small portions than if added all at once. (2) The valence of the ion bring-
ing about the coagulation. Coagulation is brought about by the ion having
the opposite charge to that of the colloid. As a general rule, the precipitat-
ing effect is increased with an increase of valence of the ion bringing about
the coagulation. There are exceptions to this rule, as some monovalent ions
have greater effect in bringing about coagulation than some polyvalent
ions. (3) Concentration of the electrolyte. In many cases there are zones in
which a definite concentration of the electrolyte brings about maximum
coagulation. Higher or lower concentrations are not so effective or may not
bring about coagulation. This is illustrated later in egg cookery. High con-
centrations of ferric or aluminum chloride do not bring about coagulation
of distilled-water custards but small concentrations cause coagulation.
(4) The concentration of the colloid also affects the amount of electrolyte
required for coagulation. (5) A definite time may be required, depending
upon the concentration of the protein and electrolyte.
Effect of electrolytes upon hydrophilic colloids. The effect of
electrolytes upon hydrophilic colloids is varied. Kruyt states that the hydro-
philic colloids are stabilized by two factors, the electric charge and the
strong hydration of the particles, and after the hydrophilic colloid is
dehydrated it is as sensitive to electrolytes as the hydrophobic colloids.
Dehydration of the hydrophilic colloids may be brought about by different
means. Some proteins may be dehydrated by heating. Alcohol may be
used to dehydrate hydrophilic colloids, and tannins may also bring about
dehydration. This dehydration by heating or other means is called denatur-
ation. If an egg white is dialyzed and the electrolytes removed it is not
coagulated when heated. But the addition of electrolytes to the heated
dialyzed egg white brings about coagulation. Kruyt states that if small
quantities of electrolytes are added to a starch or agar-agar sol the electric
charge is removed but the colloidal particles do not precipitate. If alcohol,
a dehydrating agent, is added to the above starch or agar-agar sol, coagu-
lation occurs. It is immaterial in which order the two stability factors, the
electric charge and hydration, are removed. The removal of one has no
evident effect, but the removal of both factors causes coagulation. The term
denaturation will be used in later references to indicate sensitization of
hydrophilic colloids to electrolytes. The term denotes whatever changes are
brought about during dehydration of the colloid.
The action of electrolytes upon proteins is given as follows by Buchanan
and Fulmer.
"1. Those electrolytes which bring about a reversible precipitation
in high concentration. These include the salts of the alkalis, K, Na,
NH4, Li and possibly Mg. Ammonium sulphate is commonly used
in 'salting out' of proteins. The precipitate so formed will be redis-
solved on dilution, i.e., the process is reversible.
''When the protein is on the alkaline side of its isoelectric point (i.e.,
ISOELECTRIC POINT 11
negatively charged), the order of effectiveness of the salt is on the
basis of cations: Li > K > Na > NH4 > Mg and of anions, citrate
> tartrate > SO4 > acetate > CI > NO3 > CIO3 > I > SCN.
Page 11
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
A modernized reading is not available for this page yet. You are seeing the original text.
small portions than if added all at once. (2) The valence of the ion bring-
ing about the coagulation. Coagulation is brought about by the ion having
the opposite charge to that of the colloid. As a general rule, the precipitat-
ing effect is increased with an increase of valence of the ion bringing about
the coagulation. There are exceptions to this rule, as some monovalent ions
have greater effect in bringing about coagulation than some polyvalent
ions. (3) Concentration of the electrolyte. In many cases there are zones in
which a definite concentration of the electrolyte brings about maximum
coagulation. Higher or lower concentrations are not so effective or may not
bring about coagulation. This is illustrated later in egg cookery. High con-
centrations of ferric or aluminum chloride do not bring about coagulation
of distilled-water custards but small concentrations cause coagulation.
(4) The concentration of the colloid also affects the amount of electrolyte
required for coagulation. (5) A definite time may be required, depending
upon the concentration of the protein and electrolyte.
Effect of electrolytes upon hydrophilic colloids. The effect of
electrolytes upon hydrophilic colloids is varied. Kruyt states that the hydro-
philic colloids are stabilized by two factors, the electric charge and the
strong hydration of the particles, and after the hydrophilic colloid is
dehydrated it is as sensitive to electrolytes as the hydrophobic colloids.
Dehydration of the hydrophilic colloids may be brought about by different
means. Some proteins may be dehydrated by heating. Alcohol may be
used to dehydrate hydrophilic colloids, and tannins may also bring about
dehydration. This dehydration by heating or other means is called denatur-
ation. If an egg white is dialyzed and the electrolytes removed it is not
coagulated when heated. But the addition of electrolytes to the heated
dialyzed egg white brings about coagulation. Kruyt states that if small
quantities of electrolytes are added to a starch or agar-agar sol the electric
charge is removed but the colloidal particles do not precipitate. If alcohol,
a dehydrating agent, is added to the above starch or agar-agar sol, coagu-
lation occurs. It is immaterial in which order the two stability factors, the
electric charge and hydration, are removed. The removal of one has no
evident effect, but the removal of both factors causes coagulation. The term
denaturation will be used in later references to indicate sensitization of
hydrophilic colloids to electrolytes. The term denotes whatever changes are
brought about during dehydration of the colloid.
The action of electrolytes upon proteins is given as follows by Buchanan
and Fulmer.
"1. Those electrolytes which bring about a reversible precipitation
in high concentration. These include the salts of the alkalis, K, Na,
NH4, Li and possibly Mg. Ammonium sulphate is commonly used
in 'salting out' of proteins. The precipitate so formed will be redis-
solved on dilution, i.e., the process is reversible.
''When the protein is on the alkaline side of its isoelectric point (i.e.,
ISOELECTRIC POINT 11
negatively charged), the order of effectiveness of the salt is on the
basis of cations: Li > K > Na > NH4 > Mg and of anions, citrate
> tartrate > SO4 > acetate > CI > NO3 > CIO3 > I > SCN.