HYDROGEN NITROGEN. ^5 



heat thus produced is sufficient to melt the most refractory metals. — 

 Symb. H;— Eq. 1. 



Hydrogen forms two compounds with oxygen : water, or the 

 protoxide, and the peroxide. 



Water, HO, — first proved to be composed of hydrogen and oxygen, 

 by Cavendish ; this may be shown synthetically, by mixing one 

 volume of oxygen with two of hydrogen, and exploding the mixture, 

 when water will be the sole product, — or, analytically, by decom- 

 posing water either by red hot iron, or by galvanism ; in the last 

 case, a small portion of water is interposed between 

 a pair of platinum plates, connected with the ex- ^^* ' 



tremities of a voltaic apparatus of moderate power ; 

 pure oxygen gas is evolved at the positive plate, 

 (or that connected with the copper end,) and pure 

 hydrogen at the negative, or zinc extremity ; the 

 gases may be properly collected and measured. 



The composition of water is, by weight, 8 parts 

 of oxygen, and 1 of hydrogen ; by volume, 1 vo- 

 lume of oxygen, and 2 of hydrogen. 



Prop. — Colourless, inodorous, tasteless ; power- 

 ful refractor of light ; imperfect conductor of heat 

 and electricity ; very incompressible ; sp. gr. 1. It 

 does not occur, in nature, chemically pure ; — can 

 only be procured pure by distillation. Water acts powerfully as a 

 chemical agent, forming compounds termed hydrates; sometimes 

 the reaction is accompanied with the evolution of heat, as in the 

 slaking of lime. Water also enters into the composition of many 

 crystals, constituting their water of crystallization ; its solvent pro- 

 perties are pre-eminent. Water in its natural state al\7ays contains 

 atmospheric air, as may be shown by placing it under a receiver 

 and exhausting the air ; bubbles of gas will make their escape. Re- 

 cently boiled water has the property of absorbing gases, though in 

 different degrees. 



Peroxide of Hydrogen, HO^, called also oxygenated water, is 

 procured from the peroxide of barium, by the action of dilute hydro- 

 chloric acid, and then precipitating the baryta by sulphuric acid ; 

 the excess of oxygen of the peroxide, instead of escaping, unites with 

 the water, converting it into the peroxide of hydrogen. 



Prop. — A colourless, transparent liquid ; inodorous ; has a me- 

 tallic taste; sp. gr. 1-45; remarkable for its proneness to decompo- 

 sition, — a temperature of 212° causing explosion; it also bleaches 

 and oxidizes. 



NITROGEN. 



Constitutes about |ths of the atmosphere, and is found abundantly 

 in nature, under various combinations ; may be procured in several 



