Los constructos de los indicadores, activos, potencialidades y competencias

After these discoveries a new problem arose for Lavoisier, because, if this ‘new air’ was more pure than atmospheric air, then atmospheric air might be not an elementary body, as he considered it to be, but a compound. Apart from that, in his experiments with tin (Sn) he had observed that the part of the air combined with the tin and the part of the air left after calcination had different density270. On the other hand, Priestley in December 1775 with his publication of his Experiments and Observations challenged Lavoisier’s notion that the atmospheric air was an elementary body271, therefore, as we have seen, this critique forced Lavoisier to revise his ‘Easter Memoir’ 1775. Priestley believed that atmospheric air was composed of nitrous air (today’s nitric oxide), earth and phlogiston. Lavoisier argued against that ‘when the calx of mercury (HgO) was heated and reduced to the metallic state, the metal had not gained or lost weight; therefore it could have not gained or lost phlogiston’272. For that reason Lavoisier between 1775 and 1776 continued his experiments, in order to find out the connection among nitrous air, air and acidity, since it was known that calxes of sulfur and phosphorus formed acids when mixed with water. In his Memoir read to the Academy in April 1776 he wrote that the same air, which was contained in it those calxes, was produced by analyzing acid of phosphorus and nitrous acid. Therefore he concluded that ‘the same air that combined with metals and produced calxes it was given off by the analysis of acids’273.

What was left for him was to examine whether atmospheric air was a simple body or a compound, and in the latter case he had to distinguish the components of the atmospheric air. He designed now his experiments in this way, so as first to take the atmospheric air in pieces and then to put it together again, as he explained in his memoir read to the Academy

270

See McKie (1952), pp. 132-3, Aykroyd W. R., (1935),pp. 67-8, and Donovan Arthur (1993), pp 140-41.

271

Priestley quotes it in his Experiments and Observations Volume 2, pp. 320-3 and Conant in (1950), p. 90: ‘Mr. Lavoisier, as well as Sig. Landriani, Sig. F. Fontana, and indeed all other writers except myself , seems to consider common air as a simple elementary body; whereas I have for a long time considered as a compound’.

272

See Lavoisier Oeuvres II, pp. 137-8: ‘… I would reply then that when the mercury leaves the operation exactly as it entered it, there is no evidence that it has lost or gained phlogiston…’.

273 _{See McKie (1952), pp. 135-36, and Donovan Arthur (1993), pp. 144-45. Lavoisier quotes also these}

experiments in his Oeuvres, volume II, pp. 137-8, and he concludes: ‘It is clear that air is not composed of a nitrous acid (nitrous air plus water), as Mr. Priestley supposes, but rather nitrous acid is composed of air’ (parenthesis mine).

on May 3, 1777274. First, he deprived the atmospheric air of his supposed ‘pure air’ (oxygen) through the calcination of mercury and observed that the air was decreased by about one sixth of its volume (8-9 cubic inches out of 50)275. The remained air (nowadays nitrogen), he found, would not support life and combustion, because it asphyxiated animals and extinguished flames. Then he reduced it by heating the mercury calx and recovered the same quantity of the ‘pure air’ (8-9 cubic inches) that had been combined in the calx. After having added this recovered air to the remained asphyxiating residue from the calcination, he obtained air with the properties of the original common air. This restored air no longer extinguished flames but supported also respiration276. As it had been shown earlier by Black, when animals breathed in air, their respiration led to the formation of ‘fixed air’ (CO2); however, Lavoisier noted that in respiration only the respirable ‘pure air’ (oxygen)

was changed into the ‘fixed air’ (CO2), while the asphyxiating part of the common air, the

noxious air, mofette (nitrogen), passed into the lungs and came out again unchangeable.

To sum up, Lavoisier with his experiments established that the air of the atmosphere was not a simple substance but a compound, composed of ‘pure air’, which Priestley called

‘dephlogisticated air’, and of mofette or noxious air, whose nature was unknown277. Besides, he introduced a new classification of gases, as follows: (a) common atmospheric air, (b) pure air, (c) noxious air and (d) fixed air.278 What was left for Lavoisier then was to classify and define that ‘pure air’, since he had become familiar with its chemical properties.

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

pp. 68-9, and Donovan Arthur (1993), pp 147-48. Lavoisier quotes also these experiments in his Oeuvres, volume II, pp. 176-81.

275

Lavoisier in Oeuvres, volume II, pp. 176-81, describes the result of this experiment as follows: ‘I observed that the air it had contained was diminished by 8 to 9 cubic inches, that is to say, by about a sixth of its volume; at the same time there had been formed a considerable quantity, approximately 45 grains, of mercury percipitate per se, or calx of mercury’.

276

Ibid: ‘By this operation I recovered almost the same amount of air as had been absorbed by the calcination, that is to say, 8 or 9 cubic inches, and on combining these 8 to 9 inches with the air vitiated by the calcination of mercury, I restored this air exactly enough to its state before calcination, i.e., to the state of common air: the air thus restored no longer extinguished flame, no longer caused the death of animals breathing it, and finally was almost as much diminished by nitrous air as the air of the atmosphere’

277

See Lavoisier’s Oeuvres, volume II, pp. 176-81: ‘I have established in the foregoing memoirs that the air of the atmosphere is not a simple substance, an element, as the Ancients believed and as has been supposed until our own time: that the air we breathe is composed of respirable air to the extent of only one quarter and the remainder is a noxious air, which cannot alone support the life of animals or combustion or ignition’.

278

Ibid: ‘I feel obliged, consequently, to distinguish four kinds of air or air-like fluids: First, atmospheric air; that in which we live, which we breathe. Secondly, pure air, respirable air; that which forms only a quarter of atmospheric air, and which Mr. Priestley has very wrongly called dephlogisticated air. Thirdly, the noxious air, which makes up three quarters of atmospheric air and whose nature is still entirely unknown to us. Fourthly, fixed air, which I shall call henceforward by the name of acid of chalk’.

As explained, Lavoisier knew that calxes of sulphur and phosphorus, when they mixed with water formed powerful acids, and that these calxes contained ‘pure air’ that was fixed during their calcination. By analyzing nitrous acid he had found out that it contained also ‘pure air’; therefore he concluded that this ‘pure air’ makes nitrous acid and all acids acidic, since when metals combined with ‘pure air’ in calcination, formed calxes, while these calxes when mixed with water, they formed acids279. His final conclusion was that this ‘pure air’, part of the atmospheric air, played a central role, besides respiration and combustion, also in the formation of acids; therefore in a memoir submitted to the Academy in September 1777, he named it oxigene: begetter of acids (from the Greek words, οξύς: oxys and γείνομαι: geinomai)280. Certainly, this name (begetter of acids), as principle of acidity, could not represent all acids (e.g. HCl); therefore this definition of acidity after nearly 100 years was proved to be false by Arrhenius.