THE TECHNOLOGIST. [Dec. 1, 1864. 



202 ON CHEMISTRY APPLIED TO THE ARTS. 



M. Pelouze proved some years ago that the rancidity of ordinary animal 

 as well as vegetable oils is due to a fermentation ; that is to say, that 

 under the influence of the azotised principle associated with all fats, the 

 fatty matters split into their respective fatty acids and glycerine, "which 

 in their turn undergo a further change resulting in the production of 

 volatile fatty acids, such, for example, in the case of butter, as butyric, 

 caproic, capric, and caprolic acids ; in the case of goat's milk, hirsic 

 acid ; of fish oil, phocenic acid. Further, M. Pelouze demonstrated, 

 that in the case of olive oil this change occurred a few hours after the 

 crushing of the fruit, the oil thereby coming in contact with the albu- 

 minous principles or ferment. 



I shall now have the pleasure of calling your attention to some of the 

 special applications wnich fatty matters receive. The first of these arises 

 out of the action of alkalies upon those substances, the result of which 

 is the conversion of an insoluble matter (oil) into a soluble one (soap). 

 I shall not enter into minute details of this well-known manufacture, 

 but content myself with touching upon some of the most recent improve- 

 ments. The usual mode of making soap is to add animal fats or vege- 

 tal ile oils to a weak lye, or caustic solution, carrying the mixture to the 

 boil by means of steam-pipes passing through the vessel above a false 

 bottom, and keeping the whole in constant agitation by means of 

 machinery. During this operation the oxide of sodium replaces in the 

 fatty matter the oxide of glyceryle, and when the lye is killed, that is 

 to say when all its alkali is removed by the oil, a fresh or stronger lye is 

 added, and these operations are repeated until the manufacturer considers 

 that the matter is nearly saponified, which is easily judged of in practice. 

 He then proceeds with a second series of operations, called salting, which 

 have for their object to separate the glycerine and impurities from the 

 soapy mass, and also to render the latter more firm and compact — in fact, 

 to contract it. This is effected by treating it with stronger lye mixed 

 with a certain quantity of common salt, and allowing it to stand for 

 a few hours, so that the mass of soap may separate from the fluid 

 containing glycerine and other impurities. When the second series of 

 operations are finished the clarifying or finishing process follows : this 

 requires the use of still stronger lye and salt, which not only completes 

 the saponification, but separates any remaining impurities ; the semifluid 

 mass of soap is then allowed to stand for twelve hours, when the soap 

 is either run or ladled into large wooden moulds, and allowed to remain 

 until quite cold. After standing for a day or so, the wooden frame is 

 removed from the solid mass of soap, when it is divided into bars by 

 means of a brass wire. The difference between white curd and mottled 

 soap is caused by the addition to the fluid mass of soap of about four 

 ounces of alum and green copperas to every 100 lbs. of soap, which gives 

 rise to an alumina and ferruginous soap, which on being diffused through 

 the mass by means of agitation, mottles or marbles the mass when cool. 

 When well prepared this is the most economical soap, as no large quan- 



