EUD10METRY. 



sample and expeditious, and as Humbolt 

 and Gay Lussac have remarked, has the 

 great advantage, from the bulk of the 

 mixture, and the great diminution of vo- 

 lume, from the consumption of a given 

 quantity of oxygen, of being more deli- 

 cate than any other. It also requires no 

 corrections for variations of temperature 

 or atmospheric pressure ; and any impu- 

 rity in the hydrogen gas, which it has 

 been supposed might be a source of er- 

 ror, may by avoided by care. It affords 

 also the best method of determining the 

 purity of oxygen gas, or the proportion 

 of oxygen in any mixed gas containing it. 

 Humbolt, and Gay Lussac in an elabo- 

 rate memoir, have pointed out all the cir- 

 cumstances to be attended to in employ- 

 ing it as an eudiometer. (Journal de Phy- 

 sique, t. Ix. p. 129.) 



From the practice of eudiometry, it was 

 at one time expected, as the name implies, 

 that we should be able to ascertain the 

 purity of the air with regard to its salu- 

 tary or noxious power on life. It was 

 soon found, however, particularly by 

 Priestley, (and the fact has also sincebeen 

 established by de Marti,) that the air of 

 places the most offensive and unhealthy 

 afforded as much oxygen as that of others 

 of an opposite description ; the air, for 

 example, of crowded cities, of low, 

 damp situations, or of crowded manu- 

 factories, has not been found less pure 

 than that of the country; the noxious 

 quality of the air depending not so much 

 on any deficiency of oxygen, as on the 

 presence of effluvia not discoverable by 

 this test. 



It was at one time imagined, that the 

 composition of atmospheric air is not uni- 

 form, but that it varies both at different 

 parts of the earth's surface ; and still 

 more at different heights. Ingenhouz 

 made a number of experiments to prove 

 the former fact, from which he concluded, 

 that the air is purer, or contains more 

 oxygen at sea than on land, and that in 

 the neighbourhood of marshy situations 

 it contains less oxygen than the standard. 

 (Philosophical Transactions, vol. Ixx. p. 

 354.) 



Saussure made some experiments on 

 the air at some of the elevated parts of the 

 Alps, the summit of the great St. Ber- 

 nard, the Buet, &c. : in this air the pro- 

 portion of oxygen was less than in the air 

 on the plains. (Voyages, t. ii.p. 357; t. 

 iv. p. 451) 



Von Humbolt relates, also, that air 

 brought from a great height in the atmo- 

 sphere, by a person who had ascended in 



a balloon, contained in 100 parts 25.9 of 

 oxygen, while air at the surface contained 

 27.6 ; and that at the summit of the Peak 

 of Tencriffe, the proportion of oxygen 

 amounted only to 19, while at the foot of 

 the mountain it was 27. The proportions 

 which he states prove sufficiently the er- 

 ror of the eudiometrical method he em- 

 ployed, and the eudiometer he did use ; 

 that with nitrous gas, corrected by trying 

 its purity with sulphate of iron, is indeed 

 the one which is most liable to fallacy. 

 The analysis of the air in the upper re- 

 gions of the atmosphere has since been 

 executed with accuracy by Gay Lussac, 

 assisted by Thenard. A glass balloon 

 was filled with air, at the height of 

 21.735 feet from the surface, the greatest 

 which has yet been reached, and when 

 opened under water by Gay Lussac, after 

 his descent, one half of its capacity was 

 filled by the water, a sufficient proo'f that 

 it had been accurately closed. The air 

 was subjected to trial, both by Volta's eu- 

 diometer, and by the solution of sulphu- 

 ret of potash ; it afforded by the former 

 method 21.49 of oxygen in 100 ; by the 

 latter 21.63. Atmospheric air at the sur- 

 face, analysed at the same time in the eu- 

 diometer of Volta, gave precisely the 

 same result, 21.49. (Nicholson's Journal, 

 vol. x. p. 286.) 



Saussure, junior, also found, that the 

 air on the summit of the Col-du-Geant, 

 contained within one-hundreth part as 

 much oxygen as that on the plain, and 

 even this difference may be ascribed to 

 the difficulty of making the experiment 

 with perfect accuracy. The uniformity 

 of the composition of the atmosphere at 

 different parts of the earth's surface ap- 

 pears also to be established. 



Mr. Cavendish originally observed, that 

 air subjected to examination at different 

 times, and air likewise 'from different 

 places, was of perfectly similar composi- 

 tion : (Philosophical Transactions, vol. 

 Ixxiii. p. 129 ;) and the same observation 

 had been made by Fontana, from his own 

 experiments. (Philosophical Transactions, 

 vol. Ixix.) 



Mr. Davy states, that no sensible dif- 

 ference was found in the air sent from the 

 coast of Guinea, and the air in England. 

 (Journal of the Royal Institution, vol. i. 

 p. 48.) 



Berthollet found, that the air in Egypt 

 and in France was similar, affording 22 

 of oxygen in the 100, any difference ob- 

 served not amounting to a two-hundredth 

 part of the air submitted to trial . (Memoirs 

 relative to Egypt, p. 326.) 



