Acids may be diſtinguiſhed by their proper taſte; they efferveſce with mild alkalies; and change the blue juices of vegetables and tincture of heliotropium to a red colour[[6]].
We are acquainted with many ſpecies of acids, but they are hardly ever found pure in the bowels of the earth, nor can we expect to find them ſo when we conſider how ſoon ſuch powerful menſtrua muſt meet with ſubſtances to ſaturate them. Their great abundance and their properties ſhew their various and indiſpenſible uſes in the œconomy of nature.
As mineralogy treats of thoſe bodies which are found under the ſurface of the earth, and as acids in an uncombined ſtate are not found there, it would ſeem proper to exclude them; but the ſame reaſon would likewiſe exclude the primitive earths, ſome of which have never yet been found pure. Therefore in a ſyſtem formed upon the component parts of bodies, a ſhort deſcription of the principal of theſe is not to be diſpenſed with, although they hardly ever preſent themſelves in a ſeparate ſtate.
Vitriolic ACID. When moſt concentrated by artificial means its ſpecific gravity is 2, 125. When pure, has neither colour nor ſmell. Cold ſometimes though very rarely concretes it into a ſolid form; it may be coagulated by nitrous air. This as well as the other acids is beſt known from the compounds it forms with other ſubſtances.
Mr. Vandelli[[7]] ſays that it is ſometimes mixed with the ſtreams from the hills in the neighbourhood of Sienna and Viterbo, raiſed no doubt by ſubterranean fires; but in general it is united to alkalies (§§ 44, 47, 50,) to earths (§§ 58, 59, 63, 67,) to metals (§§ 69, 70, 72, 73,) or to phlogiſton (§§ 134, 136.)
Phlogiſticated vitriolic ACID (volatile vitriolic acid) is frequently thrown out by the craters of volcanoes; its ſmell ſuffocating and penetrating. The union to phlogiſton and the matter of heat gives it an aerial form, but does not prevent its union with water.
Nitrous ACID is by ſome excluded from the foſſil kingdom, becauſe they ſuppoſe it to be produced from the putrefaction of organic bodies. But theſe bodies when deprived of life are again received amongſt the foſſils, from whence their more fixed parts were originally derived.