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eses, if 18 necessary to examine briefly the nature of emulsions and 
the conditions under which they exist. The term emulsion is usu- 
ally applied to mixtures of oils with other liquids, as water, for which 
they have no natural affinity. These mixtures are prepared by 
means of a third substance, which is soluble in the aqueous por- 
tion, and gives it a certain viscosity. For this purpose saccharine, 
mucilagenous, or soapy matters are usually employed. Any sub- 
stance, however, that renders a liquid capable of forming bubbles 
when shaken withair, that remain for some time without breaking, 
is a suitable agent for this purpose. The emulsion is formed by 
triturating or vigorously stirring the substances together, by which 
means the oil is broken into small particles, which do not readily 
unite with each other, being separated by a thin film of liquid anal- 
ogous to that which separates the bubbles of air in foam or soap 
suds, 
It is essential in the preparation of emulsions that all of the ingre- 
dients be ina fluid condition, as they are then more easily divided, 
and assume a spherical form, which is more conducive to the per- 
manence of the mixture than are the irregular forms which occur 
when solids are taken. 
A true emulsion, when once formed, may be diluted to a large 
extent without destroying its properties, but afterwards if allowed 
to stand for a sufficient time, the fatty portion will separate, form- 
ing a layer, which, however, is still an emulsion and not free fat, 
the globules being separated from each other by a film of liquid, and 
may be again diffused throughout the whole volume by gentle shak- 
ing. Alcohol and acids are quite incompatible with the formation 
or permanence of,emulsions. 
The analogies which exist between artificial emulsions, prepared 
as above, and milk are numerous, and in many cases quite obvious. 
Some of these which bear upon the structure of the globules will be 
reviewed. 
1. The microscopic appearance of the fat globules is identical in 
the two. ‘The only notable difference being the greater variation in 
the size of theglobules in the artificial emulsion. The sharp refract- 
ive rings which surround the globules of milk, and which have 
often been mistaken for a membrane by the unskilled, are equally 
sharp in an artificial emulsion of the same fats. 
2. The separation, on standing, of the globules as cream, in 
which they retain their form and microscopic appearance. This is 
promoted in milk and in artificial emulsions alike, by dilution with 
water, whereby the suspending liquid is rendered less viscous, and 
permits the globules to move more freely. 
3. Effect of churning. It is well known that by sufficient agita- 
tion, at the proper temperature, the globules of milk become united 
into granules, and finally, by continuing the operation, into larger 
masses that constitute butter. ‘The temperature at which cream 
may be churned with satisfactory results has a narrow range (56°- 
70° F.); below 50° F. or above 80° very little butter can be obtained, 
and that is usually of poor quality; below 40° and above the melting 
point of the butter fats (90° to 100°) no amount of churning will 
produce butter. All of this is equally true of artificial emulsions 
