A History of Science, vol 4 by Henry Smith Williams (the two towers ebook .TXT) 📕

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supposed to be “fixed air” or carbonic acid—the same that

escapes in effervescence of alkalies and calcareous earths, and

in the fermentation of liquors. He then examined the process of

calcination, whereby the phlogiston of the metal was supposed to

have been drawn off. But far from finding that phlogiston or any

other substance had been driven off, he found that something had

been taken on: that the metal “absorbed air,” and that the

increased weight of the metal corresponded to the amount of air

“absorbed.” Meanwhile he was within grasp of two great

discoveries, that of oxygen and of the composition of the air,

which Priestley made some two years later.

 

The next important inquiry of this great Frenchman was as to the

composition of diamonds. With the great lens of Tschirnhausen

belonging to the Academy he succeeded in burning up several

diamonds, regardless of expense, which, thanks to his

inheritance, he could ignore. In this process he found that a gas

was given off which precipitated lime from water, and proved to

be carbonic acid. Observing this, and experimenting with other

substances known to give off carbonic acid in the same manner, he

was evidently impressed with the now well-known fact that diamond

and charcoal are chemically the same. But if he did really

believe it, he was cautious in expressing his belief fully. “We

should never have expected,” he says, “to find any relation

between charcoal and diamond, and it would be unreasonable to

push this analogy too far; it only exists because both substances

seem to be properly ranged in the class of combustible bodies,

and because they are of all these bodies the most fixed when kept

from contact with air.”

 

As we have seen, Priestley, in 1774, had discovered oxygen, or

“dephlogisticated air.” Four years later Lavoisier first

advanced his theory that this element discovered by Priestley was

the universal acidifying or oxygenating principle, which, when

combined with charcoal or carbon, formed carbonic acid; when

combined with sulphur, formed sulphuric (or vitriolic) acid; with

nitrogen, formed nitric acid, etc., and when combined with the

metals formed oxides, or calcides. Furthermore, he postulated the

theory that combustion was not due to any such illusive thing as

“phlogiston,” since this did not exist, and it seemed to him that

the phenomena of combustion heretofore attributed to phlogiston

could be explained by the action of the new element oxygen and

heat. This was the final blow to the phlogiston theory, which,

although it had been tottering for some time, had not been

completely overthrown.

 

In 1787 Lavoisier, in conjunction with Guyon de Morveau,

Berthollet, and Fourcroy, introduced the reform in chemical

nomenclature which until then had remained practically unchanged

since alchemical days. Such expressions as “dephlogisticated” and

“phlogisticated” would obviously have little meaning to a

generation who were no longer to believe in the existence of

phlogiston. It was appropriate that a revolution in chemical

thought should be accompanied by a corresponding revolution in

chemical names, and to Lavoisier belongs chiefly the credit of

bringing about this revolution. In his Elements of Chemistry he

made use of this new nomenclature, and it seemed so clearly an

improvement over the old that the scientific world hastened to

adopt it. In this connection Lavoisier says: “We have,

therefore, laid aside the expression metallic calx altogether,

and have substituted in its place the word oxide. By this it may

be seen that the language we have adopted is both copious and

expressive. The first or lowest degree of oxygenation in bodies

converts them into oxides; a second degree of additional

oxygenation constitutes the class of acids of which the specific

names drawn from their particular bases terminate in ous, as in

the nitrous and the sulphurous acids. The third degree of

oxygenation changes these into the species of acids distinguished

by the termination in ic, as the nitric and sulphuric acids; and,

lastly, we can express a fourth or higher degree of oxygenation

by adding the word oxygenated to the name of the acid, as has

already been done with oxygenated muriatic acid.”[9]

 

This new work when given to the world was not merely an

epoch-making book; it was revolutionary. It not only discarded

phlogiston altogether, but set forth that metals are simple

elements, not compounds of “earth” and “phlogiston.” It upheld

Cavendish’s demonstration that water itself, like air, is a

compound of oxygen with another element. In short, it was

scientific chemistry, in the modern acceptance of the term.

 

Lavoisier’s observations on combustion are at once important and

interesting: “Combustion,” he says, “… is the decomposition

of oxygen produced by a combustible body. The oxygen which forms

the base of this gas is absorbed by and enters into combination

with the burning body, while the caloric and light are set free.

Every combustion necessarily supposes oxygenation; whereas, on

the contrary, every oxygenation does not necessarily imply

concomitant combustion; because combustion properly so called

cannot take place without disengagement of caloric and light.

Before combustion can take place, it is necessary that the base

of oxygen gas should have greater affinity to the combustible

body than it has to caloric; and this elective attraction, to use

Bergman’s expression, can only take place at a certain degree of

temperature which is different for each combustible substance;

hence the necessity of giving the first motion or beginning to

every combustion by the approach of a heated body. This necessity

of heating any body we mean to burn depends upon certain

considerations which have not hitherto been attended to by any

natural philosopher, for which reason I shall enlarge a little

upon the subject in this place:

 

“Nature is at present in a state of equilibrium, which cannot

have been attained until all the spontaneous combustions or

oxygenations possible in an ordinary degree of temperature had

taken place…. To illustrate this abstract view of the matter by

example: Let us suppose the usual temperature of the earth a

little changed, and it is raised only to the degree of boiling

water; it is evident that in this case phosphorus, which is

combustible in a considerably lower degree of temperature, would

no longer exist in nature in its pure and simple state, but would

always be procured in its acid or oxygenated state, and its

radical would become one of the substances unknown to chemistry.

By gradually increasing the temperature of the earth, the same

circumstance would successively happen to all the bodies capable

of combustion; and, at the last, every possible combustion having

taken place, there would no longer exist any combustible body

whatever, and every substance susceptible of the operation would

be oxygenated and consequently incombustible.

 

“There cannot, therefore, exist, as far as relates to us, any

combustible body but such as are non-combustible at the ordinary

temperature of the earth, or, what is the same thing in other

words, that it is essential to the nature of every combustible

body not to possess the property of combustion unless heated, or

raised to a degree of temperature at which its combustion

naturally takes place. When this degree is once produced,

combustion commences, and the caloric which is disengaged by the

decomposition of the oxygen gas keeps up the temperature which is

necessary for continuing combustion. When this is not the

case—that is, when the disengaged caloric is not sufficient for

keeping up the necessary temperature—the combustion ceases. This

circumstance is expressed in the common language by saying that a

body burns ill or with difficulty.”[10]

 

It needed the genius of such a man as Lavoisier to complete the

refutation of the false but firmly grounded phlogiston theory,

and against such a book as his Elements of Chemistry the feeble

weapons of the supporters of the phlogiston theory were hurled in

vain.

 

But while chemists, as a class, had become converts to the new

chemistry before the end of the century, one man, Dr. Priestley,

whose work had done so much to found it, remained unconverted.

In this, as in all his life-work, he showed himself to be a most

remarkable man. Davy said of him, a generation later, that no

other person ever discovered so many new and curious substances

as he; yet to the last he was only an amateur in science, his

profession, as we know, being the ministry. There is hardly

another case in history of a man not a specialist in science

accomplishing so much in original research as did this chemist,

physiologist, electrician; the mathematician, logician, and

moralist; the theologian, mental philosopher, and political

economist. He took all knowledge for his field; but how he found

time for his numberless researches and multifarious writings,

along with his every-day duties, must ever remain a mystery to

ordinary mortals.

 

That this marvellously receptive, flexible mind should have

refused acceptance to the clearly logical doctrines of the new

chemistry seems equally inexplicable. But so it was. To the

very last, after all his friends had capitulated, Priestley kept

up the fight. From America he sent out his last defy to the

enemy, in 1800, in a brochure entitled “The Doctrine of

Phlogiston Upheld,” etc. In the mind of its author it was little

less than a paean of victory; but all the world beside knew that

it was the swan-song of the doctrine of phlogiston. Despite the

defiance of this single warrior the battle was really lost and

won, and as the century closed “antiphlogistic” chemistry had

practical possession of the field.

 

III. CHEMISTRY SINCE THE TIME OF DALTON

 

JOHN DALTON AND THE ATOMIC THEORY

 

Small beginnings as have great endings—sometimes. As a case in

point, note what came of the small, original effort of a

self-trained back-country Quaker youth named John Dalton, who

along towards the close of the eighteenth century became

interested in the weather, and was led to construct and use a

crude water-gauge to test the amount of the rainfall. The simple

experiments thus inaugurated led to no fewer than two hundred

thousand recorded observations regarding the weather, which

formed the basis for some of the most epochal discoveries in

meteorology, as we have seen. But this was only a beginning. The

simple rain-gauge pointed the way to the most important

generalization of the nineteenth century in a field of science

with which, to the casual observer, it might seem to have no

alliance whatever. The wonderful theory of atoms, on which the

whole gigantic structure of modern chemistry is founded, was the

logical outgrowth, in the mind of John Dalton, of those early

studies in meteorology.

 

The way it happened was this: From studying the rainfall, Dalton

turned naturally to the complementary process of evaporation. He

was soon led to believe that vapor exists, in the atmosphere as

an independent gas. But since two bodies cannot occupy the same

space at the same time, this implies that the various atmospheric

gases are really composed of discrete particles. These ultimate

particles are so small that we cannot see them—cannot, indeed,

more than vaguely imagine them—yet each particle of vapor, for

example, is just as much a portion of water as if it were a drop

out of the ocean, or, for that matter, the ocean itself. But,

again, water is a compound substance, for it may be separated, as

Cavendish has shown, into the two elementary substances hydrogen

and oxygen. Hence the atom of water must be composed of two

lesser atoms joined together. Imagine an atom of hydrogen and one

of oxygen. Unite them, and we have an atom of water; sever them,

and the water no longer exists; but whether united or separate

the atoms of hydrogen and of oxygen remain hydrogen and oxygen

and nothing else. Differently mixed together or united, atoms

produce different gross substances; but the elementary atoms

never change their chemical nature—their distinct personality.

 

It was about the year 1803 that Dalton first