RECORD^ OF MEETINGS 253 



absorption of cobalt salts by pure chromium oxide suspensions was also 

 made and followed the usual absorption isotherm, the equilibria being- 

 reached both from the side of excess in solution and that of deficiency 

 in solution. 



Dr. Mutscheller, in discussing Professor BLiirs paper, found the re- 

 sults in full agreement with his own conclusion. The question Avhether 

 the results given have been substituted in the exponential absorption 

 equation was answered in the negative. Dr. Mutscheller believes that if 

 these substitutions had been made in this equation, different values for 

 the constant of equation for each one of the three colloids would have been 

 obtained. This constant is known to depend on the temperature, the 

 nature of the dispersion medium, and the dispersoid. This fact would 

 preclude that each one of the three colloidal hydroxides possesses a dif- 

 ferent absorption potential or affinity, by reason of which an increase or 

 decrease of the [OH ] concentration would produce proportional results. 

 This seems to be the case in the data given by Professor Hill, for the 

 values given in the columns show all proportional changes. 



Dr. Mutscheller in his work on reversible colloids found by conductiv- 

 ity measurements that they absorb ions. Moreover, by means of poten- 

 tiometric determination of the ionic concentrations, he found that they 

 absorb specifically oppositely charged ions and leave the other ion free so 

 long as certain limits of low concentration are not surpassed. Professor 

 Hill's data seems to demonstrate the same fact. An increase of acidity 

 and consequently hydrogen ion concentration, therefore, neutralizes the 

 absorption affinity of the colloids so that other cations, namel-y, the metal 

 salt in solution, are no longer absorbed by the colloid. . 



The Section then adjourned. 



V. E. Levine, 



Secretary. 



SECTIOK OF BIOLOGY 



14 Februaey, 1916 



Section met at 8 :15 p. m.^ Vice-President H. von W. Schulte presid- 

 ing. 



The following program was presented: 



R. W. Shufeldt, The Cahou and othee Extiistct Petrels. (Pre- 

 sented -by Dr. P. A. Lucas. ) 



J. D. Kernan, Jr., The Chondeocra nium of a 30 mm. Human 

 Embeyo. 



