232 



PRINCIPLES OF CIIE3IISTKY 



an equal volume of dry hydrogen is passed into the eudiometer, and the 

 volume again determined. The mixture is then exploded, as was 

 described in the determination of the composition of water. The 

 remaining volume of the gaseous mixture is again measured ; it will be 

 less than the second of the previously measured volumes. Out of three 

 volumes which have disappeared, one appertains to the oxygen and two 

 to the hydrogen, consequently one-third of the loss of volume indicates 

 the amount of oxygen held in the air. 21 



The most accurate method for the analysis of air, and one which is 

 accompanied by the least amount of error, consists in the direct weigh- 

 ing, as far as is possible, of the oxygen, nitrogen, water, and carbonic 



FIG. 38. Dumas and Bousingault's apparatus for the analysis of air bv weight. The globe B contains 

 10-15 litres. The air is first pumped out of it, and it lg weighed empty. The tube T connected 

 with it is filled with copper, and is weighed empty. It is heated in a charcoal furnace. \Vhen the 

 copper has become red-hot, the stop-cock r (near R) is slightly opened, and the air passes through 

 the vessels L, containing a solution of potash ; /, containing solutions and pieces of caustic 

 potash, which remove the carbonic anhydride from the air, and then through o and t, containing 

 sulphuric acid (which has been previously boiled to expel dissolved air) and pumice-stone, which 

 removes the moisture from the air. The pure air then gives up its oxygen to the copper in T. 

 When the air passes into T the stop-cock It of the globe B is opened, and it becomes rilled with 

 nitrogen. When the air ceases to flow in, the stop-cocks are closed, and the globe B and tube 

 T weighed. The nitrogen is then pumped out of the tube, and it is weighed again. The increase 

 in weight of the tube shows the amount of oxygen, and the difference of the second and 

 third weighings of the tuba, with the increase in "weight of the globe, gives the weight of the 

 nitrogen. 



anhydride contained in air. For this purpose, the air is first passed 

 through an apparatus for retaining the moisture and carbonic an- 

 hydride (which will be considered presently), and is then led through 



21 Details of eudiometrical analysis must, as was pointed out in Chap. III. note 82, 

 be looked for in works on analytical chemistry. The same must be remarked in reference 

 to the other analytical methods mentioned in this work. They are only described for the 

 sake of showing the diversity of the methods of chemical research. 



