330 M. Berzelius on Fluoric Acid. [Nov. 



Article IV. 



On Fluoric Acid, and its most remarkable Combinations. 

 By Jac. Berzelius.* 



I. Compounds of Fluoric Acid tvith Electropositive Oxides, or 

 with the Saline Bases properly so called. 



Fluoric acid, which may now be regarded either as a 

 hydracid, or as an oxygen acid, is distinguished before every 

 other substance by its great capacity of saturation, which, 

 according to my earlier experiments, amounted to so much as 

 Tl'l\, and, as will be subsequently demonstrated, is even some- 

 what higher than this quantity. With alkalies, it forms salts 

 which are soluble in water, and which, when in a solid crystal- 

 lized form, invariably possess either an acid or an alkaline reac- 

 tion, as is the case with the borates, seleniates, arseniates, and 

 phosphates. If a solution of a fluate be saturated until it pos- 

 sesses a perfectly neutral reaction, and if it be then committed 

 to evaporation, there is always obtained, either an acid salt, 

 while the supernatant liquid becomes alkaline, or the contrary. 

 The fluates which I shall in this memoir style neutral, are those 

 in which 100 parts of fluoric acid combine with a quantity of a 

 base containing 74-72 parts of oxygen. Those containing an 

 alkaline base, react as alkalies, and have a saline and weakly 

 alkaline taste. Those whose base is an alkaline earth, are gene- 

 rally insoluble in water, and in that case possess no reaction 

 whatever. Fluoric acid forms acid crystallizable salts with all 

 the alkalies, which possess a strongly and purely acid taste, and 

 whose solutions in water rapidity corrode glass. All the colour- 

 less crystallized fluates approach closely in refractive power to 

 that of water : hence, when immersed in water, they appear 

 semitransparent, and indeed their presence frequently remains 

 unobserved, until the liquid is decanted. All the experiments 

 alluded to in this memoir were made in vessels of platinum, 

 except when the employment of glass vessels is expressly men- 

 tioned. 



Fluate of Potash. — a. The acid fluate may be prepared by 

 mixing with fluoric acid a quantity of potash insufficient to pro- 

 duce neutralization. During evaporation, a portion of the acid 

 is dissipated, but the greater part crystallizes with the alkali on 

 coolin°\ When obtained hastily in this manner, the salt forms 

 an apparently solid mass, composed of broad plates, intersecting 

 one another, and leaving numerous trapezoidal interstices, which 



* Abstracted from Kongl. Vet. Acad. Handl. 1823, St. II. Want of room obliges 

 us to omit a comprehensive historical sketch of the experiments and opinions of preced- 

 ing inquirers. 





