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Soap-Making Manual
A practical handbook on the raw materials, their manipulation, analysis
and control in the modern soap plant.
By
_E. G. Thomssen, Ph. D._
ILLUSTRATED
NEW YORK
D. VAN NOSTRAND COMPANY
EIGHT WARREN STREET
1922
COPYRIGHT 1922
BY
D. VAN NOSTRAND COMPANY
Printed in the United States of America
* * * * *
Transcriber's note:
This is a series of articles collected into a book. There are
differences in spelling and punctuation in the different chapters (e.g.
cocoanut in one chapter and coconut in another). These differences were
left in the text as they appeared.
For Text: A word surrounded by a tilde such as ~this~ signifies that
the word is bolded in the text. A word surrounded by underscores like
_this_ signifies the word is italics in the text.
For numbers and equations: Parentheses have been added to clarify
fractions. Underscores before bracketed numbers in equations denote a
subscript. The Degree symbol has been changed to deg. in the ASCII
file.
Minor typos have been corrected and footnotes moved to the end of the
chapters.
* * * * *
PREFATORY NOTE.
The material contained in this work appeared several years ago in serial
form in the American Perfumer and Essential Oil Review. Owing to the
numerous requests received, it has been decided to now place before
those interested, these articles in book form. While it is true that the
works pertaining to the soapmaking industry are reasonably plentiful,
books are quite rare, however, which, in a brief volume, will clearly
outline the processes employed together with the necessary methods of
analyses from a purely practical standpoint. In the work presented the
author has attempted to briefly, clearly, and fully explain the
manufacture of soap in such language that it might be understood by all
those interested in this industry. In many cases the smaller plants find
it necessary to dispense with the services of a chemist, so that it is
necessary for the soapmaker to make his own tests. The tests outlined,
therefore, are given as simple as possible to meet this condition. The
formulae submitted are authentic, and in many cases are now being used
in soapmaking.
In taking up the industry for survey it has been thought desirable to
first mention and describe the raw materials used; second, to outline
the processes of manufacture; third, to classify the methods and
illustrate by formulae the composition of various soaps together with
their mode of manufacture; fourth, to enumerate the various methods of
glycerine recovery, including the processes of saponification, and,
fifth, to give the most important analytical methods which are of value
to control the process of manufacture and to determine the purity and
fitness of the raw material entering into it.
It is not the intention of the author to go into great detail in this
work, nor to outline to any great extent the theoretical side of the
subject, but rather to make the work as brief as possible, keeping the
practical side of the subject before him and not going into concise
descriptions of machinery as is very usual in works on this subject.
Illustrations are merely added to show typical kinds of machinery used.
The author wishes to take this opportunity of thanking Messrs. L. S.
Levy and E. W. Drew for the reading of proof, and Mr. C. W. Aiken of the
Houchin-Aiken Co., for his aid in making the illustrations a success, as
well as others who have contributed in the compiling of the formulae for
various soaps. He trusts that this work may prove of value to those
engaged in soap manufacture.
E. G. T.
January, 1922
TABLE OF CONTENTS.
CHAPTER I. Page.
RAW MATERIALS USED IN SOAP MAKING 1-30
1. Soap Defined 1
2. Oils and Fats 1-2
3. Saponification Defined 2-3
4. Fats and Oils Used in Soap Manufacture 3-4
Fullers' Earth Process for Bleaching Tallow 4-6
Method for Further Improvement of Color in Tallow 6
Vegetable Oils 6-9
Chrome Bleaching of Palm Oil 9-12
Air Bleaching of Palm Oil 12-16
5. Rancidity of Oils and Fats 16-18
Prevention of Rancidity 18
6. Chemical Constants of Oils and Fats 18-19
7. Oil Hardening or Hydrogenating 19-21
8. Grease 21-22
9. Rosin (Colophony, Yellow Rosin, Resina) 22-23
10. Rosin Saponification 23-24
11. Naphthenic Acids 24-25
12. Alkalis 25-26
Caustic Soda 26
Caustic Potash 26-28
Sodium Carbonate (Soda Ash) 28-29
Potassium Carbonate 29
13. Additional Material Used in Soap Making 29-30
CHAPTER II.
CONSTRUCTION AND EQUIPMENT OF A SOAP PLANT 31-34
CHAPTER III.
CLASSIFICATION OF SOAP MAKING METHODS 35-46
1. Full Boiled Soaps 36-42
2. Cold Process 43-44
3. Carbonate Saponification 45-46
CHAPTER IV.
CLASSIFICATION OF SOAPS 47-104
1. Laundry Soap 48
Semi-Boiled Laundry Soap 49-50
Settled Rosin Soap 50-54
2. Chip Soap 54-55
Cold Made Chip Soap 55-56
Unfilled Chip Soap 56
3. Soap Powders 56-59
Light Powders 60-61
4. Scouring Powders 61
5. Scouring Soap 61-62
6. Floating Soap 62-65
7. Toilet Soap 65-68
Cheaper Toilet Soaps 68-69
Run and Glued-up Soaps 69-71
Curd Soap 71-72
Cold Made Toilet Soaps 72-73
Perfuming and Coloring Toilet Soaps 73-75
Coloring Soap 75-76
8. Medicinal Soaps 76-77
Sulphur Soaps 77
Tar Soap 77
Soaps Containing Phenols 77-78
Peroxide Soap 78
Mercury Soaps 78
Less Important Medicinal Soaps 78-79
9. Castile Soap 79-81
10. Eschweger Soap 81-82
11. Transparent Soap 82-84
Cold Made Transparent Soap 84-87
12. Shaving Soaps 87-90
Shaving Powder 90
Shaving Cream 90-93
13. Pumice or Sand Soaps 93-94
14. Liquid Soaps 94-95
15. Use of Hardened Oils in Toilet Soaps 96-98
16. Textile Soaps 98
Scouring and Fulling Soaps for Wool 98-100
Wool Thrower's Soap 100-101
Worsted Finishing Soaps 101
Soaps Used in the Silk Industry 101-103
Soaps Used for Cotton Goods 103-104
17. Sulphonated Oils 104-105
CHAPTER V.
GLYCERINE RECOVERY 105-126
1. Methods of Saponification 105-106
Recovery of Glycerine from Spent Lye 106-113
Twitchell Process 113-118
Autoclave Saponification 118
Lime Saponification 118-120
Acid Saponification 120-121
Aqueous Saponification 121
Splitting Fats with Ferments 121-123
Krebitz Process 123-125
2. Distillation of Fatty Acids 125-126
CHAPTER VI.
ANALYTICAL METHODS 127-164
1. Analysis of Oils and Fats 128
Free Fatty Acids 128-130
Moisture 130
Titer 130-132
Determination of Unsaponifiable Matter 132-133
Test for Color of Soap 133-134
Testing of Alkalis Used in Soap Making 134-137
2. Soap Analysis 137-138
Moisture 138-139
Free Alkali or Acid 139-142
Insoluble Matter 143
Starch and Gelatine 143-144
Total Fatty and Resin Acids 144
Determination of Rosin 144-147
Total Alkali 147-148
Unsaponifiable Matter 148
Silica and Silicates 148-149
Glycerine in Soap 149-150
Sugar in Soap 150
3. Glycerine Analysis 150-151
Sampling 151
Analysis 151-154
Acetin Process for the Determination of Glycerol 155-156
The Method 156-159
Ways of Calculating Actual Glycerol Contents 159-160
Bichromate Process for Glycerol Determination
Reagents Required 160-161
The Method 161-162
Sampling Crude Glycerine 162-164
CHAPTER VII
STANDARD METHODS FOR THE SAMPLING AND ANALYSIS OF
COMMERCIAL FATS AND OILS 165-195
1. Scope, Applicability and Limitations of the Methods 165-166
Scope 165
Applicability 166
Limitations 166
Sampling 166-169
Tank Cars 166-167
Barrels, Tierces, Casks, Drums, and Other Packages 168
2. Analysis 169-183
Sample 169
Moisture and Volatile Matter 170-172
Insoluble Impurities 172-173
Soluble Mineral Matter 173
Free Fatty Acids 174
Titer 174-175
Unsaponifiable Matter 176-177
Iodine Number-Wijs Method 177-181
Saponification Number (Koettstorfer Number) 181
Melting Point 181-182
Cloud Test 182-184
3. Notes of the Above Methods 184-196
Sampling 183
Moisture and Volatile Matter 184-187
Insoluble Impurities 187
Soluble Mineral Matter 187-188
Free Fatty Acid 188-189
Titer 189
Unsaponified Matter 190-193
Melting Point 193-196
Plant and Machinery 198-219
Illustrations of Machinery and Layouts of the Plant
of a Modern Soap Making Establishment 198-219
Appendix 219-237
Useful Tables
Index 239
CHAPTER I
Raw Materials Used in Soap Making.
Soap is ordinarily thought of as the common cleansing agent well known
to everyone. In a general and strictly chemical sense this term is
applied to the salts of the non-volatile fatty acids. These salts are
not only those formed by the alkali metals, sodium and potassium, but
also those formed by the heavy metals and alkaline earths. Thus we have
the insoluble soaps of lime and magnesia formed when we attempt to wash
in "hard water"; again aluminum soaps are used extensively in polishing
materials and to thicken lubricating oils; ammonia or "benzine" soaps
are employed among the dry cleaners. Commonly, however, when we speak of
soap we limit it to the sodium or potassium salt of a higher fatty acid.
It is very generally known that soap is made by combining a fat or oil
with a water solution of sodium hydroxide (caustic soda lye), or
potassium hydroxide (caustic potash). Sodium soaps are always harder
than potassium soaps, provided the same fat or oil is used in both
cases.
The detergent properties of soap are due to the fact that it acts as an
alkali regulator, that is, when water comes into contact with soap, it
undergoes what is called hydrolytic dissociation. This means that it is
broken down by water into other substances. Just what these substances
are is subject to controversy, though it is presumed caustic alkali and
the acid alkali salt of the fatty acids are formed.
OILS AND FATS.
There is no sharp distinction between fat and oil. By "oil" the layman
has the impression of a liquid which at warm temperature will flow as a
slippery, lubricating, viscous fluid; by "fat" he understands a greasy,
solid substance unctuous to the touch. It thus becomes necessary to
differentiate the oils and fats used in the manufacture of soap.
Inasmuch as a soap is the alkali salt of a fatty acid, the oil or fat
from which soap is made must have as a constituent part, these fatty
acids. Hydrocarbon oils or paraffines, included in the term "oil," are
thus useless in the process of soap-making, as far as entering into
chemical combination with the caustic alkalis is concerned. The oils and
fats which form soap are those which are a combination of fatty acids
and glycerine, the glycerine being obtained as a by-product to the
soap-making industry.
NATURE OF A FAT OR OIL USED IN SOAP MANUFACTURE.
Glycerine, being a trihydric alcohol, has three atoms of hydrogen which
are replaceable by three univalent radicals of the higher members of the
fatty acids, _e. g._,
OH OR
C_{3} H_{5} OH + 3 ROH = C_{3} H_{5} OR + 3 H_{2}O
OH OR
Glycerine plus 3 Fatty Alcohols equals Fat or Oil plus 3 Water.
Thus three fatty acid radicals combine with one glycerine to form a true
neutral oil or fat which are called triglycerides. The fatty acids which
most commonly enter into combination of fats and oils are lauric,
myristic, palmitic, stearic and oleic acids and form the neutral oils or
triglycerides derived from these, _e. g._, stearin, palmatin, olein.
Mono and diglycerides are also present in fats.
SAPONIFICATION DEFINED.
When a fat or oil enters into chemical combination with one of the
caustic hydrates in the presence of water, the process is called
"saponification" and the new compounds formed are soap and glycerine,
thus:
OR OH
C_{3}H_{5} OR + 3 NaOH = C_{3}H_{5} OH + 3 NaOR
OR OH
Fat or Oil plus 3 Sodium Hydrate equals Glycerine plus 3 Soap.
It is by this reaction almost all of the soap used today is made.
There are also other means of saponification, as, the hydrolysis of an
oil or fat by the action of hydrochloric or sulfuric acid, by autoclave
and by ferments or enzymes. By these latter processes the fatty acids
and glycerine are obtained directly, no soap being formed.
FATS AND OILS USED IN SOAP MANUFACTURE.
The various and most important oils and fats used in the manufacture of
soap are, tallow, cocoanut oil, palm oil, olive oil, poppy oil, sesame
oil, soya bean oil, cotton-seed oil, corn oil and the various greases.
Besides these the fatty acids, stearic, red oil (oleic acid) are more or
less extensively used. These oils, fats and fatty acids, while they vary
from time to time and to some extent as to their color, odor and
consistency, can readily be distinguished by various physical and
chemical constants.
Much can be learned by one, who through continued acquaintance with
these oils has thoroughly familiarized himself with the indications of a
good or bad oil, by taste, smell, feel and appearance. It is, however,
not well for the manufacturer in purchasing to depend entirely upon
these simpler tests. Since he is interested in the yield of glycerine,
the largest possible yield of soap per pound of soap stock and the
general body and appearance of the finished product, the chemical tests
upon which these depend should be made. Those especially important are
the acid value, percentage unsaponifiable matter and titer test.
A short description of the various oils and fats mentioned is sufficient
for their use in the soap industry.
_Tallow_ is the name given to the fat extracted from the solid fat or
"suet" of cattle, sheep or horses. The quality varies greatly, depending
upon the seasons of the year, the food and age of the animal and the
method of rendering. It comes to the market under the distinction of
edible and inedible, a further distinction being made in commerce as
beef tallow, mutton tallow or horse tallow. The better quality is white
and bleaches whiter upon exposure to air and light, though it usually
has a yellowish tint, a well defined grain and a clean odor. It consists
chiefly of stearin, palmitin and olein. Tallow is by far the most
extensively used and important fat in the making of soap.
In the manufacture of soaps for toilet purposes, it is usually necessary
to produce as white a product as possible. In order to do this it often
is necessary to bleach the tallow before saponification. The method
usually employed is the Fuller's Earth process.
FULLER'S EARTH PROCESS FOR BLEACHING TALLOW.
From one to two tons of tallow are melted out into the bleaching tank.
This tank is jacketed, made of iron and provided with a good agitator
designed to stir up sediment or a coil provided with tangential downward
opening perforations and a draw-off cock at the bottom. The coil is the
far simpler arrangement, more cleanly and less likely to cause trouble.
By this arrangement compressed air which is really essential in the
utilization of the press (see later) is utilized for agitation. A dry
steam coil in an ordinary tank may be employed in place of a jacketed
tank, which lessens the cost of installation.
The tallow in the bleaching tank is heated to 180deg. F. (82deg. C.) and
ten pounds of dry salt per ton of fat used added and thoroughly mixed by
agitation. This addition coagulates any albumen and dehydrates the fat.
The whole mass is allowed to settle over night where possible, or for at
least five hours. Any brine which has separated is drawn off from the
bottom and the temperature of the fat is then raised to 160deg. F.
(71deg. C).
Five per cent. of the weight of the tallow operated upon, of dry
Fuller's earth is now added and the whole mass agitated from twenty to
thirty minutes.
The new bleached fat, containing the Fuller's earth is pumped directly
to a previously heated filter press and the issuing clear oil run
directly to the soap kettle.
One of the difficulties experienced in the process is the heating of the
press to a temperature sufficient to prevent solidification of the fat
without raising the press to too great a temperature. To overcome this
the first plate is heated by wet steam. Air delivered from a blower and
heated by passage through a series of coils raised to a high temperature
by external application of heat (super-heated steam) is then substituted
for the steam. The moisture produced by the condensation of the steam is
vaporized by the hot air and carried on gradually to each succeeding
plate where it again condenses and vaporizes. In this way the small
quantity of water is carried through the entire press, raising its
temperature to 80deg.-100deg. C. This temperature is subsequently
maintained by the passage of hot air. By this method of heating the poor
conductivity of hot air is overcome through the intermediary action of a
liquid vapor and the latent heat of steam is utilized to obtain the
initial rise in temperature. To heat a small press economically where
conditions are such that a large output is not required the entire press
may be encased in a small wooden house which can be heated by steam
coils. The cake in the press is heated for some time after the
filtration is complete to assist drainage. After such treatment the cake
should contain approximately 15 per cent. fat and 25 per cent. water.
The cake is now removed from the press and transferred to a small tank
where it is treated with sufficient caustic soda to convert the fat
content into soap.
Saturated brine is then added to salt out the soap, the Fuller's earth
is allowed to settle to the bottom of the tank and the soap which
solidifies after a short time is skimmed off to be used in a cheap soap
where color is not important. The liquor underneath may also be run off
without disturbing the sediment to be used in graining a similar cheap
soap. The waste Fuller's earth contains about 0.1 to 0.3 per cent. of
fat.
METHOD FOR FURTHER IMPROVEMENT OF COLOR.
A further improvement of the color of the tallow may be obtained by
freeing it from a portion of its free fatty acids, either with or
without previous Fuller's earth bleaching.
To carry out this process the melted fat is allowed to settle and as
much water as possible taken off. The temperature is then raised to 160deg.
F. with dry steam and enough saturated solution of soda ash added to
remove 0.5 per cent. of the free fatty acids, while agitating the mass
thoroughly mechanically or by air. The agitation is continued ten
minutes, the whole allowed to settle for two hours and the foots drawn
off. The soap thus formed entangles a large proportion of the impurities
of the fat.
VEGETABLE OILS.
_Cocoanut Oil_, as the name implies, is obtained from the fruit of the
cocoanut palm. This oil is a solid, white fat at ordinary temperature,
having a bland taste and a characteristic odor. It is rarely
adulterated and is very readily saponified. In recent years the price of
this oil has increased materially because cocoanut oil is now being used
extensively for edible purposes, especially in the making of
oleomargarine. Present indications are that shortly very little high
grade oil will be employed for soap manufacture since the demand for
oleomargarine is constantly increasing and since new methods of refining
the oil for this purpose are constantly being devised.
The oil is found in the market under three different grades: (1) Cochin
cocoanut oil, the choicest oil comes from Cochin (Malabar). This
product, being more carefully cultivated and refined than the other
grades, is whiter, cleaner and contains a smaller percentage of free
acid. (2) Ceylon cocoanut oil, coming chiefly from Ceylon, is usually of
a yellowish tint and more acrid in odor than Cochin oil. (3) Continental
cocoanut oil (Copra, Freudenberg) is obtained from the dried kernels,
the copra, which are shipped to Europe in large quantities, where the
oil is extracted. These dried kernels yield 60 to 70 per cent oil. This
product is generally superior to the Ceylon oil and may be used as a
very satisfactory substitute for Cochin oil, in soap manufacture,
provided it is low in free acid and of good color. The writer has
employed it satisfactorily in the whitest and finest of toilet soaps
without being able to distinguish any disadvantage to the Cochin oil.
Since continental oil is usually cheaper than Cochin oil, it is
advisable to use it, as occasion permits.
Cocoanut oil is used extensively in toilet soap making, usually in
connection with tallow. When used alone the soap made from this oil
forms a lather, which comes up rapidly but which is fluffy and dries
quickly. A pure tallow soap lathers very much slower but produces a more
lasting lather. Thus the advantage of using cocoanut oil in soap is
seen. It is further used in making a cocoanut oil soap by the cold
process also for "fake" or filled soaps. The fatty acid content readily
starts the saponification which takes place easily with a strong lye
(25deg.-35deg. B.). Where large quantities of the oil are saponified
care must be exercised as the soap formed suddenly rises or puffs up and
may boil over. Cocoanut oil soap takes up large quantities of water,
cases having been cited where a 500 per cent. yield has been obtained.
This water of course dries out again upon exposure to the air. The soap
is harsh to the skin, develops rancidity and darkens readily.
_Palm Kernel Oil_, which is obtained from the kernels of the palm tree
of West Africa, is used in soap making to replace cocoanut oil where the
lower price warrants its use. It resembles cocoanut oil in respect to
saponification and in forming a very similar soap. Kernel oil is white
in color, has a pleasant nutty odor when fresh, but rapidly develops
free acid, which runs to a high percentage.
_Palm Oil_ is produced from the fruit of the several species of the palm
tree on the western coast of Africa generally, but also in the
Philippines. The fresh oil has a deep orange yellow tint not destroyed
by saponification, a sweetish taste and an odor of orris root or violet
which is also imparted to soap made from it. The methods by which the
natives obtain the oil are crude and depend upon a fermentation, or
putrefaction. Large quantities are said to be wasted because of this
fact. The oil contains impurities in the form of fermentable fibre and
albuminous matter, and consequently develops free fatty acid rapidly.
Samples tested for free acid have been found to have hydrolized
completely and one seldom obtains an oil with low acid content. Because
of this high percentage of free fatty acid, the glycerine yield is
small, though the neutral oil should produce approximately 12 per cent.
glycerine. Some writers claim that glycerine exists in the free state
in palm oil. The writer has washed large quantities of the oil and
analyzed the wash water for glycerine. The results showed that the
amount present did not merit its recovery. Most soap makers do not
attempt to recover the glycerine from this oil, when used alone for soap
manufacture.
There are several grades of palm oil in commerce, but in toilet soap
making it is advisable to utilize only Lagos palm oil, which is the best
grade. Where it is desired to maintain the color of the soap this oil
produces, a small quantity of the lower or "brass" grade of palm oil may
be used, as the soap made from the better grades of oil gradually
bleaches and loses its orange yellow color.
Palm oil produces a crumbly soap which cannot readily be milled and is
termed "short." When used with tallow and cocoanut oil, or 20 to 25 per
cent. cocoanut oil, it produces a very satisfactory toilet soap. In the
saponification of palm oil it is not advisable to combine it with tallow
in the kettle, as the two do not readily mix.
Since the finished soap has conveyed to it the orange color of the oil,
the oil is bleached before saponification. Oxidation readily destroys
the coloring matter, while heat and light assist materially. The methods
generally employed are by the use of oxygen developed by bichromates and
hydrochloric acid and the direct bleaching through the agency of the
oxygen of the air.
CHROME BLEACHING OF PALM OIL.
The chrome process of bleaching palm oil is more rapid and the oxygen
thus derived being more active will bleach oils which air alone cannot.
It depends upon the reaction:
Na_{2}Cr_{2}O_{7} + 8HCl = Cr_{2}Cl_{6} + 2NaCl + 7O.
in which the oxygen is the active principle. In practice it is found
necessary to use an excess of acid over that theoretically indicated.
For the best results an oil should be chosen containing under 2 per
cent. impurities and a low percentage of free fatty acids. Lagos oil is
best adapted to these requirements. The oil is melted by open steam from
a jet introduced through the bung, the melted oil and condensed water
running to the store tank through two sieves (about 1/8 inch mesh) to
remove the fibrous material and gross impurities. The oil thus obtained
contains fine earthy and fibrous material and vegetable albuminous
matter which should be removed, as far as possible, since chemicals are
wasted in their oxidation and they retard the bleaching. This is best
done by boiling the oil for one hour with wet steam and 10 per cent.
solution of common salt (2 per cent. dry salt on weight of oil used) in
a lead-lined or wooden tank. After settling over night the brine and
impurities are removed by running from a cock at the bottom of the vat
and the oil is run out into the bleaching tank through an oil cock,
situated about seven inches from the bottom.
The bleaching tank is a lead-lined iron tank of the approximate
dimensions of 4 feet deep, 4 feet long and 3-1/2 feet wide, holding
about 1-1/2 tons. The charge is one ton. A leaden outlet pipe is fixed
at the bottom, to which is attached a rubber tube closed by a screw
clip. A plug also is fitted into the lead outlet pipe from above. Seven
inches above the lower outlet is affixed another tap through which the
oil is drawn off.
The tank is further equipped with a wet steam coil and a coil arranged
to allow thorough air agitation, both coils being of lead. A good
arrangement is to use one coil to deliver either air or steam. These
coils should extend as nearly as possible over the entire bottom of the
tank and have a number of small downward perforations, so as to spread
the agitation throughout the mass.
The temperature of the oil is reduced by passing in air to 110deg. F. and
40 pounds of fine common salt per ton added through a sieve. About
one-half of the acid (40 pounds of concentrated commercial hydrochloric
acid) is now poured in and this is followed by the sodium bichromate in
concentrated solution, previously prepared in a small lead vat or
earthen vessel by dissolving 17 pounds of bichromate in 45 pounds
commercial hydrochloric acid. This solution should be added slowly and
should occupy three hours, the whole mass being thoroughly agitated with
air during the addition and for one hour after the last of the bleaching
mixture has been introduced. The whole mixture is now allowed to settle
for one hour and the exhausted chrome liquors are then run off from the
lower pipe to a waste tank. About 40 gallons of water are now run into
the bleached oil and the temperature raised by open steam to 150deg. to
160deg. F. The mass is then allowed to settle over night.
One such wash is sufficient to remove the spent chrome liquor
completely, provided ample time is allowed for settling. A number of
washings given successively with short periods of settling do not remove
the chrome liquors effectually. The success of the operation depends
entirely upon the completeness of settling.
The wash water is drawn off as before and the clear oil run to storage
tanks or to the soap kettle through the upper oil cock.
The waste liquors are boiled with wet steam and the oil skimmed from the
surface, after which the liquors are run out through an oil trap.
By following the above instructions carefully it is possible to bleach
one ton of palm oil with 17 pounds of bichromate of soda and 85 pounds
hydrochloric acid.
The spent liquors should be a bright green color. Should they be of a
yellow or brownish shade insufficient acid has been allowed and more
must be added to render the whole of the oxygen available.
If low grade oils are being treated more chrome will be necessary, the
amount being best judged by conducting the operation as usual and after
the addition of the bichromate, removing a sample of the oil, washing
the sample and noting the color of a rapidly cooled sample.
A little practice will enable the operator to judge the correspondence
between the color to be removed and the amount of bleaching mixture to
be added.
To obtain success with this process the method of working given must be
adhered to even in the _smallest detail_. This applies to the
temperature at which each operation is carried out particularly.
AIR BLEACHING OF PALM OIL.
The method of conducting this process is identical with the chrome
process to the point where the hydrochloric acid is to be added to the
oil. In this method no acid or chrome is necessary, as the active
bleaching agent is the oxygen of the air.
The equipment is similar to that of the former process, except that a
wooden tank in which no iron is exposed will suffice to bleach the oil
in. The process depends in rapidity upon the amount of air blown through
the oil and its even distribution. Iron should not be present or exposed
to the oil during bleaching, as it retards the process considerably.
After the impurities have been removed, as outlined under the chrome
process, the temperature of the oil is raised by open steam to boiling.
The steam is then shut off and air allowed to blow through the oil until
it is completely bleached, the temperature being maintained above 150deg.
F. by occasionally passing in steam. Usually a ton of oil is readily and
completely bleached after the air has been passed through it for 18 to
20 hours, provided the oil is thoroughly agitated by a sufficient flow
of air.
If the oil has been allowed to settle over night, it is advisable to run
off the condensed water and impurities by the lower cock before
agitating again the second day.
When the oil has been bleached to the desired color, which can be
determined by removing a sample and cooling, the mass is allowed to
settle, the water run off to a waste tank from which any oil carried
along may be skimmed off and the supernatant clear oil run to the
storage or soap kettle.
In bleaching by this process, while the process consumes more time and
is not as efficient in bleaching the lower grade oils, the cost of
bleaching is less and with a good oil success is more probable, as there
is no possibility of any of the chrome liquors being present in the oil.
These give the bleached oil a green tint when the chrome method is
improperly conducted and they are not removed.
Instead of blowing the air through it, the heater oil may be brought
into contact with the air, either by a paddle wheel arrangement, which,
in constantly turning, brings the oil into contact with the air, or by
pumping the heated oil into an elevated vessel, pierced with numerous
fine holes from which the oil continuously flows back into the vessel
from which the oil is pumped. While in these methods air, light and heat
act simultaneously in the bleaching of the oil, the equipment required
is too cumbersome to be practical.
Recent investigations[1] in bleaching palm oil by oxygen have shown that
not only the coloring matter but the oil itself was affected. In
bleaching palm oil for 30 hours with air the free fatty acid content
rose and titer decreased considerably.
_Olive Oil_, which comes from the fruit of the olive trees, varies
greatly in quality, according to the method by which it is obtained and
according to the tree bearing the fruit. Three hundred varieties are
known in Italy alone. Since the larger portion of olive oil is used for
edible purposes, a lower grade, denatured oil, denatured because of the
tariff, is used for soap manufacture in this country. The oil varies in
color from pale green to golden yellow. The percentage of free acid in
this oil varies greatly, though the oil does not turn rancid easily. It
is used mainly in the manufacture of white castile soap.
Olive oil foots, which is the oil extracted by solvents after the better
oil is expressed, finds its use in soap making mostly in textile soaps
for washing and dyeing silks and in the production of green castile
soaps.
Other oils, as poppy seed oil, sesame oil, cottonseed oil, rape oil,
peanut (arachis) oil, are used as adulterants for olive oil, also as
substitutes in the manufacture of castile soap, since they are cheaper
than olive oil.
_Cottonseed Oil_ is largely used in the manufacture of floating and
laundry soaps. It may be used for toilet soaps where a white color is
not desired, as yellow spots appear on a finished soap in which it has
been used after having been in stock a short time.
_Corn Oil and Soya Bean Oil_ are also used to a slight extent in the
manufacture of toilet soaps, although the oils form a soap of very
little body. Their soaps also spot yellow on aging.
Corn oil finds its greatest use in the manufacture of soap for washing
automobiles. It is further employed for the manufacture of cheap liquid
soaps.
_Fatty Acids_ are also used extensively in soap manufacture. While the
soap manufacturer prefers to use a neutral oil or fat, since from these
the by-product glycerine is obtained, circumstances arise where it is
an advantage to use the free fatty acids. Red oil (oleic acid, elaine)
and stearic acid are the two fatty acids most generally bought for soap
making. In plants using the Twitchell process, which consists in
splitting the neutral fats and oils into fatty acids and glycerine by
dilute sulphuric acid and producing their final separation by the use of
so-called aromatic sulphonic acids, these fatty acids consisting of a
mixture of oleic, stearic, palmitic acids, etc., are used directly after
having been purified by distillation, the glycerine being obtained from
evaporating the wash water.
Oleic acid (red oil) and stearic acid are obtained usually by the
saponification of oils, fats and greases by acid, lime or water under
pressure or Twitchelling. The fatty acids thus are freed from their
combination with glycerine and solidify upon cooling, after which they
are separated from the water and pressed at a higher or lower
temperature. The oleic acid, being liquid at ordinary temperature,
together with some stearic and palmitic acid, is thus pressed out. These
latter acids are usually separated by distillation, combined with the
press cake further purified and sold as stearic acid.
The red oil, sometimes called saponified red oil, is often semi-solid,
resembling a soft tallow, due to the presence of stearic acid. The
distilled oils are usually clear, varying in color from light to a deep
brown. Stearic acid, which reaches the trade in slab form, varies in
quality from a soft brown, greasy, crumbly solid of unpleasant odor to a
snow white, wax-like, hard, odorless mass. The quality of stearic acid
is best judged by the melting point, since the presence of any oleic
acid lowers this. The melting point of the varieties used in soap
manufacture usually ranges from 128deg. to 132deg. F. Red oil is used in
the manufacture of textile soaps, replacing olive oil foots soap for
this purpose, chlorophyll being used to color the soap green. Stearic
acid, being the hard firm fatty acid, may be used in small quantities to
give a better grade of soap body and finish. In adding this substance it
should always be done in the crutcher, as it will not mix in the kettle.
It finds its largest use for soap, however, in the manufacture of
shaving soaps and shaving creams, since it produces the non-drying
creamy lather so greatly desired for this purpose. Both red oil and
stearic acid being fatty acids, readily unite with the alkali
carbonates, carbon dioxide being formed in the reaction and this method
is extensively used in the formation of soap from them.
RANCIDITY OF OILS AND FATS.
Rancidity in neutral oils and fats is one of the problems the soap
manufacturer has to contend with. The mere saying that an oil is rancid
is no indication of its being high in free acid. The two terms rancidity
and acidity are usually allied. Formerly, the acidity of a fat was
looked upon as the direct measure of its rancidity. This idea is still
prevalent in practice and cannot be too often stated as incorrect. Fats
and oils may be _acid_, or _rancid_, or _acid and rancid_. In an acid
fat there has been a hydrolysis of the fat and it has developed a rather
high percentage of free acid. A rancid fat is one in which have been
developed compounds of an odoriferous nature. An acid and rancid fat is
one in which both free acid and organic compounds of the well known
disagreeable odors have been produced.
It cannot be definitely stated just how this rancidity takes place, any
more than just what are the chemical products causing rancidity. The
only conclusion that one may draw is that the fats are first hydrolyzed
or split up into glycerine and free fatty acids. This is followed by an
oxidation of the products thus formed.
Moisture, air, light, enzymes (organized ferments) and bacteria are all
given as causes of rancidity.
It seems very probable that the initial splitting of the fats is caused
by enzymes, which are present in the seeds and fruits of the vegetable
oils and tissue of animal fats, in the presence of moisture. Lewkowitsch
strongly emphasizes this point and he is substantiated in his idea by
other authorities. Others hold that bacteria or micro-organisms are the
cause of this hydrolysis, citing the fact that they have isolated
various micro-organisms from various fats and oils. The acceptance of
the bacterial action would explain the various methods of preservation
of oils and fats by the use of antiseptic preparations. It cannot,
however, be accepted as a certainty that bacteria cause the rancidity of
fats.
The action of enzymes is a more probable explanation.
The hydrolysis of fats and oils is accelerated when they are allowed to
remain for some time in the presence of organic non-fats. Thus, palm
oil, lower grades of olive oil, and tallow, which has been in contact
with the animal tissue for a long time, all contain other nitrogenous
matter and exhibit a larger percentage of free fatty acid than the oils
and fats not containing such impurities.
Granting this initial splitting of the fat into free fatty acids and
glycerine, this is not a sufficient explanation. The products thus
formed must be acted upon by air and light. It is by the action of these
agents that there is a further action upon the products, and from this
oxidation we ascertain by taste and smell (chemical means are still
unable to define rancidity) whether or not a fat is rancid. While some
authorities have presumed to isolate some of these products causing
rancidity, we can only assume the presence of the various possible
compounds produced by the action of air and light which include oxy
fatty acids, lactones, alcohols, esters, aldehydes and other products.
The soap manufacturer is interested in rancidity to the extent of the
effect upon the finished soap. Rancid fats form darker soaps than fats
in the neutral state, and very often carry with them the disagreeable
odor of a rancid oil. Further, a rancid fat or oil is usually high in
free acid. It is by no means true, however, that rancidity is a measure
for acidity, for as has already been pointed out, an oil may be rancid
and not high in free acid.
The percentage of free fatty acid is of even greater importance in the
soap industry. The amount of glycerine yield is dependent upon the
percentage of free fatty acid and is one of the criterions of a good fat
or oil for soap stock.
PREVENTION OF RANCIDITY.
Since moisture, air, light and enzymes, produced by the presence of
organic impurities, are necessary for the rancidity of a fat or oil, the
methods of preventing rancidity are given. Complete dryness, complete
purification of fats and oils and storage without access of air or light
are desirable. Simple as these means may seem, they can only be
approximated in practice. The most difficult problem is the removal of
the last trace of moisture. Impurities may be lessened very often by the
use of greater care. In storing it is well to store in closed barrels or
closed iron tanks away from light, as it has been observed that oils and
fats in closed receptacles become rancid less rapidly than those in open
ones, even though this method of storing is only partially attained.
Preservatives are also used, but only in edible products, where their
effectiveness is an open question.
CHEMICAL CONSTANTS OF OILS AND FATS.
Besides the various physical properties of oils and fats, such as
color, specific gravity, melting point, solubility, etc., they may be
distinguished chemically by a number of chemical constants. These are
the iodine number, the acetyl value, saponification number,
Reichert-Meissl number for volatile acids, Hehner number for insoluble
acids. These constants, while they vary somewhat with any particular oil
or fat, are more applicable to the edible products and are criterions
where any adulteration of fat or oil is suspected. The methods of
carrying out the analyses of oils and fats to obtain these constants are
given in the various texts[2] on oils and fats, and inasmuch as they are
not of great importance to the soap industry they are merely mentioned
here.
OIL HARDENING OR HYDROGENATING.
It is very well known that oils and fats vary in consistency and
hardness, depending upon the glycerides forming same. Olein, a
combination of oleic acid and glycerine, as well as oleic acid itself
largely forms the liquid portion of oils and fats. Oleic acid
(C_{18}H_{34}O_{2}) is an unsaturated acid and differs from stearic acid
(C_{18}H_{36}O_{2}), the acid forming the hard firm portion of oils and
fats, by containing two atoms of hydrogen less in the molecule.
Theoretically it should be a simple matter to introduce two atoms of
hydrogen into oleic acid or olein, and by this mere addition convert
liquid oleic acid and olein into solid stearic acid and stearine.
For years this was attempted and all attempts to apply the well known
methods of reduction (addition of hydrogen) in organic chemistry, such
as treatment with tin and acid, sodium amalgam, etc., were unsuccessful.
In recent years, however, it has been discovered that in the presence of
a catalyzer, nickel in finely divided form or the oxides of nickel are
usually employed, the process of hydrogenating an oil is readily
attained upon a practical basis.
The introduction of hardened oils has opened a new source of raw
material for the soap manufacturer in that it is now possible to use
oils in soap making which were formerly discarded because of their
undesirable odors. Thus fish or train oils which had up to the time of
oil hydrogenating resisted all attempts of being permanently deodorized,
can now be employed very satisfactorily for soap manufacture. A Japanese
chemist, Tsujimoto[3] has shown that fish oils contain an unsaturated
acid of the composition C_{18}H_{28}O_{2}, for which he proposed the
name clupanodonic acid. By the catalytic hardening of train oils this
acid passes to stearic acid and the problem of deodorizing these oils is
solved.[4]
At first the introduction of hardened oils for soap manufacture met with
numerous objections, due to the continual failures of obtaining a
satisfactory product by the use of same. Various attempts have now shown
that these oils, particularly hardened train oils, produce
extraordinarily useful materials for soap making. These replace
expensive tallow and other high melting oils. It is of course impossible
to employ hardened oils alone, as a soap so hard would thus be obtained
that it would be difficultly soluble in water and possess very little
lathering quality. By the addition of 20-25% of tallow oil or some other
oil forming a soft soap a very suitable soap for household use may be
obtained. Ribot[5] discusses this matter fully. Hardened oils readily
saponify, may be perfumed without any objections and do not impart any
fishy odor to an article washed with same. Meyerheim[6] states that
through the use of hydrogenated oils the hardness of soap is
extraordinarily raised, so that soap made from hardened cottonseed oil
is twelve times as hard as the soap made from ordinary cottonseed oil.
This soap is also said to no longer spot yellow upon aging, and as a
consequence of its hardness, is able to contain a considerably higher
content of rosin through which lathering power and odor may be improved.
Hardened oils can easily be used for toilet soap bases, provided they
are not added in too great a percentage.
The use of hardened oils is not yet general, but there is little doubt
that the introduction of this process goes a long way toward solving the
problem of cheaper soap material for the soap making industry.
GREASE.
Grease varies so greatly in composition and consistency that it can
hardly be classed as a distinctive oil or fat. It is obtained from
refuse, bones, hides, etc., and while it contains the same constituents
as tallow, the olein content is considerably greater, which causes it to
be more liquid in composition. Grease differs in color from an off-white
to a dark brown. The better qualities are employed in the manufacture of
laundry and chip soap, while the poorer qualities are only fit for the
cheapest of soaps used in scrubbing floors and such purposes. There is
usually found in grease a considerable amount of gluey matter, lime and
water. The percentage of free fatty acid is generally high.
The darker grades of grease are bleached before being used. This is done
by adding a small quantity of sodium nitrate to the melted grease and
agitating, then removing the excess saltpeter by decomposing with
sulphuric acid. A better method of refining, however, is by
distillation. The chrome bleach is also applicable.
ROSIN (COLOPHONY, YELLOW ROSIN, RESINA).
Rosin is the residue which remains after the distillation of turpentine
from the various species of pines. The chief source of supply is in the
States of Georgia North and South Carolina. It is a transparent, amber
colored hard pulverizable resin. The better grades are light in color
and known as water white (w. w.) and window glass (w. g.). These are
obtained from a tree which has been tapped for the first year. As the
same trees are tapped from year to year, the product becomes deeper and
darker in color until it becomes almost black.
The constituents of rosin are chiefly (80-90%) abietic acid or its
anhydride together with pinic and sylvic acids. Its specific gravity is
1.07-1.08, melting point about 152.5 C., and it is soluble in alcohol,
ether, benzine, carbon disulfide, oils, alkalis and acetic acid. The
main use of rosin, outside of the production of varnishes, is in the
production of laundry soaps, although a slight percentage acts as a
binder and fixative for perfumes in toilet soaps and adds to their
detergent properties. Since it is mainly composed of acids, it readily
unites with alkaline carbonates, though the saponification is not quite
complete and the last portion must be completed through the use of
caustic hydrates, unless an excess of 10% carbonate over the theoretical
amount is used. A lye of 20deg. B. is best adapted to the saponification of
rosin when caustic hydrates are employed for this purpose, since weak
lyes cause frothing. While it is sometimes considered that rosin is an
adulterant for soap, this is hardly justifiable, as it adds to the
cleansing properties of soap. Soaps containing rosin are of the well
known yellowish color common to ordinary laundry soaps. The price of
rosin has so risen in the last few years that it presents a problem of
cost to the soap manufacturer considering the price at which laundry
soaps are sold.
ROSIN SAPONIFICATION.
As has been stated, rosin may be saponified by the use of alkaline
carbonates. On account of the possibility of the soap frothing over, the
kettle in which the operation takes place should be set flush with the
floor, which ought to be constructed of cement. The kettle itself is an
open one with round bottom, equipped with an open steam coil and skimmer
pipe, and the open portion is protected by a semi-circular rail. A
powerful grid, having a 3-inch mesh, covers one-half of the kettle, the
sharp edges protruding upwards.
The staves from the rosin casks are removed at the edge of the kettle,
the rosin placed on the grid and beaten through with a hammer to break
it up into small pieces.
To saponify a ton of rosin there are required 200 lbs. soda ash, 1,600
lbs. water and 100 lbs. salt. Half the water is run into the kettle,
boiled, and then the soda ash and half the salt added. The rosin is now
added through the grid and the mixture thoroughly boiled. As carbon
dioxide is evolved by the reaction the boiling is continued for one hour
to remove any excess of this gas. A portion of the salt is gradually
added to grain the soap well and to keep the mass in such condition as
to favor the evolution of gas. The remainder of the water is added to
close the soap and boiling continued for one or two hours longer. At
this point the kettle must be carefully watched or it will boil over
through the further escape of carbon dioxide being hindered. The mass,
being in a frothy condition, will rapidly settle by controlling the flow
of steam. The remaining salt is then scattered in and the soap allowed
to settle for two hours or longer. The lyes are then drained off the
top. If the rosin soap is required for toilet soaps, it is grained a
second time. The soap is now boiled with the water caused by the
condensation of the steam, which changes it to a half grained soap
suitable for pumping. A soap thus made contains free soda ash 0.15% or
less, free rosin about 15%. The mass is then pumped to the kettle
containing the soap to which it is to be added at the proper stage. The
time consumed in thus saponifying rosin is about five hours.
NAPHTHENIC ACIDS.
The naphtha or crude petroleum of the various provinces in Europe, as
Russia, Galacia, Alsace and Roumania yield a series of bodies of acid
character upon refining which are designated under the general name of
naphthenic acids. These acids are retained in solution in the alkaline
lyes during the distillation of the naphtha in the form of alkaline
naphthenates. Upon adding dilute sulphuric acid to these lyes the
naphthenates are decomposed and the naphthenic acids float to the
surface in an oily layer of characteristic disagreeable odor and varying
from yellow to brown in color[7]. In Russia particularly large
quantities of these acids are employed in the manufacture of soap.
The soaps formed from naphthenic acids have recently been
investigated[8] and found to resemble the soaps made from cocoanut oil
and palm kernel oil, in that they are difficult to salt out and
dissociate very slightly with water. The latter property makes them
valuable in textile industries when a mild soap is required as a
detergent, e. g., in the silk industry. These soaps also possess a high
solvent power for mineral oils and emulsify very readily. The mean
molecular weight of naphthenic acids themselves is very near that of the
fatty acids contained in cocoanut oil, and like those of cocoanut oil a
portion of the separated acids are volatile with steam. The iodine
number indicates a small content of unsaturated acids.
That naphthenic acids are a valuable soap material is now recognized,
but except in Russia the soap is not manufactured to any extent at the
present time.
ALKALIS.
The common alkali metals which enter into the formation of soap are
sodium and potassium. The hydroxides of these metals are usually used,
except in the so called carbonate saponification of free fatty acids in
which case sodium and potassium carbonate are used. A water solution of
the caustic alkalis is known as lye, and it is as lyes of various
strengths that they are added to oils and fats to form soap. The density
or weight of a lye is considerably greater than that of water, depending
upon the amount of alkali dissolved, and its weight is usually
determined by a hydrometer. This instrument is graduated by a
standardized scale, and while all hydrometers should read alike in a
liquid of known specific gravity, this is generally not the case, so
that it is advisable to check a new hydrometer for accurate work against
one of known accuracy. In this country the Baume scale has been adopted,
while in England a different graduation known as the Twaddle scale is
used. The strength of a lye or any solution is determined by the
distance the instrument sinks into the solution, and we speak of the
strength of a solution as so many degrees Baume or Twaddle which are
read to the point where the meniscus of the lye comes on the graduated
scale. Hydrometers are graduated differently for liquids of different
weights. In the testing of lyes one which is graduated from 0deg. to
50deg. B. is usually employed.
_Caustic soda_ is received by the consumer in iron drums weighing
approximately 700 lbs. each. The various grades are designated as 60,
70, 74, 76 and 77%. These percentages refer to the percentage of sodium
oxide (Na_{2}O) in 100 parts of pure caustic soda formed by the
combination of 77-1/2 parts of sodium oxide and 22-1/2 parts of water,
77-1/2% being chemically pure caustic soda. There are generally
impurities present in commercial caustic soda. These consist of sodium
carbonate, sodium chloride or common salt and sometimes lime. It is
manufactured by treating sodium carbonate in an iron vessel with calcium
hydroxide or slaked lime, or by electrolysis of common salt. The latter
process has yet been unable to compete with the former in price.
Formerly all the caustic soda used in soap making was imported, and it
was only through the American manufacturer using a similar container to
that used by foreign manufacturers that they were able to introduce
their product. This prejudice has now been entirely overcome and most of
the caustic soda used in this country is manufactured here.
CAUSTIC POTASH.
The output of the salts containing potassium is controlled almost
entirely by Germany. Formerly the chief source of supply of potassium
compounds was from the burned ashes of plants, but about fifty years ago
the inexhaustible salt mines of Stassfurt, Germany, were discovered.
The salt there mined contains, besides the chlorides and sulphates of
sodium, magnesium, calcium and other salts, considerable quantities of
potassium chloride, and the Stassfurt mines at present are practically
the entire source of all potassium compounds, in spite of the fact that
other localities have been sought to produce these compounds on a
commercial basis, especially by the United States government.
After separating the potassium chloride from the magnesium chloride and
other substances found in Stassfurt salts the methods of manufacture of
caustic potash are identical to those of caustic soda. In this case,
however, domestic electrolytic caustic potash may be purchased cheaper
than the imported product and it gives results equal to those obtained
by the use of the imported article, opinions to the contrary among soap
makers being many. Most of the caustic potash in the United States is
manufactured at Niagara Falls by the Niagara Alkali Co., and the Hooker
Electrochemical Co., chlorine being obtained as a by-product. The latter
concern employs the Townsend Cell, for the manufacture of electrolytic
potash, and are said to have a capacity for making 64 tons of alkali
daily.
Since the molecular weight of caustic potash (56) is greater than that
of caustic soda (40) more potash is required to saponify a pound of fat.
The resulting potash soap is correspondingly heavier than a soda soap.
When salt is added to a potassium soap double decomposition occurs, the
potassium soap being transformed to a sodium soap and the potassium
uniting with the chlorine to form potassium chloride. This was one of
the earliest methods of making a hard soap, especially in Germany, where
potash was derived from leeching ashes of burned wood and plants.
SODIUM CARBONATE (SODA ASH).
While carbonate of soda is widely distributed in nature the source of
supply is entirely dependent upon the manufactured product. Its uses are
many, but it is especially important to the soap industry in the so
called carbonate saponification of free fatty acids, as a constituent of
soap powders, in the neutralization of glycerine lyes and as a filler
for laundry soaps.
The old French Le Blanc soda process, which consists in treating common
salt with sulphuric acid and reducing the sodium sulphate (salt cake)
thus formed with carbon in the form of charcoal or coke to sodium
sulphide, which when treated with calcium carbonate yields a mixture of
calcium sulphide and sodium carbonate (black ash) from which the
carbonate is dissolved by water, has been replaced by the more recent
Solvay ammonia soda process. Even though there is a considerable loss of
salt and the by-product calcium chloride produced by this process is
only partially used up as a drying agent, and for refrigerating
purposes, the Le Blanc process cannot compete with the Solvay process,
so that the time is not far distant when the former will be considered a
chemical curiosity. In the Solvay method of manufacture sodium chloride
(common salt) and ammonium bicarbonate are mixed in solution. Double
decomposition occurs with the formation of ammonium chloride and sodium
bicarbonate. The latter salt is comparatively difficultly soluble in
water and crystallizes out, the ammonium chloride remaining in solution.
When the sodium bicarbonate is heated it yields sodium carbonate, carbon
dioxide and water; the carbon dioxide is passed into ammonia which is
set free from the ammonium chloride obtained as above by treatment with
lime (calcium oxide) calcium chloride being the by-product.
Sal soda or washing soda is obtained by recrystallizing a solution of
soda ash in water. Large crystals of sal soda containing but 37% sodium
carbonate are formed.
POTASSIUM CARBONATE.
Potassium carbonate is not extensively used in the manufacture of soap.
It may be used in the forming of soft soaps by uniting it with free
fatty acids. The methods of manufacture are the same as for sodium
carbonate, although a much larger quantity of potassium carbonate than
carbonate of soda is obtained from burned plant ashes. Purified
potassium carbonate is known as _pearl ash_.
ADDITIONAL MATERIAL USED IN SOAP MAKING.
Water is indispensable to the soap manufacturer. In the soap factory
_hard_ water is often the cause of much trouble. Water, which is the
best solvent known, in passing through the crevices of rocks dissolves
some of the constituents of these, and the water is known as hard. This
hardness is of two kinds, _temporary_ and _permanent_. Temporarily hard
water is formed by water, which contains carbonic acid, dissolving a
portion of calcium carbonate or carbonate of lime. Upon boiling, the
carbonic acid is driven from the water and the carbonate, being
insoluble in carbon dioxide free water, is deposited. This is the cause
of boiler scale, and to check this a small amount of sal ammoniac may be
added to the water, which converts the carbonate into soluble calcium
chloride and volatile ammonium carbonate. Permanent hardness is caused
by calcium sulphate which is soluble in 400 parts of water and cannot be
removed by boiling.
The presence of these salts in water form insoluble lime soaps which act
as inert bodies as far as their value for the common use of soap is
concerned. Where the percentage of lime in water is large this should be
removed. A method generally used is to add about 5% of 20deg. B. sodium
silicate to the hard water. This precipitates the lime and the water is
then sufficiently pure to use.
_Salt_, known as sodium chloride, is used to a large extent in soap
making for "salting out" the soap during saponification, as well as
graining soaps. Soap ordinarily soluble in water is insoluble in a salt
solution, use of which is made by adding salt to the soap which goes
into solution and throws any soap dissolved in the lyes out of solution.
Salt may contain magnesium and calcium chlorides, which of course are
undesirable in large amounts. The products on the market, however, are
satisfactory, thus no detail is necessary.
_Filling materials_ used are sodium silicate, or water glass, talc,
silex, pumice, starch, borax, tripoli, etc.
Besides these other materials are used in the refining of the oils and
fats, and glycerine recovery, such as Fuller's earth, bichromates of
soda or potash, sulphate of alumina, sulphuric and hydrochloric acids
and alcohol.
A lengthy description of these substances is not given, as their modes
of use are detailed elsewhere.
FOOTNOTES:
[1] Seifensieder Zeit, 1913, 40, p. 687, 724, 740.
[2] Official Methods, see Bull. 107, A. O. A. C., U. S. Dept. Agricult.
[3] Journ. Coll. of Engin. Tokyo Imper. Univ. (1906), p. 1. Abs. Chem.
Revue f. d. Fett-u. Harz, Ind. 16, p. 84; 20, p. 8.
[4] Meyerheim--Fort. der Chem., Physik. und Physik. Chem. (1913), 8. 6,
p. 293-307.
[5] Seifs. Ztg. (1913), 40, p. 142.
[6] Loc. cit.
[7] Les Matieres Graisses (1914), 7, 69, p. 3367.
[8] Zeit. f. Angew. Chem. (1914), 27, 1, p. 2-4.