The removal of the excise duty in England, in 1853, gave an enormous impetus to the soap industry. Manufaeturers were no longer deterred frum making large batches of soap by the fear that, if they were spoiled, double duty wonld have to be paid when they were re-made and produced fit for aale ; and, as a natural consequence, numerous experiments were tried, both with the raw materials and the apparatus employed. Soap-coppers are now made of colossal size, those oapable of turning ont 50 tons of finished soap (112,000 lb.) at one operation being by no means uncommon, and some of the large American manufacturera have built even still larger coppers, requiring a building of 3 stories to contain them. Although it is desirable that those boiled by fire should be circular in shape, and not too large—say 20 tone capacity—the coppers whose contents are boiled by steam may be of any desired shape, circular, oval, or rectangular, provided that the steam-pipes be carried into the corners (if any), and be so arranged as to ensure uniformity of ebullition throughout the whole mass. There is no necessary proportion between diameter (or superficial area) and depth ; English soap-makers are more accustomed to pans whose diameter is to their depth as 1 to 1,1 to 1.25, or 1 to 1.5 (e. g. a pan 15 ft. diam. and 15 ft. deep will turn out 25-80 tons of soap); while their Amerioan confreres, lees trammelled by tradition, increase the ratio as far /18 to 2,1 to 2.5, or even 1 to 3.
Soap-coppers are now almost invariably built of wrought-iron platea, and rivetted together in the place where they aro eventu ally to stand. Figs. 1246,1247 ehow a simple form of copper for flre-boiling, with the fire place, flues, Sic.; ABDO is the outline of the oopper, C D being a circular renew able plate, in the part most expoaed to the aotion of the fire F. At E, aro supporting lugs of cast-iron ; K L is the floor-lovel ; H I, a steam pipe ending in a perforated coil, steam being controlled by the cock at G. Figs. 1248, 1249 show a copper where steam only is used : A B is the floor line ; 0 D E, the copper, provided with a " hat " at E to receivo im purities that subaide, and to enable spent leys to be re moved completely by the draw-off at K. Another draw-off is fitted at L. Two steam - worms are provided, H, with 'cock F, whose coil is perforated, admitting " open " or " wet " steam among the copper °entente, and I, with cock 0, in which high pressure or superheated steam is circulated, for use when it is desired to evapo rate water. This lsst coil is usually omitted in the largest coppers, being only used in making curd and mottled soaps.
An important adjunct to a soap-copper is a little piece of machinery for preventing the contents from boiling over, as they are apt to do when saponification is taking place, and also in a later stage, even after the steam is turned off. It is called a fan, and is represented in Figs. 1250,1251 ; it
consists essentially of a rotating paddle, whose blades just touch tbe top of the boiling mass. The motion is derived from an overhead shaft J, on which is keyed a bevel-wheel H, gearing into a similar wheel G ; this latter slides on a feather on the shaft F, being thrown in or out of gear by a fork E, to which is attached a rod C, actuated by links B and bell-crauk A, in the bottom end of which is an eye for attaching a oord which may be drawn to right or left. The lower end of the fan-shaft drives the over-shaft 14, on which the fans N are keyed by means of bevel-wheels K L. The top and bottom of the fan-ehaft are carried by bushes driven in at each end of a piec,e of stout 2-in. steam-pipe, and the pipe S is inserted in cast-iron frames Q R. Near the lower end of the pipe, is a shackle P, to which a rope or chain is attached for lowering or raising the fan, according to the surface of liquid in the copper. The whole swinge on the axis of shaft J.
The fabrication of soft soaps will now be described. Soft soap ie a more or less impure solution of potash soap mixed with glycerine in caustic-leys, and forming at ordinary temperatures a transparent smeary jelly, containing at times, and especially in cold weather, white grains, which are impure stearates of soda or potash. The most suitable form of copper for making it is shown in Pig. 1246. In England, whale-, Beal-, and linseed-oils are chiefly used, and occasionally a little tallow to produce the grains, or "Jigging," juat described, an appearance which serves no really useful purpose. On the European continent, hempseed-, linseed-, camelina-, and poppy-oils are used, and also rapeseed- and train-oils, especially in summer, eince they produce a harder aoap. In America, cotton-seed-oil, and oleic acid, are often employed. Ilempseed-oil gives a greeniah tint much prized by consumers, which may be imitated by the addition of a little indigo precipitated by potash from its solution in sulphuric acid.
A very desirable, but not necessary, adjunct to the soap-copper is a set of tanke of iron or wood, whose contents per inch of depth are known, in order that the quantities of oil and leys let into the copper may be regulated. In many large factories, the practice is to keep a strict account of the quantity of fatty matter and roein used, but to control the amount of leye according to the judgment of the soap-boiler. Such gauge- and store-tanks may be in any convenient place, and pipes or open shutes carried from them to deliver their contents into the copper ; suitable plugs and cocks control the flow of the liquid at the pleasure of the operator.