62 ESSAY V. 



gum-arabic, hartshorn, jelly, undergoes no change. But on 

 mixing the manganese with some diluted vitriolic or pure 

 nitrous acid first, afterwards adding some of these substances 

 and exposing the whole to digestion, you perceive with 

 admiration how the black colour vanishes by degrees, and 

 the solution becomes as limpid as water. During this 

 phenomenon, a quantity of air-bubbles is discharged with a 

 violent effervescence ; they are found to be aerial acid. 

 Nay, manganese, in such a combination, shows such a strong 

 attraction for phlogiston, that metals, not even the noble 

 ones excepted, render it soluble in these acids in a limpid 

 form ; and what is still more remarkable, the volatile alkali, 

 as well as the above-mentioned vegetable and animal sub- 

 stances, is entirely destroyed. But of this I shall speak more 

 fully hereafter. At present I conclude from these experi- 

 ments, that the superficial particles of levigated manganese, 

 on touching an acid, acquire a great attraction for phlogiston ; 

 and if such an acid contains no phlogiston, nor the manganese 

 so much as is requisite for its entire solution (Sees. u. (a), 

 IV. (a)), those superficial particles attract as much of the 

 phlogiston as is required from the particles next adjacent to 

 them, which have not yet come in contact with the acid. 

 This is the reason why the external particles dissolve in 

 vitriolic or nitrous acid ; and the internal, or those lying 

 nearest under the external ones, having been deprived of 

 their phlogiston, remain undissolved; but these likewise dis- 

 solve as soon as the requisite phlogiston is communicated 

 to them from the above - mentioned substances, such as 

 sugar, etc. 



SECTION XVII, 



We now come to speak of the effects of concentrated 

 vitriolic acid on manganese (Sec. II, (c)). It is remarkable 



