48C Mr. TV. C. M. Lewis : Experimental Investigation 



An attempt was at once made to increase the adsorbing 

 area in order to get more trustworthy data. It was found, 

 however, that the limit had almost been reached in the case 

 o£ the second emulsion — only a little more than 2 c.c. of oil 

 can be emulsified by 500 c.c. of caffeine solution o£ O'l per 

 cent, concentration. The method is therefore limited in this 

 direction. A further attempt at more accurate measurement 

 was made by employing a pipette of much larger oil-capacity 

 (about 500 c.c). The drop-number against water was 2042, 

 in place of 146 in the case of the smaller pipette. The 

 drop-number against a solution of 0*1 per cent, concentra- 

 tion was 2383. One result was obtained in which the change 

 of concentration before and after emulsification amounted to 

 5 drops, which corresponded to 3'5 x 10 -8 grm./cm., but on 

 attempting to reproduce these values quite variable results 

 were obtained, owing to the change in wetting of the pipette 

 during the long course (over two hours) of a single deter- 

 mination. 



It appears probable from the foregoing attempts to measure 

 r in the case of caffeine, that we are dealing with a quantity 

 too small to be determined with accuracy by the method 

 hitherto pursued. It may be possible by employing, for 

 example, colloidal mercury instead of the oil to determine 

 the caffeine adsorption at a mercury surface with accuracy. 



Behaviour of Sodium Glycocholate and Caffeine in contact 

 with Charcoal. 

 In view of the considerable difference between tlie values for tlie 

 adsorption of these two substances at the oil-surface, it was of interest to 

 compare the results obtained with charcoal. The material was the same 

 as that employed by Freundlich — namely, Merck's blood-charcoal 

 purified by acid. Freundlich has observed that the further washing- of 

 this material does not affect the result of the adsorption determinations, 

 and this was confirmed in the present instance by the fact that there was 

 not the slightest change in the oil-water tension in the case of distilled 

 water which had been shaken up with a quantity of charcoal. 



Adsorption of Sodium Glycocholate : — 



500 c.c. of a solution 03 per cent, concentration were treated with one 

 gram of charcoal, and the decrease in bulk-concentration of the solute 

 amounted to # 125 per cent. The change in concentration was measured 

 by means of the change in value of the oil-solution tension as given by 

 the drop-pipette. The drop-difference (before and after) was 47. 



Hence 1 gram charcoal adsorbs from a 0*3 per cent, solution 

 0*625 gram sodium glycocholate. 



Adsorption of Caffeine : — ■ 



500 c.c. of solution 0*218 per cent, concentration (i. e., approximately 

 equimolar with the sodium glycocholate solution) brought into contact 

 with one gram of charcoal gives a drop-difference of 10, which corre- 

 sponds on the caffeine curve to a change in concentration of 0"108 per 

 cent. 



