Of all the "airs" that provided the impetus for the chemical revolution at the end of the 18th Century, the most important was oxygen, which provided both the basis of Lavoisier's theory of acids and the means of "ultimate" analysis of organic substances by combustion.
Among Scheele's papers at the Center for History of Science at the Royal Swedish Academy of Sciences in Stockholm is the draft of a letter he sent to Lavoisier in 1774. In this letter Scheele, the apothecary in Uppsala, thanks Lavoisier for his book and tries to establish a collaboration for the study of oxygen with the well-equipped Lavoisier. Apparently Lavoisier never replied, even though Scheele had gone to the trouble to have a friend help him render the letter from German into French.
Scheele suggests that Lavoisier use the French Academy's 33-inch burning glass to focus the sun's rays on silver carbonate. Heating will generate carbon dioxide (fixed air) and silver oxide, which decomposes (at about 340°C) to silver metal and oxygen. If the fixed air in the collecting jar is removed by alkali, the oxygen could support respiration or the burning of a candle.
It is not known whether Lavoisier carried out this experiment, or why he did not reply to Scheele. Perhaps he was reluctant to share credit for this important discovery. He later wrote that some months before Easter in 1775 he had prepared "a new kind of air entirely unknown at that time". It was surely not unknown to Scheele.
From the clarity of this first communication describing the preparation and properties of what Scheele referred to as "Feuerluft" (fire air) or "Vitriol air", it is clear that he should at least share with Lavoisier and Priestly in discovering oxygen. His laboratory notes show him preparing the gas by heating silver carbonate in 1771-72.
I have received through Secretary
Wargentin a book, which he says that you have had the
goodness to give me
For a long time I have wanted to be able to read an account of all the experiments that have been done in England, in France and in Germany on the many
[Wargentin, an astronomer, was secretary of the Royal Swedish Academy of Sciences. On April 12, 1774, Lavoisier had sent him a copy of his recently published "Opuscules physiques et chimiques" for the Academy with another copy to give to Scheele. Apparently Lavoisier never wrote directly to Scheele. Scheele never corresponded with Priestly, the third discoverer of oxygen.]
kinds of air. You have not only satisfied this wish, but by new experiments you have given scientists in the future the most beautiful opportunities to better examine fire and the calcination of metals.
During the past several years I have carried out experiments on several kinds of air, and I have also spent a good deal of time in discovering the singular properties of fire, but I have never been able to prepare ordinary air from fixed air : I have tried many times, following the opinion of M. Priestley, to produce an ordinary air from fixed air by a mixture of iron filings, sulfur, and water, but I have never succeeded because fixed air always united with the iron and made it soluble in the water. Perhaps you do not know a way to do this either.
Because I do not have
any large burning glass, I beg you to
carry out an experiment (a trial) with yours in this way :
Dissolve some silver in nitrous acid and precipitate it with
alkaline tartrate, wash the precipitate, dry it, and reduce
it with the burning glass in your machine, fig. 8, but
because the air in this bell jar (this receiver) is such
that animals die in it and a part of the fixed air separates
from the silver in this operation, it is necessary to place
a bit of quick lime in the water where one has put the bell,
so that this fixed air joins more quickly with the lime.
This is the way that I hope that you will see how much air
is formed during this reduction, and whether a lighted
candle can keep burning and animals live in
Uppsala, the _ September, 1774.
[The letter was recopied and sent on September 30. Sometime after 1890 it was thought to have disappeared from the papers of Lavoisier, but if so, it has now reappeared.]
Many thanks to Anne Wiktorsson and the staff of the Center for History of Science at the Royal Swedish Academy of Sciences for kind hospitality and for providing access to this document.
For a full discussion of Scheele's letter and its implications, see the source of most of these comments: Uno Boklund "A Lost Letter from Scheele to Lavoisier", published in Lychnos (1957) and reprinted by Almquist & Wiksells (Uppsala, 1958). Many thanks to Henri Kagan, who reported in 2008 that the original Scheele letter has (re?)surfaced in the Archives of the French Académie des Sciences. It incorporates the corrections in the draft above (except "montrer" and "recipient") and is in a different hand.