^66 Sir H. Davy on the Substances produced 



must be examined with great caution. According to my ex- 

 periments, its specific gravity is 1,0609.* It produces a high 

 degree of heat when mixed with water, and such is its degree 

 of attraction for water, that it becomes denser by combining 

 with that fluid. By adding water, in very small quantities at 

 a time, to pure liquid fluoric acid, I found that its specific gra- 

 vity gradually increased till it became 1,25: it is, I believe, the 

 only known body possessed of this property. 



The third substance is fluo-boric acid gas, which was disco- 

 vered by M. M. Gay Lussac and Thenard. It is produced 

 by intensely heating, in an iron tube, a mixture of dry boracic 

 acid and fluor spar, or by gently heating in a glass retort a 

 similar mixture with sulphuric acid. Its specific gravity is 

 rather more than thirty-two times as great as that of hydro- 

 gen. It forms a solid salt, volatile without decomposition, by 

 condensing its own volume of ammonia. The ammoniacal 

 salt dissolved in water and distilled, affords boracic acid. 



The most important phenomena of chemical change, in 

 which these bodies operate, that may be supposed to illustrate 

 their nature, is their agency upon potassium and other metals. 

 The action of potassium upon silicated fluoric gas has been 

 already referred to. M. M. Gay Lussac and Thenard, by 

 heating potassium and sodium in fluo-boric acid gas, obtained 

 fiuate of potassa or soda, and the basis of the boracic acid ; and 

 by exposing potassium to liquid fluoric acid, their results were 

 hydrogen and acid fluate of potassa. 



* Unless it is distilled through tubes and into vessels of pure silver, its specific gra- 

 vity is greater ; it readily dissolves tin, and slowly dissolves lead, and after being long 

 kept in vessels of pure silver, it is found to have taken up a small portion even of 

 that metal. 



