On hydrogenous acid and the confirmation of Lavoisier’s theory of acidity.
Sirs,
HAVING READ the honourable contributions to your journal on the subject of the two
great systems of chemistry, namely the phlogistic and the caloric or French systems, I have
taken the liberty of repeating some of the experiments therein, and to communicate to
your learned selves the results thereof, that an AVICENNA of the chemical philosophy
might one day reconcile the undoubted insights into chemistry that the proponents of
both systems have brought us. I was driven by inconsistencies I believe to exist in the
work of Messrs. CAVENDISH and PRIESTLEY, and also by an interest aroused in my
mind of MONSIEUR LAVOISIER’S theory of acids, and the commentary on them in MR.
IRONSIDE’S letter in the latest edition of your august journal. Despite MR. IRONSIDE’S
cogent criticism of the problems with MONSIEUR LAVOISIER’S theory, I believe that
these difficulties will be resolved, and that already, the French system provides a more
adequate explanation of acidity than the phlogistic system, and an equally convincing
explanation of combustion. It is MONSIEUR LAVOISIER’S theory of acids, however, that
I wish to address.
My work leads me to believe that, having previously preferred the phlogistic system of
Messrs. CAVENDISH and PRIESTLEY, for its clear and intuitive explanation of the science
of combustion, the so-called French system of MONSIEUR LAVOISIER must, for a time,
stand, due to its demonstrably correct explanation of Oxyds and Acids. On this last
subject, I believe I have made a small discovery, which because of its potential interest to
your selves, I have taken the liberty of describing in this letter.
My interest in chemistry is purely philosophical. My land and property being such that it
can provide me with a comfortable living, I have devoted my hours to the study of the
chemical philosophy and theology. The assistance of my fellow members of the Royal
Dublin Society cannot be overestimated. In repeating the experiments contained in your
journal, I hope that, while not matching the honourable gentlemen’s skill, I might bring
the insight and understanding that I have gained from many years’ search of the truth.
Particular insight I have gained from Messrs. CAVENDISH and PRIESTLEY, for their
Experiments on Air and Considerations on the Doctrine of Phlogiston and the Decomposition of Water,
respectively. I will also relate an experiment of my own design, using some Terra Ponderosa
Aerata1 which MR. KEIR has kindly provided me with, which has deepened my insight
into this particular question: while they support the Phlogistic system, I have found in
Messrs. CAVENDISH and PRIESTLEY’S works on the explosion of inflammable air and
dephlogisticated air a surprising confirmation of MONSIEUR LAVOISIER’S theory of acids.
My humble experiment with the Terra Ponderosa Aerata can only strengthen my belief in
Terra Ponderosa Aerata, Barite or Heavy Spar, used by Priestley to create carbon dioxide, is known in
modern chemical terminology as Barium Carbonate, or BaCO 3. It is a colourless, insoluble, stable
crystalline ore of the heavy metal Barium. Barium (as an element) would, however, not be discovered for
another two decades, when Davy isolated it by electrolysis. Witherite, Barium Hydroxide or Ba(OH) 2,
which also features heavily in my paper has a similar appearance and similar properties to Barium
Carbonate, but is soluble in acids. Barium Oxide, or BaO absorbs water rapidly to produce Barium
Hydroxide, while Barium Peroxide, or BaO2, dissolves in water to produce Barium Hydroxide, and turns
some of the water into Hydrogen Peroxide, H2O2, which is an oxidant and, when dissolved in water, an
acid.
1
the Truth of MONSIEUR LAVOISIER’S theory of acidity, while still hoping that greater
men than myself might one day incorporate this Fact into their theory of combustion.
I will now relate the conduct and surprising insights gained from my experimentation. By
the grace of God alone I was not injured or poisoned by the explosions, poisons, fires
&c. that my quest for Truth made me endure.
For the benefit of the reader, I propose to briefly document the first experiment I
emulated. MR. PRIESTLEY explains in his Considerations on the Doctrine of Phlogiston and the
Decomposition of Water that he combusted by the electric spark in an enclosed container an
admixture of inflammable air and dephlogisticated air. He asserts that the presence of an acid
in the resultant liquor disproves MONSIEUR LAVOISIER’S theory of the decomposition
of water into Oxygen and Hydrogen. MR. CAVENDISH, relating a similar experiment in his
letter to this Journal on his Experiments on Air, reports that the proportions of inflammable
and dephlogisticated airs determined the acidity of the liquor. He reports that
“when a mixture of inflammable and dephlogisticated air is exploded in such
proportion that the burnt air is not much phlogisticated, the condensed liquor
contains a little acid (…); but if the air is almost entirely phlogisticated 2, the
condensed liquor is not at all acid, but seems pure water, without any addition
whatever; and as, when they are mixed in that proportion, very little air remains
after the explosion, almost the whole being condensed, it follows, that almost the
whole of the inflammable and dephlogisticated air is converted into pure water.”
(p128)
In the language of MONSIEUR LAVOISIER’S chemical theory, if there is an excess of
Oxygen over the quantity of Hydrogen, then acidity of the resultant liquor will result. With
the clash of the two great chemical systems in mind, and the knowledge of the great
minds proposing these heavy on my shoulders, I proceeded to repeat these experiments.
I was particularly aware of the inability of MR. CAVENDISH’S theory of inflammable air as a
mixture of phlogiston and nitrous acid to explain the increase in acidity that occurs when more
oxygen (or in his language, more dephlogisticated air) is added to the mixture – indeed, his
theory suggests the quite opposite3.
In my experiments, I found, likewise, that the greater the proportion of oxygen in the
mixture, the greater the acidity of the liquor. According to MONSIEUR LAVOISIER’S
Elements of Chemistry,
“The first or lowest degree of oxygenation in bodies, converts them to oxyds; a
second degree of additional oxygenation constitutes the class of acids, of which
the specific names, drawn from their particular bases, terminate in ous, as the
nitrous and sulphurous acids” (p80)
‘Phlogisticated air’ is nitrogen – if the burnt air is entirely phlogisticated, it is that there is only (unreactive)
nitrogen left, and that all the hydrogen and oxygen have been consumed. This means the hydrogen and
oxygen are in the ratio of 2 to 1 in number of atoms, or 1 to 8 in weight.
3 Cavendish believes that inflammable air is a combination of nitrous acid and phlogiston (see his
Experiments on Air, p135) – if the mixture of gases in the combustion chamber contains more oxygen and
less hydrogen (to use modern terms), Cavendish reports that the resultant liquid is more acidic. Yet if the
acidic principle is coming from the inflammable air, as Cavendish claims, then the relative lack of
inflammable air in the chamber when the resultant liquid is more acidic appears to be a contradiction.
2
If water is nothing but the oxyd of hydrogen, as MONSIEUR LAVOISIER convincingly
demonstrates, then the acid produced by the combustion of hydrogen in an abundance
of oxygen must be similar to water, but posess a degree of additional oxygenation of the
hydrogen. Therefore the acid produced must be, not nitrous acid, but hydrogenous acid 4.
Not satisfied with this experiment, I repeated an apparently unrelated experiment in MR.
PRIESTLEY’S paper, that has further convinced me of this hypothetical hydrogenous acid,
and therefore confirmed to me the Truth of MONSIEUR LAVOISIER’S theory of chemistry.
Having procured from MR. KEIR a considerable supply of Terra Ponderosa Aerata, I
proceeded to repeat MR. PRIESTLEY’S method of producing fixed air from the Terra.
After passing steam over the chemical in the conditions described by MR. PRIESTLEY, I
found, like MR. PRIESTLEY, that fixed air was produced. The Terra Ponderosa Aerata
remaining in the puddle of condensed steam at the end of this experiment appeared
unchanged, however, and I ordered my servant to dispose of it in the midden.
I discovered to my surprise some days later the corpse of a fox that had clearly been
poisoned while scavenging in the midden. On repeating the experiment and examining
the Terra Ponderosa Aerata remaining after passing steam over it, I discovered that, on
giving up its fixed air, and absorbing the water that had condensed from the steam, it had
become soluble in acid, and, unlike the unused Terra Ponderosa Aerata, it was poisonous
when fed to animals5. To reiterate: Removing the fixed air from the Terra Ponderosa Aerata,
and replacing it water left this chemical subtly changed. The water in which it was bathed,
when tested with the litmus, bore no sign of acidity.
Wishing to further investigate the nature of the hydrogenous acid I believed to have found
in my attempt to repeat the experiments of Messrs. PRIESTLEY and CAVENDISH, and to
confirm in my sceptical mind that this acid was indeed oxygenated water, I spent some days
attempting to find other ways of further oxygenating water to produce the hydrogenous acid.
I finally chanced upon a method – an alteration of MR. PRIESTLEY’S method of
producing fixed air – which allowed me to produce hydrogenous acid without the
combustion of hydrogen and oxygen.
Rather than decomposing the Terra Ponderosa Aerata in steam – which, as we have seen,
allows the Terra Ponderosa Aerata to absorb water, I attempted to do so by heat alone.
After some futile attempts of my own, an associate of mine in the Royal Dublin Society,
MR. MATHERS, succeeded in doing so in a blacksmith’s forge, and found that, as before,
Actually, the acid Hydrogen Peroxide, or H2O2. It is unclear to me whether this is actually occurring, and
if not, exactly what is producing the acid in Cavendish and Priestley’s experiments. My hydrogen peroxide
theory is at least plausible, even in modern chemistry, though: given the excessive oxygen:hydrogen ratio
they record, the electrical spark could change some of the excess oxygen into ozone (O3), which reacts with
water to produce hydrogen peroxide. In addition to this, Sidgwick reports that hydrogen, when burnt in
oxygen, will produce small amounts of hydrogen peroxide anyway. Another possibility I have identified,
however, that the spark is actually disassociating the nitrogen molecules, and producing nitrous acid (as
Priestley actually suspects, though for the wrong reasons, on p151). I believe, however, that my theory of
an acid of hydrogen would have been more consistent with the knowledge of the time. Both of these
theories have evidence in their favour. There is, of course, no way of being sure.
5 What is going on here – in modern terms – is:
BaCO3 + H20 => CO2 + BaO + H2O. BaO is highly reactive with water, and immediately absorbs some
of the water (provided by the jet of steam) to produce Ba(OH) 2 (Witherite, or Barium Hydroxide), which
looks similar to BaCO3, but is soluble in acid, and highly toxic (unlike the harmless Barium Carbonate,
which is used in X-ray tests to highlight the soft tissue of the digestive tract in medical examinations,
barium hydroxide is used to this day as a rat poison).
4
the Terra Ponderosa Aerata had surrendered its fixed air, but, this time, due to the absence
of moisture, had absorbed no water6. My wish here was to acquire Terra Ponderosa Aerata
which had been relieved of its fixed air, but without the inevitable absorption of water that
accompanied this in MR. PRIESTLEY’S method, and rather, for the resultant chemical to
absorb oxygen. To do this, I heated the result of the Terra’s firing in pure oxygen. I found
that a proportion of the oxygen had been absorbed, and that I was left with Terra
Ponderosa Aerata, saturated with Oxygen rather than fixed air, or water7. My reasons for
doing this will, I hope, soon become clear.
To reiterate, in the first experiment with the Terra Ponderosa Aerata, the fixed air was
removed, and the water allowed to replace it. When such Terra Ponderosa Aerata with its
fixed air replaced by water 8 is added to water, no acidification occurs. In this second
experiment, I hoped to add Terra Ponderosa Aerata, from which the fixed air was removed
and replaced by Oxygen, to water, hoping to pass this additional oxygenation to the water,
and thus produce the same hydrogenous acid I had earlier produced by combustion alone.
I therefore added this oxygenated Terra Ponderosa Aerata to a sample of water, and observed
that an identical residue was produced as in the previous experiment, but that the water
was oxygenated, and was acidic.9
The only difference between these two experiments is the oxygenation of the Terra
Ponderosa Aerata after the removal of the fixed air, rather than the addition of water. As
the residue was identical in both experiments, it must be concluded that the additional
oxygenation was indeed passed to the water as I predicted – and produced hydrogenous acid,
just as MONSIEUR LAVOISIER’S theory directed me to predict.
To the remaining supporters of the phlogistic system, I recommend the repetition of these
experiments and others. While I do not pretend to be an authority on either doctrine of
chemistry, I cannot help but be impressed by the confirmation of the oxygen theory of
acids that my humble experiments have shown.
I remain, sirs, your most honest and humble servant,
Lord DE SELBY of DALKEY*
Lawn Mór
Dalkey
Ireland
24th June 1800
According to http://www.anvilfire.com/FAQs/coal.htm, a coal forge can heat up to a temperature of
around 1900C, which is above the temperature (1300C) required to decompose Barium Carbonate without
the need for water. This means that BaCO3 => CO2 + BaO, essentially the same decomposition as in the
previous experiment, but without the water to react with the Barium Oxide.
7 Or in modern terms, 2BaCO => 2BaO + 2CO ; then 2BaO + O => 2BaO : or barium carbonate,
3
2
2
2
minus carbon dioxide, plus oxygen, produces barium peroxide.
8 Barium hydroxide.
9 Barium peroxide, when added to water, produces Barium Hydroxide (as produced by the previous
experiment), and passes its extra oxygen onto the water, to produce Hydrogen Peroxide. This produces a
solution of hydrogen peroxide – like that (possibly) produced by the experiments in which hydrogen and
oxygen were exploded.
6
* A note on the author -- De Selby is the fictional philosopher-scientist who appears in two
novels by the 20th Century surrealist Irish novelist Flann O’Brien (real name Brian O’Nolan). In
the first, The Third Policeman (1940), the story of an amoral murderer, his soul (called Joe)
and their journey through hell, De Selby appears only in the footnotes and (bogus) references,
which describe the eccentric scientific and philosophical background of the nameless
protagonist. In the second of these novels, The Dalkey Archive (1964) (Dalkey is a small town
outside Dublin), De Selby is a character in his own right, and spends much of the book
plotting the annihilation of the atmosphere (with a chemical of his own invention). He hopes to
do so on the utilitarian grounds that the evil that would be destroyed by the extinction of all life
would be greater than the evil of causing the extinction. In one chapter of The Dalkey Archive,
De Selby destroys the air in a submarine cave, and finds that the absence of atmosphere has
summoned the spirit of Saint Augustine, with whom he has a long – and somewhat
blasphemous – conversation. Under another pseudonym, Myles na gCopaleen, O’Nolan had
a regular column in the Irish Times in which he commented incisively on politics, society,
culture and – attention C.P. Snow – science too.
ADDITIONAL WORKS CONSULTED
Apart from the papers of both editions of the Virtual Journal of Natural Philosophy, Chemistry
and the Arts (which I have tried to flag up where possible in the text), I have used the
following works in writing this essay:

For general data on chemical compounds and the reactions they can undergo, I have
used NV Sidgwick, Chemical Elements and their Compounds (Oxford: Clarendon
Press, 1950).

For the difficult task of translating names of chemicals between their old and new
names, as well as getting the formulae right, I initially used the haphazard and not
always accurate tool of the Google internet search, until I chanced upon the excellent
website http://dbhs.wvusd.k12.ca.us/webdocs/Chem-History/Obsolete-ChemTermsTOC.html, which gathers all of the definitions, translations and formulae
together into one place. It also has the advantage of being an academic study, rather
than a personal website: it is an online version of John Eklund’s The Incompleat
Chymist: Being an Essay on the Eighteenth-Century Chemist in His Laboratory, with
a Dictionary of Obsolete Chemical Terms of the Period, originally published in
Smithsonian Studies in History and Technology, Number 33 (Smithsonian Institute
Press: Washington DC, 1975).