276 



PROCEEDINGS OF THE AMERICAN ACADEMY. 



height. After the absorption of one of the components a lower pressure 

 is needed to effect the same adjustment. The loss of pressure gives the 

 means of computing the percentage composition of the gas. Of course 

 the tension of aqueous vapor should be subtracted from the total readings 

 since the gas is moist ; this important correction seems to have been over- 

 looked by Professors Hempel and Dennis in the second English edition, 

 although correctly stated in the first.* The tension of aqueous vapor does 

 not affect the change of pressure unless there is a change of temperature. 

 The following figures, of two trial analyses of air kindly made by Mr. 

 Edward Mallinckrodt, Jr., serve to illustrate the method. The minus 

 6ign before the second reading signifies that the counterpoise bulb was be- 

 low the other, almost as far as the level of the floor. 



At another time, Mr. W. N. Stull kindly made another test of the ap- 

 paratus, finding the following percentages of oxygen in the air of the 

 laboratory : — 



100 X 170.2 mm. 

 818.0 mm. 



20.80 



100 X 173.5 mm. 

 "83 1.8 mm. 



= 20-86; 



* See page 77 in edition of 1902, and page 69 in edition of 1892 (Macmillan). 



