Classification of Soap-Making Methods.
In the saponification of fats and oils to form soap through the agency
of caustic alkalis, as has been stated, the sodium or potassium salts of
the mixed fatty acids are formed. Sodium soaps are usually termed hard
soaps, and potassium soaps soft. There are, however, a great many
varieties of soaps the appearance and properties of which depend upon
their method of manufacture and the oils or fats used therein.
The various methods adopted in soap making may be thus classified:
1. Boiling the fats and oils in open kettles by open steam with
indefinite quantities of caustic alkali solutions until the finished
soap is obtained; ordinarily named _full boiled soaps_. These may be
sub-divided into (a) hard soaps with sodium hydrate as a base, in which
the glycerine is recovered from the spent lyes; (b) hard soaps with soda
as a base, in which the glycerine remains in the soap, e. g., marine
cocoanut oil soaps; (c) soft potash soaps, in which the glycerine is
retained by the soap.
2. Combining the required amount of lye for complete saponification of a
fat therewith, heating slightly with dry heat and then allowing the
saponification to complete itself. This is known as the _cold process_.
3. Utilizing the fatty acid, instead of the neutral fat, and combining
it directly with caustic alkali or carbonate, which is incorrectly
termed _carbonate saponification_, since it is merely neutralizing the
free fatty acid and thus is not a saponification in the true sense of
the word. No glycerine is directly obtained by this method, as it is
usually previously removed in the clearage of the fat by either the
Twitchell or autoclave saponification method.
In the methods thus outlined the one most generally employed is the full
boiled process to form a sodium soap. This method of making soap
requires close attention and a knowledge which can only be obtained by
constant practice. The stock, strength of lyes, heat, amount of salt or
brine added, time of settling, etc., are all influencing factors.
The principles involved in this process are briefly these:
The fat is partly saponified with weak lyes (usually those obtained from
a previous boiling in the strengthening change are used), and salt is
added to grain the soap. The mass is then allowed to settle into two
layers. The upper layer is partly saponified fat; the lower layer, or
spent lye, is a solution of salt, glycerine, and contains any albuminous
matter or any other impurity contained in the fat. This is known as the
_killing_ or glycerine change. Strong lyes are now added and the fat
entirely saponified, which is termed the _strengthening change_. The
mass is then allowed to settle and the fluid soap run off above the
"nigre." This operation is called the finish or _finishing_ change.
The method may be more fully illustrated by a concrete example of the
method of manufacture of a tallow base:
Charge--
Tallow 88 per cent.
Cocoanut oil 10 per cent.
Rosin w. w. 2 per cent.
Amount charge 10 tons
About five tons of tallow and one ton of cocoanut oil are pumped or run
into the soap kettle and brought to a boil with wet steam until it
briskly comes through the hot fat. The caustic soda (strengthening lyes
from former boilings may be used here) is gradually added by the
distributing pipe, any tendency to thicken being checked by the
introduction of small quantities of brine ("salt pickle"). If the lye is
added too rapidly the soap assumes a granular appearance, indicating
that the addition of same must be discontinued. Water should then be
added and the mass boiled through until it again closes. When the
addition of the proper amount of caustic soda is nearing its completion
the soap gradually thins. The steam is now cut down to about one turn of
the valve, and brine is rapidly added or salt shoveled in. In ten to
fifteen minutes the steam again breaks through and, from the appearance
of the soap, it can be seen whether sufficient brine has been added. A
sample taken out by means of a long wooden paddle should show the soap
in fine grains with the lyes running from it clear. The steam is then
shut off and the soap allowed to settle from one and one-half to two
hours. In all settlings the longer time this operation is permitted to
continue, the better will the subsequent operations proceed.
The mixture now consists of a partly saponified layer of fat above the
spent lyes. The lyes are drawn off until soap makes its appearance at
the exit pipe. The valve is then closed and the soap blown back into the
kettle by steam. The lyes thus obtained are known as _spent lyes_, from
which the glycerine is recovered. They should show an alkalinity of
approximately 0.5 per cent. if the operation is carefully carried out.
The remaining tallow is now added and the above operations repeated.
After the spent lyes have been drawn off, the soap is closed with water
and the proper percentage of rosin soap previously formed, or rosin
itself is added to the mass in the kettle. More lye is then allowed to
flow in until the mixture is up to "strength." This is usually tested
by the "bite" on the tongue of a small cooled sample. After boiling
until the steam comes through, the mass is grained with salt as before
and allowed to settle one and one-half to three hours. These lyes, known
as _strengthening lyes_ are run to storage to be used subsequently with
fresh fat to take up the caustic soda contained therein.
The soap is now ready for finishing and is first boiled through and
tried for strength. A drop of phenolphthalein (1 per cent.
phenolphthalein in 98 per cent. alcohol) is allowed to drop on the
molten soap taken up on a trowel. The red color should be instantly
produced and develop to a full deep crimson in a few seconds, or more
lye must be added until this condition is realized. Should it flash a
deep crimson immediately it is on the strong side. This cannot be
conveniently remedied; it can only serve as a guide for the next boil,
but in any case it is not of any serious consequence, unless it is too
strong.
With the steam on, the soap is now examined with a trowel which must be
thoroughly heated by working it about under the surface of the hot soap.
The appearance of the soap as it runs from the face of the trowel
indicates its condition. It is not possible to absolutely describe the
effect, which can only be properly judged by practice, yet the following
points may serve as a guide. The indications to be noticed are the shape
and size of the flakes of soap as the sample on the trowel breaks up and
runs from the hot iron surface, when the latter is turned in a vertical
position, as well as the condition of the iron surface from which the
soap flakes have fallen. A closed soap will run slowly into a
homogeneous sheet, leaving the trowel's surface covered with a thin
layer of transparent soap; a grained mass will run rapidly down in tiny
grains, about one-half an inch in diameter or less, leaving the hot
trowel absolutely dry. The object of the finish is to separate the
soaps of the lower fatty acids from those of the higher, and both from
excess of liquid. A point midway between "open" and "closed" is required
to arrive at this point.
Having arrived at the above condition, the soap is allowed to settle
anywhere from one to three days and then run off through the skimmer
pipes to the nigre and framed or pumped to the tank feeding the drying
machine.
The stock thus obtained should be fairly white, depending upon the grade
of tallow used and slightly alkaline to an alcoholic phenolphthalein
solution. If removed at exactly the neutral point or with a content of
free fat the soap will sooner or later develop rancidity. The soap thus
obtained is an ordinary tallow base, and the one by far greatest used in
the manufacture of toilet soaps. The percentage of cocoanut oil
indicated is not fixed and may readily be varied, while in fine toilet
soap the rosin is usually eliminated.
In the manufacture of full boiled soda soaps in which no glycerine is
obtained as a by-product, it being retained in the soap itself, the soap
formed is known as a "run" soap. The process is used most extensively in
the manufacture of marine soaps by which the method may be best
illustrated. This soap is known as marine soap because of its property
of readily forming a lather with salt water and is mostly consumed
aboard vessels.
Marine soaps are manufactured by first placing in the kettle a
calculated amount of lye of 25 deg. to 35 deg. B., depending upon the
amount of moisture desired in the finished soaps, plus a slight excess
required to saponify a known weight of cocoanut oil. With open steam on,
the cocoanut oil is then gradually added, care being taken that the soap
does not froth over. Saponification takes place readily and when the oil
is entirely saponified the finished soap is put through the process
known as running. This consists in constantly pumping the mass from the
skimmer pipe back into the top of the kettle, the object being to
prevent any settling of the nigre or lye from the soap, as well as
producing a homogeneous mass. It is customary to begin the
saponification in the morning, which should be completed by noon. The
soap is then run for about three hours and framed the next morning.
After having remained in the frame the time required to solidify and
cool, the soap is slabbed and cut into cakes. This process is difficult
to carry out properly, and one not greatly employed, although large
quantities of marine soap are purchased by the government for use in the
navy and must fulfill certain specifications required by the purchasing
department.
In making potash soaps it is practically impossible to obtain any
glycerine directly because of the pasty consistency of the soap, and no
graining is possible because the addition of salt to a soft soap, as
already explained, would form a soda soap. Large quantities of soft
soaps are required for the textile industries who desire mostly a strong
potash soap, and the large number of automobiles in use at the present
time has opened a field for the use of a soft soap for washing these. A
soap for this purpose must be neutral so as not to affect the varnish or
paint of automobiles.
A suitable soap for textile purposes may be made as follows:
Red oil 80 parts
House grease 20 parts
Caustic soda lye, 36 degs. B. 3 parts
Carbonate of potash 5-1/2 parts
Caustic potash 23-1/4 parts
Olive oil, corn oil, soya bean oil, olive oil foots or cottonseed oil
may replace any of the above oils. A large quantity of cottonseed oil
will cause the soap to fig.
To carry out the process, the caustic potash and carbonate of potash are
dissolved and placed in the kettle together with the soda lye, and the
oils added. This is most satisfactorily accomplished by being finished
the day before the boiling is begun. The next day the boiling is begun
and water added to bring the soap up to the desired percentage of fatty
acid, due allowance being made for the water formed by the condensation
of the open steam in boiling. Care must be taken that the soap in the
kettle does not swell and run over during the saponification. A good
procedure is to use open steam for a period of about two hours, then
close the valve and allow the saponification to continue without
boiling, and repeat this until it is entirely saponified. After the
saponification has been completed the soap is briskly boiled all day and
the proper corrections made; that is, if too alkaline, more oil is
added, and if free fat is present, more potash. About 2 per cent.
carbonate of potash is the proper amount for a soap containing 50 per
cent. fatty acid. The soap is sampled by allowing it to drop on a clean,
cold glass surface. In so doing, the soap should not slide or slip over
the glass surface when pressed thereon, but should adhere to the glass,
or it is too alkaline. A sample worked between the fingers showing too
much stringiness should have more strong potash and oil added. A sample
taken out in a pail and allowed to cool over night will serve as a guide
as to the body of the soap in the kettle. When the soap has thus been
properly finished it is run into barrels.
For an automobile soap the following is a good working formula:
Corn oil 1,000 parts
Potash lye, 31-1/2 degs. B. 697 parts
Proceed as in the directions just given for textile soap in placing
charge in the kettle. When the kettle is boiling up well, shut off the
steam and the saponification will complete itself. The soap may be run
into the barrels the next day.
A heavy soap with a smaller percentage of fat may be made as follows:
Corn oil 1,000 parts
Potash lye, 24-1/2 degs. B. 900 parts
Boil until the soap bunches, and shovel the finished soap into barrels.
Upon standing it will clear up. By the addition of more water the yield
of soap per pound of oil may be run up to 300 per cent.
After soft soaps have been allowed to stand for some time the phenomenon
known as "figging" often occurs. This term is applied to a
crystalline-like formation, causing spots of a star-like shape
throughout the soap. This is undoubtedly due to the stearine content of
the soap crystallizing out as it cools, and forming these
peculiarly-shaped spots. It more generally occurs in the winter and may
be produced artificially by adding a small quantity of soda to the
potash lye before saponification.
The oils usually employed in the manufacture of potash soaps are
cottonseed oil, corn oil, soya bean oil, olive oil foots, red oil,
cocoanut oil, grease and the various train oils. The usual percentage
yield is from 225 per cent. to 300 per cent., based upon the weight of
oil used. In calculating the weight of a soft soap it is to be
remembered that since potassium has a higher molecular weight (56) than
sodium (40), the corresponding soap formed is that much greater in
weight when compared with a sodium soap. Rosin may be added to soft
soaps as a cheapening agent.
COLD PROCESS.
The cold process for manufacturing soap is the simplest method of soap
making, and the equipment required is small when compared to the other
methods. All the more expensive equipment that is necessary is a
crutcher, a tank to hold the lye, frames, a slabber or cutting table,
and a press. Yet, in spite of the simplicity of thus making soap, the
disadvantages are numerous for the production of a good piece of soap.
The greatest difficulty is to obtain a thorough combination of oil or
fat and lye so that there will not be an excess of one or the other in
the finished soap. At its best there is either a considerable excess of
free fat which later exhibits itself in producing rancidity or
uncombined caustic, which produces an unpleasant effect on the skin when
the soap is consumed for washing. The latter objection, of course, can
only be applied to toilet soaps.
Cocoanut oil is used very largely in the manufacture of cold-made soaps
as it is well adapted for this purpose, although it is by no means true
that other oils may not be employed. Since by this process of
manufacture no impurity contained in the fat or oil is removed in the
making of the soap, it is necessary that in order to obtain a fine
finished product, any impurity contained in these may be removed if
present, or that the fats be as pure as can be obtained. If inedible
tallow is used for cold-made soap, it is advisable to bleach it by the
Fuller's Earth Process.
The carrying out of this method is best illustrated by an example of a
cold-made cocoanut oil soap.
Charge:
Cochin cocoanut oil 846 parts
Lye (soda), 35 degs. B. 470 parts
Water 24 parts
The oil is run into the crutcher and the temperature of the oil raised
to 100 degs. F. by dry steam. The lye and water are at room temperature.
After all the oil is in the crutcher, the lye and water are slowly added
to prevent any graining of the soap. Toward the end the lye may be added
more rapidly. When all the lye is in, the mass is crutched for about
three hours, or until upon stopping the crutcher a finger drawn over the
surface of the soap leaves an impression. If this condition is not
realized, the soap must be mixed until such is the case. Having arrived
at this point, the mixture is dropped into a frame which should remain
uncovered. The heat produced by the further spontaneous saponification
will cause the soap to rise in the middle of the frame. After having set
for some days it is ready to be slabbed and cut into cakes.
A potash soap may be made by the cold process just as readily as a soda
soap. Soaps of this type may be made by either of these formulae in a
crutcher:
Olive oil foots 600
Potash lye, 18 degs. B. hot, 20 degs. B. cold 660
or
Corn oil 800
Rosin 200
Potash lye, 27 degs. B. 790
Water 340
Heat the oils to 190 degs. F., add the lye and crutch until the soap
begins to bunch, when it is ready to be run into barrels where the
saponification will be completed.
Semi-boiled soaps differ from those made by the cold process in
temperature. In making semi-boiled soaps the fats are usually heated to
140deg. F. The addition of the lye raises the temperature to
180deg.--200deg. F. when saponification takes place.
CARBONATE SAPONIFICATION.
The method of the formation of soap by the utilization of the fatty acid
directly, from which the glycerine has already been removed by some
method of saponification other than with caustic soda, and neutralizing
this with alkali, is becoming increasingly popular. The glycerine is
more easily recovered from a previous cleavage of the fats or oils, but
a soap made from the mixed fatty acids thus obtained is seldom white in
color and retains an unpleasant odor. Since soda ash or sodium carbonate
is cheaper than caustic soda and readily unites with a fatty acid, it is
used as the alkali in the carbonate saponification. The process is
similar to that already given under Rosin Saponification. About 19 per
cent. by weight of the fatty acids employed of 58 per cent. soda ash is
dissolved in water until it has a density of 30 degs. B., and the
solution is run into the kettle, which is usually equipped with a
removable agitator. The fatty acids, previously melted, are then slowly
added while the mixture is boiled with open steam and agitated with the
stirring device. The fatty acids instantly unite with the carbonate and
rise in the kettle, due to the generation of carbon dioxide, and care
must be exercised to prevent boiling over. After all the fatty acid has
been added, and the mass is boiled through the saponification must be
completed with caustic soda, as there is as yet no practical method
known which will split a fat entirely into fatty acid and glycerine.
Thus about 10 per cent. of the fatty acids are true neutral fats and
require caustic soda for their saponification. This is then added and
the soap completed, as in full-boiled soaps.
In carrying out this method upon a large scale, large
sue\Neanderthal\doroteer\Neanderthal\Josephine\ quantities of carbon
dioxide are formed during the boiling of the soap, which replaces a
quantity of the air contained therein. The kettle room should therefore
be well ventilated, allowing for a large inflow of fresh air from out of
doors.