94 Chemical Inquiries info the Kalure of several 



:he affinity of the oil itself for" the alkalis ; so that soaps must 

 be considered as compounds in which salifiable bases were neu- 

 tralized by fat ■substances, the action of v.iuch v\'as analogous to 

 that of the acids : it wa-^ in this respect that he ccmipaied the ■ 

 oils to- the latter substances, and we shall presently see how far 

 this comparison was just. This way of thinking was adopted : 

 but afterwards they went further, and pretended that the oil was 

 not sajjonified but bv absorbing oxygen : thpy did not found 

 their opinion upon any positive fact, the slightest indications 

 appearing sufficient. 



2. In the present' state of chemistry, however, we must not 

 content ourselves with bare assertions,: to establish a theory, 

 we must be acquainted with the bodies which are in contact, 

 analyse the compounds which they have formed, and see if the 

 principles s'cparated from it are the same with those which have 

 been put in reaction. In commencing the account of my ex- 

 periments on this substance, I find the double advantage of 

 fixing the attention ujjon one of the most common products of 

 the saponification of animal fat, and at the same time facili- 

 tating the study of fatty substances, by making known a species 

 which possesses their generic properties in the highest possible 

 degree. 



8. When we immerse soap made of pork grease and potash 

 in a large quantity of water, one part is dissolved, while another 

 is precipitated in the form of several brilliant pellets, which I shall 

 call mother of pearl substance. 



Of the Pipijicafion of the, JM of. her of Pearl Sulslniiee, and of 

 its Decomposition hy the Muriatic Acid. 



4. Eighty grammes (3^ oz. or 1551 grains English) dried in 

 the air.were diluted in 12 litres (3 gallons l-^^-^g P'"ts English) 

 of water, and exposed to a temperature ranging from 50" to 60": 

 thev absorbed this liquid, and increased greatly in size. At the 

 end' of ten days, the matter was j)Ut upon a filter j when it was 

 drained, twenty litres of cold water was thrown over it, to de- 

 prive it of any soluble soap which it might retain. When thus 

 washed it was dried, t'len treated thrice successively with two 

 litres of boilir-g alcohol of the gravity of 0- 820 divided into three 

 equal portions : the first congealed almost wholly upoii cooling; 

 the second was slightly disturbed, and the third alniost not at all. 

 The residue insoluble i n alcohol weighed rather nrore than two gram- 

 mes (about 38| grain.) ; it resembled the mother of pearl sub- 

 stance : it was different, however, from the part which was dis- 

 olved. The experiment taught me that the mother of pearl 

 ,ubstance was formed of a fatty substance, absolutely new, com- 

 bined with potash, lime, and oxide of iron ; and that when we 



treated 



