TREATMENT OF SETTLED SOAP.
Cleansing—Crutching—Liquoring of Soaps—Filling—Neutralising, Colouring and Perfuming—Disinfectant Soaps—Framing—Slabbing—Barring—Open and Close Piling—Drying—Stamping—Cooling.
Cleansing.—After completion of saponification, and allowing the contents of the pan to settle into the various layers, as described in the preceding chapter, the actual soap, forming the second layer, is now transferred to the frames, this being generally termed "cleansing" the soap. The thin crust or layer at the top of the pan is gently removed, and the soap may be either ladled out and conveyed to the frames, or withdrawn by the aid of a pump from above the nigre through a skimmer (Fig. 1), and pipe, attached by means of a swivel joint (Fig. 2) (which allows the skimmer pipe to be raised or lowered at will by means of a winch, Fig. 3), to a pipe fitted in the side of the pan as fully shown in Fig. 4, or the removal may be performed by gravitation through some mechanical device from the side of the copper.
Fig. 1.—Skimmer, with flange for attachment to skimmer-pipe.
Every precaution is taken to avoid the presence of nigre in the soap being cleansed.
Fig. 2.—Swivel-joint.
The temperature at which soap may be cleansed depends on the particular grade—soaps requiring to be liquored should not be cleansed too hot or a separation will take place, 150° F. (66° C.) may be taken as a suitable temperature for this class of soap; in the case of firm soaps, such as milling base, where cooling is liable to take place in the pan (and thus affect the yield), the temperature may be 165°-170° F. (74°-77° C.). This latter class of soap is generally run direct to the frames and crutched by hand, or, to save manual labour, it may be run into a power-driven crutching pan (neutralising material being added if necessary) and stirred a few times before framing.
Fig. 3.—Winch.
Fig. 4.—Soap-boiling pan, showing skimmer pipe, swivel and winch.
Fig. 5.—Hand crutch.
Fig. 6.—Mechanical crutcher.
Crutching.—This consists of stirring the hot soap in the frames by hand crutches (Fig. 5) until the temperature is sufficiently lowered and the soap begins to assume a "ropiness". Crutching may also be performed mechanically. There are various types of mechanical crutchers, stationary and travelling. They may be cylindrical pans, jacketed or otherwise, in the centre of which is rotated an agitator, consisting of a vertical or horizontal shaft carrying several blades (Fig. 6) or the agitator may take the form of an Archimedean screw working in a cylinder (Fig. 7).
Fig. 7.—Mechanical crutcher.
The kind of soap to be crutched, whether thin or stiff, will determine the most suitable type for the purpose. The former class includes "washer" soap which is generally neutralised, and coloured and perfumed, if necessary, in these crutching pans, and in that case they are merely used for mixing the liquids with the hot soap prior to its passage along wooden spouts (Fig. 8) provided with outlets over the frames, in which the crutching is continued by hand. In the case of stiff soaps requiring complete incorporation of liquor, the screw type is preferable, the soap being forced upwards by the screw, and descending between the cylinder and the sides of the pan, while the reverse action can also be brought into play. The completion of crutching is indicated by the smoothness and stiffness of the soap when moved with a trowel, and a portion taken out at this point and cooled should present a rounded appearance. When well mixed the resultant product is emptied directly into wheel-frames placed underneath the outlet of the pan. It is important that the blades or worm of the agitating gear be covered with soap to avoid the occlusion of air and to prevent the soap becoming soft and spongy.
Fig. 8.—Wooden soap spout.
Liquoring of Soaps.—This consists of the addition of various alkaline solutions to soap to produce different qualities, and is best performed in the crutching machines, although it is in some instances carried out in the frames. In the history of soap-making a large number and variety of substances have been suggested for the purpose of accomplishing some real or supposed desirable effect when added to soap. Many of these have had only a very short existence, and others have gradually fallen out of use.
Amongst the more practical additions most frequently adopted may be mentioned carbonate of soda, silicate of soda, and pearl ash (impure carbonate of potash). The carbonate of soda may be used in the form of "soda crystals," which, containing 62.9 per cent. of water, dissolves in its own water of crystallisation on heating, and is in that manner added to the hot soap. In the case of weak-bodied soap, this addition gives firmness and tends to increase the detergent qualities.
The soda carbonate may also be added to soap as a solution of soda ash (58° alkali) either concentrated, 62° Tw. (34° B.), or of various strengths from 25° Tw. (16° B.) upwards. This solution stiffens and hardens soap, and the addition, which must not be excessive, or efflorescence will occur, is generally made at a temperature of 140° F. (60° C.). Care should always be taken in the choice of solutions for liquoring. Strong soda ash solution with a firm soap will result in a brittle product, whereas the texture of a weak soap would be greatly improved by such addition.
A slight addition of a weak solution of pearl ash, 4°-8° Tw. (2.7-5.4° B.), improves the appearance of many soaps intended for household purposes.
For yellow soaps, containing a low percentage of fatty acids, solutions of silicate of soda of varying strengths are generally used.
It is always advisable to have a test sample made with the soap to ascertain what proportion and what strength of sodium silicate solution is best suited for the grade of soap it is desired to produce. It is important that the soap to be "silicated" should be distinctly alkaline (i.e., have a distinct caustic taste), or the resultant soap is liable to become like stone with age. The alkaline silicate of soda (140° Tw., 59.5° B.) is the quality most convenient for yellow soaps; this may be diluted to the desired gravity by boiling with water. For a reduction of 3-4 per cent. fatty acids content, a solution of 6° Tw. (4° B.) (boiling) is most suitable, and if the reduction desired is greater, the density of the silicate solution should be increased; for example, to effect a reduction of 20 per cent. fatty acids content, a solution of 18° Tw. (12° B.) (boiling) would probably be found to answer.
In some instances 140° Tw. (59.5° B.) silicate may be added; experiment alone will demonstrate the amount which can be satisfactorily incorporated without the soap becoming "open," but 1/10 of the quantity of soap taken is practically a limit, and it will be found that the temperature should be low; the same quantity of silicate at different temperatures does not produce the same result. Various other strengths of sodium silicate are employed, depending upon the composition and body of the soap base—neutral silicate 75° Tw. (39.4° B.) also finds favour with some soap-makers. Mixtures of soda crystals or soda ash solution with silicate of soda solution are used for a certain grade of soap, which is crutched until smooth and stiff. Glauber's salt (sodium sulphate) produces a good smooth surface when added to soap, but, owing to its tendency to effloresce more quickly than soda carbonate, it is not so much used as formerly.
Common salt sometimes forms an ingredient in liquoring mixtures. Potassium chloride and potassium silicate find a limited use for intermixing with soft soaps.
It will be readily understood that hard and fast rules cannot be laid down for "liquoring" soap, and the correct solution to be employed can only be ascertained by experiment and experience, but the above suggestions will prove useful as a guide towards good results. A smooth, firm soap of clear, bright, glossy appearance is what should be aimed at.
Filling.—Some low-grade soaps contain filling, which serves no useful purpose beyond the addition of weight. Talc is the most frequently used article of this description. It consists of hydrated silicate of magnesium and, when finely ground, is white and greasy to the touch. The addition of this substance to the hot soap is made by suspending it in silicate of soda solution.
Whatever filling material is used, it is important that the appearance of the soap should not be materially altered.
Neutralising, Colouring and Perfuming.—The free caustic alkali in soap, intended for toilet or laundry purposes, is usually neutralised during the cleansing, although some soap manufacturers prefer to accomplish this during the milling operation. Various materials have been recommended for the purpose, those in most general use being sodium bicarbonate, boric acid, cocoa-nut oil, stearic acid, and oleic acid.
The best method is the addition of an exact quantity of sodium bicarbonate (acid sodium carbonate), which converts the caustic alkali into carbonate. The reaction may be expressed by the equation:—
| NaOH | + | NaHCO3 | = | Na2>CO3 | + | H2O |
| Caustic soda | Bicarbonate of soda | Carbonate of soda | Water |
Boric acid in aqueous or glycerine solutions, and borax (biborate of soda) are sometimes used, but care is necessary in employing these substances, as any excess is liable to decompose the soap.
The addition of cocoa-nut oil is unsatisfactory, the great objection being that complete saponification is difficult to ensure, and, further, there is always the liability of rancidity developing. Stearic and oleic acids are more suitable for the purpose, but oleic acid has the disadvantage that oleates are very liable to go rancid.
A large number of other substances have been proposed, and in many instances patented, for neutralising the free caustic alkali. Among these may be mentioned—Alder Wright's method of using an ammoniacal salt, the acid radicle of which neutralises the caustic alkali, ammonia being liberated; the use of sodium and potassium bibasic phosphate (Eng. Pat. 25,357, 1899); a substance formed by treating albumen with formalin (Eng. Pat., 8,582, 1900); wheat glutenin "albuminoses" (albumen after acid or alkaline treatment); malt extract; and egg, milk, or vegetable albumen.
The colouring matter used may be of either vegetable or coal-tar origin, and is dissolved in the most suitable medium (lye, water, or fat). The older types of colouring matter—such as cadmium yellow, ochres, vermilion, umbers—have been superseded.
In the production of washer household soaps, a small quantity of perfume is sometimes added.
Disinfectant Soaps.—To the soap base, which must be strong to taste, is added from 3 to 4 per cent. of coal-tar derivatives, such as carbolic acid, cresylic acid, creosote, naphthalene, or compounds containing carbolic acid and its homologues. The incorporation is made in the crutching pan, and further crutching may be given by hand in the frames.
Framing.—The object of framing is to allow the soap to solidify into blocks. The frames intended for mottled soaps, which require slow cooling, are constructed of wood, often with a well in the base to allow excess of lye to accumulate—for other soaps, iron frames are in general use. The frame manufactured by H. D. Morgan of Liverpool is shown in Fig. 9.
As soon as the frame is filled, or as soon as the crutching in the frame is finished, the soap is smoothed by means of a trowel, leaving in the centre a heap which slopes towards the sides. Next day the top of the soap is straightened or flattened with a wooden mallet, this treatment assisting in the consolidation.
Fig. 9.—Soap frame.
Fig. 10.—Slabbing machine.
The length of time the soap should remain in frames is dependent on the quality, quantity, and season or temperature, and varies usually from three to seven days. When the requisite period has elapsed, the sides and ends of the frames are removed, and there remains a solid block of soap weighing from 10 to 15 cwt. according to the size of frame used. The blocks, after scraping and trimming, are ready for cutting into slabs.
Slabbing.—This may be done mechanically by pushing the block of soap through a framework containing pianoforte wires fixed at equi-distances (Fig. 10, which shows a machine designed by E. Forshaw & Son, Ltd.), or the soap may be out by hand by pulling a looped wire through the mass horizontally along lines previously scribed, or, for a standard sized slab, the wire may be a fixture in a box-like arrangement, which is passed along the top of the soap, and the distance of the wire from the top of the box will be the thickness of the slab (Fig. 11).
Fig. 11.—Banjo slabber.
All tallow soaps should be slabbed whilst still warm, cut into bars, and open-piled immediately; if this type of soap is cold when slabbed its appearance will be very much altered.
Barring.—The slabs are out transversely into bars by means of the looped wire, or more usually by a machine (Fig. 12), the lower framework of which, containing wires, is drawn through the soap placed on the base-board; the framework is raised, and the bars fall upon the shelf, ready for transference into piles. It has long been the custom in England to cut bars of soap 15 inches long, and weighing 3 lb. each, or 37-1/2 bars of soap to the cwt., but in recent years a demand has arisen for bars of so many various weights that it must be sometimes a difficult matter to know what sizes to stock.
In another type of barring machine, portions of the slab, previously cut to size, are pushed against a framework carrying wires, and the bars slide along a table ready for handling (Fig. 13).
In cutting machines, through which "washer" household soap is being passed, the bar is pushed at right angles through another frame containing wires, which divides it into tablets; these may be received upon racks and are ready for drying and stamping. It is needless to say that the slabs and tablets are cut with a view to reducing the amount of waste to the lowest possible limit. Such a machine, made by E. Forshaw & Son, Ltd., is shown in Fig. 14.
Fig. 12.—Barring machine.
Fig. 13.—Bar-cutting machine.
Fig. 14.—Tablet-cutting machine.
Open- and Close-piling.—As remarked previously, tallow soaps should be cut whilst warm, and the bars "open-piled," or stacked across each other in such a way that air has free access to each bar for a day. The bar of soap will skin or case-harden, and next day may be "close-piled," or placed in the storage bins, where they should remain for two or three weeks, when they will be in perfect condition for packing into boxes ready for distribution.
Fig. 15.—Soap stamp.
Drying.—"Oil soaps," as soaps of the washer type are termed, do not skin sufficiently by the open-piling treatment, and are generally exposed on racks to a current of hot air in a drying chamber in order to produce the skin, which prevents evaporation of water, and allows of an impression being given by the stamp without the soap adhering to the dies. It is of course understood that heavily liquored soaps are, as a rule, unsuitable for the drying treatment, as the bars become unshapely, and lose water rapidly.
Stamping.—Bar soaps are usually stamped by means of a hand-stamp containing removable or fixed brass letters (Fig. 15), with a certain brand or designation of quality and the name of the manufacturer or vendor, and are now ready for packing into boxes.
A very large bulk of the soap trade consists of the household quality in tablet form, readily divided into two cakes. These are stamped in the ordinary box moulds with two dies—top and bottom impressions—the die-plates, being removable, allow the impressions to be changed. This type of mould (Fig. 16) can be adjusted for the compression of tablets of varying thickness, the box preventing the escape of soap. We are indebted to E. Forshaw & Son, Ltd., for this illustration.
Fig. 16.—Box mould.
The stamping machine may be worked by hand (Fig. 17) or power driven. Where large quantities of a particular tablet have to be stamped, one of the many automatic mechanical stampers in existence may be employed, the tablets being conveyed to and from the dies by means of endless belts. Such a machine is shown in the accompanying illustration (Fig. 18).
If necessary, the soap is transferred to racks and exposed to the air, after which it is ready for wrapping, which is generally performed by manual labour, although in some instances automatic wrapping machines are in use.
Cardboard cartons are also used for encasing the wrapped tablets, the object being that these are more conveniently handled by tradesmen and may be advantageously used to form an attractive window display.
Cooling.—Many attempts have been made to shorten the time required for the framing and finishing of soap, by cooling the liquid soap as it leaves the pan.
Fig. 17.—Soap-stamping machine, showing box mould.
With milling base, this is successfully accomplished in the Cressonnières' plant, by allowing the hot soap to fall upon the periphery of a revolving drum which can be cooled internally by means of water.
Fig. 18.—Automatic stamper.
In the case of household soaps, where the resultant product must be of good appearance and have a firm texture, the difficulty is to produce a bar fit for sale after the cooling has been performed, as soap which has been suddenly chilled lacks the appearance of that treated in the ordinary way. Several patents have been granted for various methods of moulding into bars in tubes, where the hot soap is cooled by being either surrounded by running water in a machine of similar construction to a candle machine, or rotated through a cooling medium; and numerous claims have been made both for mechanical appliances and for methods of removing or discharging the bars after cooling. In many instances these have proved unsatisfactory, owing to fracture of the crystalline structure. Moreover, in passing through some of the devices for solidification after chilling, the soap is churned by means of a worm or screw, and this interferes with the firmness of the finished bar, for, as is well known, soap which has been handled too much, does not regain its former firmness, and its appearance is rendered unsatisfactory.
A form of apparatus which is now giving satisfactory results is the Leimdoerfer continuous cooler (Fig. 19). This consists of a fixed charging hopper, A, a portable tank, B, containing tubes, and a detachable box, C, which can be raised or lowered by means of a screw, D. The bottom of the hopper is fitted with holes corresponding with the cooling tubes, e, and closed by plugs c, attached to a frame b, which terminates above in a screw spindle a, by means of which the frame and plugs can be raised and lowered so as to permit or stop the outflow of soap into the cooling tubes. The tubes are closed at the bottom by slides d, and the box B, in which they are mounted, is carried on a truck running on rails. The charging hopper can be connected with the soap-pan by a pipe, and when the hopper is filled with liquid soap the plugs c are raised and the air in the box C exhausted, thus causing the soap to descend into the cooling tubes.
Fig. 19.—Leimdoerfer cooler.
The slides d are closed, the screw D released, and the box B moved away to make room for another. At the end of the rail track is an ejecting device which pushes the cooled soap out of the tubes, and the truck is run back on a side track to the machine for use over again. In this way the apparatus can be worked continuously, the soap being received from the cooling pipes on a suitable arrangement for transport to the press or store room.
A similar idea has been made the subject of a patent by Holoubek (Eng. Pat. 24,440, 1904, Fig. 20). The soap is run into frames or moulds having open sides, which are closed by being clamped with screws and pressure plates between cooling tubes through which water circulates.
Fig. 20.—Holoubek's cooler.