487 
OSMOTIC PRESSURES OF SOME CONCENTRATED AQUEOUS SOLUTIONS. 
After this washing, any copper ferrocyanide which is only loosely adhering to the 
tubes, and not deposited in the pores, is rubbed off with pumice stone, and the tube is 
remade electrolytically. In general the resistance increases ; when steady, the tube is 
again washed, and the operation repeated after the lapse of a few days, and so on 
until there appears to be no further rise in the resistance. If the tube is a good one, 
the resistance should now be of the order of 50,000 ohms. 
It is then set up in the osmotic apparatus and tested with a solution of 
660 grammes of cane sugar in the litre—a solution whose equilibrium pressure is 
about 100 atmospheres ; the tube will probably give a turning point somewhat lower 
than this pressure, on account of a leak of solution through the membrane. The tube 
is then taken down, electrolytically remade, soaked in water for two or three days, 
and tested again with the cane sugar. It will be found that although there has been 
no apparent rise in the resistance, the turning-point pressure has perceptibly 
increased. The whole process is again repeated until a final steady value of the 
turning point is reached. A determination of the amount of sugar that has come 
through the membrane during an experiment will help to indicate whether the tube 
is likely to be of any use or not. 
The following table shows the progress of a certain tube which will be called N ; 
the membrane was originally deposited on it about March 8, 1904. 
Table I. 
Date. 
Resistance. 
March 11, 1904 
ohms 
2,700 
November 4, 1904 . . . 
29,000 
„ 15, 1904 . . 
38,000 
December 12, 1904 . . 
70,000 
August 11, 1905 .... 
September 21, 1905 . . . 
45,000 
60,000 
December 6, 1905 . . 
65,000 
„ 10, 1905 . . . 
300,000 
„ 13, 1905 . . . 
250,000 
„ 30, 1905 . . . 
250,000 
January 11, 1906. . . . 
200,000 
„ 22,1906. . . . 
270,000 
February 9, 1906 . . . 
200,000 
„ 25, 1906 . . . 
170,000 
March 6, 1906 .... 
170,000 
„ 10, 1906 .... 
170,000 
„ 14, 1906 .... 
170,000 
„ 24, 1906 .... 
170,000 
April 2,1906 . 
170,000 
„ 17,1906 . 
100,000 
„ 25,1906. 
100,000 
1 
Temperature. 
Turning point. 
Temperature. 
atmospheres 
Laboratory 
>5 
55 
— 
Laboratory 
55 
55 
55 
55 
55 
5) 
95-5 
55 
55 
55 
0° c. 
96-3 
0 ° c. 
0 
96-7 
0 
0 
99-4 
0 
0 
100-0 
0 
0 
100-0 
0 
0 
100-4 
0 
0 
0 
0 
These numbers refer to the re- 
0 
sistance of the tube when 
0 
“ remade ” aftei 
experiments 
0 
with other solutions. 
0 
0 
- 
The second column gives the resistances which the tube reached when remade—the 
order of number only is given ; they were measured by means of an ordinary Weston 
ammeter. It should be mentioned that we are not quite sure that the first four 
