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by the distillation of black oxide of manganese
with concentrated oil of vitriol, or with the
" phosphorus acid of urine " (phosphoric acid), by
distilling nitrate of magnesium, made by dissolv-
ing the " white magnesia employed in medicine "
(magnesium carbonate) in aquafortis (nitric acid),
or by distilling ' ' mercurial nitre " (mercuric nitrate).
The cheapest and the best method of producing
" fire-air " is to distil purified nitre in a glass retort.
But Scheele also obtained it from " calx of silver "
(silver carbonate) prepared from silver nitrate and
" alkali of tartar " (potassium carbonate) ; during
this process he got aerial acid, which had been
present originally in the alkali of tartar; but it
was easily removed by means of milk of lime.
Similarly, " calx of gold," obtained from a solution
of gold with "alkali of tartar," gave "fire-air"
when heated ; but no aerial acid, for that air
escapes during the precipitation of the "calx."


The brown-red precipitate obtained by adding
" alkali of tartar " to " corrosive sublimate " (po-
tassium carbonate to mercuric chloride, giving a
basic carbonate of mercury and potassium chloride)
yielded a mixture of fire-air and aerial acid when
heated. But if the " calx of mercury " had been
prepared by means of the " acid of nitre," or in
modern language by heating mercuric nitrate, a
pure " fire-air," unmixed with " aerial acid," was
the product. And lastly, arsenic acid, when heated
gave ordinary white arsenic together with " fire-air."
This fire-air was completely absorbed by " liver
of sulphur" (a polysulphide of potassium, formed
by heating together potassium carbonate and sul-
phur) ; and a mixture of four parts of " fire-air "
with fourteen parts of " vitiated air " lost the whole
of its fire-air on standing for fourteen days in
contact with liver of sulphur. Dippel's animal
oil, and burning phosphorus, charcoal, and sulphur,
all absorbed " fire-air " completely if it was pure,
incompletely if it was mixed with " vitiated air" ;
in short, the identity of "fire-air" prepared from
calces, etc., with that in ordinary air was com-
pletely established.

As "vitiated air" is lighter than ordinary air,



it follows that "fire-air" must be heavier; and
experiment proved this to be the case.

To completely disprove the possible contention
that nitre was necessary for the production of
"fire-air," some "calx of mercury" (or red oxide),
which had been prepared by boiling mercury for a
long time in contact with air, was heated. The
products were metallic mercury and "fire -air."
" This is a remarkable circumstance, that the
fire-air which had previously removed from the
mercury its phlogiston in a slow calcination, gives
the same phlogiston up to it again, when the calx
is simply made red-hot." 1 Is it not remarkable
that the true explanation should not have forced
itself upon Scheele's mind, which was so acute,
and so capable of forming true deductions ?

The next set of experiments dealt with the
phenomena of respiration. A rat, confined in air
until it died, polluted the air with one-thirtieth of
aerial acid. Kespiration from Scheele's own lungs
had the same effect. A few flies, bees, and cater-
pillars also polluted the air in the same way.
Peas, roots, herbs, and flowers all converted about
one-fourth part of ordinary air into "aerial acid."

1 80.


" These are accordingly strange circumstances, that
the air is not noticeably absorbed by animals
endowed with lungs, contains in it very little aerial
acid, and yet extinguishes fire. On the other hand,
insects and plants alter the air in exactly the same
way, but still they convert the fourth part of it
into aerial acid." 1 And so he makes experiments
which prove that it is the fire-air which is con-
verted into " aerial acid " by peas ; and that " fire-
air " is absorbed by fresh blood, and acquires no
aerial acid from it. And, further, he was able to
breathe fire-air for a long time, .especially if a
" handful of potashes" was put into the bladder.
A couple of large bees, confined in " fire-air," along
with milk of lime, consumed practically the whole
of the air in eight days. But plants, confined
in fire-air," along with milk of lime, would not
grow; however, they yielded a little aerial acid.
Scheele is again puzzled here by the circumstance
that the blood and the lungs have not the
same action on air as insects and plants, inasmuch
as the former convert it into vitiated air, and the
latter into aerial acid. We now know that air
will not support life of warm-blooded animals when

1 87.


the oxygen falls below a certain not very small
amount, while insects appear to be capable of ex-
hausting the oxygen to a great extent ; and it is
probable that the plants, under the unnatural cir-
cumstances in which they were placed, gave off a
considerable amount of carbon dioxide. Scheele's
explanation in terms of phlogiston is not successful.
He wrote : " I am inclined to believe that fire-air
consists of a subtle acid substance united with
phlogiston, and it is probable that all acids derive
their origin from fire - air. Now if this air
penetrates into plants, these must attract the
phlogiston, and consequently the acid, which
manifests itself as aerial acid, must be produced." 1
This is reversing what may be termed the true
explanation on the basis of the phlogistic theory.
For Scheele supposes that oxygen contains phlo-
giston, and by losing it, yields carbon dioxide. On
the other hand, the consistent explanation would
be that carbon is carbonic acid plus phlogiston,
and that when it burns it loses phlogiston and
becomes carbonic acid again. We see how confused
the phlogistic ideas became after the discovery of
oxygen, and how ripe the time was for Lavoisier


to formulate views which are now universally

In the concluding sections of his treatise
Scheele describes experiments which prove the
solubility of "fire-air" in water; he mentions a
convenient test for free oxygen in solution, viz. a
mixture of ferrous sulphate and lime, which turns
dark green, and finally rust-coloured, when added
to water containing oxygen ; and he shows that
water is deprived of oxygen by the presence of a
leech, kept in it for two days.

It is impossible not to recognise in Scheele one
of the most acute intellects and able experimenters
whom the world has ever seen. And although we
cannot but feel surprise that his discoveries did not
lead him to take the step of renouncing the hypo-
thesis of phlogiston, it must be borne in mind
that the doctrine was surrounded with the halo of
old age, and sanctioned by many names of great
repute in their time. We shall see later that Caven-
dish, one of the greatest of English chemists, on
weighing the rival theories, decided in favour of the
phlogistic hypothesis. The actual escape of flame,
a visible entity, from a burning substance, may have
had much to do with this decision ; and the uncer-


tainty concerning the nature of heat, and the doubt
whether it was not a form of imponderable matter,
may have led both Scheele and Cavendish to retain
the older views. It was Lavoisier who first dared to
throw off the shackles of tradition ; and this he did
before oxygen had been discovered, as early as 1772.

Antoine Auguste Lavoisier was born in Paris on
the 26th of August 1743. His father was wealthy,
and spared no expense on his education. In his
twenty-first year he obtained a gold medal from
the Academy of Sciences for an essay on the
best method of lighting the streets of Paris, but it
was some years before he made definite choice of his
subject. He published memoirs relating to geology
and to mathematics, before the fame of Black's and
Priestley's discoveries reached him and induced
him to turn his attention to scientific chemistry.
Lavoisier's life was divided between his researches
and the performance of public duties. In his
twenty-fifth year he was elected a Member of the
French Academy of Sciences, and, somewhat later,
became its treasurer. He drew up numerous reports
for the Government on questions on the borderland
of Science and Technology ; for example, on the



preparation of paper for bills, which would not
admit of forgery ; on experimental agriculture ;
and on the manufacture of gunpowder. In 1771
he married Marie Anna Pierette Paulze, the daughter
of a " fermier-ge'ne'ral," or collector of Government
revenue ; and after his death she became the wife
of Count Eumford, another distinguished scientific
man. Made a " fermier ge*ne*ral " himself, it was
during 'his tenure of this office that Lavoisier was
accused along with others holding similar posi-
tions of misappropriating revenue moneys, with
the result that, under the dictatorship of the in-
famous Kobespierre, he and twenty-eight of those
who held like office were guillotined publicly, on the
8th of May 1794. It is stated that Lavoisier's last
plea, presented by Halle* for permission to finish a
research was refused by Coffinhal, with the brutal
phrase, " La Kepublique n'a pas besoin de savants ;
il faut que la justice suive son cours." Within
twenty-four hours the execution took place.

Lavoisier was a tall, handsome man, with a
remarkably pleasing face. He possessed great
influence, and used it all for good.

The first account which we possess of Lavoisier's
revolutionary ideas, for revolutionary they were


then deemed, was in a sealed note, placed in the
hands of the Secretary of the Academy on the 1st
of November 1772. It is to the following effect:

"About eight days ago I discovered that sul-
phur, when burned, instead of losing weight, gains
weight ; that is to say, from one pound of sulphur
much more than one pound of vitriolic acid is
produced, not counting the moisture gained from
the air. Phosphorus presents the same phenomenon.
This increase of weight is due to a great quantity
of air which becomes fixed during the combustion,
and which combines with the vapours. This
discovery, which I confirmed by experiments which
I regard as decisive, led me to think that what
is observed in the combustion of sulphur and
phosphorus might likewise take place with respect
to all the bodies which augment in weight by com-
bustion and calcination ; and I was persuaded that
the gain of weight in calces of metals proceeded
from the same cause. Experiment fully confirmed
my conjectures. I effected the reduction of lith-
arge in closed vessels with Hales' apparatus, and
I observed that at the moment of the passage
of the calx into the metallic state, there was a


disengagement of air in considerable quantity, and
that this air formed a volume at least a thousand
times greater than that of the litharge employed.
As this discovery appears to me to be one of the
most interesting which has been made since the
time of Stahl, I thought it expedient to secure to
myself the property, by depositing the present note
in the hands of the Secretary of the Academy, to
remain secret till the period when I shall publish
my experiments. LAVOISIER.

"PARIS, llth November 1772."

There is no account in Hales' work of his re-
ducing litharge in closed vessels. It is to be pre-
sumed that Lavoisier heated in a retort a mixture
of litharge and charcoal, and that the air which
he speaks of was a mixture of oxides of carbon.
This account does not inform us of Lavoisier's
views on combustion, but merely shows the date
at which he had first obtained what he supposed
were results new to science. We recognise that
Mayow had anticipated him in this. 1

1 The following passage in a letter from Magellan to Madame Lavoisier
makes it probable that Lavoisier had been told of Mayow's work :
"Quand, apres les d^couvertes de Lavoisier, on lui opposa Mayow, dont
il n'avoit jamais entendu parler, il chargea son ami Magellan, qui habitait
Londres, de lui procurer les ceuvres du savant anglais. Magellan s'adressa


It was not until Priestley, when dining with him
in the autumn of 1774 (being in Paris with Lord
Shelburne at the time), had informed Lavoisier of his
discovery of "dephlogisticated" air, that the ideas
of the latter upon the subj ect became precise. Priest-
ley's own words are: "Having made the discovery
some time before I was in Paris, in the year 1774,
I mentioned it at the table of Mr. Lavoisier, when
most of the philosophical people of the city were
present, saying that it was a kind of air in which
a candle burned much better than in common air,
but I had not then given it any name. At this all
the company, and Mr. and Mrs. Lavoisier as much
as any, expressed great surprise. I told them I
had gotten it from precipitate per se, and also
from red-lead. Speaking French very imperfectly,
and being little acquainted with the terms of
chemistry, I said plombe rouge, which was not
understood till Mr. Macquer said I must mean


Shortly after this Lavoisier repeated Priestley's
experiments and confirmed their truth ; and this
led to the true explanation of experiments of

en vain a tous les libraires de Londres ; il lui fut impossible de trouver
une exemplaire des ceuvres de Mayow." Yet this work was in the
catalogue of the Royal Society's library at that date.


which an account is given in the Memoirs of the
French Academy for 1774, and which were funda-
mental in their character. They referred to the
calcination of tin in hermetically -sealed retorts.
The tin was placed in a retort which was heated
on a sand-bath until the metal had melted. The
beak of the retort, previously drawn out into a capil-
lary, was then sealed, the air expelled having been
collected and its weight noted. The retort was then
cooled and weighed. It was again heated, and the
temperature was maintained until the calcination
of the tin stopped. With a large retort the cal-
cination was more complete than when a smaller
one was employed, this implying that the degree
to which the calcination proceeded was dependent
upon the amount of air present. After cooling the
retort a second time, it was again weighed, when it
was found to have undergone no change of weight.
The beak was then broken, and air entered with a
hissing noise. The gain in weight was now about
10 grains with a large retort. The tin and its calx
were next weighed, and it was found that the gain
in weight of the tin was always equal to the loss of
weight of the air in the retort, measured by the
quantity of air which entered on breaking the


beak of the retort, less the air driven out of the
retort before hermetically sealing it. From this
Lavoisier concluded that calx of tin is a compound
of tin and air.

Lavoisier's next research, communicated to the
Academy in 1775, and published in 1778, was
entitled " On the Nature of the Principle which
combines with Metals during their Calcination, and
which increases their Weight." In this he describes
experiments showing that when metallic calces are
converted into metals by heating with charcoal, a
quantity of fixed air is expelled ; and here for the
first time he points out that fixed air is a com-
pound of carbon with the elastic fluid contained
in the calx. He then describes the preparation
of oxygen by Priestley's process of heating red
oxide of mercury (mercurius precipitatus per
se), and shows that the red oxide, when heated
with charcoal, manifests the properties of a
true calx, inasmuch as metallic mercury is
formed, and a large quantity of fixed air is

His next paper, which appeared in 1777 in the
Memoires of the Academy, deals with the combustion
of phosphorus ; and here he recapitulates Euther-


ford's experiments, and shows that one-fifth of the
air disappears, and that the residue, to which he
gave the name "mouffette atmospherique," is in-
capable of supporting combustion. It will be
remembered that Kutherford named this residue
" phlogisticated air," inasmuch as he imagined it
to have absorbed phlogiston from the burning
phosphorus ; Scheele, too, had made a similar ex-
periment with a similar result. From these obser-
vations, Lavoisier concluded that air consists of a
mixture or compound of two gases, one capable of
absorption by burning bodies, the other incapable
of supporting combustion.

This paper was immediately followed by an-
other, also published in 1777. Its title is, "On
the Combustion of Candles in Atmospheric Air,
and in Air eminently respirable." In this memoir
he distinguishes between four kinds of air :
1. Atmospheric air, in which we live and which
we breathe. 2. Pure air, alone fit for breath-
ing, constituting about one-fourth of atmospheric
air, and termed by Priestley " dephlogisticated air."
3. Azotic gas, identical with Kutherford's " mephitic
air," and of which the properties were then un-
known. 4. Fixed air, which he proposed to call


" acide crayeux," or acid of chalk, discovered
twenty-five years previously by Black.

By this time his theory was well developed.
He accounted for the phenomena of combustion
without having recourse to the phlogistic hypo-
thesis : the calx was produced by the union of the
metal with the active constituent of air ; and when
carbonaceous material burned, the carbon united
with this same constituent, producing fixed air.
But there were still difficulties in his Way : it was
known that in dissolving metals in dilute vitriol or
muriatic acid, a combustible and very light air was
evolved ; and that the metals were thereby con-
verted into calces in combination with the respective
acids. This fact was not explained even by the
supporters of the phlogistic theory, but it had the
effect of preventing them from accepting Lavoisier's
views. Some considered that hydrogen and phlo-
giston were identical, and that on dissolving a
metal the calx was formed by the escape of the
phlogiston ; while others had a hazy idea that
hydrogen was a compound of water and phlogiston ;
but of this more hereafter.

Lavoisier's objection to such a theory was that
the calx was heavier than the metal, and that


hydrogen, though light, still possessed weight. 1
Moreover, he had ascertained that the calces of
mercury, tin, and lead are compounds of these
metals with active air, and that as fixed air is
produced by heating such calces with carbon, fixed
air must be a compound of carbon and vital air, or,
as he named it, the " oxygine principle," inasmuch
as its combination with phosphorus, sulphur, and
carbon resulted in the formation of acids (of ik, an

In 1777 he read another memoir, " On the Solu-
tion of Mercury in Vitriolic Acid, and on the
Kesolution of that Acid into Aeriform Sulphurous
Acid, and into Air eminently respirable." Priestley
had already shown that this process yielded sulphur
dioxide ; Lavoisier carried the temperature higher,
and, decomposing the sulphate of mercury, produced

1 Tliis, as previously remarked, had already been noticed. In
Maquer's fiUmcns de Chymie-pratique, published in 1752, a work which
ran through many editions, we read (p. 307): "There happens during
all these calcinations, and especially in that of lead, a very strange
phenomenon for which it is very difficult to assign a reason. It is that
those bodies, which lose no small proportion of their substance, whether
by the dissipation of phlogiston, or because part of the metal is exhaled
as vapour, yield calces increased in weight after calcination ; and this
increase is by no means inconsiderable. . . . Physicists and chemists
have devised many ingenious systems to account for this phenomenon,
but no one of them is absolutely satisfactory. As no well-established
theory has been devised, we shall not undertake to attempt an explana-
tion of this singular fact,"


metallic mercury, sulphur dioxide, and oxygen.
It appeared therefore that sulphurous differed from
sulphuric acid in containing a smaller proportion
of oxygen.

He also experimented with iron pyrites, and
his experiments recall those of Boyle. Boyle found
that " marcasite," a disulphide of iron, on exposure
to air, gained in weight, while vitriol of iron was
formed. Lavoisier performed the same experiment,
not "in a very pure air," as Boyle did when he
left the pyrites exposed in a quiet dust-free room,
but in a confined quantity of ordinary air ; and he
found that the air was rendered incapable of sup-
porting combustion, or, in other words, its oxygen
was removed.

In the same volume of the Memoirs of the
Academy for 1778, another of Lavoisier's papers
" On Combustion in General " is to be found. In
this he showed that oxygen gas is the only substance
which supports combustion ; that during the burn-
ing of combustible substances in air a portion of
the oxygen disappears, and converts the burning
substance into one of two kinds of compounds :
either an acid, such as sulphuric acid from sulphur,
phosphoric acid from phosphorus, or carbonic acid


from carbon (for in those days the term " acid " was
applied to what we now term an anhydride) ; or in
the case of metals a calx, or compound of oxygen
with the metal. The processes are analogous, but
differ in the rate at which they take place ; for the
calcination of metals is a much slower operation
than the combustion of sulphur or phosphorus. It
is the rapidity of the action which leads to actual
inflammation. He next examined and attacked the
theory of phlogiston, and maintained that the exist-
ence of phlogiston is purely hypothetical, and quite
unnecessary for the explanation of the phenomena.
But his papers were received with doubt. The
change demanded was too great ; the trammels of
custom were too firmly bound. He gained no

Until the true nature of hydrogen had been
explained, the attack on the phlogistic theory
could not be said to be complete. This combina-
tion of hydrogen and oxygen to form water was
first proved by Cavendish. And as soon as Sir
Charles Blagden, in 1781, had communicated Caven-
dish's results to Lavoisier, the latter at once saw
their bearing on the new theory which he was en-
deavouring to uphold, and perceived how they


would give a final blow to the adherents of the
theory of phlogiston. For it had been frequently
adduced as an objection to his new views, that they
were incapable of explaining why hydrogen should
be evolved during the solution of metals in acids,
or why it should be absorbed during the reduction
of calces to the metallic state. Lavoisier at once
repeated Cavendish's experiments on a large scale,
and was assisted on that occasion by Laplace, Sir
Charles Blagden also being present. A consider-
able quantity of water was produced, and the
volumes of the combining gases were found to be
1 of oxygen to 1*91 of hydrogen. Shortly after,
in conjunction with Meunier, he performed the
converse operation, in decomposing steam by passing
it over iron wire heated to redness in a porcelain
tube. The iron withdrew the oxygen from the
water, while the hydrogen passed on and was
collected in the gasholder.

The explanation of the solution of metals in
acids was now easy : it depended on the decompo-
sition of water. While the oxygen united with the
metal to form a calx, the hydrogen was evolved ;
the calx dissolved in the acid, forming a salt of the
metal. And the operation of producing hydrogen


by the action of steam on red-hot iron met with an
equally simple explanation : the oxygen and iron
united to form an oxide, the ancient ethiops
martial, while the hydrogen escaped. The con-
verse took place during the reduction of a calx
to the metallic state by hydrogen. Here the
hydrogen seized on the oxygen of the calx, removed
it in the form of water, and the metal was left.
These experiments were due to Cavendish ; all that
Lavoisier did was to show the true nature of the

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Online LibraryWilliam RamsayThe gases of the atmosphere, the history of their discovery → online text (page 6 of 16)