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THE HANDBOOK OF
SOAP MANUFACTURE
BY
W. H. SIMMONS, B.Sc. (LOND.), F.C.S.
AND
H. A. APPLETON
_WITH TWENTY-SEVEN ILLUSTRATIONS_
LONDON
SCOTT, GREENWOOD & SON
"THE OIL AND COLOUR TRADES JOURNAL" OFFICES
8 BROADWAY, LUDGATE HILL, E.C.
1908
[_All rights reserved_]
Transcriber's note:
For text: A word surrounded by a cedilla 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. Greek letters
are translated into English and are in brackets, e.g. [alpha].
For numbers and equations: Parentheses have been added to clarify
fractions. Underscores before bracketed numbers/letters in equations
denote a subscript.
Footnotes have been moved to the end of the chapter and minor typos have
been corrected.
PREFACE
In the general advance of technical knowledge and research during the
last decade, the Soap Industry has not remained stationary. While there
has not perhaps been anything of a very revolutionary character, steady
progress has still been made in practically all branches, and the aim of
the present work is to describe the manufacture of Household and Toilet
Soaps as carried out to-day in an up-to-date and well-equipped factory.
In the more scientific portions of the book, an acquaintance with the
principles of elementary chemistry is assumed, and in this we feel
justified, as in these days of strenuous competition, no soap-maker can
hope to compete successfully with his rivals unless he has a sound
theoretical as well as practical knowledge of the nature of the raw
materials he uses, and the reactions taking place in the pan, or at
other stages of the manufacture. We also venture to hope that the work
may prove useful to Works' Chemists and other Analysts consulted in
connection with this Industry.
At the same time, in the greater part of the book no chemical knowledge
is necessary, the subject being treated in such a way that it is hoped
those who are not directly engaged in the manufacture of soap, but who
desire a general idea of the subject, will find it of value.
In the sections dealing with the composition and analysis of materials,
temperatures are expressed in degrees Centigrade, these being now almost
invariably used in scientific work. In the rest of the book, however,
they are given in degrees Fahrenheit (the degrees Centigrade being also
added in brackets), as in the majority of factories these are still
used.
As regards strengths of solution, in some factories the use of Baumé
degrees is preferred, whilst in others Twaddell degrees are the custom,
and we have therefore given the two figures in all cases.
In the chapter dealing with Oils and Fats, their Saponification
Equivalents are given in preference to Saponification Values, as it has
been our practice for some years to express our results in this way, as
suggested by Allen in _Commercial Organic Analysis_, and all our
records, from which most of the figures for the chief oils and fats are
taken, are so stated.
For the illustrations, the authors are indebted to Messrs. E. Forshaw &
Son, Ltd., H. D. Morgan, and W. J. Fraser & Co., Ltd.
W. H. S.
H. A. A.
LONDON, _September_, 1908.
CONTENTS
PAGE
CHAPTER I.
INTRODUCTION. 1
Definition of Soap--Properties--Hydrolysis--Detergent Action.
CHAPTER II.
CONSTITUTION OF OILS AND FATS, AND THEIR SAPONIFICATION 6
Researches of Chevreul and Berthelot--Mixed Glycerides--Modern Theories
of Saponification--Hydrolysis accelerated by (1) HEAT OR ELECTRICITY,
(2) FERMENTS, Castor-seed Ferment, Steapsin, Emulsin, and (3) CHEMICAL
REAGENTS, Sulphuric Acid, Twitchell's Reagent, Hydrochloric Acid, Lime,
Magnesia, Zinc Oxide, Soda and Potash.
CHAPTER III.
RAW MATERIALS USED IN SOAP-MAKING 24
Fats and Oils--Waste Fats--Fatty Acids--Less-known Oils and Fats of Limited
Use--Various New Fats and Oils Suggested for Soap-making--Rosin--Alkali
(Caustic and Carbonated)--Water--Salt--Soap-stock.
CHAPTER IV.
BLEACHING AND TREATMENT OF RAW MATERIALS INTENDED FOR
SOAP-MAKING 41
Palm Oil--Cotton-seed Oil--Cotton-seed "Foots"--Vegetable Oils--Animal
Fats--Bone Fat--Rosin.
CHAPTER V.
SOAP-MAKING 45
Classification of Soaps--Direct combination of Fatty Acids with
Alkali--Cold Process Soaps--Saponification under Increased or Diminished
Pressure--Soft Soap--Marine Soap--Hydrated Soaps, Smooth and
Marbled--Pasting or Saponification--Graining Out--Boiling on
Strength--Fitting--Curd Soaps--Curd Mottled--Blue and Grey Mottled
Soaps--Milling Base--Yellow Household Soaps--Resting of Pans and
Settling of Soap--Utilisation of Nigres--Transparent soaps--Saponifying
Mineral Oil--Electrical Production of Soap.
CHAPTER VI.
TREATMENT OF SETTLED SOAP 60
Cleansing--Crutching--Liquoring of Soaps--Filling--Neutralising,
Colouring and Perfuming--Disinfectant
Soaps--Framing--Slabbing--Barring--Open and Close
Piling--Drying--Stamping--Cooling.
CHAPTER VII.
TOILET, TEXTILE AND MISCELLANEOUS SOAPS 77
Toilet Soaps--Cold Process soaps--Settled Boiled Soaps--Remelted
Soaps--Milled Soaps--Drying--Milling and Incorporating Colour, Perfume,
or Medicament--Perfume--Colouring matter--Neutralising and Superfatting
Material--Compressing--Cutting--Stamping--Medicated Soaps--Ether
Soap--Floating Soaps--Shaving Soaps--Textile Soaps--Soaps for Woollen,
Cotton and Silk Industries--Patent Textile Soaps--Miscellaneous Soaps.
CHAPTER VIII.
SOAP PERFUMES 95
Essential Oils--Source and Preparation--Properties--Artificial and
Synthetic Perfumes.
CHAPTER IX.
GLYCERINE MANUFACTURE AND PURIFICATION 111
Treatment of Lyes--Evaporation to Crude
Glycerine--Distillation--Distilled and Dynamite Glycerine--Chemically
Pure Glycerine--Animal Charcoal for Decolorisation--Glycerine obtained
by other methods of Saponification--Yield of Glycerine from Fats and
Oils.
CHAPTER X.
ANALYSIS OF RAW MATERIALS, SOAP, AND GLYCERINE 117
Fats and Oils--Alkalies and Alkali Salts--Essential Oils--Soap--Lyes--Crude
Glycerine.
CHAPTER XI.
STATISTICS OF THE SOAP INDUSTRY 140
APPENDIX A.
COMPARISON OF DEGREES, TWADDELL AND BAUMÉ, WITH ACTUAL DENSITIES 147
APPENDIX B.
COMPARISON OF DIFFERENT THERMOMETRIC SCALES 148
APPENDIX C.
TABLE OF THE SPECIFIC GRAVITIES OF SOLUTIONS OF CAUSTIC SODA 149
APPENDIX D.
TABLE OF STRENGTH OF CAUSTIC POTASH SOLUTIONS AT 60° F. 151
INDEX 153
CHAPTER I.
INTRODUCTION.
_Definition of Soap--Properties--Hydrolysis--Detergent Action._
It has been said that the use of soap is a gauge of the civilisation of
a nation, but though this may perhaps be in a great measure correct at
the present day, the use of soap has not always been co-existent with
civilisation, for according to Pliny (_Nat. Hist._, xxviii., 12, 51)
soap was first introduced into Rome from Germany, having been discovered
by the Gauls, who used the product obtained by mixing goats' tallow and
beech ash for giving a bright hue to the hair. In West Central Africa,
moreover, the natives, especially the Fanti race, have been accustomed
to wash themselves with soap prepared by mixing crude palm oil and water
with the ashes of banana and plantain skins. The manufacture of soap
seems to have flourished during the eighth century in Italy and Spain,
and was introduced into France some five hundred years later, when
factories were established at Marseilles for the manufacture of
olive-oil soap. Soap does not appear to have been made in England until
the fourteenth century, and the first record of soap manufacture in
London is in 1524. From this time till the beginning of the nineteenth
century the manufacture of soap developed very slowly, being essentially
carried on by rule-of-thumb methods, but the classic researches of
Chevreul on the constitution of fats at once placed the industry upon a
scientific basis, and stimulated by Leblanc's discovery of a process for
the commercial manufacture of caustic soda from common salt, the
production of soap has advanced by leaps and bounds until it is now one
of the most important of British industries.
_Definition of Soap_.--The word soap (Latin _sapo_, which is cognate
with Latin _sebum_, tallow) appears to have been originally applied to
the product obtained by treating tallow with ashes. In its strictly
chemical sense it refers to combinations of fatty acids with metallic
bases, a definition which includes not only sodium stearate, oleate and
palmitate, which form the bulk of the soaps of commerce, but also the
linoleates of lead, manganese, etc., used as driers, and various
pharmaceutical preparations, _e.g._, mercury oleate (_Hydrargyri
oleatum_), zinc oleate and lead plaster, together with a number of other
metallic salts of fatty acids. Technically speaking, however, the
meaning of the term soap is considerably restricted, being generally
limited to the combinations of fatty acids and alkalies, obtained by
treating various animal or vegetable fatty matters, or the fatty acids
derived therefrom, with soda or potash, the former giving hard soaps,
the latter soft soaps.
The use of ammonia as an alkali for soap-making purposes has often been
attempted, but owing to the ease with which the resultant soap is
decomposed, it can scarcely be looked upon as a product of much
commercial value.
H. Jackson has, however, recently patented (Eng. Pat. 6,712, 1906) the
use of ammonium oleate for laundry work. This detergent is prepared in
the wash-tub at the time of use, and it is claimed that goods are
cleansed by merely immersing them in this solution for a short time and
rinsing in fresh water.
Neither of the definitions given above includes the sodium and potassium
salts of rosin, commonly called rosin soap, for the acid constituents of
rosin have been shown to be aromatic, but in view of the analogous
properties of these resinates to true soap, they are generally regarded
as legitimate constituents of soap, having been used in Great Britain
since 1827, and receiving legislative sanction in Holland in 1875.
Other definitions of soap have been given, based not upon its
composition, but upon its properties, among which may be mentioned that
of Kingzett, who says that "Soap, considered commercially, is a body
which on treatment with water liberates alkali," and that of Nuttall,
who defines soap as "an alkaline or unctuous substance used in washing
and cleansing".
_Properties of Soap._--Both soda and potash soaps are readily soluble in
either alcohol or hot water. In cold water they dissolve more slowly,
and owing to slight decomposition, due to hydrolysis (_vide infra_), the
solution becomes distinctly turbid. Sodium oleate is peculiar in not
undergoing hydrolysis except in very dilute solution and at a low
temperature. On cooling a hot soap solution, a jelly of more or less
firm consistence results, a property possessed by colloidal bodies, such
as starch and gelatine, in contradistinction to substances which under
the same conditions deposit crystals, due to diminished solubility of
the salt at a lower temperature.
Krafft (_Journ. Soc. Chem. Ind._, 1896, 206, 601; 1899, 691; and 1902,
1301) and his collaborators, Wiglow, Strutz and Funcke, have
investigated this property of soap solutions very fully, the researches
extending over several years. In the light of their more recent work,
the molecules, or definite aggregates of molecules, of solutions which
become gelatinous on cooling move much more slowly than the molecules in
the formation of a crystal, but there is a definite structure, although
arranged differently to that of a crystal. In the case of soda soaps the
colloidal character increases with the molecular weight of the fatty
acids.
Soda soaps are insoluble in concentrated caustic lyes, and, for the most
part, in strong solutions of sodium chloride, hence the addition of
caustic soda or brine to a solution of soda soap causes the soap to
separate out and rise to the surface. Addition of brine to a solution of
potash soap, on the other hand, merely results in double decomposition,
soda soap and potassium chloride being formed, thus:--
C_{17}H_{35}COOK + NaCl = C_{17}H_{35}COONa + KCl
potassium sodium sodium potassium
stearate chloride stearate chloride
The solubility of the different soaps in salt solution varies very
considerably. Whilst sodium stearate is insoluble in a 5 per cent.
solution of sodium chloride, sodium laurate requires a 17 per cent.
solution to precipitate it, and sodium caproate is not thrown out of
solution even by a saturated solution.
_Hydrolysis of Soap_.--The term "hydrolysis" is applied to any
resolution of a body into its constituents where the decomposition is
brought about by the action of water, hence when soap is treated with
_cold_ water, it is said to undergo hydrolysis, the reaction taking
place being represented in its simplest form by the equation:--
2NaC_{18}H_{35}O_{2} + H_{2}O = NaOH + HNa(C_{18}H_{35}O_{2})_{2}
sodium water caustic acid sodium
stearate soda stearate
The actual reaction which occurs has been the subject of investigation
by many chemists, and very diverse conclusions have been arrived at.
Chevreul, the pioneer in the modern chemistry of oils and fats, found
that a small amount of alkali was liberated, as appears in the above
equation, together with the formation of an acid salt, a very minute
quantity of free fatty acid remaining in solution. Rotondi (_Journ. Soc.
Chem. Ind._, 1885, 601), on the other hand, considered that a neutral
soap, on being dissolved in water, was resolved into a basic and an acid
salt, the former readily soluble in both hot and cold water, the latter
insoluble in cold water, and only slightly soluble in hot water. He
appears, however, to have been misled by the fact that sodium oleate is
readily soluble in cold water, and his views have been shown to be
incorrect by Krafft and Stern (_Ber. d. Chem. Ges._, 1894, 1747 and
1755), who from experiments with pure sodium palmitate and stearate
entirely confirm the conclusions arrived at by Chevreul.
The extent of dissociation occurring when a soap is dissolved in water
depends upon the nature of the fatty acids from which the soap is made,
and also on the concentration of the solution. The sodium salts of
cocoa-nut fatty acids (capric, caproic and caprylic acids) are by far
the most easily hydrolysed, those of oleic acid and the fatty acids from
cotton-seed oil being dissociated more readily than those of stearic
acid and tallow fatty acids. The decomposition increases with the amount
of water employed.
The hydrolytic action of water on soap is affected very considerably by
the presence of certain substances dissolved in the water, particularly
salts of calcium and magnesium. Caustic soda exerts a marked retarding
effect on the hydrolysis, as do also ethyl and amyl alcohols and
glycerol.
_Detergent Action of Soap._--The property possessed by soap of removing
dirt is one which it is difficult to satisfactorily explain. Many
theories, more or less complicated, have been suggested, but even now
the question cannot be regarded as solved.
The explanation commonly accepted is that the alkali liberated by
hydrolysis attacks any greasy matter on the surface to be cleansed, and,
as the fat is dissolved, the particles of dirt are loosened and easily
washed off. Berzelius held this view, and considered that the value of a
soap depended upon the ease with which it yielded free alkali on
solution in water.
This theory is considered by Hillyer (_Journ. Amer. Chem. Soc._, 1903,
524), however, to be quite illogical, for, as he points out, the
liberated alkali would be far more likely to recombine with the acid or
acid salt from which it has been separated, than to saponify a neutral
glyceride, while, further, unsaponifiable greasy matter is removed by
soap as easily as saponifiable fat, and there can be no question of any
chemical action of the free alkali in its case. Yet another argument
against the theory is that hydrolysis is greater in cold and dilute
solutions, whereas hot concentrated soap solutions are generally
regarded as having the best detergent action.
Rotondi (_Journ. Soc. Chem. Ind._, 1885, 601) was of the opinion that
the basic soap, which he believed to be formed by hydrolysis, was alone
responsible for the detergent action of soap, this basic soap dissolving
fatty matter by saponification, but, as already pointed out, his theory
of the formation of a basic soap is now known to be incorrect, and his
conclusions are therefore invalid.
Several explanations have been suggested, based on the purely physical
properties of soap solutions. Most of these are probably, at any rate in
part, correct, and there can be little doubt that the ultimate solution
of the problem lies in this direction, and that the detergent action of
soap will be found to depend on many of these properties, together with
other factors not yet known.
Jevons in 1878 in some researches on the "Brownian movement" or
"pedesis" of small particles, a movement of the particles which is
observed to take place when clay, iron oxide, or other finely divided
insoluble matter is suspended in water, found that the pedetic action
was considerably increased by soap and sodium silicate, and suggested
that to this action of soap might be attributed much of its cleansing
power.
Alder Wright considered that the alkali liberated by hydrolysis in some
way promoted contact of the water with the substance to be cleansed, and
Knapp regarded the property of soap solutions themselves to facilitate
contact of the water with the dirt, as one of the chief causes of the
efficacy of soap as a detergent.
Another way in which it has been suggested that soap acts as a cleanser
is that the soap itself or the alkali set free by hydrolysis serves as a
lubricant, making the dirt less adherent, and thus promoting its
removal.
The most likely theory yet advanced is that based on the emulsifying
power of soap solutions. The fact that these will readily form emulsions
with oils has long been known, and the detergent action of soap has
frequently been attributed to it, the explanation given being that the
alkali set free by the water emulsifies the fatty matter always adhering
to dirt, and carries it away in suspension with the other impurities.
Experiments by Hillyer (_loc. cit._) show, however, that while N/10
solution of alkali will readily emulsify a cotton-seed oil containing
free acidity, no emulsion is produced with an oil from which all the
acidity has been removed, or with kerosene, whereas a N/10 solution of
sodium oleate will readily give an emulsion with either, thus proving
that the emulsification is due to the soap itself, and not to the
alkali.
Plateau (_Pogg. Ann._, 141, 44) and Quincke (_Wiedmann's. Ann._, 35,
592) have made very complete researches on the emulsification and
foaming of liquids and on the formation of bubbles. The former considers
that there are two properties of a liquid which play an important part
in the phenomenon, (1) it must have considerable viscosity, and (2) its
surface tension must be low. Quincke holds similar views, but considers
that no pure liquid will foam.
Soap solution admirably fulfils Plateau's second condition, its surface
tension being only about 40 per cent. of that of water, while its
cohesion is also very small; and it is doubtless to this property that
its emulsifying power is chiefly due. So far as viscosity is concerned,
this can have but little influence, for a 1 per cent. solution of sodium
oleate, which has a viscosity very little different from that of pure
water, is an excellent emulsifying agent.
Hillyer, to whose work reference has already been made, investigated the
whole question of detergent action very exhaustively, and, as the result
of a very large number of experiments, concludes that the cleansing
power of soap is largely or entirely to be explained by the power which
it has of emulsifying oily substances, of wetting and penetrating into
oily textures, and of lubricating texture and impurities so that these
may be removed easily. It is thought that all these properties may be
explained by taking into account the low cohesion of the soap solutions,
and their strong attraction or affinity to oily matter, which together
cause the low surface tension between soap solution and oil.