150 
closely studied especially with regard to gold sols by Tur SvEDBERG 
(N = 6.2 10**)'), and also the diffusion determinations yielded values 
which on the whole present a same dependence on the radius as 
equation 3 leads us to expect *). 
If we examine what the expressions 1 and 3 can yield for ordinary 
solutions, it appears that only 3 is liable to be tested, and that tbe 
following conclusions offer the best opportunity. 
1. In the same solvent the produet of diffusion constant and 
radius of the diffusing molecule is constant. The relative size of the 
dissolved substances can, therefore, be determined from the diffusion 
constant. It is clear that we can only speak of testing here, when 
it is possible to compute the radii by another way. According to 
expression 3 Tue SvEDBERG found for the radius of some organic 
substances values which at least roughly *) agree with our views of 
chemical structure. The volume of the dissolved substance in pure 
state and the atom constants which follow from the additivity of 
the 4 of the equation of state, can likewise furnish an estimation 
of the radius. Another method to find the radius of the diffusing 
particle has been given by Enysrein *); it is founded on the change 
in viscosity which a solvent undergoes, when large solid spheres 
are suspended in it; we shall return to this later on. 
2. for diffusion of a substance in different solvents at the same 
temperature the product of diffusion constant and internal friction 
is constant. Here we should call attention to an investigation by 
TuHovert, who for diffusion of phenol in ten different solvents found 
values for this product which only vary between 92 and 99, the 
ratio of the diffusion constants even rising to 300°). For a number 
of substances diffusing in alcohol and water Ormorm has found 
radii of about equal length; hence J. also for these substances 
differs little in aleohol and water*). An extensive investigation by 
OxHoLm with other solvents, has, however, yielded values for the 
radius of the same diffusing particle which are to each other as 
1:2 and even as 1:37); this may be attributed to difference in 
molecular size of the dissolved substance (association), to the non- 
1) THe SvEDBERG and INouye. Kolloid Zeitschr. 1 No. 7 (1910); 2 No. 9 (1911). 
Cf. also WESTGREN la 
2) THE SvepBerG Zeitschr. f. physik. Chemie. 67. 105. (1909). 
8) Tue SvepBerc and A. ANDREEN-SVEDBERG, Zeitschr. f. physik. Chemie. 76, 
145 (1911). 
4) Einstein. Ann. d. Phys. (4) 19, 289 (1906); (4) 34, 591 (1911). 
5) Tuovert. Ann. chem. et phys. (9) 2, 369 (1914). 
6) Oenotm. Meddelanden Nobelinstitut. 2. N°. 24 (1912). 
7) Ornotm. Meddelanden Nobelinstitut. 2. No. 26 (1913). 
