History of Air-Analysis 



13 



air in Salzburg, using a nitric-oxide eudiometer. The close proximity to 

 the Alps also enabled him to study the composition of air on the top of 

 mountains as well as that in the valley. 



Although we now know that von Humboldt's oxygen determinations 

 were erroneous owing to the test used, namely, nitric oxide, nevertheless 

 his observations and the tabular statement of his results have the com- 

 pleteness which characterizes modern scientific research, and in many ways 

 the thoroughness of the investigation commends itself to modern workers. 

 Using the Fontana eudiometer, he made observations of the air in Salz- 

 burg (1302 feet above sea-level), covering practically a whole year, the 

 samples of air being taken for the most part from a garden on the south 

 side of the city. Since this air might be considered contaminated, he 

 compared it with that from the open country some distance from the city, 

 but was never able to detect any difference. The results are expressed in 

 tabular form at the end of his book, each value representing the average of 

 3 to 5 tests. 



The analysis of the Salzburg air gave a range in oxygen content from 

 23.6 per cent to 29 per cent. The author concluded that the oxygen con- 

 tent can vary 5.4 per cent and does not always remain between 27 and 28 

 per cent. In observations on 144 days he found only 7 times that the 

 oxygen rose above 28. 1 per cent. The average oxygen content was : 



per cent 



November 25.6 



December 26.8 



January 27.5 



February 27.2 



per cent 



March 26.9 



April 27.2 



Average 26.8 



He came to the conclusion that in clear weather there is an increase in 

 the oxygen, and as bad weather approaches there is a decrease. 



He also made comparative observations of mountain and valley air. 

 With the assistance of a friend, samples were taken simultaneously at 

 noon from the Geisberg (3890 feet) and from the valley. On December 

 18, 1797, the mountain air gave 23.6 per cent of oxygen and the valley air 

 26.2, or 2.6 per cent of oxygen more than the mountain air. On January 

 30, 1798, another observation was made, the results for the mountain air 

 being 26.1, and for the valley air, 27.4 per cent. On March 4, 1798, 

 another set of samples gave for mountain air 26.4 and for valley air 

 27.3 per cent. On March 11, 1798, the results for the two samples were 

 identical, namely, 26.4 per cent. 



Assuming that the nitric oxide used by earlier experimenters was not 

 below a certain degree of purity, von Humboldt computed the oxygen 

 content of the air in several cities as follows: 



per cent 



Vienna 26.1 



Gottingen 26.6 



London 26.9 



Florence 25.3 



Delft 27.0 



