Sugar solutions behave abnormally in regard to the boiling point. In
Experiment 4 it is found that the sugar solutions do not behave like the
salt solution. They do not reach a constant boiling point. A mole of sucrose
(342 grams) measures about 1^ cups. It can be readily seen by consulting
the solubility table of sucrose that its solubility will account for only a
partial elevation of the boiling point. The boiling point of the sugar solu-
tion increases with its concentration until the melting point of the sugar
is reached. Occasionally, in cooking a sucrose solution (Experiment 4A),
some of the sucrose crystallizes on the edge of the pan, thermometer, and
top of the sirup, similar to the salt solution, but this is not the usual result.
CRYSTALLIZATION
49
When the melting point of the sucrose is reached these crystals melt.
Temperatures far above the melting point of the sugars can be obtained.
However, with the very high temperatures, caramelization or decomposi-
tion of the sucrose occurs quite rapidly.
There is no very satisfactory explanation for the abnormal behavior of
the sugars. Chemists tell us that one explanation may be that the sugar
and water combine chemically giving a new compound with a new boiling
point, or the combination of the sugar with the water may give a very
concentrated solution, thus elevating the boiling point.
Boiling point of sucrose solutions. Browne in his "Handbook on
Sugar Analysis" lists the boiling point of sucrose solutions as follows.
TABLE 10
Boiling Point of Sucrose Solutions {Browne)
Per cent sucrose
10
20
30
40
50
60
70
80
90.8
Boiling point
100.4
100.6
101.0
101.5
102.0
103.0
106.5
112.0
130 0
A 10 per cent solution of sugar is one that contains 10 grams of sugar
and 90 grams of water or one having these proportions.
Heat o£ solution. Some substances that are soluble may liberate heat
when they go into solution. The example of mixing water and sulfuric
acid (H2SO4) is a well-known one. Other substances, instead of giving
off heat, cause the temperature to drop when they go into solution. They
are said to have a negative heat of solution, and heat is absorbed.
If sugar and water of the same temperature are mixed, the temperature
of the solution drops as the sugar is dissolving. Salt and many other sub-
stances also absorb heat as they go into solution. When the substances that
absorb heat as they go into solution are crystallized from solution, heat
is liberated and the temperature is elevated slightly. This is often notice-
able in making fondant or fudge. Frequently the sirup softens so that it
is not so viscous and is easier to stir when crystallization starts. As the
first crystals formed are not visible, one may think that the sirup is not
going to crystallize because of this softening. It is more noticeable with
larger amounts of fondant and fudge than with very small ones.
Crystallization
In making icings, frostings, or candy like fondant and fudge, it is neces-
sary to crystallize the sugar solution. For crystallization to occur, nuclei
must form in the solution. To these nuclei the material of the solution is
added to form crystals. Both the rate of formation of nuclei and the rate
of crystallization are affected by the nature of the crystallizing substance,
50 SUGAR COOKERY
the concentration, the temperature, agitation, and the impurities present in
the solution.
Page 43
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Sugar solutions behave abnormally in regard to the boiling point. In
Experiment 4 it is found that the sugar solutions do not behave like the
salt solution. They do not reach a constant boiling point. A mole of sucrose
(342 grams) measures about 1^ cups. It can be readily seen by consulting
the solubility table of sucrose that its solubility will account for only a
partial elevation of the boiling point. The boiling point of the sugar solu-
tion increases with its concentration until the melting point of the sugar
is reached. Occasionally, in cooking a sucrose solution (Experiment 4A),
some of the sucrose crystallizes on the edge of the pan, thermometer, and
top of the sirup, similar to the salt solution, but this is not the usual result.
CRYSTALLIZATION
49
When the melting point of the sucrose is reached these crystals melt.
Temperatures far above the melting point of the sugars can be obtained.
However, with the very high temperatures, caramelization or decomposi-
tion of the sucrose occurs quite rapidly.
There is no very satisfactory explanation for the abnormal behavior of
the sugars. Chemists tell us that one explanation may be that the sugar
and water combine chemically giving a new compound with a new boiling
point, or the combination of the sugar with the water may give a very
concentrated solution, thus elevating the boiling point.
Boiling point of sucrose solutions. Browne in his "Handbook on
Sugar Analysis" lists the boiling point of sucrose solutions as follows.
TABLE 10
Boiling Point of Sucrose Solutions {Browne)
Per cent sucrose
10
20
30
40
50
60
70
80
90.8
Boiling point
100.4
100.6
101.0
101.5
102.0
103.0
106.5
112.0
130 0
A 10 per cent solution of sugar is one that contains 10 grams of sugar
and 90 grams of water or one having these proportions.
Heat o£ solution. Some substances that are soluble may liberate heat
when they go into solution. The example of mixing water and sulfuric
acid (H2SO4) is a well-known one. Other substances, instead of giving
off heat, cause the temperature to drop when they go into solution. They
are said to have a negative heat of solution, and heat is absorbed.
If sugar and water of the same temperature are mixed, the temperature
of the solution drops as the sugar is dissolving. Salt and many other sub-
stances also absorb heat as they go into solution. When the substances that
absorb heat as they go into solution are crystallized from solution, heat
is liberated and the temperature is elevated slightly. This is often notice-
able in making fondant or fudge. Frequently the sirup softens so that it
is not so viscous and is easier to stir when crystallization starts. As the
first crystals formed are not visible, one may think that the sirup is not
going to crystallize because of this softening. It is more noticeable with
larger amounts of fondant and fudge than with very small ones.
Crystallization
In making icings, frostings, or candy like fondant and fudge, it is neces-
sary to crystallize the sugar solution. For crystallization to occur, nuclei
must form in the solution. To these nuclei the material of the solution is
added to form crystals. Both the rate of formation of nuclei and the rate
of crystallization are affected by the nature of the crystallizing substance,
50 SUGAR COOKERY
the concentration, the temperature, agitation, and the impurities present in
the solution.