488 
THE EARL OF BERKELEY AND MR. E. G. J. HARTLEY ON THE 
entries really belonged to tube N—the record was unfortunately mixed up with that 
of other tubes; the numbers give, however, the usual course of events. The third 
column states the temperature at which the tube was remade. 
The fourth column gives the turning point, obtained shortly after “ remaking,” when 
using a solution of 660 grammes of cane sugar in the litre, and the fifth column gives 
the temperature at which this was determined. 
Out of some 100 tubes of various makes only two reached the state of efficiency 
shown by N, although over 400 electrolyses were made. Some of the tubes could be 
discarded immediately after first depositing the membrane upon them ; others could 
never be made to reach a resistance of even 50,000 ohms, while a small percentage 
always allowed a fairly large amount of sugar solution to pass through them when 
tested in the osmotic apparatus, although their resistances appeared to be high enough. 
In the course of the experiments it was found that better results were obtained 
if the membranes were electrolytically remade after every osmotic pressure 
determination, and also that, for observations at 0° C., to which this communication 
is restricted, it was best to remake the membrane at 0° C., and to keep the tubes in 
water surrounded by ice during the time elapsing between “remaking” and setting 
up for an experiment. 
Remaking the Membranes under Pressure. 
All the tubes (except N) which, judging by their resistances, seemed promising, 
were also remade electrolytically under pressure. The object aimed at was to break 
down the weak places in the membrane while the current was passing, so that any 
small holes would be filled up at once by the interaction of the copper and ferrocyanide 
ions. It is probable that the pressure alone causes a considerable part of the 
improvement by forcing the membrane into the pores of the porcelain. It will have 
been noticed that in the previous table the resistance of N on December 10, 1905, 
suddenly rose from 65,000 ohms to 300,000 ohms; this may be due to either of the 
two changes in the conditions, i.e., to having previously been subjected to pressure, or 
to the change in the temperature at which the membrane was remade; we have 
found that both causes improve the membranes. 
The apparatus for remaking the membranes under pressure is shown in Diagram 3. 
AB is a strong wrought-iron cylinder* which can be connected to the U tube 
mentioned on page 485 by means of the steel pressure tubing C. The apparatus is 
filled with a strong solution of cane sugar,! in which the usual quantity of potassium 
ferrocyanide has been dissolved; the equilibrium pressure of the solution should be about 
130 atmospheres. The porcelain tube, M, filled with the copper sulphate solution, 
* It is capped by a lead washer, as indicated in the diagram. 
t The object of the sugar solution was (1) to preserve such parts of the membrane as were already good 
by preventing a great flow of water through them, (2) to prevent, by its great viscosity, the alkali, which 
is found at the walls of the cylinder, from reaching the membrane. 
