2 M. Berzelius on the Chemical Composition 
as miiieraiogical specimens, yet yielded only a small quan- 
tity of the pure crystals of the Tesselite, of which I could not 
collect more than a gramme, or 18 1 grains, 
I have analysed it in the same manner as the apophy Hites of 
Uto and of Fassa, the analyses of which are published in the 
Afhandlingar i Fysih, vol. vi. p. 181. and it has given me 
the same result as the apophylliteof Uto even in the thousandth 
parts. But in examining on the present occasion the Apophyllites 
with the most scrupulous attention, I have discovered a principle 
which had hitherto escaped notice, viz. Fluoric Acid, which can 
be easily detected by the blowpipe. 
I have tried different methods of determining the quantity of 
fluoric acid in this mineral, and I believe I have at last succeed- 
ed. The Apophyllites lose on a red heat from 16 to 16.2 hun- 
dredths of their weight ; but when exposed to a strong incan- 
descence, their loss amounts to 16.7. At a still stronger heat, 
where the: mineral is reduced to a spongy glass, its weight is not 
diminished. I have repeated the analysis of the Apophyllite of 
Uto in the following manner. The mineral, when coarsely pul- 
verised, was decomposed by cold muriatic acid, diluted with 
water. It was soon converted into a gelatinous mass, by 
which all the fluid was absorbed. Having washed it with wa- 
ter, and filtered it, 51.18 hundredths, of the weight of the apo- 
phyllite remained on the filter, and was pure Silex. 
The liquid being super-saturated with caustic ammonia, gave 
an abundant precipitate, which, when collected on the filter, 
washed, and dried, weighed 4.82 hundredths, and the nature of 
which remained to be determined. 
The rest of the liquid gave, , by means of oxalate of ammonia, 
21.71 of Lime, and, after the evaporation of the liquid, and the 
exposure of the saline, matter to the fire, 8.32 parts of Muriate 
of Potash, equivalent to 5.27 of pure Potash. 
In order to examine better the substance precipitated by the 
caustic ammonia, I prepared a greater quantity of it. When 
put in contact with sulphuric acid,, it gave a brisk effervescence. 
The gas discharged smelt of fluoric acid, but acted upon glass 
only feebly. When 100 parts of this mass was dried in the 
fire, it was decomposed by means of concentrated sulphuric acid, 
and the gas introduced into a lixivium of carbonate of soda. 
