Part 3

Laſtly, it muſt be remarked, that the ſolid ingredient determines the genus although the menſtruum be greater in quantity. Thus in magneſia vitriolata (Epſom ſalt) the earth gives the Generic name, although the vitriolic acid be the more ponderous. The same holds good in gypſum, allum, &c.

CLASSES OF FOSSILS.

§ 19.

Fossils are of four kinds, viz. ſaline, earthy, inflammable, and metallic; hence ariſe four claſſes.

§ 20.

Salts, or ſaline ſubſtances are more or leſs ſapid, and when finely powdered diſſolve in at leaſt 1000 times their weight of boiling water. They melt in the fire, which for the moſt part changes or deſtroys them.

§ 21.

Earths are inſipid, not ſoluble in water in the degree mentioned above (§ 20) though perhaps water in Papin’s digeſtor will diſſolve ſome if not all of them, eſpecially if their ſurface be greatly increaſed by a previous ſolution in and precipitation from ſome other menſtruum. In the chain of nature they are by inſenſible gradation joined to the ſalts, ſo as not to be diſtinguiſhed without artificial limits. Their form is not changed by a moderate heat, nor are they diſſipated by a violent one. Their ſpecific gravity is to water, leſs than 5 to 1.

§ 22.

Inflammable foſſils abound with phlogiſton, do not unite with water, but when pure diſſolve in oils; expoſed to the fire, they ſmoke, generally inflame, are for the moſt part conſumed, and ſometimes totally vaniſh.

§ 23.

Metals when perfect do not diſſolve at all in water; only a few of them in oils, and then only when in part deprived of their phlogiſton. They are the heavieſt of all known ſubſtances, the lighteſt of them weighing more than ſix times its bulk of water.

They melt in the fire with a ſhining ſurface, and in clay veſſels the ſurface is convex.

CLASS I. SALTS.

§ 24.

We begin with the nature and properties of ſaline bodies, for unacquainted with theſe our knowledge of other bodies muſt be exceedingly imperfect. Native ſalts are either acid, alkaline, neutral, earthy or metallic.

§ 25.

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.

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.

§ 26.

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.

§ 27.

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 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.

§ 28.

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.

In the moſt concentrated ſtate that art can procure it, its ſpecific gravity is 1, 580. Colourleſs when pure; but its ſtrong attraction to phlogiſton renders particular management neceſſary to procure it ſo. With different proportions of phlogiſton it forms phlogiſticated acid and nitrous air.