PUBLICATION _of the Theory by Beccher and Stahl._--It will be

recollected that we are tracing the history of the _progress_ only

of Chemistry, not of its errors;--that we are concerned with

doctrines only so far as they are true, and have remained part of

the received system of chemical truths. The Phlogistic Theory was

deposed and succeeded by the Theory of Oxygen. But this circumstance

must not lead us to overlook the really sound and permanent part of

the opinions which the founders of the phlogistic theory taught.

They brought together, as processes of the same kind, a number of

changes which at first appeared to have nothing in common; as

acidification, combustion, respiration. Now this classification is

true; and its importance remains undiminished, whatever are the

explanations which we adopt of the processes themselves.

The two chemists to whom are to be ascribed the merit of this step,

and the establishment of the _phlogistic theory_ which they

connected {268} with it, are John Joachim Beccher and George Ernest

Stahl; the former of whom was professor at Mentz, and physician to

the Elector of Bavaria (born 1625, died 1682); the latter was

professor at Halle, and afterwards royal physician at Berlin (born

1660, died 1734). These two men, who thus contributed to a common

purpose, were very different from each other. The first was a frank

and ardent enthusiast in the pursuit of chemistry, who speaks of

himself and his employments with a communicativeness and affection

both amusing and engaging. The other was a teacher of great talents

and influence, but accused of haughtiness and moroseness; a

character which is well borne out by the manner in which, in his

writings, he anticipates an unfavorable reception, and defies it.

But it is right to add to this that he speaks of Beccher, his

predecessor, with an ungrudging acknowledgment of obligations to

him, and a vehement assertion of his merit as the founder of the

true system, which give a strong impression of Stahl's justice and

magnanimity.

Beccher's opinions were at first promulgated rather as a correction

than a refutation of the doctrine of the three principles, salt,

sulphur, and mercury. The main peculiarity of his views consists in

the offices which he ascribes to his _sulphur_, these being such as

afterwards induced Stahl to give the name of _Phlogiston_ to this

element. Beccher had the sagacity to see that the reduction of

metals to an earthy form (_calx_), and the formation of sulphuric

acid from sulphur, are operations connected by a general analogy, as

being alike processes of combustion. Hence the metal was supposed to

consist of an earth, and of something which, in the process of

combustion, was separated from it; and, in like manner, sulphur was

supposed to consist of the sulphuric acid, which remained after its

combustion, and of the combustible part or true sulphur, which flew

off in the burning. Beccher insists very distinctly upon this

difference between his element sulphur and the "sulphur" of his

Paracelsian predecessors.

It must be considered as indicating great knowledge and talent in

Stahl, that he perceived so clearly what part of the views of

Beccher was of general truth and permanent value. Though he[11\14]

everywhere gives to Beccher the credit of the theoretical opinions

which he promulgates, ("Beccheriana sunt quæ profero,") it seems

certain that he had the merit, not only of proving them more

completely, and applying them more widely than his forerunner, but

also of conceiving them {269} with a distinctness which Beccher did

not attain. In 1697, appeared Stahl's _Zymotechnia Fundamentalis_

(the Doctrine of Fermentation), "simulque _experimentum novum_

sulphur verum arte producendi." In this work (besides other tenets

which the author considered as very important), the opinion

published by Beccher was now maintained in a very distinct

form;--namely, that the process of forming sulphur from sulphuric

acid, and of restoring the metals from their calces, are analogous,

and consist alike in the addition of some combustible element, which

Stahl termed _phlogiston_ (φλογίστον, _combustible_). The experiment

most insisted on in the work now spoken of,[12\14] was the formation

of sulphur from sulphate of potass (or of soda) by fusing the salt

with an alkali, and throwing in coals to supply phlogiston. This is

the "experimentum novum." Though Stahl published an account of this

process, he seems to have regretted his openness. "He denies not,"

he says, "that he should peradventure have dissembled this

experiment as the true foundation of the Beccherian assertion

concerning the nature of sulphur, if he had not been provoked by the

pretending arrogance of some of his contemporaries."

[Note 11\14: **Stahl, _Præf. ad Specim. Becch._ 1703.]

[Note 12\14: P. 117.]

From this time, Stahl's confidence in his theory may be traced

becoming more and more settled in his succeeding publications. It is

hardly necessary to observe here, that the explanations which his

theory gives are easily transformed into those which the more recent

theory supplies. According to modern views, the addition of oxygen

takes place in the formation of acids and of calces, and in

combustion, instead of the subtraction of phlogiston. The coal which

Stahl supposed to supply the combustible in his experiment, does in

fact absorb the liberated oxygen. In like manner, when an acid

corrodes a metal, and, according to existing theory, combines with

and oxidates it, Stahl supposed that the phlogiston separated from

the metal and combined with the acid. That the explanations of the

phlogistic theory are so generally capable of being translated into

the oxygen theory, merely by inverting the supposed transfer of the

combustible element, shows us how important a step towards the

modern doctrines the phlogistic theory really was.

The question, whether these processes were in fact addition or

subtraction, was decided by the balance, and belongs to a succeeding

period of the science. But we may observe, that both Beccher and

Stahl were aware of the increase of weight which metals undergo in

{270} calcination; although the time had not yet arrived in which

this fact was to be made one of the bases of the theory.

It has been said,[13\14] that in the adoption of the phlogistic

theory, that is, in supposing the above-mentioned processes to be

addition rather than subtraction, "of two possible roads the wrong

was chosen, as if to prove the perversity of the human mind." But we

must not forget how natural it was to suppose that some part of a

body was _destroyed_ or _removed_ by combustion; and we may observe,

that the merit of Beccher and Stahl did not consist in the selection

of one road or two, but in advancing so far as to reach this point

of separation. That, having done this, they went a little further on

the wrong line, was an error which detracted little from the merit

or value of the progress really made. It would be easy to show, from

the writings of phlogistic chemists, what important and extensive

truths their theory enabled them to express simply and clearly.

[Note 13\14: Herschel's _Introd. to Nat. Phil._ p. 300.]

That an enthusiastic temper is favorable to the production of great

discoveries in science, is a rule which suffers no exception in the

character of Beccher. In his preface[14\14] addressed "to the

benevolent reader" of his _Physica Subterranea_, he speaks of the

chemists as a strange class of mortals, impelled by an almost insane

impulse to seek their pleasure among smoke and vapor, soot and

flame, poisons and poverty. "Yet among all these evils," he says, "I

seem to myself to live so sweetly, that, may I die if I would change

places with the Persian king." He is, indeed, well worthy of

admiration, as one of the first who pursued the labors of the

furnace and the laboratory, without the bribe of golden hopes. "My

kingdom," he says, "is not of this world. I trust that I have got

hold of my pitcher by the right handle,--the true method of treating

this study. For the _Pseudochymists_ seek gold; but the _true

philosophers_, science, which is more precious than any gold."

[Note 14\14: Frankfort, 1681.]

The _Physica Subterranea_ made no converts. Stahl, in his indignant

manner, says,[15\14] "No one will wonder that it never yet obtained a

physician or a chemist as a disciple, still less as an advocate." And

again, "This work obtained very little reputation or estimation, or,

to speak ingenuously, as far as I know, none whatever." In 1671,

Beccher published a supplement to his work, in which he showed how

metal might be extracted from mud and sand. He offered to execute

{271} this at Vienna; but found that people there cared nothing about

such novelties. He was then induced, by Baron D'Isola, to go to

Holland for similar purposes. After various delays and quarrels, he

was obliged to leave Holland for fear of his creditors; and then, I

suppose, came to Great Britain, where he examined the Scottish and

Cornish mines. He is said to have died in London in 1682.

[Note 15\14: Præf. _Phys. Sub._ 1703.]

Stahl's publications appear to have excited more notice, and led to

controversy on the "so-called sulphur." The success of the

experiment had been doubted, which, as he remarks, it was foolish to

make a matter of discussion, when any one might decide the point by

experiment; and finally, it had been questioned whether the

substance obtained by this process were pure sulphur. The

originality of his doctrine was also questioned, which, as he says,

could not with any justice be impugned. He published in defence and

development of his opinion at various intervals, as the _Specimen

Beccherianum_ in 1703, the _Documentum Theoriæ Beecherianæ_, a

Dissertation _De Anatomia Sulphuris Artificialis_; and finally,

_Casual Thoughts on the so-called Sulphur_, in 1718, in which he

gave (in German) both a historical and a systematic view of his

opinions on the nature of salts and of his Phlogiston.

_Reception and Application of the Theory._--The theory that the

formation of sulphuric acid, and the restoration of metals from

their calces, are analogous processes, and consist in the addition

of _phlogiston_, was soon widely received; and the Phlogistic School

was thus established. From Berlin, its original seat, it was

diffused into all parts of Europe. The general reception of the

theory may be traced, not only in the use of the term "phlogiston,"

and of the explanations which it implies; but in the adoption of a

nomenclature founded on those explanations, which, though not very

extensive, is sufficient evidence of the prevalence of the theory.

Thus when Priestley, in 1774, discovered oxygen, and when Scheele, a

little later, discovered chlorine, these gases were termed

_dephlogisticated air_, and _dephlogisticated marine acid_; while

azotic acid gas, having no disposition to combustion, was supposed

to be saturated with phlogiston, and was called _phlogisticated air_.

This phraseology kept its ground, till it was expelled by the

antiphlogistic, or oxygen theory. For instance. Cavendish's papers

on the chemistry of the airs are expressed in terms of it, although

his researches led him to the confines of the new theory. We must

now give an account of such researches, and of the consequent

revolution in the science. {272}

CHAPTER V.

CHEMISTRY OF GASES.--BLACK. CAVENDISH.

THE study of the properties of aëriform substances, or Pneumatic

Chemistry, as it was called, occupied the chemists of the eighteenth

century, and was the main occasion of the great advances which the

science made at that period. The most material general truths which

came into view in the course of these researches, were, that gases

were to be numbered among the constituent elements of solid and

fluid bodies; and that, in these, as in all other cases of

composition, the compound was equal to the sum of its elements. The

latter proposition, indeed, cannot be looked upon as a discovery,

for it had been frequently acknowledged, though little applied; in

fact, it could not be referred to with any advantage, till the

aëriform elements, as well as others, were taken into the account.

As soon as this was done, it produced a revolution in chemistry.

[2nd Ed.] [Though the view of the mode in which gaseous elements

become fixed in bodies and determine their properties, had great

additional light thrown upon it by Dr. Black's discoveries, as we

shall see, the notion that solid bodies involve such gaseous

elements was not new at that period. Mr. Vernon Harcourt has

shown[16\14] that Newton and Boyle admitted into their speculations

airs of various kinds, capable of fixation in bodies. I have, in the

succeeding chapter (chap. vi.), spoken of the views of Rey, Hooke,

and Mayow, connected with the function of airs in chemistry, and

forming a prelude to the Oxygen Theory.]

[Note 16\14: _Phil. Mag._ 1846.]

Notwithstanding these preludes, the credit of the first great step

in pneumatic chemistry is, with justice, assigned to Dr. Black,

afterwards professor at Edinburgh, but a young man of the age of

twenty-four at the time when he made his discovery.[17\14] He found

that the difference between caustic lime and common limestone arose

from this, that the latter substance consists of the former,

combined with a certain air, which, being thus fixed in the solid

body, he called _fixed air_ (carbonic {273} acid gas). He found,

too, that magnesia, caustic potash, and caustic soda, would combine

with the same air, with similar results. This discovery consisted,

of course, in a new interpretation of observed changes. Alkalies

appeared to be made caustic by contact with quicklime: at first

Black imagined that they underwent this change by acquiring igneous

matter from the quicklime; but when he perceived that the lime

gained, not lost, in magnitude as it became mild, he rightly

supposed that the alkalies were rendered caustic by imparting their

air to the lime. This discovery was announced in Black's inaugural

dissertation, pronounced in 1755, on the occasion of his taking his

degree of Doctor in the University of Edinburgh.

[Note 17\14: Thomson's _Hist. Chem._ i. 317.]

The chemistry of airs was pursued by other experimenters. The

Honorable Henry Cavendish, about 1765, invented an apparatus, in

which aërial fluids are confined by water, so that they can be

managed and examined. This hydro-pneumatic apparatus, or as it is

sometimes called, _the pneumatic trough_, from that time was one of

the most indispensable parts of the chemist's apparatus.

Cavendish,[18\14] in 1766, showed the identity of the properties of

fixed air derived from various sources; and pointed out the peculiar

qualities of _inflammable air_ (afterwards called hydrogen gas),

which, being nine times lighter than common air, soon attracted

general notice by its employment for raising balloons. The promise

of discovery which this subject now offered, attracted the confident

and busy mind of Priestley, whose _Experiments and Observations on

different kinds of Air_ appeared in 1744-79. In these volumes, he

describes an extraordinary number of trials of various kinds; the

results of which were, the discovery of new kinds of air, namely,

_phlogisticated air_ (azotic gas), _nitrous air_ (nitrous gas), and

_dephlogisticated air_ (oxygen gas).

[Note 18\14: _Phil. Trans._ 1766.]

But the discovery of new substances, though valuable in supplying

chemistry with materials, was not so important as discoveries

respecting their modes of composition. Among such discoveries, that of

Cavendish, published in the _Philosophical Transactions_ for 1784, and

disclosing the composition of water by the union of two gases, oxygen

and hydrogen, must be considered as holding a most distinguished

place. He states,[19\14] that his "experiments were made principally

with a view to find out the cause of the diminution which common air

is well known to suffer, by all the various ways in which it is

phlogisticated." And, after describing various unsuccessful attempts,

he finds {274} that when inflammable air is used in this

phlogistication (or burning), the diminution of the common air is

accompanied by the formation of a dew in the apparatus.[20\14] And

thus he infers[21\14] that "almost all the inflammable air, and

one-fifth of the common air, are turned into pure water."

[Note 19\14: _Phil. Trans._ 1784, p. 119.]

[Note 20\14: _Phil. Trans._ 1784, p. 128.]

[Note 21\14: Ib. p. 129.]

Lavoisier, to whose researches this result was, as we shall soon

see, very important, was employed in a similar attempt at the same

time (1783), and had already succeeded,[22\14] when he learned from

Dr. Blagden, who was present at the experiment, that Cavendish had

made the discovery a few months sooner. Monge had, about the same

time, made the same experiments, and communicated the result to

Lavoisier and Laplace immediately afterwards. The synthesis was soon

confirmed by a corresponding analysis. Indeed the discovery

undoubtedly lay in the direct path of chemical research at the time.

It was of great consequence in the view it gave of experiments in

composition; for the small quantity of water produced in many such

processes, had been quite overlooked; though, as it now appeared,

this water offered the key to the whole interpretation of the change.

[Note 22\14: _A. P._ 1781, p. 472]

Though some objections to Mr. Cavendish's view were offered by

Kirwan,[23\14] on the whole they were generally received with assent

and admiration. But the bearing of these discoveries upon the new

theory of Lavoisier, who rejected phlogiston, was so close, that we

cannot further trace the history of the subject without proceeding

immediately to that theory.

[Note 23\14: _P. T._ 1784, p. 154.]

[2nd Ed.] [I have elsewhere stated,[24\14]--with reference to recent

attempts to deprive Cavendish of the credit of his discovery of the

composition of water, and to transfer it to Watt,--that Watt not

only did not anticipate, but did not fully appreciate the discovery

of Cavendish and Lavoisier; and I have expressed my concurrence with

Mr. Vernon Harcourt's views, when he says,[25\14] that "Cavendish

pared off from the current hypotheses their theory of combustion,

and their affinities of imponderable for ponderable matter, as

complicating chemical with physical considerations; and he then

corrected and adjusted them with admirable skill to the actual

phenomena, not binding the facts to the theory, but adapting the

theory to the facts."

[Note 24\14: _Philosophy_, b. vi. c. 4.]

[Note 25\14: _Address to the British Association_, 1839.]

I conceive that the discussion which the subject has recently

received, has left no doubt on the mind of any one who has perused

the {275} documents, that Cavendish is justly entitled to the honor

of this discovery, which in his own time was never contested. The

publication of his Journals of Experiments[26\14] shows that he

succeeded in establishing the point in question in July, 1781. His

experiments are referred to in an abstract of a paper of

Priestley's, made by Dr. Maty, the secretary of the Royal Society,

in June, 1783. In June, 1783, also, Dr. Blagden communicated the

result of Cavendish's experiments to Lavoisier, at Paris. Watt's

letter, containing his hypothesis that "water is composed of

dephlogisticated air and phlogiston deprived of part of their latent

or elementary heat; and that phlogisticated or pure air is composed

of water deprived of its phlogiston and united to elementary heat

and light," was not read till Nov. 1783; and even if it could have

suggested such an experiment as Cavendish's (which does not appear

likely), is proved, by the dates, to have had no share in doing so.

[Note 26\14: _Appendix_ to Mr. V. Harcourt's _Address_]

Mr. Cavendish's experiment was suggested by an experiment in which

Warltire, a lecturer on chemistry at Birmingham, exploded a mixture

of hydrogen and common air in a close vessel, in order to determine

whether heat were ponderable.]

CHAPTER VI.

EPOCH OF THE THEORY OF OXYGEN.--LAVOISIER.

_Sect._ 1.--_Prelude to the Theory.--Its Publication._

WE arrive now at a great epoch in the history of Chemistry. Few

revolutions in science have immediately excited so much general

notice as the introduction of the theory of oxygen. The simplicity

and symmetry of the modes of combination which it assumed; and,

above all, the construction and universal adoption of a nomenclature

which applied to all substances, and which seemed to reveal their

inmost constitution by their name, naturally gave it an almost

irresistible sway over men's minds. We must, however,

dispassionately trace the course of its introduction. {276}

Antoine Laurent Lavoisier, an accomplished French chemist, had

pursued, with zeal and skill, researches such as those of Black,

Cavendish, and Priestley, which we have described above. In 1774, he

showed that, in the calcination of metals in air, the metal acquires

as much weight as the air loses. It might appear that this discovery

at once overturned the view which supposed the metal to be phlogiston

_added_ to the calx. Lavoisier's contemporaries were, however, far

from allowing this; a greater mass of argument was needed to bring

them to this conclusion. Convincing proofs of the new opinion were,

however, rapidly supplied. Thus, when Priestley had discovered

dephlogisticated air, in 1774, Lavoisier showed, in 1776, that fixed

air consisted of charcoal and the dephlogisticated or pure air; for

the mercurial calx which, heated by itself, gives out pure air, gives

out, when heated with charcoal, fixed air,[27\14] which has,

therefore, since been called _carbonic acid gas_.

[Note 27\14: _Mém. Ac. Par._ 1775.]

Again, Lavoisier showed that the atmospheric air consists of pure or

vital air, and of an _unvital_ air, which he thence called _azot_.

The vital air he found to be the agent in combustion, acidification,

calcination, respiration; all of these processes were analogous: all

consisted in a decomposition of the atmospheric air, and a fixation

of the pure or vital portion of it.

But he thus arrived at the conclusion, that this pure air was added,

in all the cases in which, according to the received theory,

_phlogiston_ was subtracted, and _vice versâ_. He gave the

name[28\14] of _oxygen_ (_principe oxygène_) to "the substance which

thus unites itself with metals to form their calces, and with

combustible substances to form acids."

[Note 28\14: _Mém. Ac. Par._ 1781, p. 448.]

A new theory was thus produced, which would account for all the

facts which the old one would explain, and had besides the evidence

of the balance in its favor. But there still remained some apparent

objections to be removed. In the action of dilute acids on metals,

inflammable air was produced. Whence came this element? The

discovery of the decomposition of water sufficiently answered this

question, and converted the objection into an argument on the side

of the theory: and thus the decomposition of water was, in fact, one

of the most critical events for the fortune of the Lavoisierian

doctrine, and one which, more than any other, decided chemists in

its favor. In succeeding years, Lavoisier showed the consistency of

his theory with {277} all that was discovered concerning the

composition of alcohol, oil, animal and vegetable substances, and

many other bodies.

It is not necessary for us to consider any further the evidence for

this theory, but we must record a few circumstances respecting its

earlier history. Rey, a French physician, had in 1630, published a

book, in which he inquires into the grounds of the increase of the

weight of metals by calcination.[29\14] He says, "To this question,

then, supported on the grounds already mentioned, I answer, and

maintain with confidence, that the increase of weight arises from

the air, which is condensed, rendered heavy and adhesive, by the

heat of the furnace." Hooke and Mayow had entertained the opinion

that the air contains a "nitrous spirit," which is the supporter of

combustion. But Lavoisier disclaimed the charge of having derived

anything from these sources; nor is it difficult to understand how

the received generalizations of the phlogistic theory had thrown all

such narrower explanations into obscurity. The merit of Lavoisier

consisted in his combining the generality of Stahl with the verified

conjectures of Rey and Mayow.

[Note 29\14: Thomson, _Hist. Chem._ ii. 95.]

No one could have a better claim, by his early enthusiasm for

science, his extensive knowledge, and his zealous labors, to hope

that a great discovery might fall to his share, than Lavoisier. His

father,[30\14] a man of considerable fortune, had allowed him to

make science his only profession; and the zealous philosopher

collected about him a number of the most active physical inquirers

of his time, who met and experimented at his house one day in the

week. In this school, the new chemistry was gradually formed. A few

years after the publication of Priestley's first experiments,

Lavoisier was struck with the presentiment of the theory which he

was afterwards to produce. In 1772, he deposited[31\14] with the

secretary of the Academy, a note which contained the germ of his

future doctrines. "At that time," he says, in explaining this step,

"there was a kind of rivalry between France and England in science,

which gave importance to new experiments, and which sometimes was

the cause that the writers of the one or other of the nations

disputed the discovery with the real author." In 1777, the editor of

the Memoirs of the Academy speaks of his theory as overturning that

of Stahl; but the general acceptance of the new opinion did not take

place till later. {278}

[Note 30\14: _Biogr. Univ._ (Cuvier.)]

[Note 31\14: Thomson, ii. 99.]

_Sect._ 2.--_Reception and Confirmation of the Theory of Oxygen._

THE Oxygen Theory made its way with extraordinary rapidity among the

best philosophers.[32\14] In 1785, that is, soon after Cavendish's

synthesis of water had removed some of the most formidable

objections to it, Berthollet, already an eminent chemist, declared

himself a convert. Indeed it was so soon generally adopted in

France, that Fourcroy promulgated its doctrines under the name of

"La Chimie Française," a title which Lavoisier did not altogether

relish. The extraordinary eloquence and success of Fourcroy as a

lecturer at the Jardin des Plantes, had no small share in the

diffusion of the oxygen theory; and the name of "the apostle of the

new chemistry" which was at first given him in ridicule, was justly

held by him to be a glorious distinction.[33\14]

[Note 32\14: Thomson, ii. 130.]

[Note 33\14: Cuvier, _Eloges_, i. p. 20.]

Guyton de Morveau, who had at first been a strenuous advocate of the

phlogistic theory, was invited to Paris, and brought over to the

opinions of Lavoisier; and soon joined in the formation of the

nomenclature founded upon the theory. This step, of which we shall

shortly speak, fixed the new doctrine, and diffused it further.

Delametherie alone defended the phlogistic theory with vigor, and

indeed with violence. He was the editor of the _Journal de

Physique_, and to evade the influence which this gave him, the

antiphlogistians[34\14] established, as the vehicle of their

opinions, another periodical, the _Annales de Chimie_.

[Note 34\14: Thomson, ii. 133.]

In England, indeed, their success was not so immediate.

Cavendish,[35\14] in his Memoir of 1784, speaks of the question

between the two opinions as doubtful. "There are," he says, "several

Memoirs of M. Lavoisier, in which he entirely discards phlogiston; and

as not only the foregoing experiments, but most other phenomena of

nature, seem explicable as well, or nearly as well, upon this as upon

the commonly believed principle of phlogiston," Cavendish proceeds to

explain his experiments according to the new views, expressing no

decided preference, however, for either system. But Kirwan, another

English chemist, contested the point much more resolutely. His theory

identified inflammable air, or hydrogen, with phlogiston; and in this

view, he wrote a work which was intended as a confutation of {279} the

essential part of the oxygen theory. It is a strong proof of the

steadiness and clearness with which the advocates of the new system

possessed their principles, that they immediately translated this

work, adding, at the end of each chapter, a refutation of the

phlogistic doctrines which it contained. Lavoisier, Berthollet, De

Morveau, Fourcroy, and Monge, were the authors of this curious

specimen of scientific polemics. It is also remarkable evidence of the

candor of Kirwan, that notwithstanding the prominent part he had taken

in the controversy, he allowed himself at last to be convinced. After

a struggle of ten years, he wrote[36\14] to Berthollet in 1796, "I lay

down my arms, and abandon the cause of phlogiston." Black followed the

same course. Priestley alone, of all the chemists of great name, would

never assent to the new doctrines, though his own discoveries had

contributed so much to their establishment. "He saw," says

Cuvier,[37\14] "without flinching, the most skilful defenders of the

ancient theory go over to the enemy in succession; and when Kirwan

had, almost the last of all, abjured phlogiston, Priestley remained

alone on the field of battle, and threw out a new challenge, in a

memoir addressed to the principal French chemists." It happened,

curiously enough, that the challenge was accepted, and the arguments

answered by M. Adet, who was at that time (1798,) the French

ambassador to the United States, in which country Priestley's work was

published. Even in Germany, the birth-place and home of the phlogistic

theory, the struggle was not long protracted. There was, indeed, a

controversy, the older philosophers being, as usual, the defenders of

the established doctrines; but in 1792, Klaproth repeated, before the

Academy of Berlin, all the fundamental experiments; and "the result

was a full conviction on the part of Klaproth and the Academy, that

the Lavoisierian theory was the true one."[38\14] Upon the whole, the

introduction of the Lavoisierian theory in the scientific world, when

compared with the great revolution of opinion to which it comes

nearest in importance, the introduction of the Newtonian theory,

shows, by the rapidity and temper with which it took place, a great

improvement, both in the means of arriving at truth, and in the spirit

with which they were used.

[Note 35\14: _Phil. Trans._ 1784, p. 150.]

[Note 36\14: Pref. to Fourcroy's _Chemistry_, xiv.]

[Note 37\14: Cuvier, _Eloge de Priestley_, p. 208.]

[Note 38\14: Thomson, vol. ii. p. 136.]

Some English writers[39\14] have expressed an opinion that there was

{280} little that was original in the new doctrines. But if they

were so obvious, what are we to say of eminent chemists, as Black

and Cavendish, who hesitated when they were presented, or Kirwan and

Priestley, who rejected them? This at least shows that it required

some peculiar insight to see the evidence of these truths. To say

that most of the materials of Lavoisier's theory existed before him,

is only to say that his great merit was, that which must always be

the great merit of a new theory, his generalization. The effect

which the publication of his doctrines produced, shows us that he

was the first person who, possessing clearly the idea of

quantitative composition, applied it steadily to a great range of

well-ascertained facts. This is, as we have often had to observe,

precisely the universal description of an inductive discoverer. It

has been objected, in like manner, to the originality of Newton's

discoveries, that they were contained in those of Kepler. They were

so, but they needed a Newton to find them there. The originality of

the theory of oxygen is proved by the conflict, short as it was,

which accompanied its promulgation; its importance is shown by the

changes which it soon occasioned in every part of the science.

[Note 39\14: Brande, _Hist. Diss._ in _Enc, Brit._ p. 182. Lunn,

_Chem._ in _Enc. Met._ p. 596.]

Thus Lavoisier, far more fortunate than most of those who had, in

earlier ages, produced revolutions in science, saw his theory

accepted by all the most eminent men of his time, and established

over a great part of Europe within a few years from its first

promulgation. In the common course of events, it might have been

expected that the later years of his life would have been spent amid

the admiration and reverence which naturally wait upon the patriarch

of a new system of acknowledged truths. But the times in which he

lived allowed no such euthanasia to eminence of any kind. The

democracy which overthrew the ancient political institutions of

France, and swept away the nobles of the land, was not, as might

have been expected, enthusiastic in its admiration of a great

revolution in science, and forward to offer its homage to the

genuine nobility of a great discoverer. Lavoisier was thrown into

prison on some wretched charge of having, in the discharge of a

public office which he had held, adulterated certain tobacco; but in

reality, for the purpose of confiscating his property.[40\14] In his

imprisonment, his philosophy was his resource; and he employed

himself in the preparation of his papers for printing. When he was

brought before the revolutionary tribunal, he begged for a respite

of a few days, in order to complete some researches, the results of

which {281} were, he said, important to the good of humanity. The

brutish idiot, whom the state of the country at that time had placed

in the judgment-seat, told him that the republic wanted no sçavans.

He was dragged to the guillotine, May the 8th, 1794, and beheaded,

in the fifty-second year of his age; a melancholy proof that, in

periods of political ferocity, innocence and merit, private virtues

and public services, amiable manners and the love of friends,

literary fame and exalted genius, are all as nothing to protect

their possessor from the last extremes of violence and wrong,

inflicted under judicial forms.

[Note 40\14: _Biog. Univ._ (Cuvier.)]

_Sect._ 3.--_Nomenclature of the Oxygen Theory._

AS we have already said, a powerful instrument in establishing and

diffusing the new chemical theory, was a Systematic Nomenclature

founded upon it, and applicable to all chemical compounds, which was

soon constructed and published by the authors of the theory. Such a

nomenclature made its way into general use the more easily, in that

the want of such a system had already been severely felt; the names

in common use being fantastical, arbitrary, and multiplied beyond

measure. The number of known substances had become so great, that a

list of names with no regulative principle, founded on accident,

caprice, and error, was too cumbrous and inconvenient to be

tolerated. Even before the currency which Lavoisier's theory

obtained, these evils had led to attempts towards a more convenient

set of names. Bergman and Black had constructed such lists; and

Guyton de Morveau, a clever and accomplished lawyer of Dijon, had

formed a system of nomenclature in 1782, before he had become a

convert to Lavoisier's theory, in which task he had been exhorted

and encouraged by Bergman and Macquer. In this system,[41\14] we do

not find most of the characters of the method which was afterwards

adopted. But a few years later, Lavoisier, De Morveau, Berthollet

and Fourcroy, associated themselves for the purpose of producing a

nomenclature which should correspond to the new theoretical views.

This appeared in 1787, and soon made its way into general use. The

main features of this system are, a selection of the simplest

radical words, by which substances are designated, and a systematic

distribution of terminations, to express their relations. Thus,

sulphur, combined with oxygen in two different proportions, forms

two acids, the {282} sulphur_ous_ and the sulphur_ic_; and these

acids form, with earthy or alkaline bases, sulph_ides_ and

sulph_ates_; while sulphur directly combined with another element,

forms a sulph_uret_. The term _oxyd_ (now usually written _oxide_)

expressed a lower degree of combination with oxygen than the acids.

The _Méthode de Nomenclature Chimique_ was published in 1787; and in

1789, Lavoisier published a treatise on chemistry in order further

to explain this method. In the preface to this volume, he apologizes

for the great amount of the changes, and pleads the authority of

Bergman, who had exhorted De Morveau "to spare no improper names;

those who are learned will always be learned, and those who are

ignorant will thus learn sooner." To this maxim they so far

conformed, that their system offers few anomalies; and though the

progress of discovery, and the consequent changes of theoretical

opinion, which have since gone on, appear now to require a further

change of nomenclature, it is no small evidence of the skill with

which this scheme was arranged, that for half a century it was

universally used, and felt to be far more useful and effective than

any nomenclature in any science had ever been before.

[Note 41\14: _Journal de Physique_, 1782, p. 370.]

CHAPTER VII.

APPLICATION AND CORRECTION OF THE OXYGEN THEORY.

SINCE a chemical theory, as far as it is true, must enable us to

obtain a true view of the intimate composition of all bodies

whatever, it will readily be supposed that the new chemistry led to

an immense number of analyses and researches of various kinds. These

it is not necessary to dwell upon; nor will I even mention the names

of any of the intelligent and diligent men who have labored in this

field. Perhaps one of the most striking of such analyses was Davy's

decomposition of the earths and alkalies into metallic bases and

oxygen, in 1807 and 1808; thus extending still further that analogy

between the earths and the calces of the metals, which had had so

large a share in the formation of chemical theories. This discovery,

however, both in the means by which it was made, and in the views to

which it led, bears upon subjects hereafter to be treated of.

The Lavoisierian theory also, wide as was the range of truth which

it embraced, required some limitation and correction. I do not now

{283} speak of some erroneous opinions entertained by the author of

the theory; as, for instance, that the heat produced in combustion,

and even in respiration, arose from the conversion of oxygen gas to

a solid consistence, according to the doctrine of latent heat. Such

opinions not being necessarily connected with the general idea of

the theory, need not here be considered. But the leading

generalization of Lavoisier, that acidification was _always_

combination with oxygen, was found untenable. The point on which the

contest on this subject took place was the constitution of the

_oxymuriatic_ and _muriatic_ acids;--as they had been termed by

Berthollet, from the belief that muriatic acid contained oxygen, and

oxymuriatic a still larger dose of oxygen. In opposition to this, a

new doctrine was put forward in 1809 by Gay-Lussac and Thenard in

France, and by Davy in England;--namely, that oxymuriatic acid was a

simple substance, which they termed _chlorine_, and that muriatic

acid was a combination of chlorine with hydrogen, which therefore

was called _hydrochloric acid_. It may be observed, that the point

in dispute in the controversy on this subject was nearly the same

which had been debated in the course of the establishment of the

oxygen theory; namely, whether in the formation of muriatic acid

from chlorine, oxygen is subtracted, or hydrogen added, and the

water concealed.

In the course of this dispute, it was allowed on both sides, that

the combination of dry muriatic acid and ammonia afforded an

_experimentum crucis_; since, if water was produced from these

elements, oxygen must have existed in the acid. Davy being at

Edinburgh in 1812, this experiment was made in the presence of

several eminent philosophers; and the result was found to be, that

though a slight dew appeared in the vessel, there was not more than

might be ascribed to unavoidable imperfection in the process, and

certainly not so much as the old theory of muriatic acid required.

The new theory, after this period, obtained a clear superiority in

the minds of philosophical chemists, and was further supported by

new analogies.[42\14]

[Note 42\14: Paris, _Life of Davy_, i. 337.]

For, the existence of one _hydracid_ being thus established, it was

found that other substances gave similar combinations; and thus

chemists obtained the _hydriodic_, _hydrofluoric_, and _hydrobromic_

acids. These acids, it is to be observed, form salts with bases, in

the same manner as the oxygen acids do. The analogy of the muriatic

and fluoric compounds was first clearly urged by a philosopher who

was {284} not peculiarly engaged in chemical research, but who was

often distinguished by his rapid and happy generalizations, M.

Ampère. He supported this analogy by many ingenious and original

arguments, in letters written to Davy, while that chemist was

engaged in his researches on fluor spar, as Davy himself

declares.[43\14]

[Note 43\14: Paris, _Life of Davy_, i. 370.]

Still further changes have been proposed, in that classification of

elementary substances to which the oxygen theory led. It has been

held by Berzelius and others, that other elements, as, for example,

sulphur, form _salts_ with the alkaline and earthy metals, rather

than sulphurets. The character of these _sulpho-salts_, however, is

still questioned among chemists; and therefore it does not become us

to speak as if their place in history were settled. Of course, it

will easily be understood that, in the same manner in which the

oxygen theory introduced its own proper nomenclature, the overthrow

or material transformation of the theory would require a change in

the nomenclature; or rather, the anomalies which tended to disturb

the theory, would, as they were detected, make the theoretical terms

be felt as inappropriate, and would suggest the necessity of a

reformation in that respect. But the discussion of this point

belongs to a step of the science which is to come before us

hereafter.

It may be observed, that in approaching the limits of this part of

our subject, as we are now doing, the doctrine of the combination of

_acids_ and _bases_, of which we formerly traced the rise and

progress, is still assumed as a fundamental relation by which other

relations are tested. This remark connects the stage of chemistry

now under our notice with its earliest steps. But in order to point

out the chemical bearing of the next subjects of our narrative, we

may further observe, that _metals_, _earths_, _salts_, are spoken of

as known _classes_ of substances; and in like manner the

newly-discovered elements, which form the last trophies of

chemistry, have been distributed into such classes according to

their analogies; thus _potassium_, _sodium_, _barium_, have been

asserted to be metals; _iodine_, _bromine_, _fluorine_, have been

arranged as analogical to _chlorine_. Yet there is something vague

and indefinite in the boundaries of such classifications and

analogies; and it is precisely where this vagueness falls, that the

science is still obscure or doubtful. We are led, therefore, to see

the dependence of Chemistry upon Classification; and it is to

Sciences of Classification which we shall next proceed; as soon as

we have noticed the most general views {285} which have been given

of chemical relations, namely, the views of the electro-chemists.

But before we do this, we must look back upon a law which obtains in

the combination of elements, and which we have hitherto not stated;

although it appears, more than any other, to reveal to us the

intimate constitution of bodies, and to offer a basis for future

generalizations. I speak of the _Atomic Theory_, as it is usually

termed; or, as we might rather call it, the Doctrine of Definite,

Reciprocal, and Multiple Proportions.

CHAPTER VIII.

THEORY OF DEFINITE, RECIPROCAL, AND MULTIPLE PROPORTIONS.

_Sect._ 1.--_Prelude to the Atomic Theory, and its Publication by

Dalton._

THE general laws of chemical combination announced by Mr. Dalton are

truths of the highest importance in the science, and are now nowhere

contested; but the view of matter as constituted of _atoms_, which

he has employed in conveying those laws, and in expressing his

opinion of their cause, is neither so important nor so certain. In

the place which I here assign to his discovery, as one of the great

events of the history of chemistry, I speak only of the _law of

phenomena_, the rules which govern the quantities in which elements

combine.

This law may be considered as consisting of three parts, according

to the above description of it;--that elements combine in _definite_

proportions;--that these determining proportions operate

_reciprocally_;--and that when, between the same elements, several

combining proportions occur, they are related as _multiples_.

That elements combine in certain definite proportions of quantity,

and in no other, was implied, as soon as it was supposed that

chemical compounds had any definite properties. Those who first

attempted to establish regular formulæ[44\14] for the constitution

of salts, minerals, and {286} other compounds, assumed, as the basis

of this process, that the elements in different specimens had the

same proportion. Wenzel, in 1777, published his _Lehre von der

Verwandschaft der Körper_; or, _Doctrine of the Affinities of

Bodies_; in which he gave many good and accurate analyses. His work,

it is said, never grew into general notice. Berthollet, as we have

already stated, maintained that chemical compounds were not

definite; but this controversy took place at a later period. It

ended in the establishment of the doctrine, that there is, for each

combination, only one proportion of the elements, or at most only

two or three.

[Note 44\14: Thomson, _Hist. Chem._ vol. ii. p. 279.]

Not only did Wenzel, by his very attempt, presume the first law of

chemical composition, the definiteness of the proportions, but he

was also led, by his results, to the second rule, that they are

reciprocal. For he found that when two _neutral_ salts decompose

each other, the resulting salts are also neutral. The neutral

character of the salts shows that they are definite compounds; and

when the two elements of the one salt, _P_ and _s_, are presented to

those of the other, _B_ and _n_, if _P_ be in such quantity as to

combine definitely with _n_, _B_ will also combine definitely with

_s_.[45\14]

[Note 45\14: I am told that Wenzel (whose book I have not seen),

though he adduces many cases in which double decomposition gives

neutral salts, does not express the proposition in a general form,

nor use letters in expressing it.]

Views similar to those of Wenzel were also published by Jeremiah

Benjamin Richter[46\14] in 1792, in his _Anfangsgründe der

Stöchyometrie, oder Messkunst Chymischer Elemente_, (_Principles of

the Measure of Chemical Elements_) in which he took the law, just

stated, of reciprocal proportions, as the basis of his researches,

and determined the numerical quantities of the common bases and

acids which would saturate each other. It is clear that, by these

steps, the two first of our three rules may be considered as fully

developed. The change of general views which was at this time going

on, probably prevented chemists from feeling so much interest as

they might have done otherwise, in these details; the French and

English chemists, in particular, were fully employed with their own

researches and controversies.

[Note 46\14: Thomson, _Hist. Chem._ vol. ii. p. 283.]

Thus the rules which had already been published by Wenzel and

Richter had attracted so little notice, that we can hardly consider

Mr. Dalton as having been anticipated by those writers, when, in

1803, he began to communicate his views on the chemical constitution

of {287} bodies; these views being such as to include both these two

rules in their most general form, and further, the rule, at that

time still more new to chemists, of _multiple_ proportions. He

conceived bodies as composed of atoms of their constituent elements,

grouped, either one and one, or one and two, or one and three, and

so on. Thus, if _C_ represent an atom of carbon and _O_ one of

oxygen, _O C_ will be an atom of _carbonic oxide_, and _O C O_ an

atom of _carbonic acid_; and hence it follows, that while both these

bodies have a definite quantity of oxygen to a given quantity of

carbon, in the latter substance this quantity is _double_ of what it

is in the former.

The consideration of bodies as consisting of compound atoms, each of

these being composed of elementary atoms, naturally led to this law

of multiple proportions. In this mode of viewing bodies, Mr. Dalton

had been preceded (unknown to himself) by Mr. Higgins, who, in 1789,

published[47\14] his _Comparative View of the Phlogistic and

Antiphlogistic Theories_. He there says,[48\14] "That in volatile

vitriolic acid, a single ultimate particle of sulphur is united only

to a single particle of dephlogisticated air; and that in perfect

vitriolic acid, every single particle of sulphur is united to two of

dephlogisticated air, being the quantity necessary to saturation;"

and he reasons in the same manner concerning the constitution of

water, and the compounds of nitrogen and oxygen. These observations

of Higgins were, however, made casually, and not followed out, and

cannot affect Dalton's claim to original merit.

[Note 47\14: Turner's _Chem._ p. 217.]

[Note 48\14: P. 36 and 37.]

Mr. Dalton's generalization was first suggested[49\14] during his

examination of olefiant gas and carburetted hydrogen gas; and was

asserted generally, on the strength of a few facts, being, as it

were, irresistibly recommended by the clearness and simplicity which

the notion possessed. Mr. Dalton himself represented the compound

atoms of bodies by symbols, which professed to exhibit the

arrangement of the elementary atoms in space as well as their

numerical proportion; and he attached great importance to this part

of his scheme. It is clear, however, that this part of his doctrine

is not essential to that numerical comparison of the law with facts,

on which its establishment rests. These hypothetical configurations

of atoms have no value till they are confirmed by corresponding

facts, such as the optical or crystalline properties of bodies may

perhaps one day furnish. {288}

[Note 49\14: Thomson, vol. ii. p. 291.]

_Sect._ 2.--_Reception and Confirmation of the Atomic Theory._

IN order to give a sketch of the progress of the Atomic Theory into

general reception, we cannot do better than borrow our information

mainly from Dr. Thomson, who was one of the earliest converts and

most effective promulgators of the doctrine. Mr. Dalton, at the time

when he conceived his theory, was a teacher of mathematics at

Manchester, in circumstances which might have been considered

narrow, if he himself had been less simple in his manner of life,

and less moderate in his worldly views. His experiments were

generally made with apparatus of which the simplicity and cheapness

corresponded to the rest of his habits. In 1804, he was already in

possession of his atomic theory, and explained it to Dr. Thomson,

who visited him at that time. It was made known to the chemical

world in Dr. Thomson's _Chemistry_, in 1807; and in Dalton's own

_System of Chemistry_ (1808) the leading ideas of it were very

briefly stated. Dr. Wollaston's memoir, "on superacid and subacid

salts," which appeared in the _Philosophical Transactions_ for 1808,

did much to secure this theory a place in the estimation of

chemists. Here the author states, that he had observed, in various

salts, the quantities of acid combined with the base in the neutral

and in the superacid salts to be as one to two: and he says that,

thinking it likely this law might obtain generally in such

compounds, it was his design to have pursued this subject, with the

hope of discovering the cause to which so regular a relation may be

ascribed. But he adds, that this appears to be superfluous after the

publication of Dalton's theory by Dr. Thomson, since all such facts

are but special cases of the general law. We cannot but remark here,

that the scrupulous timidity of Wollaston was probably the only

impediment to his anticipating Dalton in the publication of the rule

of multiple proportions; and the forwardness to generalize, which

belongs to the character of the latter, justly secured him, in this

instance, the name of the discoverer of this law. The rest of the

English chemists soon followed Wollaston and Thomson, though Davy

for some time resisted. They objected, indeed, to Dalton's

assumption of atoms, and, to avoid this hypothetical step, Wollaston

used the phrase _chemical equivalents_, and Davy the word

_proportions_, for the numbers which expressed Dalton's atomic

weights. We may, however, venture to say that the term "atom" is the

most convenient, and it need not be understood as claiming our

assent to the hypothesis of indivisible molecules. {289}

As Wollaston and Dalton were thus arriving independently at the same

result in England, other chemists, in other countries, were, unknown

to each other, travelling towards the same point.

In 1807, Berzelius,[50\14] intending to publish a system of

chemistry, went through several works little read, and among others

the treatises of Richter. He was astonished, he tells us, at the

light which was there thrown upon composition and decomposition, and

which had never been turned to profit. He was led to a long train of

experimental research, and, when he received information of Dalton's

ideas concerning multiple proportions, he found, in his own

collection of analyses, a full confirmation of this theory.

[Note 50\14: Berz. _Chem._ B. iii. p. 27.]

Some of the Germans, indeed, appear discontented with the partition

of reputation which has taken place with respect to the Theory of

Definite Proportions. One[51\14] of them says, "Dalton has only done

this;--he has wrapt up the good Richter (whom he knew; compare

Schweigger, T, older series, vol. x., p. 381;) in a ragged suit,

patched together of atoms; and now poor Richter comes back to his

own country in such a garb, like Ulysses, and is not recognized." It

is to be recollected, however, that Richter says nothing of multiple

proportions.

[Note 51\14: Marx. _Gesch. der Cryst._ p. 202.]

The general doctrine of the atomic theory is now firmly established

over the whole of the chemical world. There remain still several

controverted points, as, for instance, whether the atomic weights of

all elements are exact multiples of the atomic weight of hydrogen.

Dr. Prout advanced several instances in which this appeared to be

true, and Dr. Thomson has asserted the law to be of universal

application. But, on the other hand, Berzelius and Dr. Turner

declare that this hypothesis is at variance with the results of the

best analyses. Such controverted points do not belong to our

history, which treats only of the progress of scientific truths

already recognized by all competent judges.

Though Dalton's discovery was soon generally employed, and

universally spoken of with admiration, it did not bring to him

anything but barren praise, and he continued in the humble

employment of which we have spoken, when his fame had filled Europe,

and his name become a household word in the laboratory. After some

years he was appointed a corresponding member of the Institute of

France; which may be considered as a European recognition of the

importance {290} of what he had done; and, in 1826, two medals for

the encouragement of science having been placed at the disposal of

the Royal Society by the King of England, one of them was assigned

to Dalton, "for his development of the atomic theory." In 1833, at

the meeting of the British Association for the Advancement of

Science, which was held in Cambridge, it was announced that the King

had bestowed upon him a pension of 150_l._; at the preceding meeting

at Oxford, that university had conferred upon him the degree of

Doctor of Laws, a step the more remarkable, since he belonged to the

sect of Quakers. At all the meetings of the British Association he

has been present, and has always been surrounded by the reverence

and admiration of all who feel any sympathy with the progress of

science. May he long remain among us thus to remind us of the vast

advance which Chemistry owes to him!

[2nd Ed.] [Soon after I wrote these expressions of hope, the period

of Dalton's sojourn among us terminated. He died on the 27th of

July, 1844, aged 78.

His fellow-townsmen, the inhabitants of Manchester, who had so long

taken a pride in his residence among them, soon after his death came

to a determination to perpetuate his memory by establishing in his

honor a Professor of Chemistry at Manchester.]

_Sect._ 3.--_The Theory of Volumes.--Gay-Lussac._

THE atomic theory, at the very epoch of its introduction into

France, received a modification in virtue of a curious discovery

then made. Soon after the publication of Dalton's system, Gay-Lussac

and Humboldt found a rule for the combination of substances, which

includes that of Dalton as far as it goes, but extends to

combinations of gases only. This law is the _theory of volumes_;

namely, that gases unite together _by volume_ in very simple and

definite proportions. Thus water is composed exactly of 100 measures

of oxygen and 200 measures of hydrogen. And since these simple

ratios 1 and 1, 1 and 2, 1 and 3, alone prevail in such

combinations, it may easily be shown that laws like Dalton's law of

multiple proportions, must obtain in such cases as he considered.

[2nd Ed.] [M. Schröder, of Mannheim, has endeavored to extend to

solids a law in some degree resembling Gay-Lussac's law of the

volumes of gases. According to him, the volumes of the chemical

equivalents {291} of simple substances and their compounds are as

whole numbers.[52\14] MM. Kopp, Playfair, and Joule have labored in

the same field.]

[Note 52\14: _Die molecular-volume der Chemischen Verbindungen in

festen und flüssingen Zustande_, 1843.]

I cannot now attempt to trace other bearings and developments of

this remarkable discovery. I hasten on to the last generalization of

chemistry; which presents to us chemical forces under a new aspect,

and brings us back to the point from which we departed in commencing

the history of this science.

CHAPTER IX.

EPOCH OF DAVY AND FARADAY.

_Sect._ 1.--_Promulgation of the Electro-chemical Theory by Davy._

THE reader will recollect that the History of Chemistry, though

highly important and instructive in itself, has been an interruption

of the History of Electro-dynamic Research:--a necessary

interruption, however; for till we became acquainted with Chemistry

in general, we could not follow the course of Electro-chemistry: we

could not estimate its vast yet philosophical theories, nor even

express its simplest facts. We have now to endeavor to show what has

thus been done, and by what steps;--to give a fitting view of the

Epoch of Davy and Faraday.

This is, doubtless, a task of difficulty and delicacy. We cannot

execute it at all, except we suppose that the great truths, of which

the discovery marks this epoch, have already assumed their definite

and permanent form. For we do not learn the just value and right

place of imperfect attempts and partial advances in science, except

by seeing to what they lead. We judge properly of our trials and

guesses only when we have gained our point and guessed rightly. We

might personify philosophical theories, and might represent them to

ourselves as figures, all pressing eagerly onwards in the same {292}

direction, whom we have to pursue: and it is only in proportion as

we ourselves overtake those figures in the race, and pass beyond

them, that we are enabled to look back upon their faces; to discern

their real aspects, and to catch the true character of their

countenances. Except, therefore, I were of opinion that the great

truths which Davy brought into sight have been firmly established

and clearly developed by Faraday, I could not pretend to give the

history of this striking portion of science. But I trust, by the

view I have to offer of these beautiful trains of research and their

result, to justify the assumption on which I thus proceed.

I must, however, state, as a further appeal to the reader's

indulgence, that, even if the great principles of electro-chemistry

have now been brought out in their due form and extent, the

discovery is but a very few years, I might rather say a few months,

old, and that this novelty adds materially to the difficulty of

estimating previous attempts from the point of view to which we are

thus led. It is only slowly and by degrees that the mind becomes

sufficiently imbued with those new truths, of which the office is,

to change the face of a science. We have to consider familiar

appearances under a new aspect; to refer old facts to new

principles; and it is not till after some time, that the struggle

and hesitation which this employment occasions, subsides into a

tranquil equilibrium. In the newly acquired provinces of man's

intellectual empire, the din and confusion of conquest pass only

gradually into quiet and security. We have seen, in the history of

all capital discoveries, how hardly they have made their way, even

among the most intelligent and candid philosophers of the antecedent

schools: we must, therefore, not expect that the metamorphosis of

the theoretical views of chemistry which is now going on, will be

effected without some trouble and delay.

I shall endeavor to diminish the difficulties of my undertaking, by

presenting the earlier investigations in the department of which I

have now to speak, as much as possible according to the most

deliberate view taken of them by the great discoverers themselves,

Davy and Faraday; since these philosophers are they who have taught

us the true import of such investigations.

There is a further difficulty in my task, to which I might

refer;--the difficulty of speaking, without error and without

offence, of men now alive, or who were lately members of social

circles which exist still around us. But the scientific history in

which such persons play a part, is so important to my purpose, that

I do not hesitate to incur {293} the responsibility which the

narration involves; and I have endeavored earnestly, and I hope not

in vain, to speak as if I were removed by centuries from the

personages of my story.

The phenomena observed in the Voltaic apparatus were naturally the

subject of many speculations as to their cause, and thus gave rise

to "Theories of the Pile." Among these phenomena there was one class

which led to most important results: it was discovered by Nicholson

and Carlisle, in 1800, that water was _decomposed_ by the pile of

Volta; that is, it was found that when the wires of the pile were

placed with their ends near each other in the fluid, a stream of

bubbles of air arose from each wire, and these airs were found on

examination to be oxygen and hydrogen: which, as we have had to

narrate, had already been found to be the constituents of water.

This was, as Davy says,[53\14] the true origin of all that has been

done in electro-chemical science. It was found that other substances

also suffered a like decomposition under the same circumstances.

Certain metallic solutions were decomposed, and an alkali was

separated on the negative plates of the apparatus. Cruickshank, in

pursuing these experiments, added to them many important new

results; such as the decomposition of muriates of magnesia, soda,

and ammonia by the pile; and the general observation that the

alkaline matter always appeared at the _negative_, and the acid at

the _positive_, pole.

[Note 53\14: _Phil. Trans._ 1826, p. 386.]

Such was the state of the subject when one who was destined to do so

much for its advance, first contributed his labors to it. Humphry

Davy was a young man who had been apprenticed to a surgeon at

Penzance, and having shown an ardent love and a strong aptitude for

chemical research, was, in 1798, made the superintendent of a

"Pneumatic Institution," established at Bristol by Dr. Beddoes, for

the purpose of discovering medical powers of factitious airs.[54\14]

But his main attention was soon drawn to galvanism; and when, in

consequence of the reputation he had acquired, he was, in 1801,

appointed lecturer at the Royal Institution in London (then recently

established), he was soon put in possession of a galvanic apparatus

of great power; and with this he was not long in obtaining the most

striking results.

[Note 54\14: Paris, _Life of Davy_, i. 58.]

His first paper on the subject[55\14] is sent from Bristol, in

September, 1800; and describes experiments, in which he had found

that the decompositions observed by Nicholson and Carlisle go on,

although the {294} water, or other substance in which the two wires

are plunged, be separated into two portions, provided these portions

are connected by muscular or other fibres. This use of muscular

fibres was, probably, a remnant of the original disposition, or

accident, by which galvanism had been connected with physiology, as

much as with chemistry. Davy, however, soon went on towards the

conclusion, that the phenomena were altogether chemical in their

nature. He had already conjectured,[56\14] in 1802, that all

decompositions might be _polar_; that is, that in all cases of

chemical decomposition, the elements might be related to each other

as electrically _positive_ and _negative_; a thought which it was

the peculiar glory of his school to confirm and place in a distinct

light. At this period such a view was far from obvious; and it was

contended by many, on the contrary, that the elements which the

voltaic apparatus brought to view, were not liberated from

combinations, but generated. In 1806, Davy attempted the solution of

this question; he showed that the ingredients which had been

supposed to be produced by electricity, were due to impurities in

the water, or to the decomposition of the vessel; and thus removed

all preliminary difficulties. And then he says,[57\14] "referring to

my experiments of 1800, 1801, and 1802, and to a number of new

facts, which showed that inflammable substances and oxygen, alkalies

and acids, and oxidable and noble metals, were in electrical

relations of positive and negative, I drew the conclusion, _that the

combinations and decompositions by electricity were referrible to

the law of electrical attractions and repulsions_," and advanced the

hypothesis, "_that chemical and electrical attractions were produced

by the same cause, acting in the one case on particles, in the other

on masses; . . . and that the same property, under different

modifications, was the cause of all the phenomena exhibited by

different voltaic combinations._"

[Note 55\14: Nicholson's _Journal_, 4to. iv. 275.]

[Note 56\14: _Phil. Trans._ 1826.]

[Note 57\14: Ib. 1826, p. 389.]

Although this is the enunciation, in tolerably precise terms, of the

great discovery of his epoch, it was, at the period of which we

speak, conjectured rather than proved; and we shall find that

neither Davy nor his followers, for a considerable period,

apprehended it with that distinctness which makes a discovery

complete. But in a very short time afterwards, Davy drew great

additional notice to his researches by effecting, in pursuance, as

it appeared, of his theoretical views, the decomposition of potassa

into a metallic base and oxygen. This was, as he truly said, in the

memorandum written in his journal at the {295} instant, "a capital

experiment." This discovery was soon followed by that of the

decomposition of soda; and shortly after, of other bodies of the

same kind; and the interest and activity of the whole chemical world

were turned to the subject in an intense degree.

At this period, there might be noticed three great branches of

speculation on this subject; _the theory of the pile_, _the theory

of electrical decomposition_, and **_the theory of the identity of

chemical and electrical forces_; which last doctrine, however, was

found to include the other two, as might have been anticipated from

the time of its first suggestion.

It will not be necessary to say much on the theories of the voltaic

pile, as separate from other parts of the subject. The

_contact-theory_, which ascribed the action to the contact of

different metals, was maintained by Volta himself; but gradually

disappeared, as it was proved (by Wollaston[58\14] especially,) that

the effect of the pile was inseparably connected with oxidation or

other chemical changes. The theories of electro-chemical

decomposition were numerous, and especially after the promulgation

of Davy's _Memoir_ in 1806; and, whatever might be the defects under

which these speculations for a long time labored, the subject was

powerfully urged on in the direction in which truth lay, by Davy's

discoveries and views. That there remained something still to be

done, in order to give full evidence and consistency to the theory,

appears from this;--that some of the most important parts of Davy's

results struck his followers as extraordinary paradoxes;--for

instance, the fact that the decomposed elements are transferred from

one part of the circuit to another, in a form which escapes the

cognizance of our senses, through intervening substances for which

they have a strong affinity. It was found afterwards that the

circumstance which appeared to make the process so wonderful, was,

in fact, the condition of its going on at all. Davy's expressions

often seem to indicate the most exact notions: for instance, he

says, "It is very natural to suppose that the repellent and

attractive energies are communicated from one particle to another of

the same kind, so as to establish a conducting _chain_ in the fluid;

and that the locomotion takes place in consequence;"[59\14] and yet

at other times he speaks of the element as _attracted_ and

_repelled_ by the metallic surfaces which form the _poles_;--a

different, and, as it appeared afterwards, an untenable view. Mr.

Faraday, who supplied what was wanting, justly notices this

vagueness. {296} He says,[60\14] that though, in Davy's celebrated

Memoir of 1806, the points established are of the utmost value, the

mode of action by which the effects take place is stated very

generally; so generally, indeed, that probably a dozen precise

schemes of electro-chemical action might be drawn up, differing

essentially from each other, yet all agreeing with the statement

there given." And at a period a little later, being reproached by

Davy's brother with injustice in this expression, he substantiated

his assertion by an enumeration of twelve such schemes which had

been published.

[Note 58\14: _Phil. Trans._ 1801, p. 427.]

[Note 59\14: Paris, i. 154.]

[Note 60\14: _Researches_, 482.]

But yet we cannot look upon this Memoir of 1806, otherwise than as a

great event, perhaps the most important event of the epoch now under

review. And as such it was recognized at once all over Europe. In

particular, it received the distinguished honor of being crowned by

the Institute of France, although that country and England were then

engaged in fierce hostility. Buonaparte had proposed a prize of

sixty thousand francs "to the person who by his experiments and

discoveries should advance the knowledge of electricity and

galvanism, as much as Franklin and Volta did;" and "of three

thousand francs for the best experiment which should be made in the

course of each year on the galvanic fluid;" the latter prize was, by

the First Class of the Institute, awarded to Davy.

From this period he rose rapidly to honors and distinctions, and

reached a height of scientific fame as great as has ever fallen to

the lot of a discoverer in so short a time. I shall not, however,

dwell on such circumstances, but confine myself to the progress of

my subject.

_Sect._ 2.--_Establishment of the Electro-chemical Theory by Faraday._

THE defects of Davy's theoretical views will be seen most clearly by

explaining what Faraday added to them. Michael Faraday was in every

way fitted and led to become Davy's successor in his great career of

discovery. In 1812, being then a bookseller's apprentice, he

attended the lectures of Davy, which at that period excited the

highest admiration.[61\14] "My desire to escape from trade," Mr.

Faraday says, "which I thought vicious and selfish, and to enter

into the service of science, which I imagined made its pursuers

amiable and liberal, induced me at last to take the bold and simple

step of writing to Sir H. Davy." He was favorably received, and, in

the next year, became {297} Davy's assistant at the Institution; and

afterwards his successor. The Institution which produced such

researches as those of these two men, may well be considered as a

great school of exact and philosophical chemistry. Mr. Faraday, from

the beginning of his course of inquiry, appears to have had the

consciousness that he was engaged on a great connected work. His

_Experimental Researches_, which appeared in a series of Memoirs in

the _Philosophical Transactions_, are divided into short paragraphs,

numbered into a continued order from 1 up to 1160, at the time at

which I write;[62\14] and destined, probably, to extend much

further. These paragraphs are connected by a very rigorous method of

investigation and reasoning which runs through the whole body of

them. Yet this unity of purpose was not at first obvious. His first

two Memoirs were upon subjects which we have already treated of (B.

xiii. c. 5 and c. 8), Voltaic Induction, and the evolution of

Electricity from Magnetism. His "Third Series" has also been already

referred to. Its object was, as a preparatory step towards further

investigation, to show the identity of voltaic and animal

electricity with that of the electrical machine; and as machine

electricity differs from other kinds in being successively in a

state of tension and explosion, instead of a continued current, Mr.

Faraday succeeded in identifying it with them, by causing the

electrical discharge to pass through a bad conductor into a

discharging-train of vast extent; nothing less, indeed, than the

whole fabric of the metallic gas-pipes and water-pipes of London. In

this Memoir[63\14] it is easy to see already traces of the general

theoretical views at which he had arrived; but these are not

expressly stated till his "Fifth Series;" his intermediate Fourth

Series being occupied by another subsidiary labor on the conditions

of conduction. At length, however, in the Fifth Series, which was

read to the Royal Society in June, 1833, he approaches the theory of

electro-chemical decomposition. Most preceding theorists, and Davy

amongst the number, had referred this result to _attractive powers_

residing in the _poles_ of the apparatus; and had even pretended to

compare the intensity of this attraction at different distances from

the poles. By a number of singularly beautiful and skilful

experiments, Mr. Faraday shows that the phenomena can with no

propriety be {298} ascribed to the attraction of the poles.[64\14]

"As the substances evolved in cases of electro-chemical

decomposition may be made to appear against air,[65\14] which,

according to common language, is not a conductor, nor is decomposed;

or against water,[66\14] which is a conductor, and can be

decomposed; as well as against the metal poles, which are excellent

conductors, but undecomposable; there appears but little reason to

consider this phenomenon generally as due to the attraction or

attractive powers of the latter, when used in the ordinary way,

since similar attractions can hardly be imagined in the former

instances."

[Note 61\14: Paris, ii. 3.]

[Note 62\14: December, 1835. (At present, when I am revising the

second edition, September, 1846, Dr. Faraday has recently published

the "Twenty-first Series" of his _Researches_ ending with paragraph

2453.)]

[Note 63\14: _Phil. Trans._ 1833.]

[Note 64\14: _Researches_, Art. 497]

[Note 65\14: _Researches_, Arts. 465, 469.]

[Note 66\14: 495.]

Faraday's opinion, and, indeed, the only way of expressing the

results of his experiments, was, that the chemical elements, in

obedience to the direction of the voltaic currents established in

the decomposing substance, were evolved, or, as he prefers to say,

_ejected_ at its extremities.[67\14] He afterwards states that the

influence which is present in the electric current may be

described[68\14] as _an axis of power, having_ [at each point]

_contrary forces exactly equal in amount in contrary directions_.

[Note 67\14: 493.]

[Note 68\14: 517.]

Having arrived at this point, Faraday rightly wished to reject the

term _poles_, and other words which could hardly be used without

suggesting doctrines now proved to be erroneous. He considered, in

the case of bodies electrically decomposed, or, as he termed them,

_electrolytes_, the elements as travelling in two opposite

directions; which, with reference to the direction of terrestrial

magnetism, might be considered as naturally east and west; and he

conceived elements as, in this way, arriving at the doors or outlets

at which they finally made their separate appearance. The doors he

called _electrodes_, and, separately, the _anode_ and the

_cathode_;[69\14] and the elements which thus travel he termed the

_anïon_ and the _catïon_ (or _cathïon_).[70\14] By means of this

nomenclature he was able to express his general results with much

more distinctness and facility.

[Note 69\14: 663.]

[Note 70\14: The analogy of the Greek derivation requires _catïon_;

but to make the relation to _cathode_ obvious to the English reader,

and to avoid a violation of the habits of English pronunciation, I

should prefer _cathïon_.]

But this general view of the electrolytical process required to be

pursued further, in order to explain the nature of the action. The

identity of electrical and chemical forces, which had been hazarded

as {299} a conjecture by Davy, and adopted as the basis of chemistry

by Berzelius, could only be established by exact measures and

rigorous proofs. Faraday had, in his proof of the identity of

voltaic and electric agency, attempted also to devise such a measure

as should give him a comparison of their quantity; and in this way

he proved that[71\14] a voltaic group of two small wires of platinum

and zinc, placed near each other, and immersed in dilute acid for

three seconds, yields as much electricity as the electrical battery,

charged by ten turns of a large machine; and this was established

both by its momentary electro-magnetic effect, and by the amount of

its chemical action.[72\14]

[Note 71\14: _Researches_, Art. 371.]

[Note 72\14: 537.]

It was in his "Seventh Series," that he finally established a

principle of definite measurement of the amount of electrolytical

action, and described an instrument which he termed[73\14] a

_volta-electrometer_. In this instrument the amount of action was

measured by the quantity of water decomposed: and it was necessary,

in order to give validity to the mensuration, to show (as Faraday

did show) that neither the size of the electrodes, nor the intensity

of the current, nor the strength of the acid solution which acted on

the plates of the pile, disturbed the accuracy of this measure. He

proved, by experiments upon a great variety of substances, of the

most different kinds, that the electro-chemical action is definite

in amount according to the measurement of the new instrument.[74\14]

He had already, at an earlier period,[75\14] asserted, that _the

chemical power of a current of electricity is in direct proportion

to the absolute quantity of electricity which passes_; but the

volta-electrometer enabled him to fix with more precision the

meaning of this general proposition, as well as to place it beyond

doubt.

[Note 73\14: 739.]

[Note 74\14: Arts. 758, 814.]

[Note 75\14: 377.]

The vast importance of this step in chemistry soon came into view.

By the use of the volta-electrometer, Faraday obtained, for each

elementary substance, a number which represented the relative amount

of its decomposition, and which might properly[76\14] be called its

"electro-chemical equivalent." And the question naturally occurs,

whether these numbers bore any relation to any previously

established chemical measures. The answer is remarkable. _They were

no other than the atomic weights of the Daltonian theory_, which

formed the climax of the previous ascent of chemistry; and thus

here, as everywhere in {300} the progress of science, the

generalizations of one generation are absorbed in the wider

generalizations of the next.

[Note 76\14: 792.]

But in order to reach securely this wider generalization, Faraday

combined the two branches of the subject which we have already

noticed;--the _theory of electrical decomposition_ with the _theory

of the pile_. For his researches on the origin of activity of the

voltaic circuit (his Eighth Series), led him to see more clearly

than any one before him, what, as we have said, the most sagacious

of preceding philosophers had maintained, that the current in the

pile was due to the mutual chemical action of its elements. He was

led to consider the processes which go on in the _exciting-cell_ and

in the decomposing place as of the same kind, but opposite in

direction. The chemical _composition_ of the fluid with the zinc, in

the common apparatus, produces, when the circuit is completed, a

current of electric influence in the wire; and this current, if it

pass through an electrolyte, manifests itself by _decomposition_,

overcoming the chemical affinity which there resists it. An

electrolyte cannot conduct without being decomposed. The forces at

the point of composition and the point of decomposition are of the

same kind, and are opposed to each other by means of the

conducting-wire; the wire may properly be spoken of[77\14] as

_conducting chemical affinity_: it allows two forces of the same

kind to oppose one another;[78\14] electricity is only another mode

of the exertion of chemical forces;[79\14] and we might express all

the circumstances of the voltaic pile without using any other term

than chemical affinity, though that of electricity may be very

convenient.[80\14] Bodies are held together by a definite power,

which, when it ceases to discharge that office, may be thrown into

the condition of an electric current.[81\14]

[Note 77\14: Researches Art. 918.]

[Note 78\14: 910.]

[Note 79\14: 915.]

[Note 80\14: 917.]

[Note 81\14: 855.]

Thus the great principle of the identity of electrical and chemical

action was completely established. It was, as Faraday with great

candor says,[82\14] a confirmation of the general views put forth by

Davy, in 1806, and might be expressed in his terms, that "chemical

and electrical attractions are produced by the same cause;" but it

is easy to see that neither was the full import of these expressions

understood nor were the quantities to which they refer conceived as

measurable quantities, nor was the assertion anything but a

sagacious conjecture, till Faraday gave the interpretation, measure,

and proof, of which we have spoken. The evidence of the

incompleteness of the views of his predecessor we have already

adduced, in speaking of his vague and {301} inconsistent theoretical

account of decomposition. The confirmation of Davy's discoveries by

Faraday is of the nature of Newton's confirmation of the views of

Borelli and Hooke respecting gravity, or like Young's confirmation

of the undulatory theory of Huyghens.

[Note 82\14: 965.]

We must not omit to repeat here the moral which we wish to draw from

all great discoveries, that they depend upon the combination of

_exact facts_ with _clear ideas_. The former of these conditions is

easily illustrated in the case of Davy and Faraday, both admirable

and delicate experimenters. Davy's rapidity and resource in

experimenting were extraordinary,[83\14] and extreme elegance and

ingenuity distinguish almost every process of Faraday. He had

published, in 1829, a work on _Chemical Manipulation_, in which

directions are given for performing in the neatest manner all

chemical processes. Manipulation, as he there truly says, is to the

chemist like the external senses to the mind;[84\14] and without the

supply of fit materials which such senses only can give, the mind

can acquire no real knowledge.

[Note 83\14: Paris, i. 145.]

[Note 84\14: _Pref._ p. ii.]

But still the operations of the mind as well as the information of the

senses, ideas as well as facts, are requisite for the attainment of

any knowledge; and all great steps in science require a peculiar

distinctness and vividness of thought in the discoverer. This it is

difficult to exemplify in any better way than by the discoveries

themselves. Both Davy and Faraday possessed this vividness of mind;

and it was a consequence of this endowment, that Davy's **lectures

upon chemistry, and Faraday's upon almost any subject of physical

philosophy, were of the most brilliant and captivating character. In

discovering the nature of voltaic action, the essential intellectual

requisite was to have a distinct conception of that which Faraday

expressed by the remarkable phrase,[85\14] "_an axis of power having

equal and opposite forces_;" and the distinctness of this idea in

Faraday's mind shines forth in every part of his writings. Thus he

says, the force which determines the decomposition of a body is _in_

the body, not in the poles.[86\14] But for the most part he can of

course only convey this fundamental idea by illustrations. Thus[87\14]

he represents the voltaic circuit by a double circle, studded with the

elements of the circuit, and shows how the _anïons_ travel round it in

one direction, and the _cathïons_ in the opposite. He considers[88\14]

the powers at the two places of action as balancing against each other

through the medium of the conductors, in a manner {302} analogous to

that in which mechanical forces are balanced against each other by the

intervention of the lever. It is impossible to him[89\14] to resist

the idea, that the voltaic current must be preceded by a state of

tension in its interrupted condition, which is relieved when the

circuit is completed. He appears to possess the idea of this kind of

force with the same eminent distinctness with which Archimedes in the

ancient, and Stevinus in the modern history of science, possessed the

idea of pressure, and were thus able to found the science of

mechanics.[90\14] And when he cannot obtain these distinct modes of

conception, he is dissatisfied, and conscious of defect. Thus in the

relation between magnetism and electricity,[91\14] "there appears to

be a link in the chain of effects, a wheel in the physical mechanism

of the action, as yet unrecognized." All this variety of expression

shows how deeply seated is the thought. This conception of Chemical

Affinity as a peculiar influence of force, which, acting in opposite

directions, combines and resolves bodies;--which may be liberated and

thrown into the form of a voltaic current, and thus be transferred to

remote points, and applied in various ways; is essential to the

understanding, as it was to the making, of these discoveries.

[Note 85\14: Art. 517.]

[Note 86\14: Art. 661.]

[Note 87\14: **963.]

[Note 88\14: 917.]

[Note 89\14: Art. 950.]

[Note 90\14: 990.]

[Note 91\14: 1114.]

By those to whom this conception has been conveyed, I venture to

trust that I shall be held to have given a faithful account of this

important event in the history of science. We may, before we quit

the subject, notice one or two of the remarkable subordinate

features of Faraday's discoveries.

_Sect._ 3.--_Consequences of Faraday's Discoveries._

FARADAY'S volta-electrometer, in conjunction with the method he had

already employed, as we have seen, for the comparison of voltaic and

common electricity, enabled him to measure the actual quantity of

electricity which is exhibited, in given cases, in the form of

chemical affinity. His results appeared in numbers of that enormous

amount which so often comes before us in the expression of natural

laws. One grain of water[92\14] will require for its decomposition

as much electricity as would make a powerful flash of lightning. By

further calculation, he finds this quantity to be not less than

800,000 charges of his Leyden battery;[93\14] and this is, by his

theory of the identity of the combining with the decomposing force,

the quantity of electricity {303} which is naturally associated with

the elements of the grain of water, endowing them with their mutual

affinity.

[Note 92\14: **853.]

[Note 93\14: 861.]

Many of the subordinate facts and laws which were brought to light

by these researches, clearly point to generalizations, not included

in that which we have had to consider, and not yet discovered: such

laws do not properly belong to our main plan, which is to make our

way _up to_ the generalizations. But there is one which so evidently

promises to have an important bearing on future chemical theories,

that I will briefly mention it. The class of bodies which are

capable of electrical decomposition is limited by a very remarkable

law: they are such binary compounds only as consist of _single_

proportionals of their elementary principles. It does not belong to

us here to speculate on the possible import of this curious law;

which, if not fully established, Faraday has rendered, at least,

highly probable:[94\14] but it is impossible not to see how closely

it connects the Atomic with the Electro-chemical Theory; and in the

connexion of these two great members of Chemistry, is involved the

prospect of its reaching wider generalizations, and principles more

profound than we have yet caught sight of.

[Note 94\14: Art. 697.]

As another example of this connexion, I will, finally, notice that

Faraday has employed his discoveries in order to decide, in some

doubtful cases, what is the true chemical equivalent;[95\14] "I have

such conviction," he says, "that the power which governs

electro-decomposition and ordinary chemical attractions is the same;

and such confidence in the overruling influence of those natural

laws which render the former definite, as to feel no hesitation in

believing that the latter must submit to them too. Such being the

case, I can have no doubt that, assuming hydrogen as 1, and

dismissing small fractions for the simplicity of expression, the

equivalent number or atomic weight of oxygen is 8, of chlorine 36,

of bromine 78·4, of lead 103·5, of tin 59, &c.; notwithstanding that

a very high authority doubles several of these numbers."

[Note 95\14: 851.]

_Sect._ 4.--_Reception of the Electro-chemical Theory._

THE epoch of establishment of the electro-chemical theory, like

other great scientific epochs, must have its sequel, the period of

its reception and confirmation, application and extension. In that

period we {304} are living, and it must be the task of future

historians to trace its course.

We may, however, say a word on the reception which the theory met

with, in the forms which it assumed, anterior to the labors of

Faraday. Even before the great discovery of Davy, Grotthuss, in

1805, had written upon the theory of electro-chemical decomposition;

but he and, as we have seen, Davy, and afterwards other writers, as

Riffault and Chompré, in 1807, referred the effects to the

poles.[96\14] But the most important attempt to appropriate and

employ the generalization which these discoveries suggested, was

that of Berzelius; who adopted at once the view of the identity, or

at least the universal connexion, of electrical relations with

chemical affinity. He considered,[97\14] that in all chemical

combinations the elements may be considered as electro-positive and

electro-negative; and made this opposition the basis of his chemical

doctrines; in which he was followed by a large body of the chemists

of Germany. He held too that the heat and light, evolved during

cases of powerful combination, are the consequence of the electric

discharge which is at that moment taking place: a conjecture which

Faraday at first spoke of with praise.[98\14] But at a later period

he more sagely says,[99\14] that the flame which is produced in such

cases exhibits but a small portion of the electric power which

really acts. "These therefore may not, cannot, be taken as evidences

of the nature of the action; but are merely incidental results,

incomparably small in relation to the forces concerned, and

supplying no information of the way in which the particles are

active on each other, or in which their forces are finally

arranged." And comparing the evidence which he himself had given of

the principle on which Berzelius's speculations rested, with the

speculations themselves, Faraday justly conceived, that he had

transferred the doctrine from the domain of what he calls _doubtful

knowledge_, to that of inductive certainty.

[Note 96\14: Faraday (_Researches_, Art. 481, 492).]

[Note 97\14: _Ann. Chim._ lxxxvi. 146, for 1813.]

[Note 98\14: _Researches_, Art. 870]

[Note 99\14: 960.]

Now that we are arrived at the starting-place, from which this

well-proved truth, the identity of electric and chemical forces,

must make its future advances, it would be trifling to dwell longer

on the details of the diffusion of that doubtful knowledge which

preceded this more certain science. Our history of chemistry is,

therefore, here at an end. I have, as far as I could, executed my

task; which was, to mark all the {305} great steps of its advance,

from the most unconnected facts and the most imperfect speculations,

to the highest generalization at which chemical philosophers have

yet arrived.

Yet it will appear to our purpose to say a few words on the

connexion of this science with those of which we are next to treat;

and that I now proceed to do.

CHAPTER X.

TRANSITION FROM THE CHEMICAL TO THE CLASSIFICATORY SCIENCES.

IT is the object and the boast of chemistry to acquire a knowledge

of bodies which is more exact and constant than any knowledge

borrowed from their sensible qualities can be; since it penetrates

into their intimate constitution, and discloses to us the invariable

laws of their composition. But yet it will be seen, on a little

reflection, that such knowledge could not have any existence, if we

were not also attentive to their sensible qualities.

The whole fabric of chemistry rests, even at the present day, upon

the opposition of acids and bases: an acid was certainly at first

known by its sensible qualities, and how otherwise, even now, do we

perceive its quality? It was a great discovery of modern times that

earths and alkalies have for their bases metals: but what are

_metals_? or how, except from lustre, hardness, weight, and the

like, do we recognize a body as a metal? And how, except by such

characters, even before its analysis, was it known to be an earth or

an alkali? We must suppose some classification established, before

we can make any advance by experiment or observation.

It is easy to see that all attempts to avoid this difficulty by

referring to processes and analogies, as well as to substances,

bring us back to the same point in a circle of fallacies. If we say

that an acid and alkali are known by combining with each other, we

still must ask, What is the criterion that they have _combined_? If

we say that the distinctive qualities of metals and earths are, that

metals become earths by oxidation, we must still inquire how we

recognize the process of _oxidation_? We have seen how important a

part combustion plays in the history of chemical speculation; and we

may usefully form such classes of {306} bodies as _combustibles_ and

_supporters of combustion_. But even _combustion_ is not capable of

being infallibly known, for it passes by insensible shades into

oxidation. We can find no basis for our reasonings, which does not

assume a classification of obvious facts and qualities.

But any classification of substances on such grounds, appears, at

first sight, to involve us in vagueness, ambiguity, and

contradiction. Do we really take the sensible qualities of an acid

as the criterion of its being an acid?--for instance, its sourness?

Prussic acid, arsenious acid, are not sour. "I remember," says Dr.

Paris,[100\14] "a chemist having been exposed to much ridicule from

speaking of a _sweet_ acid,--why not?" When Davy had discovered

potassium, it was disputed whether it was a metal; for though its

lustre and texture are metallic, it is so light as to swim on water.

And if potassium be allowed to be a metal, is silicium one, a body

which wants the metallic lustre, and is a non-conductor of

electricity? It is clear that, at least, the _obvious_ application

of a classification by physical characters, is attended with endless

perplexity.

[Note 100\14: _Life of Davy_, i. 263.]

But since we cannot even begin our researches without assuming a

classification, and since the forms of such a classification which

first occur, end in apparent confusion, it is clear that we must

look to our philosophy for a solution of this difficulty; and must

avoid the embarrassments and contradictions of casual and

unreflective classification, by obtaining a consistent and

philosophical arrangement. We must employ external characters and

analogies in a connected and systematic manner; we must have

_Classificatory Sciences_, and these must have a bearing even on

Chemistry.

Accordingly, the most philosophical chemists now proceed upon this

principle. "The method which I have followed," says M. Thenard, in

his _Traité de Chimie_, published in 1824, "is, to unite in one

group all analogous bodies; and the advantage of this method, which

is that employed by naturalists, is very great, especially in the

study of the metals and their compounds."[101\14] In this, as in all

good systems of chemistry, which have appeared since the

establishment of the phlogistic theory, combustion, and the

analogous processes, are one great element in the arrangement, while

the difference of metallic and non-metallic, is another element.

Thus Thenard, in the first place, speaks of Oxygen; in the next

place, of the Non-metallic Combustibles, as Hydrogen, Carbon,

Sulphur, Chlorine; and in the next place, of Metals. But the Metals

are again divided into six Sections, with reference, {307}

principally, to their facility of combination with oxygen. Thus, the

First Section is the Metals of the Earths; the Second, the Metals of

the Alkalies; the Third, the Easily Oxidable Metals, as Iron; the

Fourth, Metals Less Oxidable, as Copper and Lead; the Fifth Section

contains only Mercury and Osmium; and the Sixth, what were at an

earlier period termed the _Noble_ Metals, Gold, Silver, Platinum,

and others.

[Note 101\14: Pref., p. viii.]

How such principles are to be applied, so as to produce a definite

and consistent arrangement, will be explained in speaking of the

philosophy of the Classificatory Sciences; but there are one or two

peculiarities in the classes of bodies thus recognized by modern

chemistry, which it may be useful to notice.

1. The distinction of Metallic and Non-metallic is still employed,

as of fundamental importance. The discovery of new metals is so much

connected with the inquiries concerning chemical elements, that we

may notice the general progress of such discoveries. _Gold_,

_Silver_, _Iron_, _Copper_, _Quicksilver_, _Lead_, _Tin_, were known

from the earliest antiquity. In the beginning of the sixteenth

century, mine-directors, like George Agricola, had advanced so far

in practical metallurgy, that they had discovered the means of

extracting three additional metals, _Zinc_, _Bismuth_, _Antimony_.

After this, there was no new metal discovered for a century, and

then such discoveries were made by the theoretical chemists, a race

of men who had not existed before Beccher and Stahl. Thus _Arsenic_

and _Cobalt_ were made known by Brandt, in the middle of the

eighteenth century, and we have a long list of similar discoveries

belonging to the same period; _Nickel_, _Manganese_, and _Tungsten_,

which were detected by Cronstedt, Gahn, and Scheele, and Delhuyart,

respectively; metals of a very different kind, _Tellurium_ and

_Molybdenum_, which were brought to light by Müller, Scheele,

Bergman, and Hielm; _Platinum_, which was known as early as 1741,

but with the ore of which, in 1802 and 1803, the English chemists,

Wollaston and Tennant, found that no less than four other new metals

(_Palladium_, _Rhodium_, _Iridium_ and _Osmium_) were associated.

Finally, (omitting some other new metals,) we have another period of

discovery, opened in 1807, by Davy's discovery of _Potassium_, and

including the resolution of all, or almost all, the alkalies and

earths into metallic bases.

[2nd Ed.] [The next few years made some, at least some conjectural,

additions to the list of simple substances, detected by a more

minute scrutiny of known substances. _Thorium_ was discovered by

Berzelius in 1828; and _Vanadium_ by Professor Sefström in 1830. A

{308} metal named _Cerium_, was discovered in 1803, by Hisinger and

Berzelius, in a rare Swedish mineral known by the name of Cerit.

Mosander more recently has found combined with Cerium, other new

metals which he has called _Lanthanium_, _Didymium_, _Erbium_, and

_Terbium_: M. Klaus has found a new metal, _Ruthenium_, in the ore

of Platinum; and Rose has discovered in Tantalite two other new

metals, which he has announced under the names of _Pelopium_ and

_Niobium_. Svanberg is said to have discovered a new earth in

Eudialyt, which is supposed to have, like the rest, a new radical.

If these last discoveries be confirmed, the number of simple

substances will be raised to _sixty-two_.]

2. Attempts have been made to indicate the classification of

chemical substances by some peculiarity in the Name; and the Metals,

for example, have been designated generally by names in _um_, like

the Latin names of the ancient metals, _aurum_, _ferrum_. This

artifice is a convenient nomenclature for the purpose of marking a

recognized difference; and it would be worth the while of chemists

to agree to make it universal, by writing molybden_um_ and

platin_um_; which is sometimes done, but not always.

3. I am not now to attempt to determine how far this

class,--Metals,--extends; but where the analogies of the class cease

to hold there the nomenclature must also change. Thus, some

chemists, as Dr. Thomson, have conceived that the base of Silica is

more analogous to Carbon and Boron, which form acids with oxygen,

than it is to the metals: and he has accordingly associated this

base with these substances, and has given it the same termination,

_Silicon_. But on the validity of this analogy chemists appear not

to be generally agreed.

4. There is another class of bodies which have attracted much notice

among modern chemists, and which have also been assimilated to each

other in the form of their names; the English writers calling them

_Chlorine_, _Fluorine_, _Iodine_, _Bromine_, while the French use

the terms _Chlore_, _Phtore_, _Iode_, _Brome_. We have already

noticed the establishment of the doctrine--that muriatic acid is

formed of a base, chlorine, and of hydrogen,--as a great reform in

the oxygen theory; with regard to which rival claims were advanced

by Davy, and by MM. Gay-Lussac and Thenard in 1800. Iodine, a

remarkable body which, from a dark powder, is converted into a

violet-colored gas by the application of heat, was also, in 1813,

the subject of a similar rivalry between the same English and French

chemists. Bromine {309} was only discovered as late as 1826; and

Fluorine, or _Phtore_, as, from its destructive nature, it has been

proposed to term it, has not been obtained as a separate substance,

and is inferred to exist by analogy only. The analogies of these

bodies (Chlore, Phtore, &c.) are very peculiar; for instance, by

combination with metals they form salts; by combination with

hydrogen they form very strong acids; and all, at the common

temperature of the atmosphere, operate on other bodies in the most

energetic manner. Berzelius[102\14] proposes to call them

_halogenous_ bodies, or _halogenes_.

[Note 102\14: _Chem._ i. 262.]

5. The number of Elementary Substances which are at present

presented in our treatises of chemistry[103\14] is _fifty-three_, [or

rather, as we have said above, _sixty-two_.] It is naturally often

asked what evidence we have, that all these are _elementary_, and

what evidence that they are _all_ the elementary bodies;--how we

know that new elements may not hereafter be discovered, or these

supposed simple bodies resolved into simpler still? To these

questions we can only answer, by referring to the history of

chemistry;--by pointing out what chemists have understood by

analysis, according to the preceding narrative. They have

considered, as the analysis of a substance, that elementary

constitution of it which gives the only intelligible explanation of

the results of chemical manipulation, and which is proved to be

complete as to quantity, by the balance, since the whole can only be

equal to all its parts. It is impossible to maintain that new

substances may not hereafter be discovered; for they may lurk, even

in familiar substances, in doses so minute that they have not yet

been missed amid the inevitable slight inaccuracies of all analysis;

in the way in which iodine and bromine remained so long undetected

in sea-water; and new minerals, or old ones not yet sufficiently

examined, can hardly fail to add something to our list. As to the

possibility of a further analysis of our supposed simple bodies, we

may venture to say that, in regard to such supposed simple bodies as

compose a numerous and well-characterized class, no such step can be

made, except through some great change in chemical theory, which

gives us a new view of all the general relations which chemistry has

yet discovered. The proper evidence of the reality of any supposed

new analysis is, that it is more consistent with the known analogies

of chemistry, to suppose the process analytical than synthetical.

Thus, as has already been said, chemists admit the existence of

fluorine, from the analogy of chlorine; and Davy, when it was found

{310} that ammonia formed an amalgam with mercury, was tempted to

assign to it a metallic basis. But then he again hesitates,[104\14]

and doubts whether the analogies of our knowledge are not better

preserved by supposing that ammonia, as a compound of hydrogen and

another principle, is "a type of the composition of the metals."

[Note 103\14: Turner, p. 971.]

[Note 104\14: _Elem. Chem. Phil._ 1812, p. 481.]

Our history, which is the history of what we know, has little to do

with such conjectures. There are, however, some not unimportant

principles which bear upon them, and which, as they are usually

employed, belong to the science which next comes under our review,

Mineralogy.

{{311}}

BOOK XV.

_THE ANALYTICO-CLASSIFICATORY SCIENCE._

HISTORY OF MINERALOGY.

Κρύσταλλον φαέθοντα διαυγέα λάζεο χερσὶ,

Λᾶαν ἀπόῤῥοιαν περιφεγγέος ἀμβρότου αἴγλης,

Αἰθέρι δ' ἀθανάτων μέγα τέρπεται ἄφθιτον ἦτορ.

Τόν κ' εἴπερ μετὰ χειρὰς ἔχων, περὶ νηὸν ἵκηαι,

Οὔτις τοι μακάρων ἀρνήσεται εὐχωλῆσι.

ORPHEUS. _Lithica._

Now, if the bold but pious thought be thine,

To reach our spacious temple's inner shrine,

Take in thy reverent hands the crystal stone,

Where heavenly light in earthy shroud is shown:--

Where, moulded into measured form, with rays

Complex yet clear, the eternal Ether plays;

This if thou firmly hold and rightly use,

Not long the gods thy ardent wish refuse.

{{313}}

INTRODUCTION.

_Sect._ 1.--_Of the Classificatory Sciences._

THE horizon of the sciences spreads wider and wider before us, as we

advance in our task of taking a survey of the vast domain. We have

seen that the existence of Chemistry as a science which declares the

ingredients and essential constitution of all kinds of bodies,

implies the existence of another corresponding science, which shall

divide bodies into kinds, and point out steadily and precisely what

bodies they are which we have analysed. But a science thus dividing

and defining bodies, is but one member of an order of sciences,

different from those which we have hitherto described; namely, of

the _classificatory sciences_. Such sciences there must be, not only

having reference to the bodies with which chemistry deals, but also

to all things respecting which we aspire to obtain any general

knowledge, as, for instance, plants and animals. Indeed it will be

found, that it is with regard to these latter objects, to organized

beings, that the process of scientific classification has been most

successfully exercised; while with regard to inorganic substances,

the formation of a satisfactory system of arrangement has been found

extremely difficult; nor has the necessity of such a system been

recognised by chemists so distinctly and constantly as it ought to

be. The best exemplification of these branches of knowledge, of

which we now have to speak, will, therefore, be found in the organic

world, in Botany and Zoology; but we will, in the first place, take

a brief view of the science which classifies inorganic bodies, and

of which Mineralogy is hitherto the very imperfect representative.

The principles and rules of the Classificatory Sciences, as well as

of those of the other orders of sciences, must be fully explained

when we come to treat of the Philosophy of the Sciences; and cannot

be introduced here, where we have to do with history only. But I may

observe very briefly, that with the process of _classing_, is joined

the process of _naming_;--that names imply classification;--and that

even the rudest and earliest application of language presupposes a

distribution of objects according to their kinds;--but that such a

spontaneous {314} and unsystematic distribution cannot, in the cases

we now have to consider, answer the purposes of exact and general

knowledge. Our classification of objects must be made consistent and

systematic, in order to be scientific; we must discover marks and

characters, properties and conditions, which are constant in their

occurrence and relations; we must form our classes, we must impose

our names, according to such marks. We can thus, and thus alone,

arrive at that precise, certain, and systematic knowledge, which we

seek; that is, at science. The object, then, of the classificatory

sciences is to obtain FIXED CHARACTERS of the kinds of things; and

the criterion of the fitness of names is, that THEY MAKE GENERAL

PROPOSITIONS POSSIBLE.

I proceed to review the progress of certain sciences on these

principles, and first, though briefly, the science of Mineralogy.

_Sect._ 2.--_Mineralogy as the Analytico-classificatory Science._