on different Combinations of Finer ic Jcid. 375 



tilled " Rechcrchcs Physico-Cbemiques," in the second 

 volume oFwhich is an elaborate dissertation on fluoric acid. 

 These philosophers, I find, have anticipated many of my 

 results, and coi^sequtntly very much abridged my labour 

 of detail in the following pages. To repeat what is already 

 known would be useless, I shall therefore confine myself to 

 <lescribe what I have observed, which appears to me yet 

 novel, or ditTerent from the observations of the French 

 chemists. The order which I shall pursue, will be t'nat 

 which I observed in my experiments. I shall divide what 

 1 have to advance into four parts. The first part will relate 

 to the silicattd fluoric acid gas, and to the subsilicaled 

 fluoric acid ; the second to the combinations of ihese acids, 

 and of pure fluoric acid with ammonia; the third to fiuo- 

 boracic acid ; and the fourth to its aninjoniacal salts. 



Sect. i. On Silica ted Fluoric Acid Gas, and Suhsilkaied 

 Fluoric Acid, 



The facts which have already been published by MM. Gray 

 Lussac and Thenard and others, appear to me to be siitii- 

 cient to prove that pure fluoric acid has not yet been ob- 

 tained in the gaseous state, aiid that silex, or boracic acid, 

 is requisite that it may assume this form. Were more evi- 

 dences necessary, f could advance many in point. One 

 circunislance only I shall mention, proving that conmiou 

 fluoric acid gas is perfectly saturated with silex. I have 

 preserved this gas, made by healing, in a glass retort, a 

 mixture of fluor sparand sulphuric acid, for several weeks 

 over mercurv in a glass receiver uncoated with wax, with- 

 out observing the slightest erosion to be produced *. 



This gas, with great propriety, has lately been called si- 

 licaled fluoric. Before 1 proceed to its analysis, I shall 

 notice what method 1 have found the best for obtainins: it. 

 I have for aconsiderable time, long before MM. Gay Lussac 

 and Thenard's work was publisiied, added to the mixture 

 of fluor spar and sulphuric acid, a quantity of finely pouiiJed 

 glass, and have thus procured the gas with the greatest 

 Facili'y. '{"he advantages of ihis addition are considi-rabie. 

 The reiorl is saved, wliich otherwise, in less than one ope- 

 ration, would be destroved ; and a n)ucli larger quantity of 

 gas is procured from the same materials, and with less 



• Tlic sides of the rerciver indeed became obscure ; but this was net 

 from erosion, but from depc'^i.'ion, as appeared iron tlie iraii8p:ireiicv and 

 polish of the }jla9s beiii^j icadiiy restored by slight friction. What the de- 

 position was, 1 am ij,'iiorant of. After several weeks it was so trillinjj, as 

 to give only a slight dcgice of opacity to the receiver. 



A a 4 trouble 



