50 CHEMISTRY. 



formerly considered to be formed by a direct union of the alkali and 

 the acid ; but, at present, the acid is believed to unite with the oxide 

 of a hypothetical metal termed aynmoniiwi. This supposed metal 

 has never been isolated, but is inferred to exist from the fact that 

 when ammonia is decomposed by a galvanic current, and the nega- 

 tive wire terminates in some mercury, an amalgam is formed, having 

 all the characters of an ordinary metallic amalgam : but when left 

 to itself, this amalgam rapidly decomposes into mercury, hydrogen, 

 and nitrogen. Ammonium is believed to be composed of ammonia 

 and one eq. of hydrogen ; it is represented by NH^, and the base of 

 the ammoniacal salts would consequently be represented by NH O. 



The most important of these salts are the chloride of ammonium, 

 (sal ammoniac,) the carbonates, the nitrate, and the sulphate. 



There is believed to be yet another compound of hydrogen and 

 nitrogen, to which the name q^ amide, or amidogen, is given. Like 

 ammonium, it has never been isolated : it is represented by NH . 



Hydroge/i and sulphur. — Suljjhuretted hydrogen, hydrosulphuric 

 acid, HS. — Conveniently prepared by the action of dilute sulphuric 

 acid on sulphuret of iron ; or by chlorohydric acid on sulphate of 

 antimony, as follows : — 



Sulphuret of iron \ ^u^phur Hydrosulphuric acid. 



^ ( Iron ^ — 



Water . . . > Hydrogen^^X^ 



t Oxygen — —l^:;-^ 



Sulphuric acid ^ ^ Sulphate of iron. 



or 



Sulphuret of antimony j ^"ISon ' ^^-^-^'^ Hydrosulphuric acid. 



Hydrochloric acid . ) Hy^'"?^^" '^^^''**'^^^^-^.^ ^^, ., , . 



\ Chlorine ~:==^ Chloride of antimony. 



Frop. — A colourless gas, having the odour of rotten eggs ; irre- 

 spirable, acting as a narcotic ; combustible, burning with a blue flame, 

 producing water and sulphurous acid ; a non-supporter of combus- 

 tion ; becomes a liquid under a pressure of 17 atmospheres ; is de- 

 composed by chlorine, with a deposition of sulphur; sp. gr. ri71 ; 

 it has the properties of a weak acid, reddening litmus paper, and 

 forming salts. 



The best test is acetate of lead, with which it forms the black 

 sulphuret of lead. 



Hydrosulphuric acid is valuable to the chemist as a test for me- 

 tallic solutions, causing with them an insoluble precipitate of the 

 sulphuret of the metal. 



There is another compound of sulphur and hydrogen, called per- 

 sulphuret of hydrogen. 



Hydrogen and Selenium. — Hydroselenic acid, HSe; — in its 

 general properties, resembles hydrosulphuric acid. 



Hydrogen and Phosphorus, — Phosphuretted hydrogen, PgHg, pre- 



