I, e, 0.The method of making " hydrated" soaps is very similar to that just described. Fatty matter and (soda) leys are run into the c.opper, and the whole is boiled together, care being taken to avoid an excess of alkali at first ; wheu saponification has taken place, leys are cautiously added until the soap tastes very faintly of eaustio alkali, when the operation is finished, and the soap is ready to be transferred to the frames. Marine soap, for use with sea-water, is made in this way, the fatty matter being entirely coco-nut-oil, and the leys being usually at 20° B. This soap is soluble in weak brine, which other soaps are not (p. 1769). It is difficult to make the saponification begin, but once begun, it proceeds with extraordinary rapidity, the united mass of oil and leys swelling up almost instantaneously to many times its volume. In connection with hydrated soaps, Blake and Maxwell give the following table for the quantity of soda leys necessary for their manufacture: 100 lb. tallow require 3800° at 11° B.
coco-nut-oil 4100° 16°-20° B.
pal m-oil 11 3200° 18°-22° B.
lard 3400° 13° B.
tallow oleine 2800° 18°-22° B.
olive-oil 3000° 16° B.
To use this table, divide the larger number of degrees by the sinaller, and the quotient is the number of lb. of soda leys at the gravity of the divisor, required to make a hydrated soap with 100 lb. fat.
I, c, soaps, with so la for a base, made by open-pan boiling, in which the glycerine is eliminated. This class probably includes 90 per cent. of the total soap made in English-sneakincr countries, and may be divided into three kinds, curd, mottled, and yellow. The coppers for their production have already been sufficiently described, but a necessary and hitberto unused adjunct must now be explained, viz. the pumps required for changing tbe leys beneath the soap. They may be placed inside the copper, or outside, and, in this latter ease, are connected with the outlet pipes at K L, Fig. 1248. For small pans, a simple hand suction-pump answers ; for larger ones, a single- or double-acting lift- or force-pump may be placed inside the copper, and worked by hand, or by an eccentric on a shaft. In large soap factories, some form of centrifugal pump will be found very useful ; the usual objection to the use of these pumps, viz. the need of constant lubrication, being ohviated by the fact that, so employed, they lubricate themselves. Their great advantages are the absence of valves and of easily de ranged working parts, and the large amount of work they will do in a short time.
In England, the names of Gwynne and Appold have long been connected with centrifugal pumps ; in America, tbe one most usually employed is Hersey's patent rotary soap - pump (Hersey Bros., Boston, Mass.), which is represented in Figs. 1252,1253, and 1254.
The pump should be placed as little as possible above the outlets in the coppers, and connected therewith by 2i-in. iron pipes, provided with valves. The pipes in side the copper, communi cating with the outlets, have swing joints, so that they can be raised or lowered at pleasure. To avoid the pipe-system becoming choked by soap congealing in it, a steam-pipe should be inserted at one end, to warm the pipes and pump previous to use, and to " blow-out " all their contents BA the end of the operation. In the figures, S is the suction
pipe ; H, the delivery ; F, the blades set upon a cone (the rotation of which in the closed case pro duces the pumping), which is kept in its place by adjustable set-screws. This pump will transfer to any desired part of the factory, leys, melted fat, finished soap (if not too stiff), " nigre," and soft curd. The diameter of the pump is 10 in., of its outlet 2i in.; when making 120 rev. a, minute, it will pump 6000 gal. an hour, its contents being twice emptied in each revolution.
Whatever kind of hard sosp is to be made, the first stages of the process are the same for all ; but since a curd or a mottled soap requires the use of fire or " dose " steam to evaporate water during the final stages, it is desirable to commence making those in coppers so provided, and either bigh-pressure or superheated steam may he used in the close-steam worm. Yellow soaps may be made in coppers furnished only with an " open " or " free" steana worm. A useful addition to any copper, giving more room to boil, and hence adding to its capacity, is a " curb," or ring 2-3 ft. high loosely fitted on in segments above the angle-iron of the top ring of the copper itself, and capable of easy removal. If, as in Fig. 1248, the copper project 2i ft. above the floor, a " curb " 21-3 ft. high may be conveniently added, and the fan adjusted so that its blades revolve about 1 ft. below the top of the curb.
To commence a boiling of hard soap, melted fat and caustic soda leys (hereafter only called leys) at about 11° B. are simultaneously run into the copper, and the steam is turned on ; the same precautions to prevent an excess of leys must be observed as are detailed in making soft soap (p. 1776); if leys stronger than 12° B. be used at this early stage, saponification will not take place. When the contents of the copper present the appearance of a homogeneous magma or paste, leys of a higher sp. gr., say up to 25° B., may be cautiously added, but it is not essential to do so. The boiling, and the addition of fat and leys, must be continued until a small sample cooled between the fingers has a tolerably firm consistence, and when applied to the tongue, no caustic taste, or only a very faint one. Should there be a strong taste (or " touch," to use the American term), or should the sample separate into soap and liquor when squeezed, too much ley has been admitted, and more fat must be added. Should the sample be soft and greasy, more leys are required, especially if any unsaponified fat be visible; occasionally the two conditions obtain, both caustic liquor and fat appearing in a sample, which is evidence that combination has not taken place ; the remedy is more boiling, with occanionally the addition of water. Practice alone will enable the operator to judge of the completion of thia flrat operation, called "pasting " (French, empdtage). English phraseology, it is called " killing the goods " or raw material, and the soap is then said tu be "close" or in a " hitch " or "glue." In this condition, the soap should c,ontain about 190- of the total soda necessary for complete aaponification, with a large excess of water, which is separated from it by the next operation.