32 Professor Macaire on tlie 



precautions which the use of such an apparatus requires will 

 readily be understood, and it would probably but rarely suc- 

 ceed in the hands of a less skilful and practised experimenter. 

 According to the mode in which Theodore de Saussure 

 managed it. this process attained a high degree of accuracy ; 

 and the author is of opinion that it is susceptible of still 

 greater precision, when we can appreciate the proportion of 

 the oxygen in the gas analysed, not by the diminution of the 

 volume of the gases, but by the increase of weight in the 

 small shot. 



In the same manner as it does oxygen, moistened lead attracts 

 also carbonic acid from the air ; and although this quantity is 

 very small, it is necessary to take it into account. This the 

 author has done, by deducting it from the mean of fourteen 

 eudiometrical experiments made during the day, at different 

 times, on the Lake of Geneva, or near its shores. He found 

 that the absorption effected by the moist leaden small-shot 

 rose, as a mean, to 21 05 per cent, of atmospheric air. By di- 

 minishing this figure by 0"04, which is very nearly the amount 

 of the carbonic acid during the day in these localities, there 

 remained 21*01 of oxygen for the hundred of air. Air from the 

 summit of the Buet, 3077 metres above the sea, and analysed 

 by the same process, after having been deprived of carbonic 

 acid by potass, contained 20*903 per cent, of oxygen gas. Air 

 taken during a well-frequented ball in the theatre at Geneva, 

 contained 20-81 of oxygen gas, and 0*24 of carbonic acid gas. 



It will be remembered, that, by the ordinary eudiometrical 

 process, that which was invented by Volta, and according to 

 which the oxygen is estimated by its detonation with hydro- 

 gen, chemists have not arrived at the same figures to express 

 the oxygen of the air. Thus Humboldt and Gay-Lussac have 

 stated it at 21 per 100 ; Dalton, 20*7 or 20*8 ; Henry hesitates 

 between 20 and 21 ; and Thomson fixes it at 20. In the fourteen 

 analyses which Theodore de Saussure made by the process he 

 invented, the highest figure for absorption, including the car- 

 bonic acid, was 21-15, and the lowest 20 9 8, which may give 

 us an idea of the accuracy of this means of analysis in the 

 hands of a man so versed as he was in the difficult art of ex- 

 perimenting. 



