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TRANSACTIONS OF SECTION B. 763 
will sufficiently account for all the facts there is no occasion to have recourse 
to a new one, attended with no peculiar advantage (doc. cit. p. 548).... I 
should not feel much reluctance to adopt the xew doctrine, provided any new and 
stronger evidence be produced for it. But though I have given all the attention 
that I can to the experiments of M. Lavoisier, &c., I think that they admit of the 
easiest explanation on the old system.’ (Loc, cit. p. 563.) 
The fact that Priestley was the first to consciously isolate oxygen is not contested 
by M. Berthelot, although he is careful to point out, what is not denied, that the 
exact date of the discovery depends on Priestley’s own statement, and that: his first 
publication of it was made in a work published in London in 1775. It was known 
before Priestley’s famous experiment that the red oxide of mercury, originally 
formed by heating the metal in contact with air, would again yield mercury by the 
simple action of heat. and without the intervention of any reducing agent. 
Bayen, six months before the date of Priestley’s discovery, had observed that 
a gas was thus disengaged, but he gave no description of its nature, contenting 
himself merely by pointing out the analogy which his experiments appeared to 
possess to those of Lavoisier on the existence of an elastic fluid in certain 
substances. Afterwards, when the facts were established, Bayen drew attention 
to his earlier experiments, and claimed, not only the discovery of oxygen, but all 
that Lavoisier deduced from it. ‘But,’ says M. Berthelot, in reference to this - 
circumstance, ‘his contemporaries paid little heed to his pretensions, nor will 
posterity pay more’ (‘ La Révolution Chimique,’ p. 60). 
M. Berthelot, however, does not dismiss Lavoisier’s claims to a participation in 
the discovery in the same summary fashion. On the contrary, whilst not explicitly 
claiming for him the actual isolation, in the first instance, of oxygen, the whole 
tenor of his argument is to palliate, and even to justify, his demand to be 
regarded as an independent discoverer of the gas. He begins by asserting that 
Lavoisier had already a presentiment of its existence in 1774, and he quotes, in 
support of this assumption, an abstract from Lavoisier’s memoir, published in 
December 1774, in the ‘Journal de Physique’ of the Abbé Rozier: ‘This air, 
deprived of its fixable portion (by metals during calcination), is in some fashion 
decomposed, and this experiment would seem to afford a method of analysing the 
fluid which constitutes our atmosphere and of examining the principles of which 
itis composed... . I believe I am in a position to affirm that the air, as pure as 
it is possible to suppose it, free from moisture and from every foreign substance, 
far from being a simple body, or element, as is commonly thought, should be 
placed, on the contrary, . . . in the group of the mixtures, and perhaps even in 
that of the compounds.’ 
M. Berthelot further asserts that Lavoisier was at this time the first to 
recognise the true character of air, and he expresses his belief that it is probable 
_ that he would himself have succeeded in isolating its constituents if the path of 
inquiry had been left to him alone. It is no disparagement to Lavoisier’s 
prescience to say that there is nothing in these lines, nor in the memoir of the 
repetition of Boyle’s experiments on the calcination of tin to which they refer, to 
show that Lavoisier had made any advance beyond the position of Hooke and 
Mayow. It has been more than once pointed out that the chemists of the 
seventeenth century understood the true nature of combustion in air much better 
than their brethren of the last quarter of the eighteenth century. Hooke, in the 
_‘*Micrographia,’ and Mayow, in his ‘Opera Omnia Medicophysieca,’ indicated that 
combustion consists in the union of something with the body which is being burnt; 
and Mayow, both by experiment and inference, demonstrated in the clearest way 
the analogy between respiration and combustion, and showed that in both processes 
one constituent only of the air is concerned. He distinctly stated that, not only is 
there increase of weight attending the calcination of metals, but that this increase 
is due to the absorption of the same spiritus from the air that is necessary to 
respiration and combustion. Mayow’s experiments are so precise, and his facts so 
incontestable, that, as Chevreul has said, it is surprising that the truth was not 
fully recognised until a century after his researches. (Vide Watts’s ‘ Dictionary of 
Chemistry,’ by Morley & Muir, art. ‘Combustion,’ p. 242.) 
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