A History of Science, vol 4 by Henry Smith Williams (best novels to read for beginners txt) 📖

being the

logical outcome of a predetermined plan.

 

Scheele was the son of a merchant of Stralsund, Pomerania, which

then belonged to Sweden. As a boy in school he showed so little

aptitude for the study of languages that he was apprenticed to an

apothecary at the age of fourteen. In this work he became at

once greatly interested, and, when not attending to his duties in

the dispensary, he was busy day and night making experiments or

studying books on chemistry. In 1775, still employed as an

apothecary, he moved to Stockholm, and soon after he sent to

Bergman, the leading chemist of Sweden, his first discovery—that

of tartaric acid, which he had isolated from cream of tartar.

This was the beginning of his career of discovery, and from that

time on until his death he sent forth accounts of new discoveries

almost uninterruptedly. Meanwhile he was performing the duties of

an ordinary apothecary, and struggling against poverty. His

treatise upon Air and Fire appeared in 1777. In this remarkable

book he tells of his discovery of oxygen—“empyreal” or

“fire-air,” as he calls it—which he seems to have made

independently and without ever having heard of the previous

discovery by Priestley. In this book, also, he shows that air is

composed chiefly of oxygen and nitrogen gas.

 

Early in his experimental career Scheele undertook the solution

of the composition of black oxide of manganese, a substance that

had long puzzled the chemists. He not only succeeded in this,

but incidentally in the course of this series of experiments he

discovered oxygen, baryta, and chlorine, the last of far greater

importance, at least commercially, than the real object of his

search. In speaking of the experiment in which the discovery was

made he says:

 

“When marine (hydrochloric) acid stood over manganese in the cold

it acquired a dark reddish-brown color. As manganese does not

give any colorless solution without uniting with phlogiston

[probably meaning hydrogen], it follows that marine acid can

dissolve it without this principle. But such a solution has a

blue or red color. The color is here more brown than red, the

reason being that the very finest portions of the manganese,

which do not sink so easily, swim in the red solution; for

without these fine particles the solution is red, and red mixed

with black is brown. The manganese has here attached itself so

loosely to acidum salis that the water can precipitate it, and

this precipitate behaves like ordinary manganese. When, now, the

mixture of manganese and spiritus salis was set to digest, there

arose an effervescence and smell of aqua regis.”[6]

 

The “effervescence” he refers to was chlorine, which he proceeded

to confine in a suitable vessel and examine more fully. He

described it as having a “quite characteristically suffocating

smell,” which was very offensive. He very soon noted the

decolorizing or bleaching effects of this now product, finding

that it decolorized flowers, vegetables, and many other

substances.

 

Commercially this discovery of chlorine was of enormous

importance, and the practical application of this new chemical in

bleaching cloth soon supplanted the, old process of

crofting—that is, bleaching by spreading the cloth upon the

grass. But although Scheele first pointed out the bleaching

quality of his newly discovered gas, it was the French savant,

Berthollet, who, acting upon Scheele’s discovery that the new gas

would decolorize vegetables and flowers, was led to suspect that

this property might be turned to account in destroying the color

of cloth. In 1785 he read a paper before the Academy of Sciences

of Paris, in which he showed that bleaching by chlorine was

entirely satisfactory, the color but not the substance of the

cloth being affected. He had experimented previously and found

that the chlorine gas was soluble in water and could thus be made

practically available for bleaching purposes. In 1786 James Watt

examined specimens of the bleached cloth made by Berthollet, and

upon his return to England first instituted the process of

practical bleaching. His process, however, was not entirely

satisfactory, and, after undergoing various modifications and

improvements, it was finally made thoroughly practicable by Mr.

Tennant, who hit upon a compound of chlorine and lime—the

chloride of lime—which was a comparatively cheap chemical

product, and answered the purpose better even than chlorine

itself.

 

To appreciate how momentous this discovery was to cloth

manufacturers, it should be remembered that the old process of

bleaching consumed an entire summer for the whitening of a single

piece of linen; the new process reduced the period to a few

hours. To be sure, lime had been used with fair success previous

to Tennant’s discovery, but successful and practical bleaching by

a solution of chloride of lime was first made possible by him and

through Scheele’s discovery of chlorine.

 

Until the time of Scheele the great subject of organic chemistry

had remained practically unexplored, but under the touch of his

marvellous inventive genius new methods of isolating and studying

animal and vegetable products were introduced, and a large number

of acids and other organic compounds prepared that had been

hitherto unknown. His explanations of chemical phenomena were

based on the phlogiston theory, in which, like Priestley, he

always, believed. Although in error in this respect, he was,

nevertheless, able to make his discoveries with extremely

accurate interpretations. A brief epitome of the list of some of

his more important discoveries conveys some idea, of his

fertility of mind as well as his industry. In 1780 he discovered

lactic acid,[7] and showed that it was the substance that caused

the acidity of sour milk; and in the same year he discovered

mucic acid. Next followed the discovery of tungstic acid, and in

1783 he added to his list of useful discoveries that of

glycerine. Then in rapid succession came his announcements of the

new vegetable products citric, malic, oxalic, and gallic acids.

Scheele not only made the discoveries, but told the world how he

had made them—how any chemist might have made them if he

chose—for he never considered that he had really discovered any

substance until he had made it, decomposed it, and made it again.

 

His experiments on Prussian blue are most interesting, not only

because of the enormous amount of work involved and the skill he

displayed in his experiments, but because all the time the

chemist was handling, smelling, and even tasting a compound of

one of the most deadly poisons, ignorant of the fact that the

substance was a dangerous one to handle. His escape from injury

seems almost miraculous; for his experiments, which were most

elaborate, extended over a considerable period of time, during

which he seems to have handled this chemical with impunity.

 

While only forty years of age and just at the zenith of his fame,

Scheele was stricken by a fatal illness, probably induced by his

ceaseless labor and exposure. It is gratifying to know, however,

that during the last eight or nine years of his life he had been

less bound down by pecuniary difficulties than before, as Bergman

had obtained for him an annual grant from the Academy. But it

was characteristic of the man that, while devoting one-sixth of

the amount of this grant to his personal wants, the remaining

five-sixths was devoted to the expense of his experiments.

 

LAVOISIER AND THE FOUNDATION OF MODERN CHEMISTRY

 

The time was ripe for formulating the correct theory of chemical

composition: it needed but the master hand to mould the materials

into the proper shape. The discoveries in chemistry during the

eighteenth century had been far-reaching and revolutionary in

character. A brief review of these discoveries shows how

completely they had subverted the old ideas of chemical elements

and chemical compounds. Of the four substances earth, air, fire,

and water, for many centuries believed to be elementary bodies,

not one has stood the test of the eighteenth-century chemists.

Earth had long since ceased to be regarded as an element, and

water and air had suffered the same fate in this century. And

now at last fire itself, the last of the four “elements” and the

keystone to the phlogiston arch, was shown to be nothing more

than one of the manifestations of the new element, oxygen, and

not “phlogiston” or any other intangible substance.

 

In this epoch of chemical discoveries England had produced such

mental giants and pioneers in science as Black, Priestley, and

Cavendish; Sweden had given the world Scheele and Bergman, whose

work, added to that of their English confreres, had laid the

broad base of chemistry as a science; but it was for France to

produce a man who gave the final touches to the broad but rough

workmanship of its foundation, and establish it as the science of

modern chemistry. It was for Antoine Laurent Lavoisier

(1743-1794) to gather together, interpret correctly, rename, and

classify the wealth of facts that his immediate predecessors and

contemporaries had given to the world.

 

The attitude of the mother-countries towards these illustrious

sons is an interesting piece of history. Sweden honored and

rewarded Scheele and Bergman for their efforts; England received

the intellectuality of Cavendish with less appreciation than the

Continent, and a fanatical mob drove Priestley out of the

country; while France, by sending Lavoisier to the guillotine,

demonstrated how dangerous it was, at that time at least, for an

intelligent Frenchman to serve his fellowman and his country

well.

 

“The revolution brought about by Lavoisier in science,” says

Hoefer, “coincides by a singular act of destiny with another

revolution, much greater indeed, going on then in the political

and social world. Both happened on the same soil, at the same

epoch, among the same people; and both marked the commencement of

a new era in their respective spheres.”[8]

 

Lavoisier was born in Paris, and being the son of an opulent

family, was educated under the instruction of the best teachers

of the day. With Lacaille he studied mathematics and astronomy;

with Jussieu, botany; and, finally, chemistry under Rouelle. His

first work of importance was a paper on the practical

illumination of the streets of Paris, for which a prize had been

offered by M. de Sartine, the chief of police. This prize was not

awarded to Lavoisier, but his suggestions were of such importance

that the king directed that a gold medal be bestowed upon the

young author at the public sitting of the Academy in April, 1776.

Two years later, at the age of thirty-five, Lavoisier was

admitted a member of the Academy.

 

In this same year he began to devote himself almost exclusively

to chemical inquiries, and established a laboratory in his home,

fitted with all manner of costly apparatus and chemicals. Here he

was in constant communication with the great men of science of

Paris, to all of whom his doors were thrown open. One of his

first undertakings in this laboratory was to demonstrate that

water could not be converted into earth by repeated

distillations, as was generally advocated; and to show also that

there was no foundation to the existing belief that it was

possible to convert water into a gas so “elastic” as to pass

through the pores of a vessel. He demonstrated the fallaciousness

of both these theories in 1768-1769 by elaborate experiments, a

single investigation of this series occupying one hundred and one

days.

 

In 1771 he gave the first blow to the phlogiston theory by his

experiments on the calcination of metals. It will be recalled

that one basis for the belief in phlogiston was the fact that

when a metal was calcined it was converted into an ash, giving up

its “phlogiston” in the process. To restore the metal, it was

necessary to add some substance such as wheat or charcoal to the

ash. Lavoisier, in examining this process of restoration, found

that there was always evolved a great quantity of “air,” which