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

direction, the largest voltaic battery yet

constructed had been put in operation, and with its aid the

brilliant young experimenter was expected almost to perform

miracles. And indeed he scarcely disappointed the expectation,

for with the aid of his battery he transformed so familiar a

substance as common potash into a metal which was not only so

light that it floated on water, but possessed the seemingly

miraculous property of bursting into flames as soon as it came in

contact with that fire-quenching liquid. If this were not a

miracle, it had for the popular eye all the appearance of the

miraculous.

 

What Davy really had done was to decompose the potash, which

hitherto had been supposed to be elementary, liberating its

oxygen, and thus isolating its metallic base, which he named

potassium. The same thing was done with soda, and the closely

similar metal sodium was discovered—metals of a unique type,

possessed of a strange avidity for oxygen, and capable of seizing

on it even when it is bound up in the molecules of water.

Considered as mere curiosities, these discoveries were

interesting, but aside from that they were of great theoretical

importance, because they showed the compound nature of some

familiar chemicals that had been regarded as elements. Several

other elementary earths met the same fate when subjected to the

electrical influence; the metals barium, calcium, and strontium

being thus discovered. Thereafter Davy always referred to the

supposed elementary substances (including oxygen, hydrogen, and

the rest) as “unde-compounded” bodies. These resist all present

efforts to decompose them, but how can one know what might not

happen were they subjected to an influence, perhaps some day to

be discovered, which exceeds the battery in power as the battery

exceeds the blowpipe?

 

Another and even more important theoretical result that flowed

from Davy’s experiments during this first decade of the century

was the proof that no elementary substances other than hydrogen

and oxygen are produced when pure water is decomposed by the

electric current. It was early noticed by Davy and others that

when a strong current is passed through water, alkalies appear at

one pole of the battery and acids at the other, and this though

the water used were absolutely pure. This seemingly told of the

creation of elements—a transmutation but one step removed from

the creation of matter itself—under the influence of the new

“force.” It was one of Davy’s greatest triumphs to prove, in the

series of experiments recorded in his famous Bakerian lecture of

1806, that the alleged creation of elements did not take place,

the substances found at the poles of the battery having been

dissolved from the walls of the vessels in which the water

experimented upon had been placed. Thus the same implement which

had served to give a certain philosophical warrant to the fading

dreams of alchemy banished those dreams peremptorily from the

domain of present science.

 

“As early as 1800,” writes Davy, “I had found that when separate

portions of distilled water, filling two glass tubes, connected

by moist bladders, or any moist animal or vegetable substances,

were submitted to the electrical action of the pile of Volta by

means of gold wires, a nitro-muriatic solution of gold appeared

in the tube containing the positive wire, or the wire

transmitting the electricity, and a solution of soda in the

opposite tube; but I soon ascertained that the muriatic acid owed

its existence to the animal or vegetable matters employed; for

when the same fibres of cotton were made use of in successive

experiments, and washed after every process in a weak solution of

nitric acid, the water in the apparatus containing them, though

acted on for a great length of time with a very strong power, at

last produced no effects upon nitrate of silver.

 

“In cases when I had procured much soda, the glass at its point

of contact with the wire seemed considerably corroded; and I was

confirmed in my idea of referring the production of the alkali

principally to this source, by finding that no fixed saline

matter could be obtained by electrifying distilled water in a

single agate cup from two points of platina with the Voltaic

battery.

 

“Mr. Sylvester, however, in a paper published in Mr. Nicholson’s

journal for last August, states that though no fixed alkali or

muriatic acid appears when a single vessel is employed, yet that

they are both formed when two vessels are used. And to do away

with all objections with regard to vegetable substances or glass,

he conducted his process in a vessel made of baked tobacco-pipe

clay inserted in a crucible of platina. I have no doubt of the

correctness of his results; but the conclusion appears

objectionable. He conceives, that he obtained fixed alkali,

because the fluid after being heated and evaporated left a matter

that tinged turmeric brown, which would have happened had it been

lime, a substance that exists in considerable quantities in all

pipe-clay; and even allowing the presence of fixed alkali, the

materials employed for the manufacture of tobacco-pipes are not

at all such as to exclude the combinations of this substance.

 

“I resumed the inquiry; I procured small cylindrical cups of

agate of the capacity of about one-quarter of a cubic inch each.

They were boiled for some hours in distilled water, and a piece

of very white and transparent amianthus that had been treated in

the same way was made then to connect together; they were filled

with distilled water and exposed by means of two platina wires to

a current of electricity, from one hundred and fifty pairs of

plates of copper and zinc four inches square, made active by

means of solution of alum. After forty-eight hours the process

was examined: Paper tinged with litmus plunged into the tube

containing the transmitting or positive wire was immediately

strongly reddened. Paper colored by turmeric introduced into the

other tube had its color much deepened; the acid matter gave a

very slight degree of turgidness to solution of nitrate of soda.

The fluid that affected turmeric retained this property after

being strongly boiled; and it appeared more vivid as the quantity

became reduced by evaporation; carbonate of ammonia was mixed

with it, and the whole dried and exposed to a strong heat; a

minute quantity of white matter remained, which, as far as my

examinations could go, had the properties of carbonate of soda. I

compared it with similar minute portions of the pure carbonates

of potash, and similar minute portions of the pure carbonates of

potash and soda. It was not so deliquescent as the former of

these bodies, and it formed a salt with nitric acid, which, like

nitrate of soda, soon attracted moisture from a damp atmosphere

and became fluid.

 

“This result was unexpected, but it was far from convincing me

that the substances which were obtained were generated. In a

similar process with glass tubes, carried on under exactly the

same circumstances and for the same time, I obtained a quantity

of alkali which must have been more than twenty times greater,

but no traces of muriatic acid. There was much probability that

the agate contained some minute portion of saline matter, not

easily detected by chemical analysis, either in combination or

intimate cohesion in its pores. To determine this, I repeated

this a second, a third, and a fourth time. In the second

experiment turbidness was still produced by a solution of nitrate

of silver in the tube containing the acid, but it was less

distinct; in the third process it was barely perceptible; and in

the fourth process the two fluids remained perfectly clear after

the mixture. The quantity of alkaline matter diminished in every

operation; and in the last process, though the battery had been

kept in great activity for three days, the fluid possessed, in a

very slight degree, only the power of acting on paper tinged with

turmeric; but its alkaline property was very sensible to litmus

paper slightly reddened, which is a much more delicate test; and

after evaporation and the process by carbonate of ammonia, a

barely perceptible quantity of fixed alkali was still left. The

acid matter in the other tube was abundant; its taste was sour;

it smelled like water over which large quantities of nitrous gas

have been long kept; it did not effect solution of muriate of

barytes; and a drop of it placed upon a polished plate of silver

left, after evaporation, a black stain, precisely similar to that

produced by extremely diluted nitrous acid.

 

“After these results I could no longer doubt that some saline

matter existing in the agate tubes had been the source of the

acid matter capable of precipitating nitrate of silver and much

of the alkali. Four additional repetitions of the process,

however, convinced me that there was likewise some other cause

for the presence of this last substance; for it continued to

appear to the last in quantities sufficiently distinguishable,

and apparently equal in every case. I had used every precaution,

I had included the tube in glass vessels out of the reach of the

circulating air; all the acting materials had been repeatedly

washed with distilled water; and no part of them in contact with

the fluid had been touched by the fingers.

 

“The only substance that I could now conceive as furnishing the

fixed alkali was the water itself. This water appeared pure by

the tests of nitrate of silver and muriate of barytes; but potash

of soda, as is well known, rises in small quantities in rapid

distillation; and the New River water which I made use of

contains animal and vegetable impurities, which it was easy to

conceive might furnish neutral salts capable of being carried

over in vivid ebullition.”[1] Further experiment proved the

correctness of this inference, and the last doubt as to the

origin of the puzzling chemical was dispelled.

 

Though the presence of the alkalies and acids in the water was

explained, however, their respective migrations to the negative

and positive poles of the battery remained to be accounted for.

Davy’s classical explanation assumed that different elements

differ among themselves as to their electrical properties, some

being positively, others negatively, electrified. Electricity

and “chemical affinity,” he said, apparently are manifestations

of the same force, acting in the one case on masses, in the other

on particles. Electro-positive particles unite with

electro-negative particles to form chemical compounds, in virtue

of the familiar principle that opposite electricities attract one

another. When compounds are decomposed by the battery, this

mutual attraction is overcome by the stronger attraction of the

poles of the battery itself.

 

This theory of binary composition of all chemical compounds,

through the union of electro-positive and electro-negative atoms

or molecules, was extended by Berzelius, and made the basis of

his famous system of theoretical chemistry. This theory held

that all inorganic compounds, however complex their composition,

are essentially composed of such binary combinations. For many

years this view enjoyed almost undisputed sway. It received what

seemed strong confirmation when Faraday showed the definite

connection between the amount of electricity employed and the

amount of decomposition produced in the so-called electrolyte.

But its claims were really much too comprehensive, as subsequent

discoveries proved.

 

ORGANIC CHEMISTRY AND THE IDEA OF THE MOLECULE

 

When Berzelius first promulgated his binary theory he was careful

to restrict its unmodified application to the compounds of the

inorganic world. At that time, and for a long time thereafter,

it was supposed that substances of organic nature had some

properties that kept them aloof from the domain of inorganic

chemistry. It was little doubted that a so-called “vital force”

operated here, replacing or modifying the action of ordinary

“chemical affinity.” It was, indeed, admitted that organic

compounds are composed of familiar elements—chiefly carbon,

oxygen, hydrogen, and nitrogen; but these elements were supposed

to be united in ways