SOAP 851 



consists, by the writer's experiments, of fat, 52 ; soda, 6 ; water, 42 = 100. Nine-tenth? 

 of the fat, at least, is tallow. 



With respect to the mamifacture of sulphated soap, the process is as follows : 



To every ton of soap made in the usual way and ready to bo cleansed and crys- 

 tallised, add sulphate of soda (Glauber's salt) in the proportion of about 1 cwt. or more, 

 according to the quality of the goods employed. Tho Glauber's salt should first be 

 dissolved by turning steam into it, or in a steam-pan, in its own water of crystal- 

 lisation ; it is then added to the finished soap, and the whole must be crutched until 

 the mass has become so stiff that it cannot be crutched any longer. In the evidence 

 before the Privy Council, in the month of July 1855, this process was found by their 

 Lordships of such public value that the patent right was extended for three years. 



This process, however, has been superseded by another which Dr. Normandy 

 patented in the month of August 1855. In effect it had been found that whereas 

 sulphate of soda is more soluble in lukewarm than in either cold or boiling water, the 

 temperature of the weather in summer time interfered with or altogether prevented 

 the formation of the crystals, and that as tho crystals of this salt contain ten equi- 

 valents of water, the maker of sulphated soap was put to the trouble and expense of 

 the carriage of this, to him useless, water of crystallisation. 



Soft Soap. The manufacture of soft soap differs greatly from that of hard soap ; as, 

 in this case, nothing is separated from the mixture in the boiler ; and the alkali 

 employed is potash, and not soda. The mode of obtaining a caustic lye of potash is 

 exactly the same as with soda, except that the weak lyes are used in place of water 

 for a subsequent operation, and not pumped up into the boiler. The materials 

 employed as fats are mixtures of the vegetable and animal oils, as rape, and the fish 

 oil called ' Southern.' For the best kinds of soft soap, a little tallow is added to 

 these, which produces a peculiar kind of mottling or crystallisation in the soap, that 

 confers additional value upon it. These oils or fats are merely boiled with the strong 

 caustic potash-lye, until thorough combination has taken place, and BO much of the 

 water of tho lye is evaporated that, when a portion of the soap is poured upon a cold 

 slab and allowed to rest for a few minutes, it assumes the consistency of soft butter. 

 As soon as this happens, the whole is run out into little casks, where it cools ; it is 

 thus sent into the market. Of course no atomic arrangement can bo traced in so 

 variable a compound; and hence its analysis presents no point of interest. The 

 employment of soft soap is daily becoming more and more limited. 



The principal difference between soaps with base of soda, and soaps with base 

 of potash, depends upon their mode of combination with water. The former absorb 

 a large quantity of it, and become solid ; they are chemical hydrates. The others 

 experience a much feebler cohesive attraction ; but they retain much more water in a 

 state of mere mixture. 



Three parts of fat afford, in general, fully five parts of soda-soap, well dried in the 

 open air ; but three parts of fat or oil will afford from six to seven parts of potash- 

 soap of moderate consistency. This feebler cohesive force renders it apt to deliquesce, 

 especially if there be a small excess of the alkali. It is therefore impossible to 

 separate it from the lyes ; and the washing or relargage, practised on the hard-soap 

 process is inadmissible in the soft. Perhaps, however, this concentration or abstrac- 

 tion of water might be effected by using dense lyes of muriate of potash. Those of 

 chloride or sulphide of sodium change the potash into a soda-soap, by double decompo- 

 sition. From its superior solubility, more alkaline reaction, and lower price, 

 potash-soap is preferred for many purposes, and especially for scouring woollen yarns 

 and stuffs. 



Soft soaps are usually made in this country with whale, seal, olive, and linseed oils, 

 and a certain quantity of tallow ; on the Continent, with the oils of hempseed, sesame, 

 rapeseed, linseed, poppy-seed, and colza ; or with mixtures of several of these oils. 

 When tallow is added, as in Great Britain, the object is to produce white and some- 

 what solid grains of stearic soap in the transparent mass, called jigging, because the 

 soap then resembles the granular texture of the fig. 



The potash-lyes should be made perfectly caustic, and of at least two different 

 strengths ; tho weakest being of sp. gr. 1'05 ; and the strongest, 1'20, or even 1-25. 

 Being made from the potashes of commerce, which contain seldom more than 60 per 

 cent., and often less, of real alkali, the lyes correspond in specific gravity to double 

 their alkaline strength ; that is to say, a solution of pure potash of tho same density 

 would be fully twice as strong. Tho following is the process followed by respectable 

 manufacturers of soft soap (savon vert, being naturally or artificially green) upon the 

 Continent. 



A portion of tho oil being poured into the pan, and heated to nearly the boiling point 

 of water, a certain quantity of the weaker lye is introduced ; the fire being kept up 

 so as to bring tho mixture to a boiling state. Then some more oil and lye are added 



3i2 



