Another form (Fig. 1271) is made by Hersey Bros., Boston, and with it a smart workman cau mould 2000 cakes an hour ; it is supplied with steam at 20 lb. pressure through a tin pipe.
Hitherto, in treating of the fabrication of soap, gennine, unsophistieated, or " neat " soaps, containing not more than 32 per cent. of water when freshly made, have been described. It now remains to deal with the various substances which are mixed with soaps after they have been from the ()upper, by. almost every manufacturer, and the mode of their incorporation, known in the trade by the suggestive name of " filling." These may be classed under two heads. Tho first class, which will be considered somewhat in detail, comprises all those soluble alkaline salts, snob as silicates and carbonates, added to soap to increase its detergent power ; between the two classes rnay be placed water, which is always present te a greater or less extent in "filled " soaps, and simply reduces their actual value and economical use ; while the second class includes all insoluble substances, such as clay, steatite (i.e. soapstone, or magnesian silicate), powdered talc, sulphate of baryta, starch, fecula, and all soluble substances, such as glue and gelatine, which have no detergent power in themselves, and are simply added to increase the quantity of water in soaps, or as mere adulterants or make weights. (A notable example of this is the use of clay or steatite, 5 or even 10 per cent. of which may be mixed with soap with out its 'presence being apparent to the eye.) For obvious reasons, only the use of the first class will be described in the present article ; but further remarks on the subject, and methods for detecting and determining the quantity of these adulterants, will be given under the head of Analysis of Soap, pp. 1794-6.
With the exception of the silioated mottled (blue, grey, and red) soaps, a special descrip tion of which will he given, ail " filled " soaps are made by in corporating the soap-paste fresh from the copper with the " fill ing,'' at a temperature of about 77° (170°F.). On a small scale, this may be readily done hy stir ring the two together in the soap - frame with a " orutch," which is a perforated piece of wood or iron, whose flat side is attached at right angles to a pole, hy which it is moved by a man vertically up and down in the frame. When many tons have to be mixed, however, ma chinory in some form must be employed, and the °Mice of the form thereof depends upon the probable consistency of the mix ture. Whatever form bo decided
upon, it is quite essential that it should not merely mix the soap in one plane, but that the eontents of various planes should bo intermingled; simple rotation of arms at right angles to a vertical shaft is therefore insuf ficient.
Such an arrangement is shown in Figs. 1272-3. The blades E of the mixers are set at an angle of 45° on the shaft A B, at the top of which is a. pair of bevel-wheels, with fa-st and loose pulleys C D ; F is the discharge-bole, provided with a valve for drawing off the stiff soap. At G G', aro portions of the mixers and scrapers in section. It is desimble, but not necessary, that there should be some means of controlling the temperature of the tanks or vessels in which the " crutching " (as this rnixing process is technically called) is carried on. Close steam-worms or steara-jackets are very suitable for this purpose ; they should in all cases, however, be cased with a non-conductor, to prevent loss of heat by radiation.
Where very stiff soap has to be crutched, probably the best arrangement is an archimedean screw, which is very largely used in America, where most of the soap made is very stiff; this lifts up the various layers most effectually, and is most conveniently set inside a jacketted cylinder, whose height is about times its diameter. For crutching soaps that are somewhat thinner, such as are usually made in England, the crutching-machinery designed by Neill & Sons, St. Helens, Lancashire, is very suitable.
One of the earliest methods of cheapening, hardening, and increasing the detersive powers of soaps was that proposed by Dr. Normandy, who mixed " neat " soap with crystallized sulphate of soda, previously melted in its own water of crystallization. The salt re-crystallized in the soap as it cooled, and the soap was thereby considerably hardened, so that it wore better in the wash-tub when rubbed upon clothes, and in this way its detersive power was mechanically increased, although sulphate of soda as such, being a neutral salt, had no detersive power of its own, and its addition to soap really diminished chemically the percentage of soda available for washing. These soaps usually effloresced with white powder, and gradually fell out of use, especially as raw fatty matters became cheaper.