Chapter VII: 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Soaps of the first class are of comparatively trifling importance, having been superseded by the other qualities.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.

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.

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.

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.

(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.

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.

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.

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.