vin THE GENERAL PHYSICAL PROPERTIES OF ALBUMINS 267 



because the surface tensions and consequently the surface areas of 

 two substances in ' solution ' are inversely proportional to the amount 

 of the existing difference of potential. Therefore to remove the 

 difference of potential is equivalent to making the particles approach 

 one another and collectively offer a smaller surface, for the surface 

 increases as the square, while the cubic capacity increases as the cube. 



If the solute and the solvent in their free state are both fluids, 

 they will completely separate from one another if in solution, as soon 

 as the difference of potential which keeps them in solution is abolished ; 

 thus water and oil in the iso-electric state separate into two layers. 

 It is quite different, however, if the solute in its free state is, for 

 example, such a solid as arsenic sulphide. By the gradual addition of 

 acids or acid salts the arsenic sulphide will aggregate into larger and 

 larger particles, till ultimately an exceedingly delicate framework is 

 formed in the meshes of which is the solvent. This framework will 

 gradually become more and more resistant owing to the increase in 

 surface tension, and therefore the small trabeculse formed in this 

 way will offer greater mechanical resistance to a diminution of their 

 surface, and hence we require to add, ' after having acclimatised ' 

 colloid, still about the same amount of a coagulating electrolyte as 

 would have been sufficient in the first instance if we had added it 

 quickly. 1 



The real cause of the rapid coagulation of a colloidal solution on 

 the quick addition of an electrolyte sufficient to bring about complete 

 coagulation seems to be the following : The strong diffusion currents 

 lead to the formation of irregular mechanical aggregates, or to a 

 conglutination of the particles as described on p. 274. 



SPONTANEOUS CHANGE. For a colloid to change ' spontaneously ' 

 is a matter of impossibility, still the expression is used constantly, and 

 therefore an inquiry into the causes leading to spontaneous coagula- 

 tion is needed. Hantzsch has shown that certain colour bases are 

 especially liable to become converted into pseudo-bases, and, as pointed 

 out on p. 219, this conversion is accompanied by a loss of basic 

 capacity; if, further, albumins are mixtures of pseudo- bases and 

 pseudo-acids, it is quite conceivable that owing to the disappearance 

 of a predominating acid or basic function the albumin molecule may 

 become iso-electric, and thereby be rendered insoluble. 



Not taking into consideration the possibility of chemical action 



1 The question as to whether a colloid, by forming a resisting framework, is capable 

 of resisting the electrical stress of an electrolyte by the development of torsional 

 electricity cannot be entered into here. 



