 —— 
ON ELECTROLYSIS. 769 
It may be difficult to maintain perfect homogeneity if change of tem- 
perature be attempted, else, of course, warming a liquid ought, on this 
second hypothesis, to make it less transparent.! 
On the first hypothesis it is possible that exceedingly intense radia- 
tion might develop an opacity in liquids quite transparent to ordinary 
light. 
5. Under what circumstances is solid matter deposited in the Path 
of a Current ? 
It is known, from the experiments of Davy and others, that if at the 
junction of two liquids the opposite ions can form an insoluble compound, 
then such insoluble compound is formed, those ions drop out of action, 
and others have to convey the current. For instance, if a current be sent 
from a vessel containing a barium salt to another containing a sulphate, 
_ through an intermediate vessel containing, say, dilute HCl, then BaSO, 
is precipitated in this vessel. I propose to make this intermediate vessel 
in the form of a tube, and examine whereabouts this formation of BaSO, 
first appears; varying intensity of current, density of solutions, &c.; and 
other similar experiments. (See Question 7.) 
Sir Wm. Thomson, at the meeting, made some important observations 
about deposits of solids in general, and about the possibility of a long- 
established current producing solid concretions of a nature not naturally 
to be expected. As, for instance, nodules of copper in the sawdust of 
a Menotti cell, possible accretions in the joints of animals, &c. 
Some porous substance seems most likely, according to present obser- 
vations, to have such crystals and nodules formed in it ; and steady currents 
might be kept up through porous or cracked crockery, or sawdust, or 
sand, and secular observations made on the subject. 
It is not easy to see why deposits of this latter kind should appear, 
except by reason of the surface action known as capillary H.M.F. and 
by some interference with Faraday’s law; so that, for instance, the 
amount of copper going down current, and of SO, going up, should not 
be exactly equivalent, but a slight excess of copper be left, which has to 
drop out in mid-stream. 
If it is allowable thus to regard some deposits as isolated ions, their 
study becomes of considerable interest. 
6. Is it possible for opposite corresponding Ions to travel at different rates ? 
The notion of different speed for different ions is founded upon the 
facts of ‘ migration,’ but if it can be shown that migration phenomena 
ean be accounted for in another and simple manner, all necessity for 
the hypothesis breaks down. 
There only remains the fact that some solutions conduct better than 
others; and this may be accounted for, either by greater speed of their 
ions, or by a greater number of dissociated atoms able to take part in the 
conveyance of electricity. It affords no answer to the question as to 
whether the opposite radicles travel at the same or at different rates. 
In favour of Kohlrausch’s and the customary migration theory, it may 
be truly urged that it is reasonable to suppose that each ion should have 
1 Tt is here assumed that better conduction means more dissociation ; this is not 
at all certain, it may mean less viscosity ; and it apparently does mean this, for the 
case of rising temperature, though not for the case of increased complexity of con- 
stitution. 
1885. 3D 
