Mr. Grove on the Decomposition of Water by Heat. 25 



the hydrogen was obtained was carefully purged of air by 

 boiling and the air-pump, but yet there was a notable con- 

 traction-even when the water had been freed from air to the 

 utmost practicable extent. In the numerous experiments 

 which I made on this subject, the contraction varied from the 

 y\jth to the 7\jth of the whole volume. 



After many fruitless experiments I traced it to a small 

 quantity of oxygen which I found hydrogen to contain under 

 all circumstances in which I examined it. Phosphorus placed 

 in hydrogen, obtained with the utmost care, gives fumes of 

 phosphorous acid, shines in the dark and produces a slight 

 contraction, but there is after this a further contraction by the 

 use of the ignited wire. 



I may cite the following as an easy experiment and simple 

 illustration of the rapidity with which hydrogen appropriates 

 oxygen. Let hydrogen be collected over water well-purged 

 of air; let a piece of phosphorus remain in it until all com- 

 bustion has ceased, the hydrogen will then be full of phos- 

 phoric vapour ; fill another tube with water, and pass the 

 hydrogen rapidly into it, the second tube will instantly be 

 filled with a dense white fume of phosphorous acid ; the hy- 

 drogen having instantly carried with it oxygen from the stra- 

 tum of waier it has passed. 



A very careful experiment was made as follows : — distilled 

 water was boiled for several hours, to this was added one- 

 fortieth part by measure of pure sulphuric acid, and it was 

 cooled under the receiver of an air-pump ; it was now placed 

 in two test-glasses, connected by a narrow inverted tube, full 

 of the same liquid: platinum electrodes were placed in each 

 glass, and the hydrogen caused to ascend immediately into the 

 eudiometer tubes ; the whole was completed within two or 

 three minutes after the water had been removed from the air- 

 pump. Here the ordinary sources of impurity in hydrogen 

 were avoided ; no zinc was used, the sulphuric acid was pure, 

 and the quantity was so small, that, had it not been pure, the 

 error could have been but very trifling. The hydrogen so 

 obtained, contracted in volume ^-^ih ; hydrogen prepared in 

 the same way, and exposed to phosphorus, gave dense white 

 fumes; the phosphorus was luminous in the dark for more 

 than an hour, and the contraction (temperature and pressure 

 being carefully examined) was g\jth ; the amount of contrac- 

 tion by the wire would of course equal three times the volume 

 of oxygen mixed with the hydrogen, consequently the oxygen 

 would be y^jth of the whole volume; the platinum wire induces 

 therefore a greater absorption of oxygen than the phosphorus, 

 unless the volume of hydrogen is increased by the phosphoric 



