PROCEEDINGS OF SECTION B. 213 
ITV. Arrempts to MEASURE THE VELOCITY OF THE HYDROGEN 
Ton, AND THE REALISATION OF THE EXTREME CASE OF THE 
Hi?TvToRFIAN PRINCIPLE. 
A practical difficulty is met with in any attempt to apply the 
method already described to the case of the hydrogen or 
hydroxyl icn, for even strong jellies tend to liquefy in the pres- 
sure of an acid or an alkali. Sulphuric acid is not so bad in 
this respect as hydrochloric or nitric. A trial was therefore made 
with a (roughly) half-normal sulphuric acid jelly, kept at a low 
temperature, the conditions being otherwise the same as in the 
experiments with the chlorides and sulphates of the alkali 
metals. It was found that the migration towards the cathode 
was at first nearly five times as fast as that towards the anode, 
which accorded well with the ratio indicated by Hittorf’s and 
Kohlrausch’s results; but the apparent relative speed of the 
hydrogen diminished as the experiment proceeded. It is pos- 
sible that this unusual deviation from constancy is due to the 
fact, which is pretty well established by conductivity data, that 
sulphuric acid solutions contain not only H and SO, ions but also 
H SO,. To such a mixture the method would probably not apply, 
as H SO, and SO, would have unequal velocities, and the com- 
position of the jelly would not remain constant. 
To use hydrochloric acid and still work with a solid jelly is 
impossible unless the concentration of the acid be low. About 
one-tenth normal suffices; but then two new difficulties arise. 
The first is the faint colour of the copper indicator, which enters 
the tube in very small concentration; but this is obviated by 
using a tube of larger bore so as to render the colour more easily 
seen. The second and more serious difficulty arises from the 
presence of electrolytic impurities in the best gelatine, the quan- 
tity of which is by no means negligible when that of the added 
electrolyte is so small. The only way to overcome this difficulty 
is to remove the impurity by special treatment. It consists 
essentially of calcium phosphate. The method of purification 
adopted was to soak thin sheets of the gelatine for twenty-four 
hours in deci-normal H Cl, and then let them wash by dialysis in 
distilled water for several days, the water being changed about 
twice daily. After the acid bath the gelatine swells in water to 
about thirty times its own bulk (about four times as much as 
the same gelatine without the acid treatment), but it does not 
liquefy in the cold. The whole of the lime and phosphoric acid is 
removed by the first two or three washings, but it appears im- 
possible to remove the whole of the hydrochloric acid. For the 
present purpose, however, it was not necessary to do so. After the 
eleventh wash the gelatine was melted and proved to contain 
H Cl to the amount of about e Some of this was used for 
experiment as it was, while some was rapidly concentrated till it 
