•.8 ^1 



»»0 CHEMISTRY. 



Nit70us acid, NO^, is always formed whenever deutoxide of 

 nitrogen comes in contact with the atmospheric air, producing dense 

 orange-coloured fumes ; — procured in a liquid form by healing nitrate 

 of lead in a retort ; oxide of lead remains behind, and the°acid is 

 resolved into a mixture of oxygen and nitrous acid, the latter being 

 condensed into a liquid by surrounding the receiver by a powerful 

 freezing mixture. 



Prop. — At a low temperature it is nearly colourless ; acquires an 

 orange tint on raising the temperature; sp. gr. 1-451 ; very volatile, 

 boiling at 82°; — is acid, pungent, and corrosive ; is decomposed, on 

 being added to water, into nitric acid and deutoxide of nitrogen ; 

 very irrespirable ; supports the combustion of a burning taper and of 

 phosphorus, but extinguishes sulphur ; — a powerful oxidizing agent. 



Nitrous acid combines with nitric acid, which thereby acquires a 

 strong orange tint, and constitutes the fuming-red nitrous acid of the 

 shops, and the nitroso-nitric acid of Berzelius. The colour of the 

 mixture varies with the strength of the nitric acid, becoming yellow, 

 green, and blue, and finally disappearing altogether, as the quantity 

 of water in the acid increases. 



Nitric acid, NO^ ; procured synthetically, by passing a succession 

 of electric sparks through a mixture of nitrogen and oxygen confined 

 in a tube ; — best prepared by the action of sulphuric acid on nitre 

 (nitrate of potassa) with the aid of heat ; nitric acid vapours pass 

 over along with water, and the bisulphate of potassa remains in the 

 retort : this constitutes the aquafortis of commerce. 



Prop. — When thus procured, liquid nitric acid is of a yellowish 

 colour, which is dependent upon some nitrous acid fumes ; when 

 perfectly pure it is colourless ; sp. gr. about 1-5 ; contains about 25 

 per cent, of water ; emits dense, white, suflx)cating fumes when ex- 

 posed to the air; boils at 187°; on adding different portions of water 

 to the strong acid, several definite combinations of acid and water 

 appear to be generated, remarkable for the diflference observed in 

 their boiling and freezing points. 



The nitric acid of commerce is apt to contain traces of sulphuric 

 and hydrochloric acids ; the former is detected by adding chloride 

 of barium — an insoluble sulphate of baryta being precipitated ; the 

 latter, by nitrate' of silver — an insoluble chloride of silver being thrown 

 down. Nitric acid is a powerful oxidizer, acting with great violence 

 on many of the metals ; it decomposes all organic substances, and 

 acts on the skin as a caustic. The salts formed by nitric acid are 

 termed nitrates. 



The best tests for nitric acid are, — its solvent power over gold, if 

 hydrochloric acid be present ; the formation of the well known nitrate 

 of potassa; the red tint communicated to a salt of morphia ; and the 

 bleaching eflfect upon a boiling solution of sulphate of indigo, pro- 

 vided no chlorine be present. 



