FIU

FLU

C 105 )

rated in contact with tin filings, it remains un-changed, and very brilliant white acid crystalsof fluated suboxyd of tin are formed.

Metallic copper is not attacked by fluoricacid, even with only twice its weight of water,but the oxyd of copper easily dissolves, and smallblue acid crystals are produced.

Fluoric acid easily dissolves the oxyd of sil-ver, and the salt has a very strong metallictaste, is highly soluble in water and deliques-cent. It is not volatile by heat, but fuses likeluna cornea, losing thereby its excess of acid,but remains soluble. It cannot be crystallized.It stains the skin black. The fixed alkalies andearths decompose it, but net ammonia. Metal-lic silver is not acted on by this acid, but it isreadily dissolved by heating fluated peroxydof mercury with silver. Fluat of potash doesnot precipitate nitrat of silver.

Lead is only acted on by fluoric acid whenoxydated. Fluat of lead is readily formed byfluat of potash and acetite of lead. It precipi-tates in white flocculi, which become brilliantlaminae after washing. It is insoluble in water,but readily dissolves in nitric, muriatic, orfluoric acids. It melts at a low red heat, andturns yellow, losing part of its acid.

Metallic mercury resists fluoric acid, but thered oxyd dissolves in it when moderately dilutedand boiled in a platina vessel. This salt is insmall yellow lamellar crystals, but it forms withdifficulty, and requires a great quantity of theacid. These crystals totally exhale whenstrongly heated. They are acid, but, whenwashed with water, a part of the salt dissolvesalong with most of the excess of acid, and theremaining salt becomes of a deep orange orred. In this separation by water into a solubleacid salt, and an insoluble neutral salt, the fluatof mercury agrees with most of the other highlyoxydated mercurial salts.

The authors of this interesting memoir thenproceed to describe other properties of thefluoric acid, and in particular a very singularcompound of this with the boracic acid whichthey have discovered, and to which they givethe name of Flaoboracic add. But before weproceed with this part of the subject, we shallnotice a valuable paper on many of the proper-ties and compounds of fluoric acid by Mr. J.Davy, whose experiments appear to have beenmade nearly at the same time with those of theFrench chemists above described, though notpublished so soon. b

Pure fluoric acid, as Mr. J. Davy observes,

has never yet been obtained in a gasseous state,and only two substances have hitherto beenknown to have the power of uniting with it intoa permanently elastic gas, namely, silex and bo-racic acid. The former substance makes thewell known compound first discovered byScheele , and to which the term Si/icafcdFluoric Gas is properly applied. It is difficult,as already mentioned, to avoid obtaining this gasin treating fluor spar with sulphuric acid, unlessa very pure fluor be chosen and metallic vesselsused. It is conveniently prepared by addingpounded glass to the spar and acid, and by thismeans the glass retort may be saved for a futureoperation. This gas is perfectly saturated withsilex, for it may be long kept under glass vesselswithout taking off their polish. A hundredcubic inches of this gas at a medium pressure andtemperature, weigh J 10.78 grains, or about threetimes as much as common air, of which 100cubic inches in similar circumstances weigh36.4.5 grains.

To analyze silicated fluoric gas, Mr. J. Davycaused 40 cubic inches of it to be absorbed byliquid ammonia, and obtained from it 27.2grains of pure silex, after full edulcoration andignition. Supposing the remaining weight ofthe 40 cubic inches to be fluoric acid, (andtherefore the whole of the silex to have beenseparated by the ammonia) it would amount to17.1 grains, and hence silicated fluoric gaswould contain

61.4 Silex

38.6 Fluoric acid

. 100.0

This gas is partially and unequally decom-posed, by the action of water, into a preci-pitate of much silex and a little acid, and aliquid containing much acid and little silex.This liquid is properly termed by Mr. D.Subsilicated Fluoric Add. To analyze it,Mr. D. assumes that the precipitate formed bythe absorption of silicated fluoric gas in water,is mere silex, and that the whole of the acid re-mains in the solution, (which is contrary to theopinion of Gay Lussac ) and hence the Subsili-cated Fluoric Add differs from the formeronly by the quantity of silex separated onits absorption by water. It is therefore thuscomposed.

54.56 Silex45.44 Acid

. 100 00

‘ Phil. Trans, for 1812. part 2.

VOL. III.

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