THE TECHNOLOGIST. [Dec. 1, 1864. 



204 ON CHEMISTRY APPLIED TO THE ARTS. 



alkali is continued and the temperature is raised to 140°, it is found 

 that instead of the fatty matters requiring a long time to sapunify 

 (as is usual even at a temperature of 212°) the saponification is most 

 rapid, because each globule of fatty matter offers an immense surface 

 to the action of the alkali, and it is found that in two or three 

 hours the whole of the fatty matters are converted into soap. In 

 fact, saponification is so perfect that the mass of soap dissolves com- 

 pletely in water ; and if the purpose is to liberate the fatty acids, 

 this can be done at once by the addition of a little vitriol. The 

 fatty acids produced by this comparatively cold saponification are 

 so pure that when subjected to pressure the solid fatty acids have 

 not the slightest odour, and fuse at the point of 138 deg. As to the 

 oleic acid prepared by this process, instead of being brown (as is usual 

 with the commercial acid) it is colourless, and can be employed in 

 manufacturing soap of good quality. When M. Mouries desires to make 

 soup with the entire fatty matter, he acts at once upon the globular 

 fatty mass, by adding salt, which separates the soap from the aqueous 

 fluid ; it is then melted and run into moulds. Whilst speaking of the 

 mode in which alkalies can be made to act upon fatty matters, I ought to 

 state that M. Pelouze observed the curious fact that large quantities of 

 fatty matters could be split into their respective elements — viz., fatty 

 acids and glycerine — by heating them for some hours with a small quan- 

 tity of soap. This discovery of his, as we shall presently see, has been 

 taken advantage of in the manufacture of stearic candles. 



Permit me to state that soft soaps differ from hard soaps mainly in the 

 substitution of potash for soda, and in the omission of the salting and 

 clarifying processes, so that the soapy mass is not separated from the 

 excess of water, and therefore after the fatty matter has been saponified 

 by the alkali, the whole is evaporated to the required consistency. I 

 cannot conclude better this hasty aud imperfect sketch of the soap 

 manufacture than by the following table of compositions, showing the 

 percentages of the various elements in the following soaps : — 



Names of 



Soaps. Fatty acids. Alkali. Water. 



Curd 62 60 320 



Marseilles 60 60 34-0 



White 60 64 336 



White cocoa 22 4-5 73-5 



Yellow rosin 70 65 23.5 



Calico printers' ... 60 5-2 348 



Silk boiling 57 70 30-0 



Wool scouring 55 90 36-0 



Soft 43 100 470 



Theoretical 63 6'4 306 



As it is easy to introduce into soaps a much larger quantity of water 



