.

One more remark before concluding. The temperature
of the upper atmosphere is undoubtedly very low ; but at
such altitudes even xenon, the least volatile of the atmo-
spheric gases, possesses so high a vapour pressure that it

1 The electro-magnet belonging to a small 1 h.p. dynamo was used.

DIAGRAM OF THE EARTH AND THE POLAR AURORAS

Facing page 224

THE AURORA BOREALIS 225

would certainly remain gaseous ; for in order to liquefy or
solidify a gas, not merely reduction of temperature, but
also considerable pressure, is required. It is, however,
quite possible that water-vapour, in the lower regions
frequented by the aurora, may exist in a supersaturated
condition, and that the electric discharges may bring
about condensation, and on the large scale of nature, as
on the small scale of a laboratory experiment, produce
mists, and so give rise to the cirro-cumulus clouds which
so often accompany an aurora.

The solving of conundrums has for many people a great
attraction; Nature surrounds us with conundrums, and
it is one of the greatest pleasures in life to attempt
their solution. Whether or not I have been successful
in offering a partial solution of the one which we may
call the ' Merry Dancers,' time will show.

THE FUNCTIONS OF A UNIVERSITY

ORATION DELIVERED AT UNIVERSITY COLLEGE, LONDON
JUNE 6, 1901

I AM about to speak of the Functions of a University.
The word University has borne many significations ; and,
indeed, its functions are various, and the signification
attached to the word has depended on the particular point
of view taken at the time. An eminent German, who
visited me some years ago, made the remark after seeing
University College: — ' Aber, lieber Herr College, University
College ist eine kleine Universitat.' So it is ; for it fulfils
most of the functions of the most successful Universities in
the world. A countryman of the gifted founder of this
College, Thomas Campbell, a man who has left even a
deeper mark than he on the literature of the world,
said : —

' 0 wad some Pow'r the giftie gie us
To see oursels as ithers see us ! '

Were that gift given us, I am confident that we should
have no cause to blush. One of the most necessary
conditions of success is confidence in oneself — 'a gude
consait of oursels,' as the Scots saying has it; and I
know that learned men throughout the world look on the
work done at University College as among the best pro-
duced. And why is this ? Because the traditions of
University College have always been that it is not merely
a place where known facts and theories should be ad-

227

228 ESSAYS BIOGRAPHICAL AND CHEMICAL

ministered in daily doses to young men and young women,
but that the duty of the professors, assistant-professors,
teachers, and advanced students is to increase knowledge.
That is the chief function of a University — to increase
knowledge. But it is not the only one.

A University has always been regarded as a training
school for the ' learned professions,' i.e. for Theology, Law,
and Medicine. The terms of our charter have excluded
the first of these branches of knowledge. Founded as it
was in the 'twenties, when admission to Oxford or Cam-
bridge involved either belief in the tenets of the Church
of England, or insincerity, it was not possible to provide
courses in Theology which should be acceptable to Non-
conformists, Jews, and others who desired education. On
the whole, it appears to me better that a subject, about
which so much difference of opinion exists, should be
taught in a separate institution. There are many branches
of knowledge which can be adequately discussed without
intruding into any sphere of religious controversy ; and,
indeed, it would be difficult, I imagine, to treat mathe-
matics or chemistry from a sectarian standpoint. I, at
least, have never tried. There are subjects which may be
placed on the border-line, for example, Philosophy; but
such subjects, and they are few in number, might well
form part of the curriculum of the theological college, if
thought desirable. It is a thousand pities that instead
of founding King's College, a theological college had not
been established in the immediate neighbourhood of
University College ; it would have strengthened us, and it
would have tended, too, to the advantage of the Church
of England. However, what is done can't be undone ;
and let us wish all prosperity to our sister college, and
a long and useful life. We are now friends, and have
been friends for many years. May that friendship long
continue !

THE FUNCTIONS OF A UNIVERSITY 229

Dismissing the Faculty of Theology, therefore, as out of
our power, as well as beyond our wishes, let us turn to the
remaining two learned professions. University College, I
believe, was the first place in England where a systematic
legal education could be obtained. Our chairs of Roman
Law, Constitutional Law, and Jurisprudence were the first
to be established in England, although such chairs had
for long been known on the Continent and in Scotland.
' Imitation is the sincerest flattery ' ; and in the fulness of
time, the Inns of Court started a school of their own.
Our classes, which used to be crowded, dwindled, and our
law -school is certainly not our strongest feature. I am
not sufficiently acquainted with English legal education
to pronounce an opinion as to whether methods of train-
ing as they at present exist in England are the most
effective : I have heard rumours that they are not. That
must be left to specialists to decide. But arguing from
the experience of another faculty, in which the apprentice-
ship system once existed, and which has changed that
system with a view to reform, and judging, too, from
experience abroad and in Scotland, I venture to think
that some improvement in legal education is possible. If
that opinion is correct, it is surely not too much to hope
that the claims of University College may be considered
as having made the first attempt to systematise legal
education in England.

The Faculty of Medicine has existed in a flourishing state
since the inception of University College. Not long after
the College was built, the old Hospital buildings, were
erected. One of my predecessors, on a similar occasion to
this, has given you an entrancing account of the early
history of this side of the College, and has discoursed on
the eminent men who filled the chairs in the Medical
Faculty. Here young men whose intention it is to enter
the medical profession are trained ; they now receive five

230 ESSAYS BIOGRAPHICAL AND CHEMICAL

years' instruction in the various branches of knowledge
bearing on their important calling. I would point out
that this function of a University is professedly a technical
one : the training of medical men. True, many researches
have been made by the eminent men who have held
chairs in this Faculty ; but that is not the primary duty
of such men ; their duty is to train others to exercise a
profession. If they advance their subject in doing so, so
much the better ; it increases the fame of the school, it
imparts enthusiasm to their students, and in many cases
their discoveries have been of unspeakable benefit to the
human race. In a certain sense, every medical man is an
investigator ; the first essential is that he shall be able to
make a correct diagnosis ; the next, that he shall prescribe
correct treatment. But novelty is not essential ; few men
evolve new surgical operations or introduce new remedies;
and though we have in the past had not a few such, they
are not essential for a successful medical school, the object
of which is to train good practical working physicians and
surgeons. The teaching staff of the Medical Faculty must
of necessity be almost all engaged in practice, and, indeed,
it would be unfortunate for their students if they were
merely theoretical teachers. Let me recapitulate my
point: the Medical Faculty is essentially a technical
Faculty ; the hospital is its workshop.

In England, of recent years, schools of engineering
have been attached to the Universities. Abroad and in
America they are separate establishments, and are some-
times attached to large engineering works, where the
pupils pursue their theoretical and practical studies
together, taking the former in the morning, the latter in
the afternoon. Here again the subject is a professional
one. The object of the student is to become a practical
engineer, and all his work is necessarily directed to that
end. Like other workers in different fields, his aim is the

THE FUNCTIONS OF A UNIVERSITY 231

acquisition and utilisation of 'power/ but in his case it is
his object to direct mechanical and electrical power so as
to add to the convenience of the public. A machine is an
instrument for converting heat or electrical energy into
what is termed ' kinetic energy,' and it is with the laws
and modes of this conversion that he has to deal. Such
abstract sciences as chemistry, physics, and geology,
therefore, are studied as means to an end ; not for their
own sakes. They afford him a glimpse of the principles
on which his engineering practice is based ; and mathe-
matics is essential in order that he may be able to apply
physical principles to the practical problems of his pro-
fession.

We see, then, that a University, as it at present exists,
provides, or may provide, technical instruction for theo-
logians, for lawyers, for medical men, and for engineers.
It is, in fact, an advanced technical school for these
subjects.

But it is more, and I believe that its chief function lies
in the kind of work which I shall attempt now to describe.
The German Universities possess what they term a
' Philosophical Faculty ' ; and this phrase is to be accepted
in the derivational meaning of the word — a faculty
which loves wisdom or learning. The watchword of the
members of this faculty is Research; the searching out
the secrets of Nature, to use a current phrase; or the
attempt to create new knowledge. The whole machinery
of the Philosophical Faculty is devised to achieve this
end ; the selection of the teachers, the equipment of the
laboratories and libraries, the awarding of the degrees.

What are the advantages of research ? Much is heard
nowadays regarding the necessity of state provision for
its encouragement, and the Government places at the
disposal of the Royal Society a sum of no less than £4000
a year, which is distributed in the form of grants to

232 ESSAYS BIOGRAPHICAL AND CHEMICAL

applicants who are deemed suitable by committees
appointed to consider their claims to assistance.

There are two views regarding the advantage of research
which have been held. The first of these may be termed
the utilitarian view. You all know the tale of the man
of science who was asked the use of research, and who
parried with the question — What is the use of a baby ?
Well, I imagine that one school of political economists
would oppose the practice of child-murder on the ground
that potentially valuable property was being destroyed.
These persons would probably not be those who stood to
the baby in a parental relation. Nor are the most suc-
cessful investigators those who pursue their inquiries with
the hope of profit, but for the love of them. It is, how-
ever, a good thing, I believe, that the profanum vulgus
should hold the view that research is remunerative to the
public — as some forms of it undoubtedly are.

The second view may be termed the philosophical one.
It is one held by lovers of wisdom in all its various forms.
It explains itself, for the human race is differentiated
from the lower animals by the desire which it has to know
' why.' You may have noticed, as I have, that one of the
first words uttered by that profound philosopher, a small
child, is 'why?' Indeed it becomes wearisome by its
iteration. We are the superiors of the brutes in that we
can hand down our knowledge. It may be that some
animals also seek for knowledge ; but at best, it is of use
to themselves alone; they cannot transmit it to their
posterity, except possibly by way of hereditary faculties.
We, on the contrary, can write and read ; and this places
us, if we like, in possession of the accumulated wisdom of
the ages.

Now the most important function, I hold, of a Uni-
versity is to attempt to answer that question ' why ? '
The ancients tried to do so; but they had not learned

THE FUNCTIONS OF A UNIVERSITY 233

that its answer must be preceded by the answer to the
question ' how ? ' and that in most cases — indeed in all —
we must learn to be contented with the answer to ' how ? '
The better we can tell hmu things are, the more nearly
shall we be able to say why they are.

Such a question is applicable to all kinds of subjects :
to what our forerunners on this earth did ; how they
lived : if we go even further back, what preceded them on
the earth. The history of these inquiries is the function
of geology, palaeontology, and paleaontological botany ; it
is continued through archaeology, Egyptian and Assyrian,
Greek and Roman ; it evolves into history, and lights are
thrown on it by languages and philology; it dovetails
with literature and economics. In all these, research is
possible; and a University should be equipped for the
successful prosecution of inquiries in all such branches.

Another class of inquiries relates to what we think and
how we reason ; and here we have philosophy and logic.
A different branch of the same inquiry leads us to mathe-
matics, which deals with spatial and numerical concepts
of the human mind, geometry and algebra. By an easy
transition we have the natural sciences ; those less closely
connected with ourselves as persons, but intimately related
to our surroundings. Zoology and botany, anatomy,
physiology and pathology deal with living organisms as
structural machines ; and they are based on physics and
chemistry, which are themselves dependent on mathe-
matics.

Such inquiries are worth making for their own sakes.
They interest a large part of the human race ; and not to
feel interested in them is to lack intelligence. The man
who is content to live from day to day, glad if each day
will but produce him food to eat and a roof to sleep under,
is but little removed from an uncivilised being. For the
test of civilisation is prevision ; care to look forward ; to

234 ESSAYS BIOGRAPHICAL AND CHEMICAL

provide for to-morrow ; the morrow of the race, as well as
the morrow of the individual ; and he who looks furthest
ahead is best able to cope with Nature, and to conquer
her.

The investigation of the unknown is to gather experience
from those who have lived before us, and to secure know-
ledge for ourselves and for those who will succeed us. I
see, however, that I am insensibly taking a utilitarian
view; I by no means wish to exclude it, but the chief
purpose of research must be the acquisition of knowledge,
and the second its utilisation.

I will try to explain why this is so, and here you must
forgive me if I cite well-known and oft-quoted instances.

If attempts were made to discover only useful know-
ledge (and by useful I accept the vulgar definition of
profitable, i.e. knowledge which can be directly trans-
muted into its money equivalent) these attempts would,
in many, if not in most cases, fail of their object. I do
not say that once a principle has been proved, and a
practical application is to be made of it, that the working
out of the details is not necessary. But that is best done
by the practical man, be he the parson, the doctor, the
engineer, the technical electrician, or the chemist, and
best of all on a fairly large scale. If, however, the prac-
tical end be always kept in view, the chances are that
there will be no advance in principles. Indeed, what we
investigators wish to be able to do, and what in many
cases we can do, although perhaps very imperfectly, is to
prophesy, to foretell what a given combination of circum-
stances will produce. The desire is founded on a belief
in the uniformity of Nature ; on the conviction that what
has been will again be, should the original conditions be
reproduced. By studying the consequences of varying
the conditions our knowledge is extended; indeed it is
sometimes possible to go so far as to predict what will

THE FUNCTIONS OF A UNIVERSITY 235

happen under conditions, all of which have never before
been seen to be present together.

When Faraday discovered the fact that if a magnet
is made to approach a coil of wire, an electric current is
induced in that wire, he made a discovery which at the
time was of only scientific interest. That discovery has
resulted in electric light, electric traction, and the utilisa-
tion of electricity as a motive power ; the development of
a means of transmitting energy, of which we have by no
means seen the end; nay, we are even now only at its
inception, so great must the advance in its utilisation
ultimately become.

When Hofmann set Perkin as a young student to
investigate the products of oxidation of the base aniline,
produced by him from coal-tar, it would have been
impossible to have predicted that one manufactory alone
would possess nearly 400 large buildings and employ
5000 workmen, living in its own town of 25,000 inhabi-
tants, all of which is devoted to the manufacture of colours
from aniline and other coal-tar products. In this work
alone at least 350 chemists are employed, most of whom
have had a university training.

Schonbein, a Swiss schoolmaster, interested in chemistry,
was struck by the action of nitric acid on paper and
cotton. He would have been astounded if he had been
told that his experiments would have resulted in the
employment of his nitrocelluloses in colossal quantity for
blasting, and for ordnance of all kinds, from the 90- ton
gun to the fowling-piece.

But discoveries such as these, which lead directly to
practical results, are yet far inferior in importance to
others in which a general principle is involved. Joule
and Robert Mayer, who proved the equivalence of heat
and work, have had far more influence on succeeding ages
than even the discoverers above mentioned, for they have

236 ESSAYS BIOGRAPHICAL AND CHEMICAL

imbued a multitude of minds with a correct understanding
of the nature of energy, and the possibility of converting
it economically into that form in which it is most directly
useful for the purpose in view. They have laid the basis
of reasoning for machines ; and it is on machines, instru-
ments for converting unavailable into available energy,
that the prosperity of the human race depends.

You will see from these instances that it is in reality
' philosophy ' or a love of wisdom Avhich, after all, is most
to be sought after. Like virtue, it is its own reward ; and
as we all hope is the case with virtue too, it brings other
rewards in its train; not, be it remarked, always to the
philosopher, but to the race. Virtue, pursued with the
direct object of gain, is a poor thing; indeed, it can
hardly be termed virtue, if it is dimmed by a motive.
So philosophy, if followed after for profit, loses its
meaning.

But I have omitted to mention another motive which
makes for research ; it is a love of pleasure. I can
conceive no pleasure greater than that of the poet — the
maker — who wreathes beautiful thoughts with beautiful
words; but next to this, I would place the pleasure of
discovery, in whatever sphere it be made. It is a pleasure
not merely to the discoverer, but to all who can follow the
train of his reasoning. And after all, the pleasure of the
human race, or of the thinking portion of it, counts for a
good deal in this life of ours.

To return: — attempts at research, guided by purely
utilitarian motives, generally fail in their object, or at
least are not likely to be so productive as research without
ulterior motive. I am strengthened in this conclusion by
the verdict of an eminent German who has himself put
the principle into practice ; who after following out a
purely theoretical line of experiment, which at first
appeared remote from profit, has been rewarded by its

THE FUNCTIONS OF A UNIVERSITY 237

remunerative utilisation. He remarked, incidentally, that
the professors in Polytechnika — (what we should term
technical colleges, intended to prepare young men for the
professions of engineering and technical chemistry) — were
less known for their influence on industry than University
professors. The aim is different in the two cases; the
Polytechnika train men for a profession ; the Philosophical
Faculty of a German University aims at imparting a love
of knowledge ; and as a matter of fact the latter pay in
their influence on the prosperity of the nation better than
the former. And this brings me to the fundamental
premiss of my Oration. It is this : — That the best prepara-
tion for success in any calling is the training of the student
in methods of research. This should be the goal to be
clearly kept in view by all teachers in the Philosophical
Faculties of Universities. They should teach with this
object: — to awaken in each of their students a love of his
subject, and a consciousness that if he persevere, he, too,
will be able to extend its bounds.

Of course it is necessary for the student to learn, so far
as is possible, what has already been done. I would not
urge that a young man should not master, or at all events
study, a great deal of what has already been discovered,
before he attempts to soar on his own wings. But there
is all the difference in the world between the point of
view of the student who reads in order to qualify for
an examination, or to gain a prize or a scholarship,
and the student who reads because he knows that
thus he will acquire knowledge which may be used
as a basis of new knowledge. It is that spirit in
which our Universities in England are so lamentably
deficient; it is that spirit which has contributed to
the success of the Teutonic nations, and which is
beginning to influence the United States. For this con-
dition of things our examinational system is largely to

238 ESSAYS BIOGRAPHICAL AND CHEMICAL

blame ; originally started to remedy the abuses of our Civil
Service, it has eaten into the vitals of our educational
system like a canker ; and it is fostered by the farther
abuse of awarding scholarships as the results of examina-
tions. The pauperisation of the richer classes is a crying
evil; it must some day be cured. Let scholarships be
awarded to those who need them ; not to those whose
fathers can well afford to pay for the education of their
children. 'Pot-hunting' and Philosophy have absolutely
nothing in common.

There are some who hold that the time of an investi-
gator is wasted in teaching the elements of his subject. I
am not one of those who believe this doctrine, and for two
reasons : — first, it is more difficult to teach the elements
of a subject than the more advanced branches ; one learns
the tricks of the trade by long practice ; and the tricks of
this trade consist in the easy and orderly presentment of
ideas. And it is the universal experience that senior
students gain more good from instruction in advanced
subjects by demonstrators than juniors would in elementary
subjects. For the senior student makes allowances ; and
the keenness and interest of the young instructor awakens
his interest. Second, from the teachers' point of view, it
is always well to be obliged to go back on fundamentals.
One is too apt, without the duty of delivering elementary
lectures, to take these fundamentals for granted ; whereas,
if they are recapitulated every year, the light of other
knowledge is brought to bear on them, and they are given
their true proportion; indeed, ideas occur which often
suggest lines of research. It is really the simplest things
which we know least of; the atomic theory; the true
nature of elasticity; the cause of the ascent of sap in
plants; the mechanism of exchange in respiration and
digestion; all these lie at the base of their respective
sciences, and all could bear much elucidation. I believe

THE FUNCTIONS OF A UNIVERSITY 239

therefore, that it is conducive to the furtherance of know-
ledge that the investigator should be actively engaged in
teaching. But he should always keep in view the fact
that his pupils should themselves learn how to investi-
gate ; and he should endeavour to inculcate that spirit in
them.

It follows that the teachers in the Philosophical Faculty
should be selected only from those who are themselves
contributing to the advancement of knowledge ; for if they
have not the spirit of research in them how shall they
instil it into others ? It is our carelessness in this respect
(I do not speak of University College, which has always
been guided by these principles, but of our country as a
whole) which has made us so backward as compared with
some other nations. It is this which has made the vast
majority of our statesmen so careless, because so ignorant,
of the whole frame of mind of the philosopher ; and which
has made it possible for men high in the political estima-
tion of their countrymen to misconceive the functions
of a University. It is true that one of these functions of a
University is to ' train men and women fit for the manifold
requirements of the Empire ' ; that we should all heartily
acknowledge ; but no man who has any claim to university
culture can possibly be contented if the University does
not annually produce much work of research. It is its
chief excuse for existence ; a University which does not
increase knowledge is no University ; it may be a technical
school ; it may be an examining board ; it may be a
coaching establishment ; but it has no claim to the name
University. The best way of fitting young men for the
manifold requirements of the Empire is to give them the
power of advancing knowledge.

It may be said that many persons are incapable of
exhibiting originality. I doubt it. There are many
degrees of originality, as there are many degrees of

240 ESSAYS BIOGRAPHICAL AND CHEMICAL

rhyming, from the writer of doggerel to the poet, or many
degrees of musical ear, from the man who knows two
tunes, the tune of 'God save the King' and the other
tune, to the accomplished musician. But in almost all
cases, if caught young, the human being can be trained,
more or less ; and, as a matter of fact, natural selection
plays its part. Those young men and women who have
no natural aptitude for such work — and they are usually
known by the lack of interest which they take in it— do
not come to the University. My experience is that the
majority, or at least a fair percentage of those who do
come, possess germs of the faculty of originating, germs
capable of development, in many instances, to a very high
degree. It is such persons who are of most value to the
country ; it is from them that advance in literature and
in science is to be expected ; and many of them will con-
tribute to the commercial prosperity of the country. We
hear much nowadays of technical education ; huge sums
of money are being annually expended on the scrappy
scientific education in evening classes of men who have
passed a hard day in manual labour, men who lack the
previous training necessary to enable them to profit by
such instruction. It may be that it is desirable to pro-
vide such intellectual relaxation ; I even grant that such
means may gradually raise the intellectual level of the
country ; but the investment of money in promoting such
schemes is not the one likely to bear the most immediate
and remunerative fruit. The Universities should be the
technical schools ; for a man who has learned to investi-
gate can bring his talents to bear on any subject brought
under his notice, and it is on the advance, and not the
mere dissemination of knowledge, that the prosperity of
a country depends. To learn to investigate requires a
long and a hard apprenticeship ; the power cannot be
acquired by an odd hour spent now and again ; it is as

THE FUNCTIONS OF A UNIVERSITY 241

difficult to become a successful investigator as a successful
barrister or doctor, and it requires at least as hard appli-
cation and as long a period of study.

I do not believe that it is possible for young men or
women to devote sufficient time during the evening to
such work. Those who devote their evening hours to
study and investigation do not bring fresh brains to bear
on the subject; they are already fatigued by a long day's
work ; and, moreover, it is the custom in most of the
colleges which have evening classes to insist upon their
teachers doing a certain share of day work ; they, too, are
not in a fit state to direct the work of their pupils nor to
make suggestions as to the best method of carrying it out.
Moreover, the official evening class is from seven to ten
o'clock, and for investigation in science a spell of three
hours at a time is barely sufficient to carry out success-
fully the end in view ; indeed, an eight hours' day might
profitably be lengthened into a twelve hours' day, as it not
infrequently is. It is heartrending in the middle of some
important experiment to be obliged to close and postpone
it till a future occasion, when much of the work must
necessarily be done over again.

These are some of the reasons why I doubt whether
University education, in the Philosophical Faculty at
least, can be successfully given by means of evening
classes.

Although my work has lain almost entirely in the
domain of science, I should be the last man not to do my
best to encourage research in the sphere of what is gener-
ally called ' arts.' In Germany of recent years a kind of
institution has sprung up which is termed a Seminar.
The word may be translated a ' literary laboratory.' I will
endeavour to give a short sketch on the way in which
these literary laboratories are conducted. After the
student has attended a course of lectures on the subjects
Q

242 ESSAYS BIOGRAPHICAL AND CHEMICAL

to which he intends to devote himself, and is ripe for
research, he enters a Seminar, in which he is provided
with a library, paper, pens and ink, and a subject. The
method of using the library is pointed out to him, and he
is told to read books which bear on the particular subject
in question ; he is made to collate the information which
he gains by reading, and to elaborate the subject which
is given him. Naturally his first efforts must be crude, but
ce riest que le premier pas qui cotite. It probably costs him
blame at the hands of his instructor ; after a few unsuc-
cessful efforts, however, if he has any talent for the par-
ticular investigation to which he has devoted himself,
his efforts improve and at last he produces something
respectable enough to merit publication. Thus he is
exposed to the criticism of those best competent to judge,
and he is launched in what may be a career in Historical,
Literary, or Economic research.

Such a Seminar is carried on in philological and
linguistic studies, in problems of economy involving
statistics, in problems of law involving judicial decision,
and of history in which the relations between the develop-
ment of the various phases in the progress of nations is
traced. The system is borrowed from the well-known
plan of instruction in a physical or chemical laboratory.
Experiments are made in literary style. These experi-
ments are subjected to the criticism of the teacher, and
thus the investigator is trained. But it may be objected
that the youths who frequent our Universities have not a
sufficient knowledge of facts connected with such subjects
to be .'capable of at once entering on a training of this
kind. That may be so ; if it is the case, our schools must
look to it that they provide sufficient training. Even
under present circumstances, however, I do not think I
am mistaken in supposing that a young man or woman
who enters a University at the age of eighteen years with

THE FUNCTIONS OF A UNIVERSITY 243

the intention of spending three years in literary or his-
torical studies will not at the end of the second year be
more benefited by a course at the Seminar, even though it
should result in no permanent addition to literature or
history, than if he were to spend his time in mere assimi-
lation. It is not the act of gaining knowledge which
profits, it is the power of using it, and while in order to
use knowledge it is necessary to gain it, yet a training in
the method of using knowledge is much more important
and profitable than a training in the method of gaining
it. I do not know whether there exists in this country a
single example of the continental Seminar ; there was some
talk of founding such a literary laboratory in University
College, but, as usual, the attempt was frustrated by a
lack of funds ; the attempt would also have been frustrated
by the requirements of the present system of examination
in the University of London ; but there is, fortunately,
good hope of changing that system and of developing the
minds of students on those lines which have proved so
fruitful where they have been systematically followed.1

There is one subject, of which the votaries are so few,
that it is difficult to treat in the same manner as those
literary and scientific subjects of which I have been speak-
ing ; that subject is mathematics. While many persons
have a certain amount of mathematical ability which
they cultivate as a means to an end, those who are born
mathematicians are as few as those who are born
musicians. I have had the privilege of discussing this
question with one of the foremost mathematicians of
Europe — Professor Klein of Gottingen. He tells me that
while he is content for the most part to treat mathematics
as a technical study, imparting to his pupils so much as is
necessary for them to use it easily as an instrument, he

1 Several Seminars have now been started at University College
(Sept. 1908).

244 ESSAYS BIOGRAPHICAL AND CHEMICAL

discourages young men, unless they are especially
endowed by Nature, from pursuing the study of mathe-
matics with the object of cultivating a gift for that
subject. Especially gifted men occasionally turn up, and
those who possess mathematical insight are able to profit
by the instruction of the professor in developing some
special branch of the subject. Mathematical problems,
he tells me, are numerous, but they demand such an ex-
tensive knowledge of what has already been done that
very few persons who do not devote their lives to the sub-
ject are able to cope with them, and it is only those who
are born with a mathematical gift who can afford to
devote their lives to mathematics, for the standard is high,
and the prizes are few.

Many, I suppose, who are at present listening to me
would be disappointed were I not to refer to the functions
of a University with reference to examinations. A long
course of training, lasting now for the best part of seventy
years, has convinced the population of London that the
chief function of a University is to examine. Believe me,
the examination should play only a secondary part in the
work of a University. It is necessary to test the acquire-
ments of the students whom the teachers have under
their charge, but the examination should play an entirely
subordinate part. To be successful in examinations is
unfortunately too often the goal which the young student
aims at, but it is one which all philosophical teachers
deprecate. To infuse into his pupils a love of the sub-
ject which both are at the same time teaching and learn-
ing, is the chief object of an enthusiastic teacher; there
should be an atmosphere of the subject surrounding them
— an umbra — perhaps I should call it an aura; for it
should exert no depressing influence upon them. The
object of both classes of students (for I count the teacher
a student) should be to do their best to increase know-

THE FUNCTIONS OF A UNIVERSITY 245

ledge of the subject on which they are engaged. That
this is possible, many teachers can testify to by experi-
ence; and it is the chief lesson learned by a sojourn in a
German laboratory. Where each student is himself
engaged in research, interest is taken by the students in
each others' work; numerous discussions are raised
regarding each questionable point; and the combined
intelligence of the whole laboratory is focussed on the
elucidation of some difficult problem. There is nothing
more painful to witness than a dull and decorous labora-
tory, where each student keeps to his own bench, does not
communicate with his fellow-students, does not take an
interest in their work, and expects them to manifest no
interest in his. It is only by friction that heat can be
produced, and heat, by increasing the frequency of
vibration, results, as we know, in light.

The student should look forward to his examination
not as a solemn ordeal which he is compelled to go
through with the prospect of a degree should he be suc-
cessful, but as a means of showing his teacher and his
fellows how much he has profited by the work which he
has done ; those who pursue knowledge in this spirit and
those, be it remarked, who examine in this spirit will look
forward to examination with no apprehension ; not, per-
haps, with joy, for after all it is a bore to be examined
and perhaps a still greater bore to examine, but it is a
necessary step for the student in gaining self-assurance
and the conviction of having profited by his exertions ;
and for the teacher, as a means of insuring that his
instruction has not been profitless to his student. In this
connection I cannot refrain from remarking, that that
genius for competition which has over-ridden our nation
of England, appears to me to be misplaced. Far too
much is thought of the top man ; very likely the second
or even the tenth, or it may be the fiftieth has a firmer

246 ESSAYS BIOGRAPHICAL AND CHEMICAL

grasp of his subject, and in the long-run would display
more talent. Let us take coinfort, however, in the
thought, that the day of examinations, for the sake of
examinations, is approaching an end.

It may surprise many to learn that the suggestion that
in England teachers do not usually examine their own
pupils for degrees, is, abroad, received in a spirit of sur-
prise not unmixed with incredulity. Americans and
Germans to whom I have mentioned this state of matters,
cannot realise that the teacher is not considered fit to be
trusted to examine his own pupils, and, singular to state,
they maintain that no one else can possibly do so with
any attempt at fairness ; it appears to them, as it appears
to me, an altogether untenable position to hold that a
man selected to fill an important professorship, after many
years' trial in a junior position, should be suspected of
such (shall I say) ambiguous ideas regarding common
honesty, that he will always arbitrate unfairly in favour of
his own pupils. Such a supposition is an insult to the
professor; and the exclusion of the teacher elevates
examination to the position of a fetish ; it is that, together
with the spirit of emulation and competition, which has
done so much to ruin our English education. The idea of
competitive examination is so ingrained in the minds of
Englishmen, that it is difficult for them to realise that
the object of a University is not primarily to examine its
pupils, but to teach them to teach themselves ; and also
they have still to acquire the conviction that students
should be found not merely among the alumni of the
University but also among all members of the staff. The
spirit which should prevail with us should be the spirit
of gaining knowledge — gaining knowledge not for the
satisfaction of one's own sense of acquisitiveness, but in
order to be able to increase the sum-total of what is
known. All should work together, senior and junior staff,

THE FUNCTIONS OF A UNIVERSITY 247

graduates and undergraduates, in order to diminish man's
ignorance.

To sum up. As it exists at present, a University is a
technical school for theology, law, medicine, and engineer-
ing. It ought to be also a place for the advancement of
knowledge, for the training of philosophers, of those who
love wisdom for its own sake ; and while as a technical
school it exercises a useful function in preparing many
men and women for their calling in life, its philosophical
faculty should impart to those who enter its halls that
faculty of increasing knowledge which cannot fail to be
profitable not only to the intellect of the nation, but also
to its industrial prosperity. I regard this as the chief
function of a University.

Printed by T. and A. CONSTABLB, Printers to His Majesty
at the Edinburgh University Press

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