20 REPORTS ON THE STATE OF SCIENCE.—1918. 
of comparatively simple and coarse systems may perhaps constitute 
a theoretical edifice somewhat disproportionately large for its slight 
experimental foundation, there can be no doubt that the trend of 
research is in the right direction. 
Technically also emulsions are of considerable importance. They 
are employed—speaking, of course, very generally—where it is 
necessary to administer or exhibit a liquid in a varying degree of 
dilution, while the ordinary solvents for it are inadmissible on 
economical, technical, or physiological grounds. In such cases, or in 
a great number of them, the active liquid may be used as disperse 
phase of an emulsion, the continuous phase of which is so selected as 
to be indifferent; in addition it must wet, or be absorbed by, 
the surfaces to which the emulsion is eventually applied. Examples 
are: the medicinal emulsions of such liquids as cod-liver oil or 
petroleum (in which further desirable ingredients like malt extract, 
hypophosphites, &c., may be in solution in the aqueous phase); 
emulsions of cresols and other substances for use as antiseptic and 
' anti-parasitic preparations ; fat solvents such as carbon tetrachloride 
emulsified with ‘monopol’ soap (obtained by saponifying sul- 
phonated castor oil) ; emulsions of fats ina great variety of menstrua 
and used as leather ‘foods’ and dressings, &c. The preparation of 
such emulsions is of course generally a trade secret ; as regards the 
emulsifying agent, this is, however, very generally a soap in all 
technically used emulsions. 
Emulsions occur in industrial processes as undesirable by-products, 
such as very persistent emulsions of mineral oils or of wool-fat in 
the course of refining; the condense water from reciprocating 
engines, which contains the oil used in the lubrication of slide valves 
and cylinders and is a very perfect type of the stable oil-water 
emulsion, &c. In all these cases the means of preventing the forma- 
tion of an emulsion, or of separating it when formed, can he deduced 
from the theoretical considerations set forth above, although unfortu- 
nately their practical application is in many cases some what difficult. 
BIBLIOGRAPHY, 
Wm. C. McC. Lewis, The size and electric charge of oil particles in oil-water 
emulsions, ‘ Koll.-Zeitschr.’, 4, 211, 1909. 
Size and charge in highly disperse and dilute oil-water emulsions are of the 
same order as in suspensoid sols. 
Wm. C. McC. Lewis, The surface tension of colloid and emulsoid particles and 
its dependence on the limit size of the latter, ‘ Koll.-4eitschr.’, 5, 91, (1909). 
T. BRAILSFORD ROBERTSON, Notes on some factors which determine the 
constitution of oil-water emulsions, ‘ Koll.-Zeitschr.’, '7, 7, 19i0. 
WALTER OsTWALD, Contributions to the knowledge of emulsions, ‘ Koll.- — 
Zeitschr.’, §, 103, 1910. 
Experiments to determine which of two constituents will form the disperse 
phase under definite conditions of agitation, etc. The conclusion that closest 
packing of spheres constitutes a limiting phase ratio, pronounced by the author, is 
untenable. 
8. U. PICKERING, On emulsions, ‘ Koll.-Zeitschr.’, ‘7, 11, 1910. 
Highly concentrated emulsions of mineral oil in soap solution (up to 99 per cent. 
disperse phase) ; emulsification by solid particles. 
E, HAtscH&K, The direct separation of emulsions by filtration and ultra- 
filtration, ‘J. Soc. Chem. Ind.’, 29, 3, 1910. 
E. HATSCHEK, The filtration of emulsions and the deformation of emulsified 
particles under pressure, ‘ Koll.-Zeitschr.’, '7, 81, 1910. 
