SOAP 



SOAPBERRY 



539 



more fresh fat. The contents of the 'copper' are 

 again boiled with open steam and lye for several 

 hours, to complete the saponification of the last 

 traces of fat, and ' make ' the soap. 



The method of finishing the soap varies with the 

 kind of soap required, and will now be explained 

 under the names of the three varieties. 



Curd Soaps. The finest quality is made from 

 tallow, but other fats may be used. When the 

 soap has been ' made,' as just explained, the lye 

 is concentrated by means of close steam, until a 

 sample of the soap appears hard. The boiling is 

 then stopped, and the soap removed, after settling. 



Mottled Soaps, as far as composition is con- 

 cerned, are practically ' curd ' soaps ; darker fats, 

 however, are used in their manufacture, and after 

 the soaps have been ' made ' the lye is not con- 

 centrated so far as with ' curd ' soaps. Many pre- 

 cautions require to be observed in order to obtain 

 the natural ' mottling * which characterises them. 

 It is due to the presence of small quantities of lime, 

 magnesia, &c., from the materials used, and to 

 oxide of iron, from the 'copper.' These oxides 

 form insoluble soaps, and when the soap, retaining 

 a little lye, is transferred to the cooling frames, 

 they collect together, producing the well-known 

 appearance. 



Natural ' mottling ' may lie accepted as a guar- 

 antee of the absence of an undue amount of water 

 in a soap. Artificial 'mottling' of inferior qualities 

 of soap with ultramarine, oxide of iron, &c. is 

 largely practised, sometimes withr fraudulent in- 

 tentions. ' Mottled ' soaps are much used for 

 laundry work and such purposes. 



Yellow Soaps contain rosin as an essential con- 

 stituent. The finest qualities are made from the 

 best tallow and light-coloured rosin ; inferior quali- 

 ties from darker tallow, bleached palm-oil, &c., and 

 darker rosin. The rosin is usually introduced after 

 the second stage of the general process. The finish- 

 ing operation, or ' fitting ' of yellow soaps, requires 

 much experience. After the soap has been ' made ' 

 the ' copper ' is allowed to stand for about twelve 

 hours, tne lye removed, and the soap well boiled 

 until homogeneous, with some fresh lye if neces- 

 sary. - When a sample has been found to be in 

 the proper state, the 'copper' is covered up, and 

 allowed to stand for some days, when a separation 

 into three layers takes place the scum or ' fob ' 

 on the top, the 'nigre' (or dark alkaline soap-lye) 

 underneath, and the finished or ' neat ' soap in the 

 centre, which is then removed to frames. The 

 ' nigres ' are utilised in the making of darker soaps. 

 The principal soap-manufacturers now recover the 

 glycerine from their ' spent lyes." 



Cocoa-nut or Marine Soap. Cocoa-nut oil is 

 saponified in the heat, with strong lye, without 

 salting out, &c. A hard soap is formed, although 

 much water may be present, and is serviceable on 

 board ship, when condensed water is not available, 

 on account of its solubility in salt water. 



The operations subsequent to the soap leaving 

 the ' copper ' require little explanation. When no 

 Milling^ substances are to be added the melted 

 soap is run, or ladled, into large oblong boxes of 

 wood or iron, called ' cooling frames.' After stand- 

 ing for several days to allow the soap to harden, 

 the sides of the frames are removed, and the blocks 

 of soap cut, first into slabs, by means of a thin 

 steel wire, and then into 'bars' by a special 

 machine, consisting generally of a strong frame or 

 lever, carrying a number of wires stretched across 

 it. The ' bars,' after having been stamped with 

 the name of the maker, and the brand of the soap, 

 are ready for being sent out. 



The demand of the public for cheap soap has led 

 to what is known as 'filling.' This consists in 

 mechanically mixing with or 'crntching into' the 



soap, after it leaves the 'copper,' certain substances, 

 added either with the view of increasing the deter- 

 gent power of the soap, or simply to lessen the 

 cost. Silicate of soda belongs to the first class, 

 and is used with advantage in certain soaps. Such 

 substances, however, as water, talc, clay, chalk, 

 sulphate of baryta, &c. must be looked upon merely 

 as adulterants. 



Soft Soaps are really impure solutions of potash- 

 soaps, with glycerine, in caustic lye. They form 

 transparent jellies, and often exhibit, in cold 

 weather, a white graining, or ' figging, ' due to 

 alkaline stearates. The oil (e.g. linseed, or any 

 other of those named abov^) is run into the 

 'copper,' potash lye added, and the steam turned 

 on. The boiling is continued, latterly by close 

 steam or fire heat, and lye added, until a small 

 sample appears clear on cooling, and no liquid 

 separates from it. When finished the soap is run 

 into barrels or tins. 



Toilet Soaps. The basis or ' stock ' of the better 

 qualities is generally good curd or yellow soap, 

 special precautions being taken to ensure absence 

 of free alkali. The finest toilet soaps are now 

 'milled.' For this purpose the soap is cut into 

 shavings, dried partially, the colouring material 

 and perfumes added, and passed several times 

 between granite rollers, to make it perfectly homo- 

 geneous. It is then subjected to great pressure, 

 or 'plotted,' to form it into bars, which are after- 

 wards cut, and stamped into tablets. The lower 

 qualities of toilet soaps are generally made by the 

 'cold process.' 



'Transparent* soaps are prepared by dissolving 

 good dry soap in alcohol, pouring off the clear solu- 

 tion, and removing the bulk of the spirit by dis- 

 tillation. The remaining soap is transferred to 

 moulds, allowed to cool, and preserved in warm 

 chambers for several months, until it becomes quite 

 transparent. Many transparent soaps, however, 

 are made by the 'cold process,' their transparency 

 being obtained by the audition of sugar. Glycerine 

 is often added to both opaque and transparent 

 soaps, imparting to them its characteristic emollient 

 properties, while such substances as carbolic acid, 

 coal-tar, eucalyptus-oil, &c. are added to soaps 

 intended for disinfecting purposes. 



The following table gives the average com- 

 position of some genuine soaps of English make : 



The commercial value of a soap depends upon its 

 percentage of fatty anhydride. Soap is used other- 

 wise than as a detergent as a handy ointment for 

 skin irritated by friction, as a laxative medicine, 

 in making pills, liniments, and plasters, and as a 

 test for the hardness of Water ( q. v. ). 



See R. S. Cristiani, Technical Treatise on Soap and 

 Candles ( 1881 ); W. L. Carpenter, Soap, Candles, Lubri- 

 cants, and Glycerine ( 1885 ) ; A. Watt, The Art of Soap- 

 making (1885; 4th ed. 1890); J. Cameron, Soap and 

 Candles (Churchill's 'Technological' series, 1888); and 

 C. F. Cross's ' Health Exhibition Lecture on Soap ' 

 (1884). 



Soapberry. The fruits of several species of 

 trees belonging to the genus Sapindus (natural 

 order Sapindaceoe) contain a pulp which is useful 

 as a substitute for soap in cleaning linen and other 



