SOAP MAKING. 229 



place for twenty-four hours ; at the end of this time, if the opera- 

 tion is successful, you will have a block of moderately solid soap, 

 sufficiently well made to be capable of use for scouring purposes, 

 but probably not of desirable quality for application to the skin ; 

 for, when dealing with small quantities, it is almost impossible to 

 make the double decomposition complete, so that the mass ulti- 

 mately obtained is liable to contain a considerable proportion of 

 unaltered fat and a corresponding amount of unneutralised caustic 

 soda, which excoriates the skin frightfully. Addition of cocoanut 

 oil to the grease treated promotes the soap making action or 

 saponification, and furnishes a better product. When working 

 in this way, the glycerine formed together with the true soap 

 during saponification remains mixed up with the soap in the result- 

 ing mass ; but in manufacturing processes on the large scale, the 

 glycerine is usually separated from the soap, and the latter purified 

 by various devices ; in the case of soft soaps (potash soaps), 

 however, the glycerine is not separated. 



Expt. 276. Soap made by the Boiling Process. Most of the 

 soap used for ordinary household purposes is prepared by a some- 

 what different process, which may be thus imitated on the small 

 scale. Dissolve solid caustic soda in about twenty times its weight 

 of water, and heat the liquor to boiling ; then add the fatty matter 

 to be converted into soap (tallow, dripping, olive oil, or a mixture 

 of such substances) to the extent of five or six times the weight 

 of the solid caustic soda used, and keep the whole gently boiling 

 in a capacious saucepan or other vessel for some hours, taking care 

 that the mixture does not froth over ; at the end of this time the 

 process of saponification will be nearly complete, when the soap 

 may be made to separate from the watery liquor by throwing in a 

 handful or two of common salt and allowing to stand till cold 

 (compare Expt. 65). A cake of crude soap will then be found to 

 have separated as a soft solid mass at the top, whilst the brine 

 will contain the glycerine dissolved therein ; so that the boiling 

 process differs from the one described in the last experiment 

 (called for the sake of contrast the " cold process," being carried out 

 at a temperature below that of boiling water) in that glycerine is 

 separated from the soap in the one case and retained intermixed 

 therewith in the other. 



The crude soap thus obtained by the boiling process in practical 

 manufacture on the large scale is separated from the brine 

 before it completely cools and solidifies, and is put through various 

 purifying and finishing operations, after which it is ladled out or 

 pumped into moulds (holding 10 cwt. and upwards), in which it 

 solidifies to large blocks, which are subsequently cut up into bars. 



