431 



region where a change practically no longer takes place. Dnring the 

 ice-formation all the water is extracte-l from it wilhonl a possibilit}- 

 of large particles being formed. By subsequently raising the temperature 

 above the freezing-point this anhydrous gelatin is brought in contact 

 with excess of water, on which immediately a condition of perfect 

 homogeneity sets in ; not only is the solution perfectly transparent, 

 bnt there is not a single local irregnlarity to be seen, and it flows 

 so regnlarly through a viscosi meter as can only be expected from 

 perfectly homogeneous liquids. 



If during the freezing many large particles are formed, the possi- 

 bility of a perfectly regular distribution after the thawing is excluded. 

 The absoi'ption of water by the gelatin follows the type of imbibition. 

 We then have as it were an infinite number of small gel-particles, 

 which retain their individuality". A more or less turbid, opaque mass 

 is obtained, which does not get clear again without heating. 

 * In conclusion a remark on the signification of the quantity of 

 water, with which the gelatin is brought together. For the imbibition 

 it is practically immaterial whether so much water is added ttiat the 

 condition of equilibrium bec(»mes p or /•. If, however, the quantity 

 of water is very slight, things aro different. If for the anhydrous 

 gelatin the condition a (fig. 5) is assumed, so great a tendency to 

 diminution of the number of large particles will not exist in this 

 case that the change is represented by df — a' ; but a line will be 

 followed along which the number of large particles changes but 

 slightly: a — z. The change may of course go so far until the line 

 of the maxima of imbibition L — L is reached, and no further; 

 and as appears from the figure it is reached here at a slighter water- 

 content than when the change was represented by a — a' . Absorption 

 of only a very small quantity of water takes place when the dry 

 gelatin is brought in contact with water-vapour. Imbibition in water- 

 vapour and in water cannot lead to the same result. 



Here the paradoanl plienomenon described by von Schroeder will 

 be recognized that gelatin ivhich has had a maximum imbibition in 

 vapour, absorps a great deal of water more lohen it is subsequently 

 immersed into liquid ivater, which he thought in conflict with the 

 second law of thermodynamics. Led by the given considei-ations it 

 is possible to form a conception of the influences that come into 

 play here. 



