1818.] their Combinations with Alkalies. 191 



the principal operation of this substance is to yield to the fatty- 

 matters a portion of its alkali, so as to form them into a super- 

 soap, while it is itself reduced to the same state. 



M. ChevreaVs Third Memoir* 



The object of this memoir is to ascertain whether the bodies 

 which are found after the process of saponification are the essen- 

 tial products of that process, or if they previously existed in the 

 fat, and in this way to become acquainted with the theory of 

 saponification and with the composition of fat. M. Chevreul 

 first inquires whether the acetic and carbonic acids, which are 

 found in certain stages of the operation, are essential to it ; and 

 the result of his inquiry is, that they are not so, but that they 

 depend upon some impurity in the substances employed. He 

 next inquires whether oxygen gas be necessary to saponification ; 

 and by forming a portion of soap in a situation where it was 

 deprived of all contact with the air, he found that it was not 

 necessary for the union of the fat and the potash, nor for the 

 separation of the pearly matter, provided the soap be diffused 

 through a sufficient quantity of water. 



The next topic is respecting the change which the fat expe- 

 riences during saponification ; and in order to ascertain this 

 point, M. Chevreul enters into a detailed examination of the 

 nature and properties of fat before and after it has undergone 

 this process. The differences were found to be considerable : 

 besides a change in colour and consistence, the melting point is 

 different, being 78*5° for the fat in its natural state, and 103° 

 after saponification ; in the former state it is nearly insoluble in 

 alcohol, and does not redden litmus, while in the latter state it is 

 extremely soluble in alcohol, and powerfully affects the colour of 

 litmus. We must, therefore, conclude, either that the fat has 

 experienced a considerable alteration by the action of the potash, 

 or that it originally consists of margarine, fluid fat, together with 

 a colouring, an odoriferous, and a sweet principle ; and that 

 these bodies have so strong an affinity for each other as to 

 conceal their specific properties ; it is, however, very difficult to 

 conceive how this could be the case, when we consider the 

 nature of the difference which there is between the two bodies. 

 In order to throw further light upon this point, M. Chevreul 

 proceeds to investigate whether fat ought to be considered as a 

 simple proximate principle. By dissolving the fat in a large 

 quantity of alcohol, and observing the manner in which its 

 different portions were acted upon by this substance, and again 

 separated from it, it is concluded that fat is composed of an oily 

 substance, which remains fluid at the ordinary temperature of the 

 atmosphere ; and of another fatty substance which is much less 

 fusible. Hence it follows that fat is not to be regarded as a 



* Abstracted from Ann. dc Chim. xciv. 113. 



