I 



8 COLLOID CHEMISTRY AND THE 



surrounding molecules ? Will it not rather behave like a large 

 molecule, so that its mean ene'rgy is that of a single molecule ? " 



The movement of suspended particles was first described by 

 the botanist Brown in 1827. Various later workers (Wiener, 

 M. Gouy) confirmed its existence, and traced its origin to the 

 movements of the molecules. Perrin was able to produce 

 gamboge suspensions of particles of the same size by fractional 

 centrifuging, and, by counting the number of particles at 

 various depths in a cell under the microscope, was able to 

 show that the distribution under the force of gravity followed 

 the same exponential law as is found, for instance, in the 

 distribution of the air in the atmosphere. Thus a difference of 

 lop, in depth in the cell gave the same decrease in number of 

 particles as occurs in a height of 6 kilometres in the atmosphere. 

 The value of the constant N, calculated from the distribution 

 equation of various emulsions is 70 X io 22 , a value for Avo- 

 gadro's constant which agrees exceedingly well with that 

 obtained by Van der Waals. 



From the above and from other demonstrations of the 

 applicability of the kinetic theory of gases to colloid systems 

 (see The. Svedberg), we can perceive no fundamental distinction 

 between the behaviour of particles of molecular dimensions and 

 that of colloid particles up to those of a coarse suspension. 

 We shall see -further that a similar transition occurs in electro- 

 chemical properties. 



Under these circumstances, there can be no question of a sharp 

 demarcation between the general chemistry of substances of 

 high molecular weight, such as proteins, and their colloid 

 chemistry. The difference is certainly not a matter of size of 

 particles, but rather a matter of structure. If a metal or a 

 simple compound is brought to the colloid state, the dispersed 

 particles are always aggregates of simpler but similar smaller 

 portions. If, on the other hand, the particles are those of a 

 non-associated substance of high molecular weight, of the same 

 degree of dispersity as the above, we have particles formed of a 

 combination of several heterogeneous groups of atoms (for 

 instance, albumin, which is formed of various ammo-acids) . 

 We have so far absolutely no knowledge of the distribution of 



