November 24, 1916] 



SCIENCE 



751 



dynamic equilibrium Professor Tolman's rea- 

 soning loses its validity. What is our criterion 

 of stability? Colloidal gold solutions pre- 

 pared by the reduction of dilute gold chloride 

 solutions with phosphorus are looked upon as 

 being exceedingly stable, in fact they appear 

 almost optically homogeneous under the ultra 

 microscope; yet those prepared by Faraday by 

 this method are still preserved at the Royal 

 Institution — long since coagulated. And of 

 course the rate of change (viscosity) of the 

 hydrophyllic sols mentioned by Professor Tol- 

 man is measured in hours and minutes, i. e., 

 they are to be regarded as anything but stabile 

 in the thermodynamic sense. Are we not to 

 consider this question of time at all? Are we 

 to abandon our hope of a kinetic explanation 

 of the change of size of particles when under 

 the ultra microscope we can observe the clump- 

 ing together of particles and the cessation of 

 the Brownian movement? 



As experimental evidence of negative sur- 

 face tension Professor Tolman cites the gel-sol 

 change of a number of reversible colloids. 

 Perhaps there is an increase of surface in 

 such changes, but our knowledge of the internal 

 surface of gels of gelatine, agar-agar, ferric 

 hydroxide, etc., is, at best, somewhat limited. 

 It can, however, be experimentally shown, 

 from vapor pressure studies of these same 

 gels, that the internal surface is enormous. 3 

 Furthermore if the internal surface of the gel 

 is decreased (dehydration) the gel-sol change 

 in many cases does not take place. It is there- 

 fore an open question as to just what increase 

 of surface occurs in the gel-sol change. 



But Professor Tolman should not limit him- 

 self to the gel-sol change as experimental evi- 

 dence of negative surface tension; as a matter 

 of fact he is forced to extend it to include 

 the solution of all substances. For in the 

 process of solution we surely have an enor- 

 mous increase of surface, consequently an ex- 

 hibition of negative surface tension. This 

 leads at once to a general theory of solution. 

 Here we meet an old idea that one frequently 



3 1 have calculated that the internal surface of 

 one gram of silic acid gel is approximately 2,000,- 

 000 cm 2 . 



comes across in scientific literature, but which 

 has never been seriously considered because it 

 represented no real progress. 



The fundamental concept of surface tension 

 is molecular attraction, and until we can ex- 

 perimentally show repulsion between molecules 

 without the addition of external energy, we 

 must regard negative surface tension- as a 

 mathematical quantity to which not much 

 meaning may be attached. In other words, 

 until we can obtain a substance which spon- 

 taneously increases its surface (wrinkles and 

 folds), and we must here clearly separate phe- 

 nomena of solution, vaporization and osmose, 

 we have not much right to speak of negative 

 surface tension. 



Professor Tolman quotes Professor F. G. 

 Donnan as a possible exponent of negative 

 surface tension. I can say from a year's asso- 

 ciation with Professor Donnan that he has long 

 since recognized the futility of ordinary ener- 

 getics in giving a solution to the perplexing 

 and intricate problems of disperse systems. Is 

 it not better, in view of the multitude of 

 factors involved, to push our experimental 

 study of these systems a bit further, before we 

 burden ourselves with an intricate systematic 

 of doubtful validity? The lines of attack 

 laid out by Freundlich, Zsigmondy, Svedberg 

 and van Weimarn are infinitely more hopeful. 

 W. A. Patrick 



Syracuse University 



the relation of osmotic pressure and 

 imbibition in living cells 



In ~No. 1115 of this journal Jacques Loeb 1 

 publishes some ideas regarding the above, 

 which he himself considers " so self-evident 

 that their publication would seem superfluous 

 were it not for the fact that Wolfgang Ostwald 

 and other colloid chemists deny the existence 

 of semi-permeable membranes in the muscle on 

 account of the fact that acid causes proteins to 

 undergo imbibition." Since this article by 

 Jacques Loeb is, therefore, published chiefly 

 for my benefit, I beg to point out the following : 



Never, and in none of my publications, have 

 I said anything of this kind. I have never 



i Jacques Loeb, Science, 43, 688 (1916). 



