PROOFS OK THE PROPERTIES OF FLUORIC ACID GAS. 347

Remark. ..The art of etching on glass, which is generallyconsidered as of modern date, does not entirely belong to ourcotemporaries; even to assert that the ancients were altogetherunacquainted with it, would be unjust. It seems rather thatthis art belongs to the discoveries which were made in thosetimes, in which men were little inclined to transmit an account oftheir inventions to posterity, and thus may have been forgottenor lost. Scheele discovered the fluoric acid and re-invented theart of etching on glass, in 1“71 • But that it was practised a cen-tury before, by a German, whose name was Swanhard, we haveendeavoured to prove in Nicholson's Journal for April, 1800.

Had this person been able to pursue properly the discoverywhich either accident or ingenuity presented to him, he mighthave enriched us with an art which acquired great reputation toScheele a hundred years after.

Experiment V.

Fluoric acid gas not only dissolves, but also volatilizes siliceous

earth.

This may be shown by decomposing fluate of lime in a glassretort, and receiving the gas in a vessel filled with water, andresting upon mercury. Each bubble of the gas which passesthrough the mercury into the water becomes immediatelyenveloped in silex, and leaves, as it ascends to the surface ofthe water, traces in the form of tubes, which frequently decreaseto a point upwards, because the bubble diminishes in propor-tion as the water dissolves it, and the silex is carried off.

Rationale. ..The gas when disengaged in the glass retortdissolves part of the silex of that vessel, which it keeps in anaeriform state. On coming into contact with the water itabandons its caloric and becomes converted into liquid fluoricacid, depositing at the same time the siliceous earth.