on different ComUnat'ions of Fluoric Add. 383 



Like the neutral carbonats, it is decomposed bv heat ; hut 

 there is this difference between them, part of the pure 

 alkali is expelled instead of the acid, and an acid fluat of 

 ammonia is formed. A gentle heat only is required for 

 ihe purpose, that of boiling water is nearly sufficient. 

 When the heat is much stronger, the salt fuses and passes 

 off in dense fumes of a most peculiar suffocating odour. 

 The effects of these fumes, when inhaled, are very power- 

 ful and disagreeable, and even dangerous, I might venture 

 to say, were f to speak from my own experience. In one 

 instance, when I inhaled only a small quantity, they pro- 

 duced in a few minutes a violent cough and catarrh, and 

 apparent accumulation of blood in the neck and head, and 

 symptoms altogether not unlike those the attendants of 

 apoplexy, which continued for about a quarter of an hour, 

 and then slowly diminished, and gradually disappeared 

 without leaving any permanent bad effect. The fluat of 

 ammonia, when heated in a metallic vessel, appears to 

 sublime unaltered. But the result is different when the ex- 

 periment is made in a glass one. Ammonia is expelled, 

 the glass is corroded, and subsilicated fluat of ammonia is 

 formed and sublimed. Its action on glass is so powerful, 

 that I have successfully employed it instead of fluoric acid 

 itself, for etching on this substance. It has one advantage, 

 that it is more manageable. The solution may be applied 

 by means of a hair pencil or a common pen to the glass, 

 and the erosion will be produced by exposure to a moderate 

 temperature. 



The fixed alkalies, and all the earths that I have tried, 

 decompose this salt; they expel the ammonia, and form 

 true fluats with the acid itself. I have examined all the 

 fluats thus formed, and have endeavoured to ascertain the 

 proportions of their constituent parts j but I am not suffi- 

 ciently satisfied of the accuracy of the results, to venture to 

 give an account of them. 



Sect. III. On Fluoloracic Acid Gas. 



MM. Gay Lussac and Thenard, who first discovered this 

 gas, obtaijied it by heating strongly, in an iron tube, a 

 mixture of fluor spar and fused boracic acid. I have found 

 that it may be more easily procured, in greater abundance, 

 and at less expense, by gently heating, in a common glass 

 retort, a mixture of finely pounded boracic acid* and fluor 



• Common calcined borax answers tlie *ame end, but not so well. Its 

 only recommeadatioQ to prclcifitcc is cheapness. 



spar 



