History of Air-Analysis 67 



mechanical reasons, chiefly to the solubility of gases in water, the diffi- 

 culties of physical measurements, the lack of knowledge concerning the 

 physical properties of gases, the inadequate and incorrect calibrations of 

 the glassware then in use, improper temperature control, and the imperfect 

 preparation of the hydrogen these factors affecting more or less the accu- 

 racy of the data obtained with the earlier methods. 



As the more popular chemical processes for the determination of oxy- 

 gen in the air have varied materially the eudiometric method first 

 being used, then the gravimetric, and finally the eudiometric method 

 again similarly we find that the prevailing opinion has fluctuated with 

 regard to the constancy or lack of constancy in the composition of the 

 air. When the eudiometer was first used it was firmly believed that the 

 oxygen percentage varied enormously, and, indeed, that the salubrity of 

 any climate was directly proportional to the amount of oxygen present. 

 Just at this time Cavendish, although using an imperfect apparatus, 

 made a remarkable series of experiments, coming to the conclusion that 

 the composition of the air was constant; in other words, that there were 

 no fluctuations that were measurable on his instrument. 



Then followed the development of the law of gases and of union by 

 volume, with the measurement of the oxygen and nitrogen in the air as 

 approximately 1 to 4, which led to the belief that the air was a chemical 

 compound, having the formula N 4 0. This belief, however, was soon dis- 

 carded, inasmuch as it was found possible to separate the nitrogen and 

 oxygen by mere physical processes, particularly that of diffusion. Evi- 

 dence began to be accumulated to demonstrate that the percentage of 

 oxygen in the air was not sufficiently constant to justify the use of the 

 formula N 4 0; indeed, there appeared to be considerable variation in the 

 composition of the air. As experimental work progressed, however, the 

 variations began to grow less. In a long series of investigations, covering 

 50 years, no variations in the oxygen content greater than 0.15 per cent 

 were found, save in desultory observations made under conditions that 

 do not inspire the greatest degree of confidence. The only exception 

 was the interesting research in 1887 of von Jolly in Munich, who, by ab- 

 sorbing the oxygen in his copper eudiometer, found much greater varia- 

 tions than had formerly been obtained. Independently and simulta- 

 neously, but employing a somewhat different form of apparatus with the 

 highest grade of technique, Morley in Cleveland found similar results, 

 although the fluctuations were much smaller than those found by von 

 Jolly. Morley's experiments continued over a period of several years, 

 ultimately resulting in the belief that the oxygen content of the air was 

 affected by downward currents, particularly following a sudden drop in 

 temperature. The researches of Morley and von Jolly stimulated further 

 study and were followed by the cooperative investigations of Morley, 

 Kreusler, and Hempel, which showed that under proper control the 

 fluctuations formerly found in part disappeared. 



