Mr Barlow, On the Osmotic Pressure of Aqueous Solutions. 233 



pressure set up when the cell is closed. Taking this difference to 

 be 6*4 mm. as at the beginning, the osmotic pressure is 



31 - 6-4 = 246 mm. 

 No correction is needed for any capillary depression in the narrow 

 tube, as this will affect both open and closed levels to the same 

 extent. 



The theoretical pressure, assuming the gas laws to hold, is 

 207 mm. at 10° C. 



Hence 1=^-^=1-188, 



207 

 i-\ 



a = 



(for three ions) 



2 



= -094, 

 or 9*4 °/ o of the salt is dissociated. 



Jones*, from freezing-point measurements, finds for a "001 

 normal solution of potassium sulphate that a = about -94. 



In this experiment the cell may safely be regarded as clean ; 

 the result is thus interesting as showing that dissociation can be 

 detected in a direct way, though no satisfactory measure of it can 

 be looked for. 



(2) Cell e. After the last experiment the cell was washing for 

 four days in changes of distilled water. 



On Monday, Feb. 29, it was used with -00094 N . K 2 S0 4 solution. 

 Theoretical osmotic pressure = 16 mm. at 0° C. 



Time 



Gauge levels 



Temperature 

 (degrees C.) 



narrow- 

 limb 



wide-limb 



Monday, Feb. 29 



Tuesday 



Thursday 



Friday, Mar. 4. Pressure added 



Friday, Mar. 11 



Wednesday 



(open 

 ! 273 

 j closed 

 I 277 



277 



280 



292-2 



280 



280 



267 



266-1 



266 

 264 

 266 

 265-6 



9 



8 



The osmotic pressure set up seems to be 14 — 6 = 8 mm. at 9° C., 

 the steady value for the last five days of the experiment. This is 

 only half the theoretical value at 0° C. 



* Phil. Mag., Vol. XXXVI. p. 472. 



16—3 



