Ee 
7 
ON COLLOID CHEMISTRY AND ITS INDUSTRIAL APPLICATIONS. 2] 
Mathematical and experimental demonstration of the high rigidity of small 
liquid particles. 
F.G. DonNAN and H.E. Porrs, On the emulsification of hydrocarbon oils by 
aqueous solutions of fatty acid salts, ‘ Koll.-Zeitschr.’, 9, 208, 1911. 
Experiments showing parallelism between the emulsifying effect of fatty acid 
salts and decrease in surface tension of their solutions. 
HE. HatscHEK, The stability of oil-water emulsions, ‘ Koll.-Zeitschr.’, 9, 159, 1911. 
E. GroscHurr, The stability of emulsions of water in hydrocarbon oils, ‘ Koll.- 
Zeitschr.’, 9, 257, 1911. 3 
RipsDALE ELLis, The properties of oil-water emulsions, ‘Zeitschr. phys. 
Chem,’: I. The electric charge, 78. 321, 1912; II. The stability and size of the 
particles, 80, 697, 1912. 
A very complete experimental investigation showing similarity between oil- 
water emulsions and suspensoid sols. 
Wiper D. BANCROFT, The theory of emulsification, ‘ J. phys. chem.’; I. 16, 
177 ; II. 16, 345 ; III. 16, 475; IV. 16, 739, 1912; V. 17, 501, 1913. 
A very complete critical review of the whole literature, summarised in the 
conclusion quoted above. 
G, A. H. CLowsgs, On reversible emulsions and the réle played by electrolytes in 
determining the equilibrium of aqueous oil systems, ‘Proc. Soc. for Exp. Biol. and 
Med.’ ; 1], 1, 1913. 
G. A. H. CLowEs, The action of electrolytes in the formation and inversion of 
oil-water systems, with some biological applications, 
This paper, like the preceding one, describes experiments with emulsions 
obtained by dispersing olive oil in dilute NaOH solution. By adding CaCl, in 
excess of the alkali they are spontaneously transformed into emulsions having 
water as disperse phase, which can be re-transformed into the first type by adding 
NaOH in excess. 
M. H. FiscHER and M. O. Hooker, On the formation and decay of emulsions, 
‘Koll.-Zeitschr.’ ; 18, 129, 1916. 
A. U. M. ScHLAEPFER, Water-in-oil emulsions, ‘J, Chem. Soc.’, 113, 522, 1918. 
The author, following Pickering, concludes that a finely divided solid more 
easily wetted by oil than by water should be capable of producing emulsions with 
water as disperse phase and proves his conclusion experimentally by using soot as 
emulsifying agent. 
THE LIESEGANG PHENOMENON. 
By H. HATScHEK, Sir John Cass Technical Institute, London. 
This pbenomenon was observed by its discoverer, after whom it 
is called, when carrying out the following experiment in the course 
of some researches on Golgi’s method of staining animal tissues with 
silver chromate : 
A glass plate is coated with 5 per cent. gelatin gel containing a 
small amount of potassium bichromate. A drop of strong silver 
nitrate solution is then placed on the gel and immediately begins to 
diffuse into the latter. The silver nitrate of course reacts with 
the bichromate in the gel, the products of reaction being silver 
bichromate and potassium nitrate. Although there is thus a con- 
tinous supply of both components, the insoluble silver salt is, 
however, not deposited in a continuous zone round the periphery 
of the original drop, but in a series of concentric rings, separated 
by apparently clear zones, the width of which increases with the 
distance from the centre. 
The importance of the phenomenon was immediately perceived 
by R. E. Liesegang, who made it the subject of a very large 
number of experiments of great ingenuity, and who first suggested 
that it supplied the simplest explanation of the formation of a 
natural product, viz., of banded agates. It may be as well to 
