560 



treated by drying at 162° over phosphorus pentoxide, and then gave 

 an isotherm with a flat middle piece (possibly even with a faint 

 retrograde piece), wliich shows a close analogy with the shape of 

 the isotlierm for water and carbon. When the glass-wool had been 

 well moistened beforehand, it gave an S-form, as they have been 

 found in mixtures of sulphuric acid and water, and in swelling 

 bodies with water as imbibition-liquid; characteristic is there the 

 beginning with a strongly pronounced horizontal piece foj- small 

 i, in which region Freundi.ich's adsorption formula is valid. Similar 

 curves were found by Herf, and Andress for the adsorption of those 

 •liquids that moisten the carbon well. 



This conception might also be able to explain why the adsorption 

 by carbon of water presents such strong hysteresis, wheieas that 

 of organic vapours seems to take place without hysteresis. It is, 

 however, possible that solid solution in the boundary layers also 

 plays a part in this'). 



The experiments are being continued. 



5. Conclusions. 



1. In the investigation of the phenomena of sorption it is in- 

 sufficient to determine the isolheriri of binding; it is necessary to 

 determine at the same time (he heat of sorption as function of the 

 quantity of absorbed substance at the same material. 



2. The examined animal carbon appeared to have an isotherm 

 with an almost flat middle piece, analogous to the isotherm of newly- 

 made silicic acid. The sorption-heat had a course corresponding with 

 this, a flattened middle piece. 



3. By assuming that this course is explained by a system of 

 micro-capillaries, I calculate the radius of these capillaries from the 

 isotherm at 1.2 to 2.6 juft (as for silicic acid). That this dimension agrees 

 so closely with that for silicic acid, is somewhat strange and striking. 



4. It is, however, doubtful whether this explanation by the 

 assumption of a system of micro capillaries is the true one. It 

 seems probable to me that the difficult moistening of the carbon by 

 water accounts for it. 



5. Very striking is the strong hysteresis in the isotherm '). 



1) In the search for possible explanations for the deviating behaviour of water at 

 carbon much light was thrown on the subject by conversations with Dr. M. Polanyi. 



') The complicated results of B. Gustaver (Kolloidchem, Beihefte, 1922) and 

 HaLLSTRONo's experiments (Diss. Helsingfors, 1920) will be discussed in a following 

 paper. Not to lengthen this communication, 1 confine myself to only mentioning 

 them here. 



