electric discharge with the chloride op silver battery. 
97 
rapidly, and forms a star-like appearance on the positive disc ; when the point is 
negative, before the jump of the spark, a very pale glass-shade -like halo, of a 
saddened olive tint, extends from the point almost to the outer periphery of the disc. 
The arc in nitrogen is reddish-violet, the jump with 8040 cells being 0‘402 inch 
when the point is positive, and 0'272 inch when negative, or in the ratio of negative 
to positive of 0‘677. 
In oxygen the arc presents a similar appearance to that in air, the mean jump with 
8040 cells being 0'216 inch with the point positive, and the mean when negative 
0‘1 37 inch, the ratio of negative to positive being 0’634 to 1. The arc in carbonic 
anhydride is shown in 3, fig. 23. 
From the foregoing observations, it would appear that hydrogen in a residual vacuum, 
together with the employment of aluminium for terminals, present the most favourable 
conditions for the passage of the voltaic current. 
The spark with 8040 cells jumped O' 5 inch between two points placed vertically 
one over the other in a tube containing absolute alcohol, and provided with a vent to 
permit of the alcohol vapour escaping as soon as the arc is formed. Dr. Bleekrode, it 
Fig. 24. 
will be remembered, communicated to the Royal Society a paper { On Electrical 
Conductivity and Electrolysis in Chemical Compounds,’ * in which he gave an account 
of some experiments performed in our laboratory ; as we do not propose to enter 
into this subject already in the skilful hands of that able chemist and physicist, 
* Proc. Roj. Soc., Ho. 175, 1876. 
MDCCCLXXVIII. 
o 
