252 



Dr. W. M. Bayliss. 



[June 30, 



experiments with benzo-purpurin, "conductivity" water being outside and 

 frequently changed before these readings were taken : — 



Date. 





Date. 





1910. 





1910. 





May 25 



49 



May 31 



49 



„ 27 



49 





48 



„ 30 



48-5 



„ 6 



48 





In all 



288 hours. 





The effect of carbon dioxide was described in my former paper. In order 

 to discover how this effect is produced I have made further experiments as 

 follows : — 



A solution of Congo red was placed in an osmometer of Graham's pattern 

 and carbon dioxide passed for some time through the outer water. It was 

 found that the dye became purple-brown in colour and for the most part 

 precipitated. The outer water on evaporation to dryness deposited crystals 

 of sodium carbonate. The explanation of this fact is clearly that when H" 

 ions are present in the outer fluid there is no hindrance to the free inter- 

 change between these and Na* ions through the membrane. Accordingly the 

 latter pass out and combine with C0 3 ' ions when the solution is concentrated 

 by evaporation. The hydrogen ions entering the dye solution cause 

 aggregation of the acid salt formed. 



Graham* noticed that if he placed within a dialyser a solution of the 

 sodium salt of albumen, the whole of the sodium was ultimately found in the 

 outer water in combination with carbon dioxide derived from the air. I find 

 that a similar loss of sodium occurs with the sodium salt of caseinogen. 



Biltz and v. Vegesackf state that solutions of Congo red through which 

 carbon dioxide has been passed recover their original- state when boiled, even 

 supposing that they have been dialysed. I find that this statement is correct 

 for non-dialysed solutions ; as the carbon dioxide is driven off, the dye acid 

 displaces more of it from the sodium carbonate and enters itself into com- 

 bination with the sodium. If the solution has been dialysed after subjection 

 to the action of carbon dioxide, so that the sodium carbonate has been 

 removed, I find it impossible to regenerate the dye by boiling, provided that 

 this be done in a quartz flask fitted with a reflux condenser also of quartz. 

 The corresponding experiment of Biltz and v. Vegesack; was made with a 



* 'Phil. Trans.,' 1861, vol. 151, p. 217. 



+ ' Zeits. f. physik. Chem.,' 1910, vol. 73, p. 487. 



f ' Zeits. f. physik. Chem.,' 1910, vol. 73, p. 488. 



