4 Composition of the Atmosphere 



of air is well worth undertaking. But such a study, especially the study 

 of the oxygen content of the air, has a still higher value in its relation to 

 human life. No one chemical element enters so extensively into vital 

 processes as does oxygen. The human body may live without food for 

 many weeks; it may live without water for several days; but without air 

 or oxygen it can live for only a very few minutes. Not only is oxygen es- 

 sential to life, but the purity of the air is of fundamental hygienic impor- 

 tance. That this fact has been recognized is evidenced by the emphasis 

 recently laid upon the necessity of an outdoor existence in combating tu- 

 berculosis. Furthermore, a knowledge of the composition of the air is 

 necessary for the solution of the important problems of the ventilation of 

 houses, mines, rapid-transit subways, and railroad tunnels. Of still more 

 special significance, and with a more intimate bearing upon problems in 

 physiology, is the fact that the determination of the oxygen consumption 

 of man and important quantitative determinations in respiration experi- 

 ments depend usually upon an exact knowledge of the composition of the 

 air taken into the lungs. It is peculiarly fitting, therefore, that a study 

 of this subject should be made a part of the scheme of research carried out 

 in the Nutrition Laboratory. 



The two forms of gas-analysis apparatus conceded by all experimenters 

 to give the most exact results are the apparatus of Haldane in England 

 and that of Sonden and Pettersson in Stockholm. Several forms of the 

 Haldane apparatus are in the possession of the Nutrition Laboratory, and 

 also a Sonden apparatus specially designed for the determination of carbon 

 dioxide and oxygen in the air of the respiration chamber. This latter 

 apparatus was devised by Dr. Sonden after a conference with the author 

 in Stockholm four years ago, in which the various difficulties in the way of 

 exact gas-analysis were carefully considered. With this apparatus the 

 Nutrition Laboratory found itself in a position to carry out a more com- 

 plete study of the percentage of oxygen in outdoor air than had hitherto 

 been made. The ingenuity of Dr. Sonden and the technical skill of 

 Miss Alice Johnson, of the laboratory staff, made such a study of atmos- 

 pheric oxygen possible. 



EARLY INVESTIGATIONS ON THE COMPOSITION OF AIR. 



Although much has been written in recent years regarding the chemi- 

 cal composition of the atmosphere, there exists nowhere, at least in Eng- 

 lish, an historical account of the development of knowledge regarding the 

 percentage of oxygen in the air; it is therefore deemed fitting to collect 

 in this memoir the widely scattered records of the development of this 

 most interesting subject. 



The tenacity with which the belief in the elemental nature of air was 

 held is well exemplified by the fact that not until the latter part of the 

 eighteenth century did scientists begin to appreciate the fact that air con- 

 sisted of two or more gases. This recognition of the composition of air 



