SOAP 847 



weak lye or water. As soon as combination has taken place, a quantity of very 

 strong lye is added, until an incipient separation begins to show itself. The heat is 

 now increased, and the boiling continued for a considerable time, the mass being 

 prevented from boiling over the vessel by workmen armed with shovels, who dash 

 the soap to and fro, so as to break the froth upon the surface and favour evaporation. 

 At first the soap is divided into an innumerable number of small globules, each 

 separate and distinct from its fellow; but as the boiling goes on, those gradually run 

 together into larger and larger globules, till at last the soap is seen to assume a pasty 

 consistency, and to unite in one uniform mass, through which the steam from below 

 slowly forces its way in a series of bursts of little explosions. The process is now 

 finished, and all that remains to be done is to shut down the lid of the copper, having 

 previously extinguished the fire. In from one to two or three days, according to the 

 nature and quantity of the soap in question, the lid is again raised, and the semifluid 

 soap ladled from the precipitated lye by means of ladles ; the product being thrown 

 into a wooden or iron frame of specific dimensions, where its weight is estimated by 

 measurement. In making common yellow or resin soap, the resin is usually added 

 after the saponification of the tallow, in the proportion of one-third or one-fourth of the 

 tallow employed. The subsequent operations are much about the same as those above 

 described ; but in addition, just before closing the lid of the copper a quantity of water 

 or weak lye is sprinkled over the melted soap, which carries down with it the mecha- 

 nical impurities of the resin ; and these constitute a dark layer of soap resting upon 

 the lye, which is not poured into the frame with the rest, but is placed apart under 

 the name of ' niger' and brings a less price. Good curd or white soap should contain 

 of grease, 61 - parts ; soda, 6'2 ; water, 32'8 ; total 100 ; or consist of grease-acid, 

 1 atom = 315; soda, 1 atom = 32; water, 17 atoms = 153. Resin soap has a 

 more variable composition, but when not adulterated with water should contain about 

 as follows : grease and resin, 60 ; soda, 6 ; water 34 ; total 100. 



Manufacture of mottled soap. Soda which contains sulphides is preferred for 

 making the mottled or marbled soap, whereas the desulphuretted soda makes the best 

 white curd soap. Mottling is usually given in the London soap-works, by introducing 

 into the nearly-finished soap in the pan a certain quantity of the strong lye of crude 

 soda, through the rose spout of a watering-can. The dense sulphuretted liquor, in 

 descending through the pasty mass, causes the marbled appearance. In France a 

 small quantity of solution of sulphate of iron is added during the boiling of the soap, 

 or rather with the first service of the lyes. The alkali seizes the acid of the sulphate, 

 and sets the protoxide of iron free to mingle with the paste, to absorb more or less 

 oxygen, and to produce thereby a variety of tints. A portion of oxide combines also 

 with the stearine to form a metallic soap. When the oxide passes into the red state, it 

 gives the tint called manteau Isdbelle. As soon as the -mottler has broken the paste, 

 and made it pervious in all directions, he ceases to push his rake, from right to left, 

 but only plunges it perpendicularly till he reaches the lye ; then he raises it suddenly 

 in a vertical line making it act like the stroke of a piston in a pump, whereby he lifts 

 some of the lye, and spreads it over the surface of the paste. In its subsequent descent 

 through the numerous fissures and channels on its way to the bottom of the pan, the 

 coloured lye impregnates the soapy particles in various forms and degrees, whence a 

 varied marbling results. 



The best and most esteemed soap on the Continent is that known under the name 

 of Marseilles soap, and it differs from the English mottled soap by a different disposi- 

 tion of the mottling, which in that soap is granitic instead of being streaky. It has 

 also an agreeable odour, somewhat resembling that of the violet, whereas the English 

 mottled soap, generally made of coarse kitchen and bone-fat, has an odour which 

 reminds one of the fat employed. The best English mottled soap in which tallow is 

 employed has no unpleasant smell, and if bleached palm oil has been used it acquires 

 an agreeable odour, analogous to that of the Marseilles soap, which is made of olive 

 oil alone, or mixed with rape or other grain or seed oil, which, however, seldom ex- 

 ceeds 10 per cent., for otherwise it would not have the due proportion of blue to the 

 white which is characteristic of soap made of genuine olive oil, the mottling becoming 

 more closely granular when an undue proportion of grain has been used, a sign of 

 depreciation which the dealers are perfectly well acquainted with, and of which they 

 at once avail themselves, to compel the maker to reduce his price. 



Pelouze and Fremy, in their Traite de Chimie gentrale, give the following reliable 

 observations : 



'The best olive oil for the use of the soap-maker is Provence oil; that of Aix 

 comes next ; it is cheaper, but the same weight of it yields less soap than the other, and 

 the latter has then a slight lemon-yellow tinge. The oil from Calabre contains less 

 margarine, and yields a softer soap. 



