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ON COLLOID CHEMISTRY AND ITS INDUSTRIAL APPLICATIONS. 113 
water be dispersed in oil, a very unstable system is produced, separ- 
ation into two layers taking place as soon as beating-up ceases. Now 
milk by virtue of its colloidal content is an excellent emulsifying 
agent, when oil is the disperse phase. Consequently if milk be ina 
churn in bulk, and oil is slowly fed in, with continuous agitation, an 
excellent emulsion of great oil concentration can be produced, and 
will set to a homogeneous mass afterwards. But if the oil be in the 
churns in bulk, and milk is fed in, a very unstable system results, 
which easily separates into layers on stopping the agitation for a 
while. This has been proved many times and the explanation seems 
clear :—To get a suitable emulsion of water in oil, one would require 
an emulsifying agent which should form an oi/-soluble colloidal 
solution but in milk the colloids are wader-soluble. Both theory and 
practice condemn any form of churning which would lead to 
emulsion with oilas the continuous medium. Such emulsions when 
cooled by iced water, or on drums, solidify with clot formation, and 
the resultant margarines are ‘ spotted’ in texture.” (Clayton, Loc. cit.). 
In order to aid emulsification many colloidal substances have 
been proposed for use in making margarine, ¢.g., starch, gelatin, 
glycerin, egg-yolk, lecithin compositions, etc. These agents are 
added to the milk, and certainly do have a most helpful effect when 
churning. So small a quantity as 0:1 per cent. of glycerine added 
to the milk or oils (since it mixes with oils) leads to much improved 
emulsification. The usually-accepted theory accounting for this 
phenomenon is that the emulsifying agent forms a membrane or 
film around the oil globules and so prevents their coalescence. 
Egg-yolk, usually compounded in Sesame Oil, has been fairly 
widely used in margarine works as an aid to churning, and it is very 
interesting to note that egg-yolk, containing about 10 per cent. of 
lecithin, and 15 per cent. albumen, both colloids, is an exceptionally 
stable emulsion, not separating into phases even on long standing or 
centrifuging. 
Practically all the physico-chemical questions relating to mergarine 
involve discussion of emulsions, and unfortunately rather too little is 
understood concerning them, whilst the physical chemistry of a solid 
emulsion, such as margarine as a finished article presents, is only in 
its infancy. 
The first question which arises is concerned with the determi- 
nation of the nature of the external, and disperse phases of a given 
sample of margarine, 7.c., is it a solidified oil-water or water-in-oil 
emulsion ? That isa hard question to answer. With liquid emul- 
sions the problem is easier, and three methods at Jeast may be 
employed to differentiate :-— 
(1) By a Kataphoresis test, since the internal phase being nega- 
tively charged Will wander to the anode. 
(2) Indicator Method. This method depends on the fact that if 
one adds an oil-soluble dye to an emulsion, the dye will spread if the 
oil be the continuous medium. Thus Robertson used Sudan III, a 
red dye, in his work on emulsions of olive oil in water (cf Koll. 
Zeit., 7, 7-10 (1910).) With an emulsion of oil in water, the colour 
would not spread, but be confined to those globules of oil with which 
the colour grains were actually in contact. 
