History of Air-Analysis 7 



5 to 20, the quantity of vital air was 24 to 27 per cent; on November 20 

 30 per cent, and on November 21, 24 per cent. During December the 

 quantity of vital air was constantly between 24 and 27 per cent. 



Scheele's investigation slowly but surely claimed the attention of 

 scientists in other countries. In this connection it is of interest to quote 

 the words of Dr. Joseph Black: 1 



But Scheele was the first person who, from a number of ingeniously contrived ex- 

 periments, concluded by very fair reasoning that atmospherical air is a mixed fluid 

 composed of about two parts of azotic gas, and one part of vital air or oxygen gas, along 

 with a very small admixture of carbonic acid. 



The ingenuity and industry of this great Swede may properly be con- 

 sidered as having started the investigation of the composition of the air 

 an investigation that has had almost the continuous attention of chemists 

 for over 130 years. 



THE NITRIC-OXIDE EUDIOMETER. 



Contemporaneously with Scheele, Priestley in England published sev- 

 eral volumes of his "Observations on Air." In 1772 Priestley observed 

 that when nitric oxide, prepared a number of years before by Stephen 

 Hales, was added to common air confined in a vessel over water, a diminu- 

 tion in volume resulted. Experimenting in this way, Priestley showed 

 that about one-fifth of the air combined with the nitric oxide and was ab- 

 sorbed by the water. 2 



Priestley's discovery of oxygen, which he found by heating the red ox- 

 ide of mercury, was made on August 1, 1774. He was so wedded to the 

 phlogiston theory, however, that he could only consider this oxygen as 

 dephlogisticated air; hence its elemental nature was never admitted by 

 him. This discovery was shortly followed by researches on the relation- 

 ship between oxygen and the vital processes. It was early believed that 

 the vital processes were more active in oxygen-rich air than in air that was 

 deficient in oxygen; this stimulated innumerable investigations of the 

 purity or salubrity of the air, chiefly by means of the simple nitric-oxide 

 reaction of Priestley. The attempts to measure quantitatively the oxy- 

 gen in the air early led to the development of special forms of apparatus 

 for these measurements ; as a matter of fact so extensively was the nitric- 

 oxide test employed for studying the oxygen content of air, and so univer- 

 sal was the belief that the larger the amount of oxygen in the air the better 

 was the air, that the instrument was actually designated an eudiometer, 

 i.e., a measurer of the goodness or salubrity of the air. As the dephlogisti- 

 cated air supported respiration and combustion much better than ordi- 

 nary air, it was natural to ascribe the healthfulness of the latter to the 

 amount of dephlogisticated air present in it. 



1 Black, Lectures on the elements of chemistry, 1st Am. ed. from the last London ed., 

 1806, 2, p. 344. See also Scheele, Efterlemnade bref och anteckningar, edited by A. E. 

 Nordenskiold, Stockholm, 1892, p. 78. 



* Priestley, Experiments and observations on different kinds of air, 1775, 1, p. 111. 



