178 BIO-CHEMICAL JOURNAL 



solution is more easily worked with. For the same reasons, the filter- 

 paper used was Schleicher and Sch (ill's analytical paper, and of this a 

 disc 12-5 cm. diameter was added to each of the above flasks. After 

 24 hours standing the depth of colour in each solution was determined 

 by Gallenkamp-Heele's colorimeter, the results being as follows : 



Concentration of Proportion of dye Proportion of dye 



solution in solution in paper 



0-014 40% 60% 



C-OI2 20% 80% 



o-oio 9-3% 907% 



0-008 4 % 96 % 



0-006 1-3% 98-7% 



0-004 trace practically all 



0-002 



The figures show at once that the amount of dye taken out of 

 solution by the paper is not directly proportional to the concentration 

 of the solution ; nor, on the other hand, is it independent of this 

 concentration as would be the case if a true chemical compound were 

 formed. In fact, from a 0-014 per cent, solution -^- x ^ = 0-0028 



105 1 



gram is taken up by a certain amount of paper, whereas from a O'OoS 

 per cent, solution only - x '^ = 0*00028 gram, or one-tenth of the 

 former, is taken up by the same amount of paper, although there was 

 still a quantity of free congo-red in the solution. The peculiarity 

 of these phenomena, which I have spoken of above as f the law of 

 adsorption,' is well shown by the series of numbers in the third 

 column. 



Now, if we put these data into the form of a curve as is done in 

 Fig. i, where the ordinates represent the percentage of dye left in solu- 

 tion and the abscissae the original concentration of the solution, we see 

 that the curve forms part of a hyperbola, and only approaches the axis 

 (/.<?., zero concentration) asymptotically. 1 In other words, however 

 diluted the original solution may be, there will practically be always a 

 certain amount of the dye left unadsorbed by the paper. It follows 



I. This hyperbolic form of the curve is pointed out by Ostwald, sillgcmcin. Chanic., Bti. I, 

 p. 1,096. 



Walker and Appleyard (Jour. Chem. Soc., 69, 1896), p. 1334, also rind a logarithmic formula for the 

 adsorption of picric acid by silk. 



