TOILET, TEXTILE AND MISCELLANEOUS SOAPS.
_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._
_Toilet Soaps._--By the term "toilet soap" is inferred a soap specially
adapted for toilet use by reason not only of its good detergent and
lathering qualities, but also on account of its freedom from caustic
alkali and any other ingredient likely to cause irritation or injury to
the skin.
Toilet soaps may be simply classified according to their method of
preparation into the following four classes:--
(1) Cold process soaps.
(2) Settled boiled soaps.
(3) Remelted soaps.
(4) Milled soaps.
Soaps of the first class are of comparatively trifling importance,
having been superseded by the other qualities. Details of the "cold
process" have already been given on page 46; it is only necessary to add
the desired perfume and colouring matter to the soap.
The second class consists of good quality settled soaps, direct from the
copper, to which have been added, prior to framing, suitable perfume and
colouring matter, also, if necessary, dealkalising materials.
The third class is represented by soaps made by the old English method
of remelting, which are often termed "perfumers'," or "little pan"
soaps. The soap-base or mixture of various kinds of soap is remelted in
a steam-jacketed pan, or pan provided with steam coils, and agitated.
The agitation must not be too vigorous or lengthy, or the soap will
become aerated. When all the soap is molten, additions of pearl ash
solution are made to give it a finer and smoother texture, render it
more transparent, and increase its lathering properties. The necessary
colour, in a soluble form, is well incorporated, and lastly the perfume.
Owing to volatilisation, much of the perfume is lost when added to hot
soap, and it is necessary to add a large quantity to get the desired
odour; hence the cheaper essential oils have to be used, so that the
perfume of this class of soap is not so delicate as that of milled
soaps, although it is quite possible to produce remelted soaps as free
from uncombined alkali as a milled toilet soap.
Palm-oil soap often forms the basis for yellow and brown toilet soaps of
this class. The old-fashioned Brown Windsor soap was originally a curd
soap that with age and frequent remelting had acquired a brown tint by
oxidation of the fatty acids--the oftener remelted the better the
resultant soap.
Medicaments are sometimes added to these soaps, _e.g._, camphor, borax,
coal-tar, or carbolic. Oatmeal and bran have been recommended in
combination with soap for toilet purposes, and a patent (Eng. Pat.
26,396, 1896) has been granted for the use of these substances together
with wood-fibre impregnated with boric acid.
After cooling in small frames, the soap is slabbed, and cut into blocks,
and finally into portions suitable for stamping in a press (hand or
steam driven) with a design or lettering on each side.
_Milled Toilet Soaps._--Practically all high-class soaps now on the
market pass through the French or milling process. This treatment, as
its name implies, was first practised by the French who introduced it to
this country, and consists briefly of (i.) drying, (ii.) milling and
incorporating colour, perfume or medicament, (iii.) compressing, and
(iv.) cutting and stamping.
The advantages of milled soap over toilet soap produced by other methods
are that the former, containing less water and more actual soap, is more
economical in use, possesses a better appearance, and more elegant
finish, does not shrink or lose its shape, is more uniform in
composition, and essential oils and delicate perfumes may be
incorporated without fear of loss or deterioration.
Only soap made from best quality fats is usually milled, a suitable base
being that obtained by saponifying a blend of the finest white tallow
with a proportion, not exceeding 25 per cent., of cocoa-nut oil, and
prepared as described in Chapter V.
The first essential of a milling base is that the saponification should
be thorough and complete; if this is not ensured, rancidity is liable to
occur and a satisfactory toilet soap cannot be produced. The soap must
not be short in texture or brittle and liable to split, but of a firm
and somewhat plastic consistency.
(i.) _Drying._--The milling-base, after solidification in the frames,
contains almost invariably from 28 to 30 per cent. of water, and this
quantity must be reduced to rather less than half before the soap can be
satisfactorily milled. Cutting the soap into bars or strips and open
piling greatly facilitates the drying, which is usually effected by
chipping the soap and exposing it on trays to a current of hot air at
95-105° F. (35-40° C.).
There are several forms of drying chambers in which the trays of chips
are placed upon a series of racks one above another, and warm air
circulated through, and Fig. 21 shows a soap drying apparatus with fan
made by W. J. Fraser & Co., Ltd., London.
The older method of heating the air by allowing it to pass over a pipe
or flue through which the products of combustion from a coke or coal
fire are proceeding under the floor of the drying chamber to a small
shaft, has been superseded by steam heat. The air is either drawn or
forced by means of quickly revolving fans through a cylinder placed in a
horizontal position and containing steam coils, or passed over
steam-pipes laid under the iron grating forming the floor of the
chamber.
[Illustration: FIG. 21.--Soap-drying apparatus.]
It will be readily understood that in the case of a bad conductor of
heat, like soap-chippings, it is difficult to evaporate moisture
without constantly moving them and exposing fresh surfaces to the
action of heat.
In the Cressonnières' system, where the shavings of chilled soap are
dried by being carried through a heated chamber upon a series of endless
bands (the first discharging the contents on to a lower belt which
projects at the end, and is moving in the opposite direction, and so
on), this is performed by intercepting milling rollers in the system of
belts (Eng. Pat. 4,916, 1898) whereby the surfaces exposed to the drying
are altered, and it is claimed that the formation of hardened crust is
prevented.
In the ordinary methods of drying, the chips are frequently moved by
hand to assist uniform evaporation.
The degree of saturation of the air with moisture must be taken into
consideration in regulating the temperature and flow of air through the
drying chamber, and for this purpose the use of a hygrometer is
advantageous.
It is very important that the correct amount of moisture should be left
in the soap, not too much, nor too little; the exact point can only be
determined by judgment and experience, and depends to a considerable
extent upon the nature of the soap, and also on the amount of perfume or
medicament to be added, but speaking generally, a range of 11 to 14 per
cent. gives good results. If the soap contains less than this amount it
is liable to crumble during the milling, will not compress
satisfactorily, and the finished tablet may have a tendency to crack and
contain gritty particles so objectionable in use. If, on the other hand,
the soap is left too moist, it is apt to stick to the rollers and mill
with difficulty, and during compression the surface assumes a blistered
and sticky appearance.
(ii.) _Milling and Incorporation of Colour, Perfume or Medicament._--The
object of milling is to render the soap perfectly homogeneous, and to
reduce it to a state in which colour, perfume, or any necessary
neutralising material or other substance may be thoroughly incorporated.
The milling machine consists of smooth granite rollers, fitted with
suitable gearing and working in an iron framework (Fig. 22). The rollers
are connected in such a manner that they rotate at different speeds, and
this increases the efficiency of the milling, and ensures that the
action of the rollers is one of rubbing rather than crushing.
By means of suitably arranged screws the pressure of the rollers on one
another can be adjusted to give the issuing soap any desired thickness;
care should be taken that the sheets of soap are not unnecessarily thick
or the colour and odour will not be uniform.
The soap, in the form of chips, is introduced on to the rollers through
a hopper, and after one passage through the mill, from bottom to top,
one of the serrated knife edges is applied and the ribbons of the soap
are delivered into the top of the hopper where the colour, perfume, and
any other desired admixture is added, and the milling operation repeated
three or four times. When the incorporation is complete the other
scraper is fixed against the top roller and the soap ribbon passed into
the receptacle from which it is conveyed to the compressor. A better
plan, however, especially in the case of the best grade soaps, where the
perfumes added are necessarily more delicate and costly, is to make the
addition of the perfume when the colour has been thoroughly mixed
throughout the mass. Another method is to mill once and transfer the
mass to a rotary mixing machine, fitted with internal blades, of a
peculiar form, which revolve in opposite directions one within the other
as the mixer is rotated. The perfume, colouring matter, etc., are added
and the mixer closed and set in motion, when, after a short time, the
soap is reduced to a fine granular condition, with the colour and
perfume evenly distributed throughout the whole. By the use of such
machines, the loss of perfume by evaporation, which during milling is
quite appreciable, is reduced to a minimum, and the delicacy of the
aroma is preserved unimpaired.
[Illustration: FIG. 22.--Milling machine.]
Prolonged milling, especially with a suitable soap base, tends to
produce a semi-transparent appearance, which is admired by some, but the
increased cost of production by the repeated milling is not accompanied
by any real improvement in the soap.
_Perfume._--The materials used in perfuming soap will be dealt with
fully in the next chapter. The quantity necessary to be added varies
considerably with the nature of the essential oils, and also the price
at which the soap is intended to be sold. In the cheaper grades of
milled soaps the quantity will range from 10-30 fluid ozs. per cwt., and
but rarely exceeds 18-20 ozs., whereas in more costly soaps as much as
40-50 fluid ozs. are sometimes added to the cwt.
_Colouring Matter._--During recent years an outcry has been made against
highly coloured soaps, and the highest class soaps have been
manufactured either colourless or at the most with only a very delicate
tint. It is obvious that a white soap guarantees the use of only the
highest grade oils and fats, and excludes the introduction of any rosin,
and, so far, the desire for a white soap is doubtless justified. Many
perfumes, however, tend to quickly discolour a soap, hence the advantage
of giving it a slight tint. For this purpose a vegetable colouring
matter is preferable, and chlorophyll is very suitable.
[Illustration: FIG. 23.--Compressor.]
A demand still exists for brightly coloured soaps, and this is usually
met by the use of coal-tar dyes. The quantity required is of course
extremely small, so that no harm or disagreeable result could possibly
arise from their use.
_Neutralising and Superfatting Material._--If desired, the final
neutralisation of free alkali can be carried out during the milling
process, any superfatting material being added at the same time. The
chief neutralising reagents have already been mentioned in Chapter VI.
With regard to superfatting material, the quantity of this should be
very small, not exceeding 6-8 ozs. per cwt: The most suitable materials
are vaseline, lanoline, or spermaceti.
[Illustration: FIG. 24--Hand soap-stamping press.]
(iii.) _Compressing._--The next stage is the compression and binding of
the soap ribbons into a solid bar suitable for stamping, and the plant
used (Fig. 23) for this purpose is substantially the same in all
factories. The soap is fed through a hopper into a strong metal
conical-shaped tube like a cannon, which tapers towards the nozzle, and
in which a single or twin screw is moving, and the soap is thereby
forced through a perforated metallic disc, subjected to great pressure,
and compressed. The screws must be kept uniformly covered with shavings
during compression to obviate air bubbles in the soap.
[Illustration: FIG. 25.--Screw press.]
The soap finally emerges through the nozzle (to which is attached a
cutter of suitable shape and size according to the form it is intended
the final tablet to take) as a long, polished, solid bar, which is cut
with a knife or wire into lengths of 2 or 3 feet, and if of satisfactory
appearance, is ready for cutting and stamping. The nozzle of the plodder
is heated by means of a Bunsen burner to about 120° or 130° F. (49°-55°
C.) to allow the soap to be easily forced out, and this also imparts a
good gloss and finish to the ejected bar--if the nozzle is too hot,
however, the soap will be blistered, whereas insufficient heat will
result in streaky soap of a poor and dull appearance.
(iv.) _Cutting and Stamping._--In cutting the soap into sections for
stamping, the cutter should shape it somewhat similar to the required
finished tablet.
Many manufacturers cut the soap into sections having concave ends, and
in stamping, the corners are forced into the concavity, with the result
that unsightly markings are produced at each end of the tablet. It is
preferable to have a cutter with convex ends, and if the stamping is to
be done in a pin mould the shape should be a trifle larger than the
exact size of the desired tablet.
[Illustration: FIG. 26--Pin mould.]
The stamping may be performed by a hand stamper (Fig. 24), a screw press
(Fig. 25), or by a steam stamper. The screw press works very
satisfactorily for toilet soaps.
There are two kinds of moulds in use for milled soaps:--
(_a_) _Pin Moulds_ in which tablets of one size and shape only can be
produced (Fig. 25). The edges of the mould meet very exactly, the upper
part of the die carries two pins attached to the shoulder, and these are
received into two holes in the shoulder of the bottom plate. The
superfluous soap is forced out as the dies meet.
(_b_) _Band or Collar Moulds._--In this form (Fig, 27) the mould may be
adjusted to stamp various sized tablets, say from 2 ozs. to 5-1/3 ozs.
and different impressions given by means of removable die plates. The
band or collar prevents the soap squeezing out sideways. We are indebted
to R. Forehaw & Son, Ltd., for the loan of this illustration.
It is usual to moisten the soap or mould with a dilute solution of
glycerine if it should have a tendency to stick to the die plates.
The soap is then ready for final trimming, wrapping, and boxing.
[Illustration: FIG. 27--Band Mould.]
MEDICATED SOAPS.
The inherent cleansing power of soap renders it invaluable in combating
disease, while it also has distinct germicidal properties, a 2 per cent.
solution proving fatal to B. coli communis in less than six hours, and
even a 1 per cent. solution having a marked action on germs in fifteen
minutes.
Many makers, however, seek more or less successfully to still further
increase the value of soap in this direction by the incorporation of
various drugs and chemicals; and the number of medicated soaps on the
market is now very large. Such soaps may consist of either hard or soft
soaps to which certain medicaments have been added, and can be roughly
divided into two classes, (_a_) those which contain a specific for
various definite diseases, the intention being that the remedy should be
absorbed by the pores of the skin and thus penetrate the system, and
(_b_) those impregnated with chemicals intended to act as antiseptics or
germicides, or, generally, as disinfectants.
The preparation of medicinal soaps appears to have been first taken up
in a scientific manner by Unna of Hamburg in 1886, who advocated the use
of soap in preference to plasters as a vehicle for the application of
certain remedies.
Theoretically, he considered a soap-stock made entirely from beef tallow
the most suitable for the purpose, but in practice found that the best
results were obtained by using a superfatted soap made from a blend of
one part of olive oil with eight parts of beef tallow, saponified with a
mixture of two parts of soda to one part of potash, sufficient fat being
employed to leave an excess of 3 or 4 per cent. unsaponified. Recent
researches have shown, however, that even if a superfatted soap-base is
beneficial for the preparation of toilet soaps (a point which is open to
doubt), it is quite inadmissible for the manufacture of germicidal and
disinfectant soaps, the bactericidal efficiency of which is much
restricted by the presence of free fat.
Many of the medicaments added to soaps require special methods of
incorporation therein, as they otherwise react with the soap and
decompose it, forming comparatively inert compounds. This applies
particularly to salts of mercury, such as _corrosive sublimate_ or
mercuric chloride, and _biniodide of mercury_, both of which have very
considerable germicidal power, and are consequently frequently added to
soaps. If simply mixed with the soap in the mill, reaction very quickly
takes place between the mercury salt and the soap, with formation of the
insoluble mercury compounds of the fatty acids, a change which can be
readily seen to occur in such a soap by the rapid development on
keeping, of a dull slaty-green appearance. Numerous processes have been
suggested, and in some cases patented, to overcome this difficulty. In
the case of corrosive sublimate, Geissler suggested that the soap to
which this reagent is to be added should contain an excess of fatty
acids, and would thereby be rendered stable. This salt has also been
incorporated with milled soap in a dry state in conjunction with
ammonio-mercuric chloride, [beta]-naphthol, methyl salicylate, and
eucalyptol. It is claimed that these bodies are present in an unchanged
condition, and become active when the soap is added to water as in
washing. Ehrhardt (Eng. Pat. 2,407, 1898) patented a method of making
antiseptic mercury soap by using mercury albuminate--a combination of
mercuric chloride and casein, which is soluble in alkali, and added to
the soap in an alkaline solution.
With biniodide of mercury the interaction can be readily obviated by
adding to the biniodide of mercury an equal weight of potassium iodide.
This process, devised and patented by J. Thomson in 1886, has been
worked since that time with extremely satisfactory results. Strengths of
1/2, 1, and 3 per cent. biniodide are sold, but owing to the readiness
with which it is absorbed by the skin a soap containing more than 1/2
per cent. should only be used under medical advice.
A similar combination of _bromide of mercury_ with potassium, sodium, or
ammonium bromide has recently been patented by Cooke for admixture with
liquid, hard, or soft soaps.
_Zinc and other Metallic Salts._--At various times salts of metals other
than mercury have been added to soap, but, owing to their insolubility
in water, their efficiency as medicaments is very trifling or nil.
Compounds have been formed of metallic oxides and other salts with oleic
said, and mixtures made with vaseline and lanoline, and incorporated
with soap, but they have not met with much success.
Another chemical commonly added to soap is _Borax_. In view of its
alkaline reaction to litmus, turning red litmus blue, this salt is no
doubt generally regarded as alkaline, and, as such, without action on
soap. On the contrary, however, it is an acid salt containing an excess
of boric acid over the soda present, hence when it is added to soap,
fatty acids are necessarily liberated, causing the soap to quickly
become rancid. As a remedy for this it has been proposed to add
sufficient alkali to convert the borax into neutral mono-borate of soda
which is then added to the soap. This process is patented and the name
"Kastilis" has been given to the neutral salt. The incorporation of
borax with the addition of gum tragasol forms the subject of two patents
(Eng. Pats. 4,415, 1904; and 25,425, 1905); increased detergent and
lasting properties are claimed for the soap. Another patented process
(Eng. Pat. 17,218, 1904) consists of coating the borax with a protective
layer of fat or wax before adding to the soap with the idea that
reaction will not take place until required. _Boric acid_ possesses the
defects of borax in a greater degree, and would, of course, simply form
sodium borate with liberation of fatty acids, so should never be added
to a neutral soap.
_Salicylic Acid_ is often recommended for certain skin diseases, and
here again the addition of the acid to soap under ordinary conditions
results in the formation of sodium salicylate and free fatty acids.
To overcome this a process has recently been patented for rubbing the
acid up with vaseline before addition to soap, but the simplest way
appears to be to add the soda salt of the acid to soap.
Amongst the more common milled medicated toilet soaps may be mentioned,
in addition to the above:--
_Birch Tar Soap_, containing 5 or 10 per cent. birch tar, which has a
characteristic pungent odour and is recommended as a remedy for eczema
and psoriasis.
_Carbolic Soap._--A toilet soap should not contain more than 3 per cent.
of pure phenol, for with larger quantities irritation is likely to be
experienced by susceptible skins.
_Coal Tar._--These soaps contain, in addition to carbolic acid and its
homologues, naphthalene and other hydrocarbons derived from coal,
naphthol, bases, etc. Various blends of different fractions of coal tar
are used, but the most valuable constituents from a disinfectant point
of view are undoubtedly the phenols, or tar acids, though in this case
as with carbolic and cresylic soaps, the amount of phenols should not
exceed 3 per cent. in a toilet soap. An excess of naphthalene should
also be avoided, since, on account of its strong odour, soaps containing
much of it are unpopular. The odour of coal tar is considerably modified
by and blends well with a perfume containing oils of cassia, lavender,
spike, and red thyme.
_Formaldehyde._--This substance is one of the most powerful
disinfectants known, and it may be readily introduced into soap without
undergoing any decomposition, by milling in 2-3 per cent. of formalin, a
40 per cent. aqueous solution of formaldehyde, which is a gas. White
soaps containing this chemical retain their whiteness almost
indefinitely.
New combinations of formaldehyde with other bodies are constantly being
brought forward as disinfectants. Among others the compound resulting
from heating lanoline with formaldehyde has been patented (Eng. Pat.
7,169, 1898), and is recommended as an antiseptic medicament for
incorporation with soap.
_Glycerine._--Nearly all soaps contain a small quantity of this body
which is not separated in the lyes. In some cases, however, a much
larger quantity is desired, up to some 6 or 8 per cent. To mill this in
requires great care, otherwise the soap tends to blister during
compression. The best way is to dry the soap somewhat further than
usual, till it contains say only 9 or 10 per cent. moisture and then
mill in the glycerine.
_Ichthyol_ or _Ammonium-Ichthyol-Sulphonate_ is prepared by treating
with sulphuric acid, and afterwards with ammonia, the hydrocarbon oil
containing sulphur obtained by the dry distillation of the fossil
remains of fish and sea-animals, which form a bituminous mineral deposit
in Germany. This product has been admixed with soap for many years, the
quantity generally used being about 5 per cent.; the resultant soap is
possessed of a characteristic empyreumatic smell, very dark colour, and
is recommended for rosacea and various skin diseases, and also as an
anti-rheumatic. Ichthyol has somewhat changed its character during
recent years, being now almost completely soluble in water, and stronger
in odour than formerly.
_Iodine._--A soap containing iodine is sometimes used in scrofulous skin
diseases. It should contain some 3 per cent. iodine, while potassium
iodide should also be added to render the iodine soluble.
_Lysol._--This name is applied to a soap solution of cresol, "Lysol
Soap" being simply another form of coal-tar soap. The usual strength is
10 per cent. lysol, and constitutes a patented article (Fr. Pat.
359,061, 1905).
_Naphthol._--[beta]-Naphthol, also a coal-tar derivative, is a good
germicide, and, incorporated in soap to the extent of 3 per cent.
together with sulphur, is recommended for scabies, eczema and many other
cutaneous affections.
_Sulphur._--Since sulphur is insoluble in water, its action when used in
conjunction with soap can be but very slow and slight. Sulphur soaps
are, however, very commonly sold, and 10 per cent. is the strength
usually advocated, though many so-called sulphur soaps actually contain
very little sulphur. They are said to be efficacious for acne and
rosacea.
Sulphur soaps, when dissolved in water, gradually generate sulphuretted
hydrogen, which, although characteristic, makes their use disagreeable
and lessens their popular estimation.
_Terebene._--The addition of this substance to soap, though imparting a
very refreshing and pleasant odour, does not materially increase the
disinfectant value of the soap. A suitable strength is 5 per cent.
_Thymol._--This furnishes a not unpleasant, and very useful antiseptic
soap, recommended especially for the cleansing of ulcerated wounds and
restoring the skin to a healthy state. The normal strength is 3 per
cent. It is preferable to replace part of the thymol with red thyme oil,
the thymene of which imparts a sweeter odour to the soap than if
produced with thymol alone. A suitable blend is 2-1/2 per cent. of
thymol crystals and 1-1/2 per cent. of a good red thyme oil.
Of the vast number of less known proposed additions to toilet soaps,
mention may be made in passing of:--
_Fluorides._--These have been somewhat popular during recent years for
the disinfection of breweries, etc., and also used to some extent as
food preservatives. Of course only neutral fluorides are available for
use in soap, acid fluorides and soap being obviously incompatible. In
the authors' experience, however, sodium fluoride appears to have little
value as a germicide when added to soap, such soaps being found to
rapidly become rancid and change colour.
_Albumen._--The use of albumen--egg, milk, and vegetable--in soap has
been persistently advocated in this country during the past few years.
The claims attributed to albumen are, that it neutralises free alkali,
causes the soap to yield a more copious lather, and helps to bind it
more closely, and a further inducement held out is that it allows more
water to be left in the soap without affecting its firmness. Experiments
made by the authors did not appear to justify any enthusiasm on the
subject, and the use of albumen for soap-making in this country appears
to be very slight, however popular it may be on the Continent. Numerous
other substances have been proposed for addition to soaps, including
yeast, tar from peat (sphagnol), Swedish wood tar, permanganate of
potash, perborates and percarbonates of soda and ammonia, chlorine
compounds, but none of these has at present come much into favour, and
some had only ephemeral existence. Of the many drugs that it has been
suggested to admix in soap for use in allaying an irritable condition of
the skin, the majority are obviously better applied in the form of
ointments, and we need not consider them further.
_Ether Soap._--Another form of medicated soap made by a few firms is a
liquid ether soap containing mercuric iodide, and intended for surgeons'
use. This, as a rule, consists of a soap made from olive oil and potash,
dissolved in alcohol and mixed with ether, the mercuric iodide being
dissolved in a few drops of water containing an equal weight of
potassium iodide, and this solution added to the alcohol-ether soap.
_Floating Soaps._--Attempts have been made to produce tablets of soap
that will float upon the surface of water, by inserting cork, or floats,
or a metallic plate in such a manner that there is an air space between
the metal and the soap. The more usual method is to incorporate into
hot soap sufficient air, by means of a specially designed self-contained
jacketed crutcher, in which two shafts carrying small blades or paddles
rotate in opposite directions, to reduce the density of the soap below
that of water and so enable the compressed tablet to float. The
difference in weight of a tablet of the same size before and after
aerating amounts to 10 per cent.
Ordinary milling soap is used as a basis for this soap; the settled soap
direct from the copper at 170° F. (77° C.) is carefully neutralised with
bicarbonate of sodium, oleic or stearic acids, or boro-glyceride,
perfumed and aerated.
Floating soap, which is usually white (some are of a cream tint), cannot
be recommended as economical, whilst its deficiency in lathering
properties, owing to occluded air, is a serious drawback to its
popularity as a toilet detergent.
_Shaving Soaps._--The first essential of a shaving soap, apart from its
freedom from caustic alkali or any substance exerting an irritating
effect upon the skin, is the quick production of a profuse creamy lather
which is lasting. Gum tragacanth is used in some cases to give lasting
power or durability, but is not necessary, as this property is readily
attained by the use of a suitable proportion of potash soap. The best
shaving soaps are mixtures of various proportions of neutral soda and
potash soaps, produced by the combination of ordinary milling base with
a white potash soap, either melted or milled together. Glycerine is
sometimes added, and is more satisfactorily milled in.
Every precaution should be taken to ensure thorough saponification of
the soaps intended for blending in shaving soap, otherwise there will be
a tendency to become discoloured and develop rancidity with age. Shaving
soaps are delicately perfumed, and are placed on the market either in
the form of sticks which are cut from the bar of soap as it leaves the
compressor, or stamped in flat cakes.
Shaving creams and pastes are of the same nature as shaving soaps, but
usually contain a larger proportion of superfatting material and
considerably more water.
TEXTILE SOAPS.
In the woollen, cloth, and silk textile industries, the use of soap for
detergent and emulsifying purposes is necessary in several of the
processes, and the following is a brief description of the kinds of soap
successfully employed in the various stages.
1. _Woollen Industry._--The scouring of wool is the most important
operation--it is the first treatment raw wool is subjected to, and if it
is not performed in an efficient manner, gives rise to serious
subsequent troubles to manufacturer, dyer, and finisher.
The object of scouring wool is to remove the wool-fat and wool
perspiration (exuded from the skin of sheep), consisting of cholesterol
and isocholesterol, and potassium salts of fatty acids, together with
other salts, such as sulphates, chlorides, and phosphates. This is
effected by washing in a warm dilute soap solution, containing in the
case of low quality wool, a little carbonate of soda; the fatty matter
is thereby emulsified and easily removed.
Soap, to be suitable for the purpose, must be free from uncombined
caustic alkali, unsaponified fat, silicates, and rosin.
Wool can be dissolved in a moderately dilute solution of caustic soda,
and the presence of this latter in soap, even in small quantities, is
therefore liable to injure the fibres and make the resultant fabric
possess a harsh "feel," and be devoid of lustre.
Unsaponified fat denotes badly made soap--besides reducing the
emulsifying power of the liberated alkali, this fat may be absorbed by
the fibres and not only induce rancidity but also cause trouble in
dyeing.
Soaps containing silicates may have a deleterious action upon the
fibres, causing them to become damaged and broken.
By general consent soaps containing rosin are unsuitable for use by
woollen manufacturers, as they produce sticky insoluble lime and
magnesia compounds which are deposited upon the fibres, and give rise to
unevenness in the dyeing.
A neutral olive-oil soft soap is undoubtedly the best for the purpose of
wool scouring, as, owing to its ready solubility in water, it quickly
penetrates the fibres, is easily washed out, and produces a good "feel"
so essential in the best goods, and tends to preserve the lustre and
pliability of the fibre.
The high price of olive-oil soap, however, renders its use prohibitive
for lower class goods, and in such cases no better soap can be suggested
than the old-fashioned curd mottled or curd soaps (boiled very dry), as
free as possible from uncombined caustic alkali. The raw wool, after
this cleansing operation, is oiled with olive oil or oleine, prior to
spinning; after spinning and weaving, the fabric, in the form of yarn or
cloth, has to be scoured to free it from oil. The soap in most general
use for scouring woollen fabrics is neutral oleine-soda soap. Some
manufacturers prefer a cheap curd soap, such as is generally termed
"second curd," and in cases where lower grades of wools are handled, the
user is often willing to have soap containing rosin (owing to its
cheapness) and considers a little alkalinity desirable to assist in
removing the oil.
Another operation in which soap is used, is that of milling or fulling,
whereby the fabric is made to shrink and thus becomes more compact and
closer in texture. The fabric is thoroughly cleansed, for which purpose
the soap should be neutral and free from rosin and silicates, otherwise
a harsh feeling or stickiness will be produced. Curd soaps or
finely-fitted soaps made from tallow or bleached palm oil, with or
without the addition of cocoa-nut oil, give the best results. All traces
of soap must be carefully removed if the fabric is to be dyed.
The woollen dyer uses soap on the dyed pieces to assist the milling,
and finds that a good soap, made from either olive oil, bleached palm
oil, or tallow, is preferable, and, although it is generally specified
to be free from alkali, a little alkalinity is not of consequence, for
the woollen goods are, as a rule, acid after dyeing, and this alkalinity
would be instantly neutralised.
2. _Cotton Industry._--Cotton fibres are unacted upon by caustic alkali,
so that the soap used in cleaning and preparing cotton goods for dyeing
need not be neutral, in fact alkalinity is a distinct advantage in order
to assist the cleansing.
Any curd soap made from tallow, with or without the addition of a small
quantity of cocoa-nut oil, may be advantageously used for removing the
natural oil.
In cotton dyeing, additions of soap are often made to the bath, and in
such cases the soap must be of good odour and neutral, lest the colours
should be acted upon and tints altered. Soaps made from olive oil and
palm oil are recommended. The same kind of soap is sometimes used for
soaping the dyed cotton goods.
The calico-printer uses considerable quantities of soap for cleansing
the printed-cloths. The soap not only cleanses by helping to remove the
gummy and starchy constituents of the adhering printing paste, but also
plays an important part in fixing and brightening the colours. Soaps
intended for this class of work must be quite neutral (to obviate any
possible alteration in colour by the action of free alkali), free from
objectionable odour and rosin, and readily soluble in water. These
qualities are possessed by olive-oil soaps, either soft or hard. A
neutral olive-oil soft soap, owing to its solubility in cold water, may
be used for fibres coloured with most delicate dyes, which would be
fugitive in hot soap solutions, and this soap is employed for the most
expensive work.
Olive-oil curd (soda) soaps are in general use; those made from palm oil
are also recommended, although they are not so soluble as the olive-oil
soaps. Tallow curd soaps are sometimes used, but the difficulty with
which they dissolve is a drawback, and renders them somewhat unsuitable.
3. _Silk Industry._--Silk is secured to remove the sericin or silk-glue
and adhering matter from the raw silk, producing thereby lustre on the
softened fibre and thus preparing it for the dyer.
The very best soap for the purpose is an olive-oil soft soap; olive-oil
and oleine hard soaps may also be used. The soap is often used in
conjunction with carbonate of soda to assist the removal of the sericin,
but, whilst carbonates are permissible, it is necessary to avoid an
excess of caustic soda.
Tallow soaps are so slowly soluble that they are not applicable to the
scouring of silk.
The dyer of silk requires soap, which is neutral and of a pleasant
odour. The preference is given to neutral olive-oil soft soap, but hard
soaps (made from olive oil, oleine, or palm oil) are used chiefly on
account of cheapness. It is essential, however, that the soap should be
free from rosin on account of its frequent use and consequent
decomposition in the acid dye bath, when any liberated rosin acids would
cling to the silk fibres and produce disagreeable results.
_Patent Textile Soaps._--Stockhausen (Eng. Pat. 24,868, 1897) makes
special claim for a soap, termed Monopole Soap, to be used in place of
Turkey-red oils in the dyeing and printing of cotton goods and finishing
of textile fabrics. The soap is prepared by heating the sulphonated oil
(obtained on treatment of castor oil with sulphuric acid) with alkali,
and it is stated that the product is not precipitated when used in the
dye-bath as is ordinary soap, nor is it deposited upon the fibres.
Another patent (Eng. Pat. 16,382, 1897), has for its object the
obviating of the injurious effects upon wool, of alkali liberated from a
solution of soap. It is proposed to accomplish this by sulphonating part
of the fat used in making the soap.
_Miscellaneous Soaps._--Under this heading may be classed soaps intended
for special purposes and consisting essentially of ordinary boiled soap
to which additions of various substances have been made.
With additions of naphtha, fractions of petroleum, and turpentine, the
detergent power of the soap is increased by the action of these
substances in removing grease.
Amongst the many other additions may be mentioned: ox-gall or
derivatives therefrom (for carpet-cleaning soap), alkali sulphides (for
use of lead-workers), aniline colours (for home-dyeing soaps), pumice
and tripoli (motorists' soaps), pine-needle oil, in some instances
together with lanoline (for massage soaps), pearl-ash (for soap intended
to remove oil and tar stains), magnesia, rouge, ammonium carbonate,
chalk (silversmiths' soap), powdered orris, precipitated chalk,
magnesium carbonate (tooth soaps).
Soap powders or dry soaps are powdered mixtures of soap, soda ash, or
soda crystals, and other chemicals, whilst polishing soaps often contain
from 85 to 90 per cent. siliceous matter, and can scarcely be termed
soap.