Chap. 4.] Vegetable Acids. 39 



nitrous acid. The acid of apples, by the continu- 

 ance of the operation, becomes converted into acid 

 of fugar, or acid of forrel, which are the fame thing. 

 The fame procefs further continued, affords vine- 

 gar. Hence it fhould feem that according to the 

 greater progrefs of the operation of combuftion, or 

 the combination of vital air with the bafis, the 

 acids of tartar, of apples or unripe fruit, of forrel 

 or fugar, of vinegar, and laftly of charcoal, are pro- 

 duced. In this order of proceeding, the/ acids be- 

 come more and more perfect, and lefs eafily de- 

 compofable; and it probably proceeds from this 

 caufe, that the reverfe of thefe procefles could never 

 be completely accomplifhed. 



Profeffor Murray, of Gottingen, has affured us, that 

 he has obtained acid of fugar by repeated diftilla- 

 tions and congelation, without ufmg nitrous acid. 

 Abbe Fontana obtained an acid perfectly like that 

 of fugar from all the gums and relins. Mr. Watt 

 of Birmingham, when making fome experiments 

 relative to ink, obferved a number of particles 

 floating in the fluid, which had the fhape of cryftals 

 of the faccharine acid, and upon examihatiqn were 

 found to be really fuch ; and, conducting the procefs 

 in the ufual way with the nitrous acid, he found that 

 aftringent vegetable matters contain the acid of fugar 

 in greater abundance than that fublhnce from which 

 it derives its. name. 



. Thefe faline matters are called eflential falts of ve- 

 getables. There are fome others which are alfo called 

 eflential falts, but are not peculiar- to vegetables. 

 Such as the fixed vegetable alkali, which may be 

 extracted by incineration from plants in general, and 

 the fixed foffil alkali, which is only extracted from 

 D 4 marine 



