. 206 Chemical Inquiries into the Nature of fatty Substances. 



acids, arc the only characters admissible for ascertaining acidity : 

 that, in this case, we shall be forced to exclude one or other of 

 these characters, since the oxide of tin at the maximum, with^ 

 out having an acid taste, acts on the hematine in the manner of 

 an acid. Finally, that by determining for the colouring princi- 

 ples, we shall be reduced to the employment of hematine only, 

 since the tinctvne of violets has an action too limited. 2. That 

 the indication of turnsole being absolutely insignificant, we must 

 submit to a new examination all the bodies which have been 

 ranked among the acids, from the sole consideration that tliey 

 were combined with the bases with sufficient force to redden 

 turnsole, that it is not doubtful that several of these bodies will 

 be separated from them. 3. That margarine ought to be 

 ranked among the fatty substances, without having any regard 



■ to its properties. 



40. After having appreciated the indication of each of the 

 characters of acidity in particular; after having demonstrated 

 that some were too general, while others were too limited; I 

 have detailed the consequences to which we are led, according 

 as we admit such or such of those characters. 1 have not de- 

 cided, because I have regarded my individual opinion as of little 

 importance. Whatever may be the case, however, it is \etf re- 

 markable to see a fatty substance in which hydrogen and car- 

 bon prevail, possessing in as marked a degree as certain acids, 

 one of the most characteristic properties of the latter. But let it 

 not be supposed that margarine alone is in this predicament : 



* I have already met with several analogous substances, which I 

 shall describe in future papers : and the observation of Messrs. 

 Bouillon Lagrange andVogcl, that the resins redden turnsole, 

 proves that it exists completely formed in vegetables. These 

 facts, therefore, permit me to think that we shall be able to 

 make a group of fatty substances, the affinities of which for the 

 alkaline bases will be analogous to those of the oxygenated acids, 

 and whose combinations will present species of saline compounds 

 to which we may give the generic name of soaps, which several 

 of them have so long gone under. This analogy of properties 

 which we observe between oxygenated and inflammable bodies 

 is well adapted for supporting a principle which had already 

 guided me in my experiments on astringent substances ; namely, 

 that an analogy of properties is not always a consetjuence of 

 an analogy of composition. 



XXXIII. On 



