THE MEMBRANES. 83 



The improvement in the method which followed the replacement of 

 the potassium salt by lithium sulphate was very striking. A 0.005 nor- 

 mal solution was employed. The cell is nearly filled with the solution 

 and immersed in the same to the lower limit of the glazed portion. The 

 electrodes are of platinum and the one within the cell is made the 

 cathode. Provision is made for the automatic removal of the water 

 which is drawn into the cell through the pores. At intervals the elec- 

 trolysis is interrupted for the purpose of mixing the liquid which has 

 been removed by the siphon with the solution in the outer vessel. 

 When it is thought that all the air has been expelled from the pores, the 

 cell is taken out, emptied, and rinsed with pure water; it is then soaked 

 for a time in distilled water, which is frequently renewed; lastly, it is 

 filled with, and partially immersed in, pure water, and the electrolysis is 

 resumed. When the conductivity, after frequent renewals of the water, 

 has fallen nearly to that which is normal for the distilled water, the cell 

 is ready for the deposition of the membrane. If the membrane is not to 

 be deposited immediately, the cell is placed, and kept until needed, in 

 water in which a little thymol or formaldehyde has been dissolved. The 

 reason for this precaution will appear later when the subject of the infec- 

 tion of the membrane is taken up. It is also well to take any other pre- 

 cautions against infection which suggest themselves, such as boiling all 

 the water which comes in contact with the cells, covering the vessels in 

 which they are kept, etc. Such precautions are by no means superfluous. 



The arrangement for the deposition of the membrane is as follows: 

 the anode, which consists of a cylinder of copper, nickel, or cobalt, 

 according to the composition of the membrane to be deposited, is placed 

 in an empty glass vessel, and within the cylinder is placed the cell, 

 which is closed by a rubber stopper carrying (1) the cathode, a platinum 

 cylinder; (2) a funnel with a stem nearly long enough to reach the bottom 

 of the cell; and (3) an overflow tube. The circuit is closed, and, as 

 nearly simultaneously as possible, the cell and the vessel outside of it 

 are filled, each with its appropriate solution. The solutions, which in 

 the majority of the experiments to be reported are potassium or lithium 

 ferrocyanide, and copper or nickel sulphate, are made one-tenth normal. 

 The voltage employed is 1 10. At first the resistance is very high, owing 

 to the fact that the cell wall is filled with nearly pure water. Very soon, 

 however, the current begins to increase, and within a short time it 

 attains a maximum. It then drops steadily for two or three hours, and 

 perhaps longer, when it reaches a minimum corresponding to the maxi- 

 mum resistance of the membrane which it is possible to obtain at that 

 "running." If the electrolysis is continued very long after the current 

 has reached a minimum, the resistance begins to fall again, and the 

 decline persists until the circuit is broken. This strange behavior of 

 the membrane appears to have some connection with an accumulation 

 of alkali in the cell and perhaps in the membrane itself; accordingly, 



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