Bhatnagar emphasizes the influence of the electric charge of the emulsi-
fying agent upon the type of emulsion formed. He makes the following
generalization. **A11 emulsifying agents having an excess of negative ions
on them and wetted by water will yield oil-in-water emulsions, while
those having an excess of adsorbed positive ions and wetted by oil will
give w\iter-in-oil emulsions."
Seifriz, in his work with petroleum oil emulsions stabilized with casein
solution, found that the oils with a specific gravity of 0.828 or below
form oll-In-water emulsions. When the specific gravity of the oil is greater
than 0.857 a water-in-oil emulsion is formed, and oils with specific gravity
between 0.828 and 0.857 give coarse, unstable emulsions or cannot be emul-
sified at all.
Reversal of type of emulsion. No definite rule can be given concern-
ing the reversal of emulsions. The addition of an electrolyte In definite
concentrations may stabilize some emulsions and bring about reversal of
others. Reversal of some emulsions may occur upon the addition of a
definite quantity of a hydroxide. Sometimes the addition of more of the
hydroxide will again bring about a reversal of the emulsion into the origi-
nal type. Shaking after standing may cause reversal of some emulsions.
Some ions are antagonistic to each other. Thus Clowes has shown that,
if a rancid oil is dropped from a pipette which has the end immersed
under w^ater, drops of a certain size are formed. But if the oil Is dropped
into a sodium chloride solution, the drops are very much smaller. This Is
probably due to the formation of sodium soaps with the rancid oil and the
lowering of the interfaclal tension. If the oil is dropped Into a calcium
chloride solution the interfaclal tension is increased and very large oil
drops are formed, owing in this case to the formation of calcium soaps.
If both sodium and calcium are in the solution they antagonize each other
and the result obtained will depend on the concentration of each present.
Sodium and potassium are antagonistic to calcium and magnesium.
Means of determining the type of emulsion. Several ways have
been proposed to determine which of the two liquids Is the continuous
phase.
The drop-dilution method may be used to determine the type of emul-
sion by the microscope. To a small portion of the emulsion placed on a
slide add a drop of water with a pin point and stir slightly. If the water
blends with the emulsion, it Is an oil-in-water emulsion, but if oil blends
with the outside phase it Is a water-in-oil emulsion.
SOME FOOD EMULSIFIERS 271
Another method of determining the type of emulsion is to use Sudan
III or Scharlach R, red dyes soluble in the oil but not in the water. A
small portion of the finely powdered dye is dusted over the surface of the
emulsion. If oil is the external phase the color gradually spreads through-
out the emulsion. But if water is the external phase the color does not
spread but is confined to the oil with which it comes in contact on the
surface.
Page 218
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Bhatnagar emphasizes the influence of the electric charge of the emulsi-
fying agent upon the type of emulsion formed. He makes the following
generalization. **A11 emulsifying agents having an excess of negative ions
on them and wetted by water will yield oil-in-water emulsions, while
those having an excess of adsorbed positive ions and wetted by oil will
give w\iter-in-oil emulsions."
Seifriz, in his work with petroleum oil emulsions stabilized with casein
solution, found that the oils with a specific gravity of 0.828 or below
form oll-In-water emulsions. When the specific gravity of the oil is greater
than 0.857 a water-in-oil emulsion is formed, and oils with specific gravity
between 0.828 and 0.857 give coarse, unstable emulsions or cannot be emul-
sified at all.
Reversal of type of emulsion. No definite rule can be given concern-
ing the reversal of emulsions. The addition of an electrolyte In definite
concentrations may stabilize some emulsions and bring about reversal of
others. Reversal of some emulsions may occur upon the addition of a
definite quantity of a hydroxide. Sometimes the addition of more of the
hydroxide will again bring about a reversal of the emulsion into the origi-
nal type. Shaking after standing may cause reversal of some emulsions.
Some ions are antagonistic to each other. Thus Clowes has shown that,
if a rancid oil is dropped from a pipette which has the end immersed
under w^ater, drops of a certain size are formed. But if the oil Is dropped
into a sodium chloride solution, the drops are very much smaller. This Is
probably due to the formation of sodium soaps with the rancid oil and the
lowering of the interfaclal tension. If the oil is dropped Into a calcium
chloride solution the interfaclal tension is increased and very large oil
drops are formed, owing in this case to the formation of calcium soaps.
If both sodium and calcium are in the solution they antagonize each other
and the result obtained will depend on the concentration of each present.
Sodium and potassium are antagonistic to calcium and magnesium.
Means of determining the type of emulsion. Several ways have
been proposed to determine which of the two liquids Is the continuous
phase.
The drop-dilution method may be used to determine the type of emul-
sion by the microscope. To a small portion of the emulsion placed on a
slide add a drop of water with a pin point and stir slightly. If the water
blends with the emulsion, it Is an oil-in-water emulsion, but if oil blends
with the outside phase it Is a water-in-oil emulsion.
SOME FOOD EMULSIFIERS 271
Another method of determining the type of emulsion is to use Sudan
III or Scharlach R, red dyes soluble in the oil but not in the water. A
small portion of the finely powdered dye is dusted over the surface of the
emulsion. If oil is the external phase the color gradually spreads through-
out the emulsion. But if water is the external phase the color does not
spread but is confined to the oil with which it comes in contact on the
surface.