vii THE BURNING OF INFLAMMABLE AIR .125 



They found the ratio : 



oxygen : hydrogen 88 '9 : 1 1 ' i 

 = 8-01: 1 



This experiment was repeated on a very large scale by 

 the French chemist Jean Baptiste Dumas (1800-1884) in 

 1842 ( " Researches on the Composition of Water," 

 Ann. de Chimie, 1843, 8,189-207). In Dumas' experiments 

 (Fig. 28), the hydrogen, prepared by the action of zinc on dilute 

 oil of vitriol, was purified and dried by passing through seven 

 U -tubes, each a metre in height ; the purifying agents were 

 (i) lead nitrate solution to remove sulphuretted hydrogen, (2) 

 silver sulphate solution to remove arseniuretted hydrogen, 

 (3) potash (three tubes) to remove acid vapours. The dry- 

 ing agent was (4) sulphuric acid cooled in ice, or phosphoric 

 anhydride (two tubes). The purifying agents were distributed 

 over broken glass or pumice in order to secure proper con- 

 tact with the gas. After the purification no odour could be 

 detected even when a hundred litres of the gas were allowed 

 to escape into the air. 



The copper oxide was contained in a large bulb of hard 

 glass provided with a beak a metre long to condense the 

 water formed on reduction. The bulb was weighed, after 

 removing the air by means of a pump. Before heating, the 

 air in the apparatus was displaced by hydrogen, but a cor- 

 rection was needed for the fact that the sulphuric acid used 

 in making the gas contained a little oxygen, which con- 

 tributed something to the weight of water produced. 1 

 During the reduction, which occupied 10 to 12 hours, 

 the bulb was heated by a large spirit lamp. After 

 allowing the copper to cool, the hydrogen in the apparatus 

 was displaced by air; the bulb was again exhausted by 

 means of a pump and the loss of weight was determined by 

 a second weighing of the bulb. 



1 In later experiments this was got rid of by passing the gas over hot 

 copper before drying it. 



