240 



Dr. W. M. Bayliss. 



[June 30, 



on the lines of these facts ; the data at present available seem scarcely 

 sufficient. 



Why the osmotic pressure is a linear function of the molar concentration, 

 although the dye is dissociated and all the ions are osmotically active, it is 

 impossible to explain. It can only be suggested that the dissociation is not 

 normal, but that complex ions are formed. Whether these are of the 

 nature of chemical compounds, like the ferrocyanic ion, or whether they are 

 associations similar to those of colloidal solutions, requires further investigation 

 to decide. 



Electrolysis of Congo Red. 



It was hoped that some light might be thrown on the nature of the 

 ionisation of the dye by electrolysis of its solutions. 



When the experiment is made in a U-tube containing the dye solution at 

 the bend and above it, in both limbs, distilled water, and a current passed 

 through platinum electrodes immersed in the water, the phenomena are 

 complex and difficult to interpret. In the cathodic limb the boundary 

 surface remains sharp, but a second sharp meniscus travels slowly towards 

 the anode, so that behind it on the cathodic side the solution is pale red and 

 in front of it deep red. The water on this side remains colourless. In the 

 anodic limb there is also a sharp meniscus separating a lower deep red 

 solution from a paler one above, but there is no definite boundary between 

 this pale solution and the water above it. From the upper part of this 

 indefinite boundary pale pink streamers pass through the water to the 

 anode. When they reach this they become blue. I am inclined to regard 

 these streamers as dissociated anions ; when discharged at the anode the blue 

 insoluble free acid is formed. I am unable to express an opinion as to 

 whether the existence of a pale red instead of a colourless solution area 

 travelling from the cathode means that Na" ions were not present. 



Other experiments were made by arranging three flasks in series, connected 

 by glass syphon tubes and provided with platinum electrodes in the two end 

 flasks. A current of about 2 milliamperes was passed for five days, by which 

 time it was calculated that sufficient current had passed to decompose the 

 whole of the salt present. The amounts of dye-acid and of sodium were then 

 estimated in the anodic and cathodic flasks, the sodium by the usual 

 method of conversion to sulphate and the former by subtracting the sodium 

 values from the total solids. It was found that the proportion of Na' to 

 anion in the positive flask was 1 to 1*9, and in the negative flask 4 to 1. If 

 the proportion in the former had been 1 to 1, the dissociation equation 

 might be 



3(S)Na 2 ^ Na 2 (S)" + (S)Na 4 " ', 



