18 Composition op the Atmosphere 



4th, That I did not observe any variation in the air thus taken while the mercury of 

 the barometer was very low, and when it exceeded 28 inches. 



In a word, during winter, in summer, in spring, and in autumn, in every month and 

 at all hours, I found the air of my country, taken in the open fields, to be always composed 

 of from 21 to 22 parts of vital air, and of from 78 to 79 of azotic gas. 



But though this proportion does not vary a hundredth part in the course of several 

 months, and even years, may it vary a very small part, such as a thousandth part, which 

 after a very long time may become sufficiently sensible to make the proportion of the 

 vital air of the atmosphere experience a progressive or periodical increase or diminution? 



De Marti's researches, though carried out in 1787, were not translated 

 into English until 1801, but his success with the sulphide of calcium evi- 

 dently stimulated others to use the sulphides as reagents. 



Berger 1 reports a series of experiments, using several forms of sul- 

 phide. With potassium sulphide, he found 21.65 per cent of oxygen; 

 with iron sulphide, 21.19 per cent; with calcium sulphide, 20.88 per cent; 

 and with sodium sulphide, 20.38 per cent. The agreement in these deter- 

 minations led Berger to conclude that these eudiometric substances ab- 

 sorb from the air only one substance, namely, oxygen. 



Henderson, 2 studying the changes which air undergoes as a result of 

 respiratory processes, used "sulphuret of lime." On three days, June 16, 

 1803, June 18, 1803, and February 11, 1804, he analyzed common air and 

 found 22 per cent of oxygen in all three cases. 



Gay-Lussac, 3 using both the hydrogen eudiometer and the absorp- 

 tion by alkaline sulphides, made analyses of air collected in a balloon. 

 He found with the hydrogen-explosion method that the air at a height of 

 6636 meters had the same composition as that on the surface of the earth, 

 and that at both places they gave 21.49 per cent of oxygen. With the 

 alkaline sulphide solution, he found 21.63 per cent in the air brought down 

 in the balloon, and maintained that this slight increase over 21.49 per cent 

 was inside the limit of error of the apparatus. 



Julia de Fontanelle, 4 while making a tour of Europe, analyzed over 50 

 samples of air in France at the foot and summit of Canigou, with an ele- 

 vation of 2780 meters, on the Corbires, on the Clape, and on the plains 

 of Roussillon and Narbonne; also in Spain on the plains of Figueras, 

 Gironne, and Barcelona, and on the mountains of St. Jerome-D' Ebron, 

 Mont-Joui, etc. Using calcium sulphide, he found constantly 21 per 

 cent of oxygen, with slightly more oxygen at noon than at midnight. 



The last recorded use of the sulphide of calcium for air-analysis was 

 made by Dalton, 5 who, however, gives no results, and by Moyle, 6 who 

 analyzed the air of mines by this method in comparison with several 

 others, including the long-discarded nitric-oxide method. 



1 Berger, Journal de Physique, 1802, 56, p. 375. 

 * Henderson, Nicholson's Journal, 1804, 8, p. 40. 

 Gay-Lussac, Annates de Chimie, 1804, 52, p. 75. 



4 J.-S.-E.-Julia, Recherches historiques, chimiques et mdicales sur l'air mare- 

 cageaux, Paris, 1823. 



6 Dalton, Philosophical Magazine, 1838, 3d ser., 12, p. 158. 



8 Moyle, Annales de Chimie et de Physique, 1841, 3d ser., 3, p. 318. 



