SEE

SER

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merely evolved, fince no change in the colour oflitmus is produced by the contadt of fat, or ofwater employed to lixiviate it. That the adtionof heat or fulphuric acid Ihould produce acetousacid from materials which abound in its con-ftituent parts, may readily be conceived, andthe hiitory of the pyroligneous, ladtic, andfome other acids {hews how readily the acetousacid undergoes particular modifications bywhich its proper characters are difguifed fo asnot eafily to be detected.

However, till the nature of the pungentvolatile acid of fat is fully cleared up, it maybe right to give fome of the general charactersof its faline combinations, 1 though we ihouldhefitate to give them the term of Sebats.

When the alkalies are faturated with thisacid, and the mixture is evaporated to drynefs,rediffolved and concentrated, cryftals are form-ed generally in plates and not deliquefcent.

• ^ Thefe are all decompofable by fulphuric acid,and give out vapours, ftrongly fmelling ofacetous acid, but with a peculiar pungency.A fimilar fait is formed with lime, but with■ magnefia and alumine no cryftals can beobtained.

This acid has no adtion on gold or filver, butdilfolves the oxyd of the latter metal. It actson mercury when repeatedly abftradted from it,but dilfolves the white carbonated oxyd witheafe in the cold. This fait evaporated to dry-nefs and heated, yields a mercurial fublimatein a very moderate temperature.

Copper dilfolves in this acid with eafe, andyields fmall deliquefcent cryftals. Iron givesan aftringent folution, and by evaporation leavesacicular cryftals, fcarcely deliquefcent. Lead,antimony, zinc, and tin, are diflolved withmore or lefs eafe.

With fome of the metallic folutions this acidproduces fenfible effects. Added to nitratedfilver, a reddifh grey precipitate falls down.With nitrated mercury a white precipitate isproduced, and even corrofive fublimate is madeturbid by this acid. With nitrat of lead, fmallacicular cryftals are depofited which are readilyfoluble in water, and this latter folution isdecompofea by fulphuric acid.

It is obvious that thefe properties do notbelong fingly either to the acetous or to themuriatic acid, fo that till we have further ex-periments, we muft for the prefent admitfomething peculiar in the pungent diftilled acidof fat.

SELENITE. See Gtfsum.

SEMI-METAL. A name given by the oldchemifts to the brittle unmalleable metals. SeeMetal •

SEMIOPAL. See Opal.

SENEGAL, Gum. See Mucilage.

SERPENTINE. Setpentin, Germ. Serpen-tine, Broch.

Of this mineral there are the two followingfubfpecies.

i. Sub/p. Common ferpentine.

Its colour is chiefly green of different {hades,from pale leek green to olive and blackilhgreen, it alfo occurs blood red, fcarlet red,light crimfon, and reddiflh brown, fometimes,though rarely, brownilh yellow. The coloursare arranged in dots, clouds, veins, and ftripes,and are very much intermixed. It occurs inmafs. It is internally dull, or faintly glimmer-ing when mixed with foreign particles. Itsfradture is fplintery pafling into fine graineduneven, alfo flat conchoidal. Its fragments areindeterminate, blunt-edged. It is ufually tranf-lucent on the edges ‘, it is foft, eafily frangible,and unctuous to the touch. Sp. gr. 2.57—2.7.

It is infufible before the blow-pipe withoutaddition. It appears to admit of confiderablevariety in its analyfis, as appears from its exa-mination by Kirwan and by Bayen.

Kirwan. Bayen.

Silex - - 45 — 41

Magnefia - 23 35

Alumine - 18 ■— xo

Iron - - 3 — 3

Water - - 12

98 89

A little oxyd of chrome is alfo faid to havebeen lately found in this mineral.

2. Sub/p. Noble ferpentine.

Its colour is deep leek green, pafling intogreenilh black. It occurs in mafs or diflemin-ated. It has a flight greafy or refinous luftre.Its fradture is conchoidal pafling into fplin-tery. It is tranflucent, foft, undtuous to thetouch.

Serpentine ranks among the primitive rocks jit very rarely contains beds of other minerals.It is not unfrequently penetrated by veins con-fining of calcareous fpar, granular limeftone,fteatite, talc, albeit, garnet, copper, and mag-netic iron.

There appear to be two diftindt formationsof this mineral; the molt ancient is in fmallerrock mafies than the other, and refts upon gra-