342 M. Berzelius on Fluoric Acid. [Nov. 



out any sensible loss. That lithia forms an insoluble double 

 salt with fluoric acid and alumina is already well known ; for 

 the mineral called amblygonite consists of a compound of this 

 nature mixed with a double subphosphate of the same bases. 



Fluate of alumina possesses a similar tendency to form double 

 salts with the metallic fluates. I have examined its compounds 

 with the fluates of the oxides of copper, nickel, and zinc. They 

 are in general more soluble in water than the simple metallic 

 fluates, and, contrary to what takes place with the latter, they 

 pass into solution without undergoing decomposition ; neverthe- 

 less, like the fluate of alumina, after they have been once reduced 

 to a solid form, a long time elapses before they can be again 

 redissolved by cold water. The double salt of copper is pale 

 bluish green, that of nickel pale apple green, that of zinc colour- 

 less ; and they may be all obtained crystallized in long prismatic 

 needles by spontaneous evaporation. Ammonia precipitates 

 from the aqueous solution an aluminate of the oxide. I have not 

 entered more minutely into the investigation of these compounds 

 than was necessary to demonstrate the remarkable tendency of 

 fluoric acid when in union with oxides which act not only very 

 feebly as acids, to form double salts with the fluates of a differ- 

 ent class of oxides, which invariably possess the characters of 

 bases when combined either with the electronegative oxides, or 

 with the weaker acids. Other oxides also, which, like alumina, 

 contain three atoms of oxygen, as, for example, oxidule of chro- 

 mium, oxide of iron, yield similar series of double salts, which 

 are in general either insoluble, or very difficultly soluble in water. 

 In most cases these compounds do not precipitate until the 

 mixed solutions are heated. The double salts formed by fluate 

 of oxidule of chromium with the alkaline fluates are grass green 

 pulverulent precipitates ; those of oxide of iron are pale straw 

 yellow, or almost colourless. 



The alkaline fluates containing an excess of acid resemble the 

 acid sulphates, tartrates, and oxalates of potash or soda, in the 

 great readiness with which they combine with other bases, par- 

 ticularly metallic oxides, in order to form double salts. 1 have 

 examined the double salts which they form with the oxides of 

 iron, copper, nickel, cobalt, manganese, and zinc. They are in 

 general difficultly soluble in water, and possess only a faint shade 

 of the colour of their metallic oxide. The alkaline fluates form 

 double salts also with the fluate of oxide of platinum. They 

 crystallize only from a very concentrated solution, and the crys- 

 tals have a dark brown colour, more intense even than that of 

 the simple salts of platinum. They are insoluble in alcohol. 

 The fluate of uranium forms double fluates with the utmost faci- 

 lity : most of them dissolve in water, and those containing an 

 alkaline fluate shoot in yellow coloured crystals. Oxide of 

 antimony also forms a series of double salts, which are crystalli* 



