COMPOUNDS OF HYDROGEN. 49 



Under this head it will be convenient to allude to some other com- 

 pounds of fluorine. 



Fluosilicic acid, SiFg, — is formed whenever hydrofluoric acid 

 comes in contact with glass; it is best made by heating a mixture 

 of powdered fluor spar and glass with strong sulphuric acid; the 

 changes are as follows : — the hydrofluoric acid (generated by the 

 action of the sulphuric acid on fluoride of calcium) reacts with the 

 silicic acid of the glass so as to form water and fluosilicic acid, thus: 



Hydrofluoric acid ^ ^T'"' ^^Fluosilicic acid. 



•' ( Hydrogen ^^^^^---'^ 



Smcioacid )Swn— =^^Water. 



Prop, — A colourless irritating gas, producing white fumes on 

 escape into the air, from the action of moisture ; is decomposed by 

 water into pure silicic acid, which is deposited in flakes, and into a 

 new acid termed hydrofluosilicic acid — a compound of hydrofluoric 

 and fluosilicic acids. 



Fluoboric acid, BFg. — Prepared by heating a mixture of powdered 

 fluoride of calcium and vitrified boracic acid together ; fluoboric acid 

 and lime are generated. 



Prop. — A colourless pungent gas ; decomposed by water into 

 boracic acid and boro hydrojiuoric acid. 



Hydrogen and Nitrogen. — Ammonia, or volatile alkali, NHg ; — 

 prepared by heating a mixture of powdered sal ammoniac and quick 

 lime ; by a double decomposition we have gaseous ammonia, chlo- 

 ride of calcium, and water, thus : 



C Ammonia —Ammonia. 



Sal ammoniac < Flydrochloric 5 Chlorine — "L..--^' Chloride of Calcium. 



f acid 



T . 5 Calcium ^^^ 



l.ime . . J Oxygen -^Water. 



Prop. — A colourless gas, of a strong and pungent odour ; very 

 rapidly absorbed by water, (more than 700 times its own volume;) 

 sp. gr. -589 ; has a powerful alkaline reaction ; is condensed into a 

 liquid under a pressure of 6-5 atmospheres at 60° ; cannot be formed 

 artificially by a direct union of its elements, but is an abundant 

 product of the putrefaction of animal substances ; it may be decom- 

 posed by the electric spark, by chlorine, and by being passed through 

 a red-hot porcelain tube. 



The solution of ammonia {aqiia ammonice) may be prepared by 

 simply saturating water with gaseous ammonia ; it is colourless, and 

 possesses the pungent odour and alkaline reaction of the gas. 



Ammonia forms salts with the different acids, which are all de- 

 composed by a red heat, and by a less powerful heat, if they are 

 mixed with an alkali or alkaline earth. The ammoniacal salts were 



5 



