Constructos de los indicadores, activos, potencialidades y competencias tangibles

Priestley in August 1774 conducted experiments with heating mercurius calcinatus per se (mercury calx: HgO), a red powder produced by heating mercury for a long time in air, and he found out that air was readily given off260. This air separated from the precipitate of mercury had some unexpected properties that differed completely from those of fixed air: it proved to be insoluble in water; a candle burned in it with remarkably vigorous flame, and a piece of red-hot wood sparkled in it and was rapidly consumed261. Priestley visited Paris in

258 _{Beretta (1993), who in his study emphasizes Lavoisier’s linguistic realism and his contribution to the}

establishment of the new chemical nomenclature, on p. 171, concludes to these three Lavoisier’s priorities. He cites as evidence Lavoisier’s Memorandum of February 20, 1773, cited originally in French by Guerlac (1961), pp. 228-30, and translated by Meldrum (1930), pp. 9-10.

259

McKie in (1952), pp. 107-108, cites Lavoisier’s memoir, which was read before the Academy on November 12, 1774 and published in the December issue of Rozier’s journal (Observations sur la Physique). See also Aykroyd (1935), pp. 51-52. Musgrave in (1976), pp 191-2, cites Lavoisier’s notes on Boyle’s experiments from his Oeuvres II, pp. 105-21.

260 _{This experiment is regarded as one of the most ‘crucial’ in the Chemical Revolution, as I am going to}

show later, and by some historians as the discovery of oxygen. See Conant (1950).

261

See Aykroyd W. R. (1935), pp. 54-5, McKie (1952), pp. 115-16, and Donovan Arthur (1993), pp 136-7. Priestley’s account in his (1775-79), vol. 2, section iii, is full of words like ‘astonishment’ and ‘surprise’

October 1774, and in conversation with Lavoisier and other members of the Academy he mentioned his unpublished discovery of the new air, and he spoke of its properties262.

This property of mercury calx, that it could be converted into metallic mercury on heating without charcoal, was known to the French chemists before Priestley’s informal report, however, the properties of the air released from it were not known. Actually, on September 3, 1774, Cadet, colleague of Lavoisier, had reported to the Academy that he had found a way to reduce the precipitate of mercury to the metallic state without using charcoal263. Therefore Lavoisier repeated Priestley’s experiment in November and again, more carefully, in February and March of the following year. Afterwards, on April 26, 1775, he read before the Academy a Memoir entitled: ‘On the Nature of the Principle which

combines with the Metals during their Calcination and increases their Weight’, a paper

which he revised later and it is regarded as one of the most interesting in the history of science264.

There he described his earlier experiments, i.e. when he had heated calxes with addition of charcoal, in that reduction the charcoal was consumed. It followed therefore, for Lavoisier, that the air given off in the reduction was not a simple substance, but a combination of at least two, and therefore he concluded that it was ‘fixed air’ (CO2 as explained with the

chemical representation of the calx of lead), which means that with this paper Lavoisier

corrected his initial hypothesis of November 1772. In the same paper he also explained that

due to the difficulties of reducing iron oxides without charcoal he decided to use calx of mercury265. Then by appealing to his experiments with mercury calx he described the properties of the air given off in the reduction, as follows: ‘it supported animal respiration,

it lighted candles and burning bodies, and it burned with brilliant flames’. Therefore he

about his discovery. It is also cited by Musgrave (1976), p 194. The reaction, as we know today, is represented as follows:2HgO → 2Hg + O2.

262 _{See Cooper Thomas (1806), p. 257, who cites Priestley’s memoir. Also Aykroyd W. R. (1935),}

pp. 61-2, McKie (1952), pp. 115-16, Donovan Arthur (1993), pp 136-7, and Bensaude-Vincent, Stengers (1996), p. 81.

263

See McKie (1952), pp. 122-3 and Donovan Arthur (1993), pp 136-37. Lavoisier gives a detailed description in Chapter 3, Elements of Chemistry.

264

This is Lavoisier’s famous ‘Easter Memoir’, which was published in Rozier’s Journal de Physique, May 1775. Its revised version appeared in 1775 volume of the Memoires de l’ Académie des Sciences, published in 1778. Translations of the two versions are printed in Conant (1950), pp. 22-28.

265

See Ibid, also Aykroyd W. R. (1935), pp. 64-5, Lavoisier’s notes from this memoir: ‘The difficulties arising from the nature of iron, due to the refractory nature of his calxes and the impossibility of reducing them without addition of charcoal I came to regard it as un-surmountable. Therefore I decided to study another kind of calx, which would have the property of being reducible without addition. Mercury percipitate per se … seemed to be suitable for this purpose I had in mind’.

concluded that this air appeared to be common air but in a purer state266, and as a result, the principle combined with metals during calcination and combustion was air, but purer than the one of atmosphere. In the first version of the memoir Lavoisier concluded that it was

‘elemental air in a highly purified form’, however after having been criticized for the word

‘elemental’ by Priestley in December 1775, as we are going to see, he revised it to ‘more pure, more respirable … than the air of the atmosphere’267.

At the same time Priestley continued also his experiments with his new air obtained from mercury calx. This time he put a mouse into its sample and found out that survived much longer than it would have in common air. He also breathed himself and found out that the feeling to the lungs was better than that of common air in respiration; therefore he described it as ‘pure air’. On March 15, 1775 he reported his discovery in a letter to the President of the Royal Society that was published in the Philosophical Transactions268, and which is

also considered to be one of the most interesting papers in the history of science. But his interpretation of the quality of the new air was different than Lavoisier’s, since he was exponent of the phlogiston theory. According to this theory, in respiration phlogiston was exhaled from the lungs, just as it was given off by all burning bodies, which was absorbed by the common air, and it was supposed that a limited amount of air could absorb only a limited amount of phlogiston, as afterwards it became saturated. The fitness of this new air for combustion and respiration was due to its pureness, for Priestley, because he thought it to be free from phlogiston, therefore he named it ‘dephlogisticated air’269.

266 _{See Aykroyd W. R., (1935),}

pp. 64-5, who cites Lavoisier’s notes from his Elements of Chemistry: ‘A taper burned in it with a dazzling splendour; and charcoal instead of consuming quietly as it does in common air, burnt with a flame…’ Also Donovan Arthur (1993), pp 137-38, cites Lavoisier’s notes from his memoir, as translated by Conant (1950): ‘… It is the air itself entire without alteration and decomposition, even to the point that if one sets it free after it has been so combined, it comes out more pure, more respirable, if this expression may be permitted, than the air of the atmosphere, and is more suitable to support ignition and combustion’.

267 _{See Donovan Arthur (1993), pp 137-38, who cites Lavoisier’s two versions of the memoir, as translated}

by Conant (1950).

268

See McKie (1952), pp. 118-21, Aykroyd W. R., (1935),pp. 66-7, and Donovan Arthur (1993), pp 139-40. Priestley quotes it in his Experiments and Observations Volume 2, p. 90. The description of this new gas was as follows: ‘But the most remarkable of all the kinds of air that I have produced by this process is, one that is five or six times better than common air for the purpose of respiration, inflammation, an, I believe, every other use of atmospheric air… A candle burned in this air with an amazing strength of flame… But to complete the proof of the superior quality of this air, I introduced a mouse into it; … it lived at two different times, a whole hour and was taken out quite vigorous…’

269

See Priestley, Ibid: ‘As I think I have sufficiently proved that the fitness of this air for respiration depends upon its capacity to receive the phlogiston exhaled from the lungs, this species may not be improperly called depholgisticated air’.