A History of Science, vol 4 | Page 7

a piece of burning
charcoal in the end of a bellows, he arranged a tube so that the gas
coming from the charcoal would pass through the lime-water, and, as in
the case of the bubbles from the brewer's vat, he found that the white
precipitate was thrown down; in short, that carbonic acid was given off
in combustion. Shortly after, Black discovered that by blowing through
a glass tube inserted into lime-water, chalk was precipitated, thus
proving that carbonic acid was being constantly thrown off in
respiration.
The effect of Black's discoveries was revolutionary, and the attitude of
mind of the chemists towards gases, or "airs," was changed from that
time forward. Most of the chemists, however, attempted to harmonize
the new facts with the older theories--to explain all the phenomena on
the basis of the phlogiston theory, which was still dominant. But while
many of Black's discoveries could not be made to harmonize with that
theory, they did not directly overthrow it. It required the additional
discoveries of some of Black's fellow-scientists to complete its
downfall, as we shall see.
HENRY CAVENDISH
This work of Black's was followed by the equally important work of his
former pupil, Henry Cavendish (1731-1810), whose discovery of the
composition of many substances, notably of nitric acid and of water,
was of great importance, adding another link to the important chain of
evidence against the phlogiston theory. Cavendish is one of the most
eccentric figures in the history of science, being widely known in his
own time for his immense wealth and brilliant intellect, and also for his
peculiarities and his morbid sensibility, which made him dread society,
and probably did much in determining his career. Fortunately for him,
and incidentally for the cause of science, he was able to pursue
laboratory investigations without being obliged to mingle with his

dreaded fellow-mortals, his every want being provided for by the
immense fortune inherited from his father and an uncle.
When a young man, as a pupil of Dr. Black, he had become imbued
with the enthusiasm of his teacher, continuing Black's investigations as
to the properties of carbonic-acid gas when free and in combination.
One of his first investigations was reported in 1766, when he
communicated to the Royal Society his experiments for ascertaining
the properties of carbonic-acid and hydrogen gas, in which he first
showed the possibility of weighing permanently elastic fluids, although
Torricelli had before this shown the relative weights of a column of air
and a column of mercury. Other important experiments were continued
by Cavendish, and in 1784 he announced his discovery of the
composition of water, thus robbing it of its time-honored position as an
"element." But his claim to priority in this discovery was at once
disputed by his fellow-countryman James Watt and by the Frenchman
Lavoisier. Lavoisier's claim was soon disallowed even by his own
countrymen, but for many years a bitter controversy was carried on by
the partisans of Watt and Cavendish. The two principals, however,
seem. never to have entered into this controversy with anything like the
same ardor as some of their successors, as they remained on the best of
terms.[1] It is certain, at any rate, that Cavendish announced his
discovery officially before Watt claimed that the announcement had
been previously made by him, "and, whether right or wrong, the honor
of scientific discoveries seems to be accorded naturally to the man who
first publishes a demonstration of his discovery." Englishmen very
generally admit the justness of Cavendish's claim, although the French
scientist Arago, after reviewing the evidence carefully in 1833, decided
in favor of Watt.
It appears that something like a year before Cavendish made known his
complete demonstration of the composition of water, Watt
communicated to the Royal Society a suggestion that water was
composed of "dephlogisticated air (oxygen) and phlogiston (hydrogen)
deprived of part of its latent heat." Cavendish knew of the suggestion,
but in his experiments refuted the idea that the hydrogen lost any of its
latent heat. Furthermore, Watt merely suggested the possible

composition without proving it, although his idea was practically
correct, if we can rightly interpret the vagaries of the nomenclature then
in use. But had Watt taken the steps to demonstrate his theory, the great
"Water Controversy" would have been avoided. Cavendish's report of
his discovery to the Royal Society covers something like forty pages of
printed matter. In this he shows how, by passing an electric spark
through a closed jar containing a mixture of hydrogen gas and oxygen,
water is invariably formed, apparently by the union of the two gases.
The experiment was first tried with hydrogen and common air, the
oxygen of the air uniting with the hydrogen to form water, leaving the
nitrogen of the air still to be accounted for. With