FLUORIC ACID. 501 



on shaking the bottle, the movement of the liquid fluoric acid will 

 be distinctly perceived.* 



4. PROPERTIES. 



(a.) An exceedingly volatile fluid; extremely corrosive, suffoca- 

 ting ', and dangerous. 



(b.) Jit 32 Fahr. it is a colorless fluid. Sp. gr. 1.0609, and by 

 gradual additions of water, its density is increased to 1.25.f 



(c.) Retains its liquid form at 60, if preserved in well stopped 

 silver bottles :J those of lead answer but imperfectly, as the acid cor- 

 rods them and escapes. 



Sd.) Does not congeal at 4 Fahr. 

 e.) When strong, emits into the air dense white fumes, which evi- 

 dently arise from a combination with the watery vapor. 



(f.) Potassium burns, or rather detonates in the liquid fluoric 

 acid ; hydrogen gas is disengaged, and a solid white substance is 

 formed. This experiment must be performed in a metallic vessel ; 

 a platinum crucible or capsule answers well. 



(.) Dropped into water, it hisses like a hot iron, and there is 

 great agitation, and even ebullition, especially when water is added to 

 the acid. 



* See Am. Jour. Vol. XVI, p. 354. 



With the proportion of acid mentioned in the text, (that of Gay-Lussac and The- 

 nard,) the silver alembic is sometimes attacked, and corroded through and through, 

 as I have more than once experienced. If we diminish the quantity of acid, using 

 3 to 2 of fluor, or even equal weights, the danger to the vessel is much diminish- 

 ed, but the product of fluoric acid is less, and the residuum in the alembic is much 

 more difficult to remove. To a certain extent, the smaller the proportion of sulphu- 

 ric acid used, the stronger and more fuming is the fluoric acid obtained. A similar 

 effect is produced by previously heating the sulphuric acid, for some time, near to its 

 boiling point. The reason is obvious ; it is the water of the sulphuric acid that 

 serves to condense the fluoric acid, otherwise incoercible, at least at the tempera- 

 ture of ice, and under the ordinary pressure, and therefore, the less in quantity, 

 and the stronger the sulphuric acid, (provided it is sufficient for the decomposition,) 

 the more concentrated will be the fluoric acid. I have known the latter so active 

 as to be of very difficult condensation ; blowing out the silver ground stopper with 

 violent puffs, and rapidly wasting away by its own evaporation. A little water in 

 the receiver, however, prevents this, and if our object is to etch on glass, a diluted 

 acid is much preferable. The strong acid of Gay-Lussac is needed only to display 

 its own dangerous and wonderful energy, and too much caution cannot be recom- 

 mended to those who prepare it. 



t This is said to be unlike other fluids, but is it however, really an exception ? 

 Alcohol and water, and sulphuric acid and water, acquire by union, a gravity great- 

 er than the mean. This acid appears to attract water with more energy than the 

 sulphuric, much more heat is evolved by the condensation, and the density ought 

 to be increased considerably. 



t In silver bottles, with well ground stoppers, in a cellar, it can'be kept the 

 year round; but from lead bottles, however well ground and luted, it almost always 

 makes its escape, corroding the lead ; and glass vessels in the vicinity are extensive- 

 ly covered with a white deposit of silica, rendering them opake. This eeffct men- 

 tioned by Dr. Thomson, (First Principles, Vol. II, p. 165.) I have often seen. 



