To the Student. In this work the class should be organ-
ized into as many groups as there are brands of commercial
gelatine to be studied. The groups may consist of two or
more students. A table should be framed by each group,
and filled out under the following heads after its particu-
lar brand of gelatine has been studied: (1) Name, of
commercial variety. (2) Description — color, light or
darker; texture, whether finely or coarsely granulated,
shredded, in sheets, etc. (3) Price per box. (4) Volume
in box. (5) Yield in jelly. (6) General Characteristics,
e. g., easy or difficult of hydration, easily or difficultly
soluble, yielding a clear or a dull jelly, possessing or not
possessing an acid reaction, having or not having a strong
odor or flavor, and being easily affected by acid.
In order to test the gelatine four kinds of jelly
should be made from each box, namely, milk, lemon,
orange, and coffee. At the close of the lesson the work
of all the groups should be compared, and a complete
table framed. (See table on page 47.)
GELATINE
47
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48 PRINCIPLES OF FOOD PREPARATION
Experiments to Aid or Confirm Inferences
I
Comparison of Gelatine and Albumin
1. Compare the appearance of commercial gelatine
with that of dried egg albumin. Of thoroughly hydrated
gelatine with that of fresh white of egg.
2. Treat about 4 grams of hydrated gelatine and of
fresh white of egg with 15-20 cc. cold water in test tubes,
and allow to stand 10-15 m. Note solubility in each
case.
3. Apply heat (water bath) to test tubes from 2. Note
result.
4. Divide the gelatine from 3 into two equal parts,
A and B. To A add enough cold water to bring up the
total volume of water used to 56 cc. To B add a similar
volume of a mixture of water and vinegar in equal parts.
Stand both A and B in a cool place until no further change
takes place.
5. Recall the effect of acid on albumin (see page 36).
6. Recall the effect of beating on both albumin (page
36) and gelatine (page 42).
7. Arrange in tabular form the effects of water, heat,
acid, and manipulation on albumin and gelatine re-
spectively. Consult instructor before framing your
table.
II
Chemical Tests for Protein
1. Make a solution of egg albumin, by vigorously
shaking a few cc. of white of egg in 15-20 times its volume
of water. Divide into four parts — A, B, C, and D.
GELATINE 49
To A add concentrated nitric acid. Note precipitate,
and its color. Boil; note change in color. After cooling
add ammonia water; note further color change.
Note. This is known as the xanthoproteic test for albumin and
other "simple proteins," and its characteristic color reactions indicate
the presence of these bodies.
2. To B add a few drops of Millons reagent. Note
precipitate, and its color change when boiled.
Note. This is the most delicate test for protein, and will indicate
the presence of even a trace of this substance by the characteristic
color reaction, though no precipitate will be formed when only a mi-
nute quantity of protein is present.
3. To C add a saturated solution of magnesium sul-
phate.
Page 22
Presented as published in 1914. 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
To the Student. In this work the class should be organized into as many groups as there are brands of commercial gelatine to be studied. The groups may consist of two or more students. A table should be framed by each group, and filled out under the following heads after its particular brand of gelatine has been studied: (1) Name, of commercial variety. (2) Description — color, light or darker; texture, whether finely or coarsely granulated, shredded, in sheets, etc. (3) Price per box. (4) Volume in box. (5) Yield in jelly. (6) General Characteristics, e. g., easy or difficult of hydration, easily or difficultly soluble, yielding a clear or a dull jelly, possessing or not possessing an acid reaction, having or not having a strong odor or flavor, and being easily affected by acid.
In order to test the gelatine four kinds of jelly should be made from each box, namely, milk, lemon, orange, and coffee. At the close of the lesson the work of all the groups should be compared, and a complete table framed. (See table on page 47.)
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Experiments to Aid or Confirm Inferences
Comparison of Gelatine and Albumin
1. Compare the appearance of commercial gelatine with that of dried egg albumin. Of thoroughly hydrated gelatine with that of fresh white of egg.
2. Treat about 4 grams of hydrated gelatine and of fresh white of egg with 15-20 cc. cold water in test tubes, and allow to stand 10-15 m. Note solubility in each case.
3. Apply heat (water bath) to test tubes from 2. Note result.
4. Divide the gelatine from 3 into two equal parts, A and B. To A add enough cold water to bring up the total volume of water used to 56 cc. To B add a similar volume of a mixture of water and vinegar in equal parts. Stand both A and B in a cool place until no further change takes place.
5. Recall the effect of acid on albumin (see page 36).
6. Recall the effect of beating on both albumin (page 36) and gelatine (page 42).
7. Arrange in tabular form the effects of water, heat, acid, and manipulation on albumin and gelatine respectively. Consult instructor before framing your table.
Chemical Tests for Protein
1. Make a solution of egg albumin, by vigorously shaking a few cc. of white of egg in 15-20 times its volume of water. Divide into four parts — A, B, C, and D.
To A add concentrated nitric acid. Note precipitate, and its color. Boil; note change in color. After cooling add ammonia water; note further color change.
Note. This is known as the xanthoproteic test for albumin and other "simple proteins," and its characteristic color reactions indicate the presence of these bodies.
2. To B add a few drops of Millons reagent. Note precipitate, and its color change when boiled.
Note. This is the most delicate test for protein, and will indicate the presence of even a trace of this substance by the characteristic color reaction, though no precipitate will be formed when only a minute quantity of protein is present.
3. To C add a saturated solution of magnesium sulphate.