510 PLUATES. 



FLUATE OF SODA. 



1. PREPARATION. 



(a.) In the same manner as the preceding, and also by decompos- 

 ing the acid fluate of silica by soda.* 



(b.) Dr. Thomson formed itf by passing fluo-silicic gas, to satura- 

 tion, through solution of carbonate of ammonia, which was then de- 

 composed by carbonate of soda, added by little and little ; after evap- 

 oration to dryness in a silver vessel, resolution and filtration to get rid 

 of a little silica, it was again evaporated and crystallized. The crys- 

 tals are small and crackle between the teeth. 



2. PROPERTIES. 



(a.) In transparent crusts like ice; after the expulsion of the water 

 of crystallization forms opaque white crusts, becoming again transpa- 

 rent by immersion in water. 



(b.) Not deliquescent or efflorescent ; a little more soluble in hot 

 than in cold water ; effervesces vigorously with sulphuric acid ; taste 

 bitter and styptic ; but not so strong as the fluate of potassa ; suffers 

 the aqueous fusion. 



FLUATE OF AMMONIA. J 



1. PREPARATION. 



(a.) Pulverized fluor 1 part and sulphate of ammonia 2 ; heat 

 them in a subliming apparatus ; ammoniacal gas is liberated at first, 

 and then fluate of ammonia sublimes and incrusts the capital. 



in 6 or 7 hundred parts of water; the filtered fluid, on evaporation, gives a fluate of 

 silica and potassa, gelatinous, very transparent, tasteless, without effect on blue 

 colors becoming pulverulent with a mild heat, and with ignition, exhales silicated 

 fluoric acid gas. Both the powder and the jelly effervesce vigorously with sulphuric 

 acid. 



Caustic potash, soda and ammonia, in the cold, do not decompose it in 24 hours; 

 potassa and soda dissolve it with heat. 



It is not possible, by potash, to extract pure silica from silicated fluoric acid gas, 

 for it forms with it an insoluble triple salt. Gay-Lussac and Thenard, in Recher. Ph. 

 Ch. T. II, p. 20. 



* The effect of soda upon the acid fluate of silica, is very different from that of po- 

 tassa. There -is no prompt precipitate, but boiling produces readily a transparent 

 jelly of pure silica, while the fluid is pure fluate of soda. In this manner, pure 

 silica may be advantageously prepared even from the insoluble fluate of silica, which 

 is completely decomposed by soda, with the same results as are obtained from the 

 acid fluate. Id. 



t First Principles, Vol. II, p. 168. 



J Ammonia affects the acid fluate of silica in a manner very different from potassa, 

 and even from soda. It promptly precipitates pure gelatinous silica, opake, and 

 white, but a little silica remains in solution in the fluate of ammonia, as appears from 

 its repeated precipitation, on the addition of pure ammonia, from lime to time, after 

 evaporation. 



Ammonia also decomposes the solid acid fluate of silica, as perfectly as the fluid. 



Pure silica then can be obtained by ammonia, from either of them, although we 

 cannot in this way obtain a pure fluate of ammonia, as we do a pure fluate of soda in 

 the parallel process with that alkali. Id. 



