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F. F. Blackman . 
marked. Still more marked are these effects when the same 
volume of water is stretched into a film, or better into a thread, 
for then the relation of the surface to the mass is still further 
increased. 
The purest natural manifestation of micro-chemical effects 
occurs when two different substances are intimately mixed, the 
particles of one being distributed in a liquid medium of the other, 
as in suspension and emulsion colloids. “ Kolloid-Chemie ” has 
naturally, then, become quite a separate branch of investiga¬ 
tion, with its own specialists and its own journals, and this is so 
because surface-energy, due to the enormous surface presented 
by the colloid particles, is always the conditioning energy of 
the chemical processes in colloids. In Ostwald’s terminology 
colloidal chemistry is the typical part of Microchemistry, and the 
characteristic chemical changes are those that are grouped as 
adsorption ; to these belong dyeing and many other technical 
processes. Such are governed by special quantitative laws, which 
make the process of adsorption intermediate between physical 
absorption and chemical union. The physical chemistry of toxins, 
antitoxins, agglutinins, etc., illustrate the complexity of the 
quantitative laws holding in this field. 
Of peculiar importance in “ microchemistry,” is the law 
governing the spatial distribution of dissolved substances which 
alter the surface-tension of the water in which they are dissolved. 
Established on thermo dynamical considerations by Willard Gibbs 
in 1878, this law is generally known as “Gibbs’ theorem”: 
developed also by J. J. Thomson in 1887, it has been called by 
Macallum 1 the “ Gibbs-Thomson rule.” According to this rule 
substances in solution, which tend to lower the surface-tension 
of the solvent must accumulate in the surface layers, and this 
local accumulation will increase until the work done against 
osmotic pressure equals that gained by diminution of surface- 
tension and a state of equilibrium is arrived at. Substances which 
tend to raise the surface-tension will be repelled from the surface, 
and will be less concentrated there than in the general mass of the 
solution. 
Colloid particles, having very slight osmotic pressure, will 
' British Association Reports, 1910. Presidential Address to 
Section I. In this address Macallum elaborates the part 
that surface-tension may play in the functioning of animal 
organs, and correlates his studies of the localisation of salts 
in the cell with the Gibbs-Thomson rule. 
