fatty Substances, and on their Comlinations ivilh theJlkaHs.2QQ 



4. Tliat although the indication of turnsole has not been ap- 

 preciated at its true value, it is nevertheless this character which 

 has been most generally employed, and that which chemists 

 seem unanimously to have adopted by tacit consent ; for none 

 of the bodies reputed to be acid are deprived of it; and this cha- 

 racter, which differs from the foregoing only in so far as it values 

 the strength at a given point, has been sufficient to place several 

 bodies among the acids, and to exclude others from the latter, 

 because they did not possess it as at first supposed. I know 

 but two objections which can be made to this. The first is, that 

 there may exist bodies wliich do not redden turnsole on account 

 of their cohesion, and which may nevertheless approach closely 

 to the acids : the second is, that if we have demonstrated that 

 the property of neutralizing the alkalinity does not belong solely 

 to the acids, we may suppose one of those bodies which, not 

 having any other property of acidity, will redden turnsole, be- 

 cause it will attract its alkali more strongly than it does the co- 

 louring principle. 



5. That the property of reddening the tincture of violets is 

 not sufficiently common to entitle us to draw any conclusion 

 relative to tlie bodies which do not possess it. 



6. That although the indication of the hcmatine is much 

 more general than the foregoing, it is nevertheless difficult to 

 admit it exclusively, because there are acids almost insoluble, 

 whose affinity for it is so weak that it is diflicult to approach its 

 action. 



39. To resume our conclusions: We see in the first place, that 

 turnsole appears to !je adopted by all chemists to detect acidity. 

 That if we do not pay some attention to the objections alluded to 

 above as to its value, and if we persist in following the principle.'- 

 which have hitherto been taken as guides in the classification of 

 the acids, we shall'be compelled to rank margarine among the 

 latter ; since it reddens turnsole, takes up potash from the car- 

 bonic acid, and since its combinations with this base have the 

 greatest analogy with the salts. If it be objected that its com- 

 position removes it too far from the series of the acids, we may 

 cite a single example, that of sulphuretted hydrogen, which evi- 

 dently possesses the characters of acidity, as M. Bertbollet has 

 proved. All the chemists, in regarding this body as an acid, 

 have, I beliuve, established that in tlie chemical system the 

 analogy of properties has been consulted in prefeience to that 

 of composition. Secondly, that if we refiise to rank margarine 

 among the acids, we are led to these conclusions: 1. That the 

 taste and action of the colouring princijjlos which undergo 

 changes of colour by their inmiediatc combination with tlie 



