NATURE 
[May 15, 1875 
THE BIRTH OF CHEMISTRY 
X. 
The Theory of Phlogiston—Comparison with Hooke's Theory of 
Combustion.—Early Ideas regarding Calcination.— Stephen 
Hales—His Pneumatic Experiments,—Boerhaave.— Conclu- 
Sion. 
AvouT the year 1669 we find the first dawnings of a theory 
which was proposed in order to connect together various 
chemical phenomena, and notably for the explanation of com- 
bustion, the common and most obvious of all chemical actions. 
This theory, known as the ‘‘ Theory of Phlogiston,” powerfully 
influenced chemistry for a century; indeed upon its ruins the 
structure of modern chemistry was raised by the labours of 
Lavoisier, Priestley, and Scheele. The proposers of this theory 
—John Joachim Becher (b. 1625, d. 1682) and George Ernest 
Stahl (b. 1660, d. 1734) endeavoured to trace the cause of 
various phenomena of chemical change to the assimilation or re- 
jection of what they called ‘‘ materia aut principium ignis, non 
ipse ignis”’—not actual fire, but the principle of fire; a some- 
thing not much unlike the pure, elemental, celestial fire which a 
few ancient and many Middle Age writers had feigned to exist. 
Stahl believed this #a/erta ignis to be a very subtle, invisible, 
substance, which neither burns nor glows ; its particles penetrate 
the most dense substances, and are agitated by a very rapid mo- 
tion. When a body is burned it loses phlogiston ; when a body 
is un-burned, if we may use such an expression, or de-oxidised, 
it assimilates phlogiston (pAoyiords, burnt). Thus if lead is 
heated for some length of time it is converted into a powdery 
substance which they called ca/x of lead, and we, lead oxide ; the 
lead has lost Phlogiston, said Stahl. On thie other hand, if this 
same calx of lead is heated with red-hot charcoal, it is deoxi- 
dised and becomes lead again. It has now assimilated the 
Phlogiston, which it had before lost. 
But here arose a difficulty. A metal was found to be heavier 
after calcination than before; thus loss of Phlogiston lead to 
gain of weight, which was altogether anomalous, and apparently 
incapable of explanation. But the Phlogistians were equal to 
the occasion ; the supporters of a pet theory will create any 
number of the most vague and impossible hypotheses, rather 
than yield up their darling to destruction: so, said they, Phlo- 
giston is a principle of levity; it confers negative weight ; it 
makes bodies lighter, just as bladders attached to a swimmer 
lighten him. 
The theory was applicd as generally as possible :—thus sul- 
phuric acid is produced by burning sulphur under certain condi- 
tions of oxidation ; the sulphur loses Phlogiston, and becomes 
heavier like the metallic calx ; hence sulphuric acid is sulphur 
minus Phiogiston, while sulphur is consequently sulphuric acid 
plus Phiogiston. In fact /oss of phlogiston was synonymous with 
what we call oxidation ; and gain of phiogiston with deoxidation, 
The existence of Phiogiston was so utterly unsupported by 
experimental proof that the theory could s-arcely exist with- 
out many opponents. The endurance of the most false chi- 
merical theory is ofien really wonderful. The Phlogistians were 
attack<d first in one direction, then in another, yet the theory 
continued to find supporters. At last, as a last resource, hydrogen 
gas—recently investigated by Cavendish—was said to be Phlo- 
giston, but this was so entirely different from the Phlogiston of 
Stahl that the theory was now seen on all sides to be fast giving 
way. At length Lavoisier, a century ago, conclusively disproved 
the theory by means which cannot be discussed here, because 
they belong to the more advanced history of the science. 
How the crude, unscientific, illogical theory of Phlogiston 
could have arisen in the face of Hooke’s admirable theory of 
combustion, and Mayow’s experiments in support of it, must 
always remain a mystery. _It is probable that if Mayow had not 
died a young man, or if Hooke had found leisure to prosecute 
his views, the theory of Phlogiston would never have been pro- 
pounded. The theory has been much over-praised. The only 
service which it rendered to the science was that it introduced a 
certain amount of order and system, which was hitherto wanting. 
It led to the grouping together of certain classes of facts, and, to 
a slight extent, to the application of similar modes of reasoning 
to similar chemical phenomena. And although that reasoning 
was altogether wrong, it seemed to indicate the means by which, 
with a more perfect and advanced system, chemistry might 
become an exact science subject to definite modes of treat- 
ment, 
We have more than once spvken of calcination, which was 
indeed one of the most prominent operations of old chemistry. 
Since the examination of the process led to the proposal of just 
ideas concerning the materiality of the air—most often denied by 
ancient and middle-age writers—it may be well to glance at the 
early ideas regarding calcination. Here then was the dominant 
experiment in this direction : I take a bright lustrous metal, tin 
or lead, melt it, keep itin a molten state for awhile, and it is 
converted into powder, which weighs more than the original 
metal. Again I heat this same powder with charcoal, and it 
becomes metal again $ yet nothing that can be seen has been 
added to the metal, or taken away from its calx. Geber defines 
calcination as ‘‘ the pulverisation of a thing by fire, by deprivi 
it of the humidity which consolidates its parts.” He observ 
that the metal increases in weight during the operation, although 
‘* deprived of its humidity.” Cardanus asserted that the increase 
of weight in the case of lead amounted to one-thirteenth the 
weight of the metal calcined ; and he accounted for it on the 
supposition that all things possess a certain kind of life, a celestial 
heat, which is destroyed during calcination; hence they become 
heavier for the same reason that animals are heavier after death, 
for the celestial heat tends upwards. This idea was almost 
similar to that of the Phlogistians, although published more than 
a century before Becher wrote his Z/ysica Subterranea. In 
Fic. 21. 
Fic. 22, 
Fic. 2t.—Hales’ method of measuring a gas. Fig 22.—Measurement 
cf the elastic force of the gas produced by ferm snting peas. 
1629 Jean Rey, a physician of Bergerac, attempted to discover the 
cause of increase, and attributed it to the absorption of “ thick- 
ened air” (/’air espessi) by the metal during calcination. Lemery, 
as we have seen, attributed the gain to the absorption of corfus- 
cules de feu. Afterwards came the nitre-air of Mayow, then a 
century later the increase was proved to be due to the union of 
the body with a constituent of the air which Lavoisier named 
oxygen gas ; and this gas was first discovered by heating one ot 
the calces (calx of mercury), about which so much speculation 
had been wasted, and so little experiment bestowed, by earlier 
writers. 
We are drawing towards the end of our subject, but we think 
any account of the earlier history of chemistry would be very in- 
complete without a notice of the work of Dr. Stephen Hales 
(Lorn 1677, died 1761). Ina number of papers communicated 
Re 
eS ee 
to the Royal Society, and afierwards published in a work - 
entitled Svatical Essays, we findsa variety of experiments by 
Hales, c} iefly relating to pneumatic chemis'ry. Herein we find 
an account of ‘a specimen of an attenipt to analyse the air by a 
great variety of chymico-statical experiments, which show in how 
great a proportion air is wrought into the composition of animal, 
vegetable, and mineral substances, and withal how readily it 
resumes its former elastick state, when in the dissolution of those 
