CHAPTER II Construction and Equipment of a Soap Plant. No fixed plan for the construction and equipment of a soap plant can be given. The specifications for a soap factory to be erected or remodeled must suit the particular cases. Very often a building which was constructed for a purpose other than soap manufacture must be adapted for the production of soap. In either case it is a question of engineering and architecture, together with the knowledge obtained in practice and the final decision as to the arrangement is best solved by a conference with those skilled in each of these branches. An ideal soap plant is one in which the process of soap making, from the melting out of the stock to the packing and shipping of the finished product, moves downward from floor to floor, since by this method it is possible to utilize gravitation rather than pumping liquid fats and fluid soaps. Convenience and economy are obtained by such an arrangement. The various machinery and other equipment for soap manufacture are well known to those connected with this industry. It varies, of course, depending upon the kind of soap to be manufactured, and full descriptions of the necessary machinery are best given in the catalogs issued by the manufacturers of such equipment, who in this country are most reliable. To know just what equipment is necessary can very easily be described by a brief outline of the process various soaps undergo to produce the finished article. After the saponification has taken place in the soap kettle the molten soap is run directly into the soap frames, which consist of an oblong compartment, holding anywhere from 400 to 1,200 pounds, with removable steel sides and mounted upon trucks, in which it solidifies. In most cases it is advisable to first run the soap into a crutcher or mixer which produces a more homogeneous mass than if this operation is omitted. Color and perfume may also be added at this point, although when a better grade of perfume is added it must be remembered that there is considerable loss due to volatilization of same. When a drying machine is employed the molten soap is run directly upon the rollers of this machine, later adding about 1.0% zinc oxide to the soap from which it passes continuously through the drying chamber and is emitted in chip form ready for milling. After the soap has been framed, it is allowed to cool and solidify, which takes several days, and then the sides of the frame are stripped off. The large solid cake is cut with wires by hand or by a slabber into slabs of any desired size. These slabs are further divided into smaller divisions by the cutting table. In non-milled soaps (laundry soaps, floating soaps, etc.), these are pressed at this stage, usually by automatic presses, after a thin hard film has been formed over the cake by allowing it to dry slightly. In making these soaps they are not touched by hand at any time during the operation, the pressing, wrapping and packing all being done by machinery. For a milled soap the large slabs are cut into narrow oblong shapes by means of the cutting table to readily pass into the feeder of the chipper, the chips being spread upon trays and dried in a dry house until the moisture content is approximately 15%. The process of milling is accomplished by passing the dried soap chips through a soap mill, which is a machine consisting of usually three or four contiguous, smooth, CONSTRUCTION AND EQUIPMENT granite rollers operated by a system of gears and set far enough apart to allow the soap to pass from a hopper to the first roller, from which it is constantly conveyed to each succeeding roller as a thin film, and finally scraped from the last roller to fall into the milling box in thin ribbon form. These mills are often operated in tandem, which necessitates less handling of soap by the operator. The object of milling is to give the soap a glossy, smooth finish and to blend it into a homogeneous mass. The perfume, color, medication or any other material desired are added to the dried soap chips prior to milling. Some manufacturers use an amalgamator to distribute these uniformly through the soap, which eliminates at least one milling. When a white soap is being put through the mill, it is advisable to add from 0.5% to 1% of a good, fine quality of zinc oxide to the soap, if this substance has not been previously added. This serves to remove the yellowish cast and any translucency occasioned by plodding. Too great a quantity of this compound added, later exhibits itself by imparting to the soap a dead white appearance. Inasmuch as the milling process is one upon which the appearance of a finished cake of toilet soap largely depends, it should be carefully done. The number of times a soap should be milled depends upon the character of a soap being worked. It should of course be the object to mill with as high a percentage of moisture as possible. Should the soap become too dry it is advisable to add water directly, rather than wet soap, since water can more easily be distributed through the mass. As a general statement it may be said it is better policy to overmill a soap, rather than not mill it often enough. After the soap has been thoroughly milled it is ready for plodding. A plodder is so constructed as to take the soap ribbons fed into the hopper by means of a worm screw and continuously force it under great pressure through a jacketed cylinder through which cold water circulates in the rear to compensate the heat produced by friction and hot water at the front, to soften and polish the soap which passes out in solid form in bars of any shape and size depending upon the form of the shaping plate through which it is emitted. The bars run upon a roller board, are cut into the required length by a special cake cutting table, allowed to dry slightly and pressed either automatically or by a foot power press in any suitable soap die. The finished cake is then ready for wrapping and after due time in stock reaches the consumer. Besides the various apparatus mentioned above there are many other parts for the full equipment of a modern soap plant, such as remelters, pumps, mixers, special tanks, power equipment, etc. As has been stated, however, practical experience will aid in judging the practicability as to installation of these. The various methods of powdering soap are, however, not generally known. Where a coarse powder is to be produced, such as is used for common washing powders, no great difficulty is experienced with the well known Blanchard mill. In grinding soap to an impalpable powder the difficulties increase. The methods adapted in pulverizing soaps are by means of disintegrators, pebble mills and chaser mills. The disintegrator grinds by the principle of attrition, that is, the material is reduced by the particles being caused to beat against each other at great velocity; a pebble mill crushes the substance by rubbing it between hard pebbles in a slowly revolving cylinder; the chaser mill first grinds the material and then floats it as a very fine powder above a curb of fixed height. The last method is particularly adapted for the finest of powder (140 mesh and over). CHAPTER III Classification of Soap-Making Methods. In the saponification of fats and oils to form `soap through the agency of caustic alkalis, as has been stated, the sodium or potassium salts of the mixed fatty acids are formed. Sodium soaps are usually termed hard soaps, and potassium soaps soft. There are, however, a great many varieties of soaps the appearance and properties of which depend upon their method of manufacture and the oils or fats used therein. The various methods adopted in soap making may be thus classified: 1. Boiling the fats and oils in open kettles by open steam with indefinite quantities of caustic alkali solutions until the finished soap is obtained; ordinarily named full boiled soaps. These may be sub-divided into (a) hard soaps with sodium hydrate as a base, in which the glycerine is recovered from the spent lyes; (b) hard soaps with soda as a base, in which the glycerine remains in the soap, e. g., marine cocoanut oil soaps; (c) soft potash soaps, in which the glycerine is retained by the soap. 2. Combining the required amount of lye for complete saponification of a fat therewith, heating slightly with dry heat and then allowing the saponification to complete itself. This is known as the cold process. 3. Utilizing the fatty acid, instead of the neutral fat, and combining it directly with caustic alkali or carbonate, which is incorrectly termed carbonate saponification, since it is merely neutralizing the free fatty acid and thus is not a saponification in the true sense of the word. No glycerine is directly obtained by this method, as it is |