DOI Page / Citation link:
https://doi.org/10.11588/diglit.1311#0210
OF THE WORLD'S INDUSTRY. ] 77
and chlorides, for example), and a minute quantity of caustic-lime. Common resin (colo-
pony) is the residue of the distillation of natural turpentines, and consists principally of
pinic acid, together with a litte sylvic and colophonic acids. When resin is boiled with
alkalies, carbonated or not, a compound is readily obtained, but of course no glycerin.
Thus, when it is boiled with soda, a pinate of soda is chiefly produced. This compound
exists in considerable quantity in yellow soap, and gives to it its distinctive character.
The character of soap is not only affected by the nature of the acids which it contains,
but also by that of the alkali which has served-for its preparation; the soaps containing
potash are generally soft and pasty; those prepared with soda are hard and solid.
The compounds of stearic, margaric, oleic, palmitic, cocinic, pinic, and sylvic acids, with
potash and soda, are all readily soluble in alcohol and hot water, but more so in the
former, which, on evaporation, leaves the soap in a translucent state; hence its application
in the preparation of " transparent soaps." Soaps, however, are insoluble in a solution
of many neutral salts, particularly when concentrated ; this property is of great use to the
soap-boiler, who employs it for the separation of the soap from its solution in water,
generally adding common salt to set the soap at liberty. As soaps are likewise insoluble
in strong alkaline lyes, the same end is sometimes attained by boiling down the soap to a
certain consistence, when it separates from the excess of lye. The soap made with cocoa-
nut oil is, however, soluble in a very strong brine, and the same plan of separation does
not succeed with it; but, as it is more generally employed together with other fats, this
difficulty is then overcome. Its property of dissolving in salt water renders it peculiarly
adapted to the formation of a marine soap. One remarkable property of cocoa-nut oil
soap is, that of solidifying with a much larger quantity of water than most other
soaps, thus giving a larger yield, but, of course, being of proportionally less value. This
property is, however, unfortunately, often turned to profitable account by the soap-maker.
As an instance, may be quoted an analysis of Dr. Ure, who found a London cocoa-nut oil
soap to contain seventy-five per cent, of water, whereas twenty-five per cent, of water is a
large quantity for any but potash soaps to contain, and these generally contain less
than fifty per cent. The greater part of our knowledge concerning the chemical con-
stitution of fats, and the changes winch accompany their decomposition under the
influence of alkalies, is due to the masterly researches of Chevreul, prosecuted with
wonderful acuteness and perseverance, from 1813 to 1823, when they were published in
Paris in a collected form, under the title of Recherches Chimigues sur les Corps Gras
d'Origine Animate, a work which will ever remain a model of philosophical inquiry.
There are two processes chiefly employed in the preparation of soaps, the most simple of
which is that called the cold process, or the small-boiler process. For the purpose of
making soap in this manner, the alkaline lye is prepared from the purest commercial soda,
and concentrated by evaporation. As the chloride of sodium and sulphate of soda, which
commercial soda contains, are nearly insoluble in a strong alkaline solution, they crystallize
out, especially on allowing the lye to stand for some days, thus leaving it much purer.
A weighed quantity of fat is melted, and the strength of the lye having been pre-
viously ascertained by taking its specific gravity, a certain portion is weighed or measured,
and separately heated, and then stirred with the melted fat. Saponification soon occurs,
and on cooling, the soap solidifies. It is very evident that soap made in this manner must
contain the glycerin; moreover, as it is very difficult to obtain an exact neutralization of
the fat or alkali, one or the other is often in excess, generally the fat; this prevents such
soap from giving so good a lather as those prepared by the more usual method.
The ordinary method is called the large-boiler process, and it is usually conducted
on a very large scale, in boilers capable of holding many tons. A quantity of weak
soda-lye is put into the iron or copper boiler, and raised to the boiling point; and
vol. ii. 2 z
and chlorides, for example), and a minute quantity of caustic-lime. Common resin (colo-
pony) is the residue of the distillation of natural turpentines, and consists principally of
pinic acid, together with a litte sylvic and colophonic acids. When resin is boiled with
alkalies, carbonated or not, a compound is readily obtained, but of course no glycerin.
Thus, when it is boiled with soda, a pinate of soda is chiefly produced. This compound
exists in considerable quantity in yellow soap, and gives to it its distinctive character.
The character of soap is not only affected by the nature of the acids which it contains,
but also by that of the alkali which has served-for its preparation; the soaps containing
potash are generally soft and pasty; those prepared with soda are hard and solid.
The compounds of stearic, margaric, oleic, palmitic, cocinic, pinic, and sylvic acids, with
potash and soda, are all readily soluble in alcohol and hot water, but more so in the
former, which, on evaporation, leaves the soap in a translucent state; hence its application
in the preparation of " transparent soaps." Soaps, however, are insoluble in a solution
of many neutral salts, particularly when concentrated ; this property is of great use to the
soap-boiler, who employs it for the separation of the soap from its solution in water,
generally adding common salt to set the soap at liberty. As soaps are likewise insoluble
in strong alkaline lyes, the same end is sometimes attained by boiling down the soap to a
certain consistence, when it separates from the excess of lye. The soap made with cocoa-
nut oil is, however, soluble in a very strong brine, and the same plan of separation does
not succeed with it; but, as it is more generally employed together with other fats, this
difficulty is then overcome. Its property of dissolving in salt water renders it peculiarly
adapted to the formation of a marine soap. One remarkable property of cocoa-nut oil
soap is, that of solidifying with a much larger quantity of water than most other
soaps, thus giving a larger yield, but, of course, being of proportionally less value. This
property is, however, unfortunately, often turned to profitable account by the soap-maker.
As an instance, may be quoted an analysis of Dr. Ure, who found a London cocoa-nut oil
soap to contain seventy-five per cent, of water, whereas twenty-five per cent, of water is a
large quantity for any but potash soaps to contain, and these generally contain less
than fifty per cent. The greater part of our knowledge concerning the chemical con-
stitution of fats, and the changes winch accompany their decomposition under the
influence of alkalies, is due to the masterly researches of Chevreul, prosecuted with
wonderful acuteness and perseverance, from 1813 to 1823, when they were published in
Paris in a collected form, under the title of Recherches Chimigues sur les Corps Gras
d'Origine Animate, a work which will ever remain a model of philosophical inquiry.
There are two processes chiefly employed in the preparation of soaps, the most simple of
which is that called the cold process, or the small-boiler process. For the purpose of
making soap in this manner, the alkaline lye is prepared from the purest commercial soda,
and concentrated by evaporation. As the chloride of sodium and sulphate of soda, which
commercial soda contains, are nearly insoluble in a strong alkaline solution, they crystallize
out, especially on allowing the lye to stand for some days, thus leaving it much purer.
A weighed quantity of fat is melted, and the strength of the lye having been pre-
viously ascertained by taking its specific gravity, a certain portion is weighed or measured,
and separately heated, and then stirred with the melted fat. Saponification soon occurs,
and on cooling, the soap solidifies. It is very evident that soap made in this manner must
contain the glycerin; moreover, as it is very difficult to obtain an exact neutralization of
the fat or alkali, one or the other is often in excess, generally the fat; this prevents such
soap from giving so good a lather as those prepared by the more usual method.
The ordinary method is called the large-boiler process, and it is usually conducted
on a very large scale, in boilers capable of holding many tons. A quantity of weak
soda-lye is put into the iron or copper boiler, and raised to the boiling point; and
vol. ii. 2 z