ON THE HALOGEN HYDRIDES AS CONDUCTING SOLVENTS. 143 



In order that the determination of acid by titration should be strictly comparable 

 with the weighing of the solution, the alkali was standardised by direct comparison 

 with about 60 grammes of pure hydrogen bromide which was weighed in the absorber. 

 Duplicate standardisations of the same alkali solution gave the following figures for 

 the amount of hydrobromic acid equivalent to 1 gramme of alkali solution : 



(1) 1 gramme solution = 0'149293 HBr, 



(2) 1 0-149301 HBr. 



The Electrolysis. 



In designing an electrolytic cell it was necessary to consider the changes of density 

 which were brought about during electrolysis, and to construct an apparatus in which 

 the lighter solution would be formed at the top and the heavier at the bottom. 

 Preliminary experiments were undertaken to ascertain the influence of an increase in 

 concentration of the dissolved substance on the density of the solution, and it was 

 found that in all the cases examined the less concentrated solution was the heavier. 



The experiments which had been conducted to test FARADAY'S law having shown 

 that the bromine is carried to the anode, the apparatus was designed to enable the 

 cathode solution to be analysed. The anode solution was neglected, as its analysis 

 was complicated by the presence of bromine. 



The apparatus which has been employed is shown diagrammatically in fig. 5. It 

 consisted of a U-tube, both arms of which were provided with side tubes. The 

 anode a consisted of a platinum wire, which was sealed through the bottom of the 

 side tube 0, the other end of the wire projecting into the glass tube h, by means of 

 which connection with the battery could be made. A small side tube n was also 

 attached to the same arm of the U-tube, and there was a constriction at r into which 

 the hollow stopper s was ground to fit tightly. The stopper A- was sealed to a branch 

 of the transferrer T', and a hole was bored in its shoulder to allow the free passage of 

 liquid through the transferrer. 



It was found in the preliminary experiments that a considerable amount of mixing 

 was occasioned by the escape of hydrogen at the cathode, and in order to reduce 

 this to a minimum, the side tube P was attached to the apparatus. In the centre 

 of P a narrow tube u was fastened, inside which the cathode was placed, so that the 

 escaping bubbles of hydrogen were confined to this tube and very little mixing took 

 place outside P. A small hole had been blown in the wall of the tube u so that the 

 pressure should be equal at all parts of the surface of the liquid. The tube P was 

 made long enough to be held in the clamp outside the vacuum vessel in which the 

 apparatus was placed and its end was closed by a stopper w, through which passed 

 the platinum wire which was used as cathode. One end of the transferrer T was 

 made long enough and bent so as to reach to the bottom of the U-tube, and both the 



