THK COMPOSITION ol- WATKK. HYDROGEN 115 



the closed end is entirely filled with water 4 acidified with sulphuric 

 acid, and another platinum wire, terminating in a plate, is immersed in 

 the open end. If a current from a galvanic battery be now passed 

 through the wires an evolution of gases will be observed, and the gas 

 which is obtained in the open branch mixes with the air, while that in 

 the closed branch accumulates above the water. As this gas accumu- 

 lates it displaces the water, which continues to descend in the closed 

 and ascend into the open branch of the tubes. When the water, in 

 this way, reaches the top of th'e open end, the passage of the current is 

 stopped, and the gas which was evolved from one of the electrodes only 

 is obtained in the apparatus. By this means it is easy to prove that a 

 particular gas appears at each electrode. If the closed end be con- 

 nected with the negative pole i.e., with that joined to the zinc then 

 the gas collected in the apparatus is capable of burning. This may be 

 demonstrated by the following experiment : The bent tube is taken 

 off the stand, and its open end stopped up with the thumb and inclined 

 in such a manner that the gas passes from the closed to the open end. 

 It will then be found, on applying a lighted lamp or taper, that the 

 gas burns. This combustible gas is hydrogen. If the same experiment 

 be carried on with a current passing in the opposite direction that is, 

 if the closed end be joined up with the positive pole (i.e., with the 

 carbon, copper, or platinum), then the gas which is evolved from it does 

 not burn of itself, but it supports combustion very vigorously, so that 

 in it a smouldering taper immediately bursts into flame. This gas, 

 which is collected on the anode or positive pole, is oxygen, which is 

 obtained, as we saw before (in the Introduction), from mercury oxide 

 and is contained in air. 



Thus in the decomposition of water oxygen appears at the positive 

 pole and hydrogen at the negative pole, so that detonating gas will be 

 a mixture of them both. Hydrogen burns in air from the fact that in 

 doing so it re-forms water, with the oxygen of the air. Detonating 

 gas explodes from the fact that the hydrogen burns in the oxygen 

 mixed with it. It is very easy to measure the relative quantities of one 

 Miid the other gas which are evolved in the decomposition of water. 

 For this purpose a funnel is taken, whose orifice is closed by a cork 

 through which two platinum wires pass. These wires are connected 

 with a battery. Acidified water is poured into the funnel, and a glass 

 cylinder full of water is placed over the end of each wire (fig. 18). 

 On passing a current, hydrogen and oxygen collect in these cylinders, 



4 In order to fill the tube with water, it is turned up, so that the closed end points 

 (1 >\v 11 wards and the open end upwards, and water acidified with sulphuric acid is poured 

 into it. 



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