204 Chemical Inquiries into the Nature of several 



sisted \ipon ; but this character does not differ essentially from 

 the foregoing ; for, the turnsole being a combination of red co- 

 louring matter and potash, it happens that it is reddened by all 

 the bodies whose affinity for alkali is superior to that of the co- 

 louring matter. Consequently this reagent announces that the 

 body which reddens it is susceptible of being united to potash 

 with a greater force than its colouring mattei- ; it does not there- 

 fore indicate acidity by itself, it simply establishes a relation of 

 attraction between bodies wliich have affinity for the alkalis. 

 The case is not the same with the indications by the violet co- 

 lour of the hemotine : those reagents announce the acidity by a 

 change of colour resulting from the combination of the acid with 

 the colouring principle itself. 



5. Hitherto, the acids only have been supposed to redden the 

 colour of violets, but tliere are some which act differently: thus 

 tlie borie acid and i)riissic acids do not redden it. In all proba- 

 bility, it is the same with sulphuretted hydrogen. 



6. The action of the acids on hematine is much more genera! 

 than that which they exercise on the colour of violets : thus all 

 of them make it pass to the yellow or the red, and there is 

 scarcely one but sulphuretted hydrogen, which seems to make 

 an exception ; it forms with it a conil)ination of a yellow so 

 slight that it seems to be colourless when it is in a thin layer ; 

 and it ought to be added, that almost all the oxides which neu- 

 tralize the acids act with it like the alkalis, with the exception, 

 however, of the oxide of tin at the maximum, which acts in the 

 manner of an acid. 



oS. If v,-e now compare the whole of these characters, we find: 



1. That the sotn- taste does not belong to all tlie acids : con- 

 sequently it. has not been regarded as being essential to those 

 bodies. 



2. That the property of being attracted by surfaces positively 

 electrified is too gcner;il to characterize acidity. 



3. That the case is the same with the neutralization of the 

 alkalinity ; for those chemists who have been uiost forcibly 

 struck with this character have never formally said that it is 

 sufficient for a'-sigiiing acidity to a body which ])ossesses it. If 

 some of those chemists have regarded sulphur as an acid, no 

 jierson has ever as--crted that the oxides of lead and of zinc were 

 in the same predicament : nevertheless, in ranking sulphur 

 among the acids, thcie was no reason for separating from it the 

 latter, which belong very evidently to the class of salifiable bases, 

 since they form solts with the acids, and they react on hematine 

 in the manner of potashj barytes, &;c.: hence it follows that 

 the faculty of neutralizing an alkali d6es not convey the idea 

 of aciditv. 



A. That 



