156 Selections from Foreign Science. 



soniugs on the composition of some of these bodies, to which we 

 shall take an opportunity of returning. 



III. Fluonc Acid. 



[Extract from a Letter from INI. Berzelius to M. Duiong.] 

 " I have examined the combinations of fluoric acid with bases, 

 and have found that what have been taken for fluates are only 

 double salts. I have analyzed fluo-silicic gas and its combination 

 ■with bases ; all these compounds are formed in the same manner, 

 and contain a quantity of fluoric acid combined with the silica, 

 twice as much as that combined with the base. Fluoric acid gives 

 analogous combinations with the acids of titanium, tantalium, 

 tungsten, molybdenum, chromium, selenium, antimony, and arsenic, 

 also with the hyposulphurous and sulphurous acids, and probably 

 with the phosphorous and hypophosphorous acids, though I have 

 not examined these last. 



" Fluoric acid is a most convenient agent in the analysis of in- 

 organic substances, as it dissolves all those substances which other 

 acids will not attack. It has furnished me with the means of de- 

 termining the exact atomic weight of many substances on which I 

 still had doubts. To extract the alkali of minerals it is sufficient 

 to treat them with fluoric acid, or with a mixture of fluate of lime 

 and sulphuric acid." —Ann. de Ckini. xxvi. 40. 



IV. Silicium and Zirconium. 



[From M. Beuzelius' Letter to M. Dulong.] 



" In trying to reduce fluoric acid by potassium, I succeeded in 

 reducing silica, zirconia, and the other earths, but I have only 

 been able to separate silicium and zirconium. The others decom- 

 pose water with the greatest energy. Pure silicium is incombus- 

 tible even in oxygen gas. Water, nitric acid, or nitro-muriatic 

 acid, do not attack it, nor does caustic potash ; but fluoric acid 

 dissolves it a little, especially if nitric acid be added. It does not 

 decompose nitre, except at a very intense heat, but it detonates 

 with carbonate of potash at a dull red heat ; carbonic oxide gas is 

 liberated, and carbon is set at liberty. When it is heated with 

 nitre, if a small piece of dry carbonate of soda is introduced into 

 the mixture there is immediate detonation. When the vapour 

 of sulphur is passed over silicium heated to redness, the metal 

 quickly becomes incandescent. When the combination is perfect, 

 which seldom happens, the substance is in the form of a white 

 earthy mass, and decomposes water with great rapidity. The silica 

 is dissolved, and sulphuretted hydrogen gas liberated. By this means 

 a solution of silica in water may be obtained, so concentrated, that 



