1 94 ^^^- Dclaval on the Caiife cfthe 



colours, eRentially depend on the knowledge of 

 this fuhjefl:. 



Solutions effeded by means of phlogifton, fre- 

 quently are wrongly attributed to the operation 

 of fuppofed acid menllrua : as feveral kinds of 

 fubflances are capable of being diflfolved indifcri- 

 minately, either by acids, or phlogifton. 



For the purpofe of diftinguilking, in any in- 

 flance, between the ad ion of the acid fol vents, 

 and that of the inflammable menftrua, it is proper 

 to examine the nature of tlie matter, by which 

 either of thofe principles is furniflied. 



Fixed air is generally fuppofed to poflTefs an 

 acid quality, and feveral of its properties are 

 afcribed to its acidity. 



The change of colour, produced in vegetable 

 juices by the eledtric fpark, is adduced as a proof 

 of the acidity of fixed air. But it has been already 

 fiiewn that this effed: does not arife from acid, 

 but from phlogiftic, matter. 



The acid quality of fixed air is alfo generally 

 inferx'ed, from its power of difiTolving iron. Bur, 

 phlogifton alfo is a folvent of iron. Thus, a con- 

 fiderable portion of that metal is always diflblved 

 -and held in folution, by the phlognlicated alcaline 

 •lijiivium, which confifts of inflammable matter 

 'Calcined with fixed alcali. M. Margraf has Ihewh 

 that feveral other metals are foluble in this lixi- 

 vium. Hence it is evident that the folubility of 

 " iron does n6t prove the acidity of the folK'cnt, but 

 may arife from the phlogifton contained in it. 



Fixed 



