History of Air- Analysis 19 



With the passing of the nitric-oxide 1 and the alkaline-sulphide methods, 

 we may consider the historical development of such methods as have sur- 

 vived a century or more of keen analytical criticism. Since this article 

 has to deal primarily with the development of the knowledge regarding 

 the composition of the outdoor air and but secondarily with methods, we 

 may now advantageously consider the chronological records of progress 

 in air-analysis. 



In 1774, the brilliant Italian physicist, Volta, 2 announced his eudio- 

 metric method of employing the explosion of a confined volume of air 

 with hydrogen by the electric spark. No results of his analyses are re- 

 ported, but the process evidently attracted much attention, for we find 

 that Cavendish, 3 while working on the composition of water, published 

 the following interesting statements : 



From the fourth experiment it appears that 423 measures of inflammable air are 

 nearly sufficient to completely phlogisticate 1000 of common air; and that the bulk of 

 the air remaining after the explosion is then very little more than four-fifths of the com- 

 mon air employed; so that as common air can not be reduced to a much less bulk than 

 that by any method of phlogistication, we may safely conclude, that when they are mixed 

 in this proportion, and exploded, almost all the inflammable air, and about one-fifth part 

 of the common air, lose their elasticity, and are condensed into the dew which lines the 

 glass. 



Although Cavendish was in no sense appreciative of the fact that this 

 series of experiments proved the accuracy of the Volta eudiometer for air- 

 analysis, the results are surprisingly accurate. 



Shortly afterwards the method was adversely criticized by Seguin, 4 

 who maintained that the apparatus gave only comparative results and 

 could never be taken as an absolute measure, and by Berthollet, 5 who ob- 

 jected to the complicated apparatus. The latter remarked on the prob- 

 able contamination of the hydrogen by carbonaceous gases and pointed 

 out that we do not as yet know enough about the specific weight of the 

 two different gases. But in spite of this adverse criticism, the method 

 was most carefully employed in analyzing samples of air brought from a 

 great height by Gay-Lussac in a balloon flight. 6 Later, von Humboldt 

 and Gay-Lussac 7 published a long research with the Volta eudiometer 

 on the composition of air taken over the Seine under varying weather 



1 It is interesting to note that in 1890 Wanklyn and Cooper resurrected the nitric- 

 oxide method and enthusiastically recommended its use, reporting three analyses of 

 pure air as giving 20.59, 20.54, and 20.67 per cent of oxygen respectively. Chemists 

 have not accepted the method for modern use. (See Wanklyn and Cooper, Air-analysis, 

 London, 1890, p. 35.) 



1 Volta, Sopra Un Nova Eudiometro. Lettera al Signor Dottore Giuseppe Priestley, 

 Como, 2 Settembre, 1777. Published in Collezione dell'Opere. del Cavaliere Conte 

 Alessandro Volta, Firenze, 1816, 3, p. 177. Originally published, Scelta di Opuscoli 

 interessanti di Milano, 1777, 34, p. 65. 



3 Cavendish, Philosophical Transactions, 1784, 74, pp. 119-153. 



* Seguin, Annales de Chimie, 1791, 9, p. 293. 



6 Berthollet, Memoires sur 1'Egypt publies pendant les Campagnes du Gen6ral Bona- 

 parte. Paris, 1800(Annee8),p.2S4. 



6 Gay-Lussac, Annales de Chimie, 1805, 52, p. 75. 



7 v. Humboldt and Gay-Lussac, Journal de Physique, 60, p. 129. 



