Per Cent NaCl
Fig. 13. — The freezing point of solutions containing different percentages of
sodium chloride and the solubility of sodium chloride below 0°C.
ings. If the heat is taken from the brine the temperature of the brine
is lowered.
When salt is added to ice, one of three things may happen, depending
upon the proportion of ice and salt, and the surrounding temperature or
insulation. All the salt may be dissolved. When this happens the melting
of the ice lessens the concentration of the salt solution and the tempera-
ture is not lowered beyond the point obtained when the solution con-
tains the highest concentration of salt. All the ice may melt. When the ice
is melted the temperature cannot be lowered to a greater extent, for
there is no more ice to melt to absorb the heat. The cryohydric point may
be reached. At this point the solution becomes solid and separates into
ice and salt.
Ice-cream freezers. An ice-and-salt mixture is used to lower the
temperature of other substances. An ice-cream freezer is a utensil made
to freeze a substance placed in a center metal container. Outside this metal
TWO PROCEDURES USED IN FREEZING 87
container there is a space in which the cooling medium is placed. The outer
wall of the ice-cream freezer is often of wood, which is a poor conductor
of heat. Since it conducts heat slowly it partially insulates the ice and
salt from the surrounding air. The freezing mixture absorbs heat. In
doing this it lowers the temperature of the brine and removes heat from
the contents of the center can. In order to freeze the contents of the can
the temperature of the brine formed must be lower than the freezing point
of the mixture to be frozen.
To freeze the contents of the ice-cream can, considerable heat must be
removed from it. As a result, a corresponding amount of ice must melt to
absorb the heat. Therefore, the contents of the can do not begin to freeze
until considerable brine has formed. Conduction of heat is more rapid by
water than by air. Before the brine forms and replaces the air spaces around
the ice, conduction of heat from the can is slow. After all the salt is dis-
solved or all the ice is melted, the temperature of the brine cannot be
lowered, unless the temperature of the surrounding air is lower than the
temperature of the brine. In ice-cream making the temperature of the sur-
roundings is usually much higher than the temperature of the brine.
When the quantity of ice left in the freezer is small the temperature of the
surrounding air may heat the brine more than the melting of the small
amount of ice cools it. Before this stage is reached the freezer needs fresh
ice and salt packed around it.
The lowest temperature obtainable for a brine from a salt and ice mix-
ture is about — 22°C. (Walker reports —21° and Bigelow — 22.4°C.)
This temperature is called the cryohydric point. If calcium chloride is
used with ice the lowest temperature obtainable is — 55 °C.
At the cryohydric point 29 parts of salt are soluble in 71 parts of water.
No more salt can be dissolved at this temperature. This proportion of salt
to ice is about 1 to 3 and is often used in freezing mixtures.
Page 69
Presented as published in 1932. Historical recipes may not meet modern food-safety standards. Cook from the modern interpretation, not the original instructions.
AI-modernized reading of the original text
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Per Cent NaCl
Fig. 13. — The freezing point of solutions containing different percentages of
sodium chloride and the solubility of sodium chloride below 0°C.
ings. If the heat is taken from the brine the temperature of the brine
is lowered.
When salt is added to ice, one of three things may happen, depending
upon the proportion of ice and salt, and the surrounding temperature or
insulation. All the salt may be dissolved. When this happens the melting
of the ice lessens the concentration of the salt solution and the tempera-
ture is not lowered beyond the point obtained when the solution con-
tains the highest concentration of salt. All the ice may melt. When the ice
is melted the temperature cannot be lowered to a greater extent, for
there is no more ice to melt to absorb the heat. The cryohydric point may
be reached. At this point the solution becomes solid and separates into
ice and salt.
Ice-cream freezers. An ice-and-salt mixture is used to lower the
temperature of other substances. An ice-cream freezer is a utensil made
to freeze a substance placed in a center metal container. Outside this metal
TWO PROCEDURES USED IN FREEZING 87
container there is a space in which the cooling medium is placed. The outer
wall of the ice-cream freezer is often of wood, which is a poor conductor
of heat. Since it conducts heat slowly it partially insulates the ice and
salt from the surrounding air. The freezing mixture absorbs heat. In
doing this it lowers the temperature of the brine and removes heat from
the contents of the center can. In order to freeze the contents of the can
the temperature of the brine formed must be lower than the freezing point
of the mixture to be frozen.
To freeze the contents of the ice-cream can, considerable heat must be
removed from it. As a result, a corresponding amount of ice must melt to
absorb the heat. Therefore, the contents of the can do not begin to freeze
until considerable brine has formed. Conduction of heat is more rapid by
water than by air. Before the brine forms and replaces the air spaces around
the ice, conduction of heat from the can is slow. After all the salt is dis-
solved or all the ice is melted, the temperature of the brine cannot be
lowered, unless the temperature of the surrounding air is lower than the
temperature of the brine. In ice-cream making the temperature of the sur-
roundings is usually much higher than the temperature of the brine.
When the quantity of ice left in the freezer is small the temperature of the
surrounding air may heat the brine more than the melting of the small
amount of ice cools it. Before this stage is reached the freezer needs fresh
ice and salt packed around it.
The lowest temperature obtainable for a brine from a salt and ice mix-
ture is about — 22°C. (Walker reports —21° and Bigelow — 22.4°C.)
This temperature is called the cryohydric point. If calcium chloride is
used with ice the lowest temperature obtainable is — 55 °C.
At the cryohydric point 29 parts of salt are soluble in 71 parts of water.
No more salt can be dissolved at this temperature. This proportion of salt
to ice is about 1 to 3 and is often used in freezing mixtures.