OXYGEN. 9 



position of n'ater is readily calculated. Dulong and Berzelius made but 

 three experiments, with the following results for the percentages of 

 oxygen and h3'drogen in water : 



O. H. 



88.942 11.058 



88.809 1 1. 191 



88.954 11.046 



From these figures we get, for the atomic weight of oxygen, the values — 



16.124 

 15.863 

 16.106 



Mean, 16.031, =iz .057. 



As the weighings were not reduced to a vacuum, this correction was 

 afterwards applied by Clark,* who showed that these syntheses really 

 make = 15.894 ; or, in Berzelian terms, if = 100, H = 12.583. The 

 value 15.894, ± .057 we may therefore take as the true result of Dulong 

 and Berzelius' experiments, a result curiously close to that reached in 

 the latest and best researches. 



In- 1842 Dumas t published his elaborate investigation upon the com- 

 position of water. The first point was to get pure h3^drogen. This gas, 

 evolved from zinc and sulphuric acid, might contain oxides of nitrogen^ 

 sulphur dioxide, h3^drosulphuric acid, and arsenic hydride. These im- 

 purities were removed in a series of wash bottles ; the HjS by a solution 

 of lead nitrate, the H.^As by silver sulphate, and the others by caustic 

 potash. Finally, the gas was dried by passing through sulphuric acid, 

 or, in some of the experiments, over phosphorus pentoxide. The copper 

 oxide was thoroughly dried, and the bulb containing it was weighed. 

 By a current of dr}^ hydrogen all the air was expelled from the apparatus, 

 and then, for ten or twelve hours, the oxide of copper was heated to dull 

 redness in a constant stream of the gas. The reduced copper was allowed 

 to cool in an atmosphere of hydrogen. The weighings were made with 

 the bulbs exhausted of air. Tlie following table gives the results : 



Column A coiltains the symbol of the drying substance ; B gives the 

 weight of the bulb and copper oxide ; C, the weight of bulb and reduced 

 copper ; D, the weight of the vessel used for collecting the water ; E, the 

 same, plus the water ; F, the weight of oxygen ; G, the weight of water 

 formed ; H, the crude equivalent of H when = 10,000 ; I, the equiva- 

 lent of H, corrected for the air contained in the sulphuric acid employed. 

 This correction is not explained, and seems to be questionable. 



* Philosophical Magazine, 3d series, 20, 341. 

 tCorapt. Rend., 14, 537. 



