42 



CHEMISTRY. 



becomes sufficiently saturated, it is drawn off and concentrated in 

 platinum vessels, by heat, until it attains the sp. gr. of about 1*84. 

 The theory of the process may be expressed thus : — 



Nitrous acid. ) 2 Oxygen——^ ^:=— Deutoxide of Nitrogen, 



f 2 Oxygen n^ 



2 Sulphurous acid. | ^ ^^P^'^^ _ 



Water . 



2 Hydrated Sulphuric acid. 



F/'op. — A dense, colourless, oily liquid, of an intensely sour taste 

 and acid reaction; — consists of 40 parts, or 1 eq. anhydrous acid, 

 and 9 parts or 1 eq. water; — extremely corrosive; — decomposes all 

 organic substances; — has a powerful attraction for water, and when 

 mixed with it gives rise to a great elevation in the temperature ; 

 — freezes at 15°. 



Anhydrous sulphuric acid may be procured by heating the Nord- 

 hausen acid in a retort, to which is adapted a receiver surrounded with 

 ice ; a vapour passes over, which condenses into white silky crystals, 

 resembling asbestos. It has such a strong affinity for water, that 

 when put into that liquid it hisses like a hot iron ; it is very volatile, 

 boiling at 104°; — it does not display any acid reaction unless mois- 

 ture be present. Test — chloride of barium. 



Hyposidphiirous acid^ S^O^, cannot exist in an isolated form ; it 

 is produced when sulphur is digested in a solution of sulphate of 

 potassa, — a JtyjJosulphite of potassa is formed. 



Hy2J0sulphuric acid, S^O^, is procured in solution by suspending 

 peroxide of manganese in water artificially cooled, and then trans- 

 mitting through it a stream of sulphurous acid gas ; the hyposulphate 

 of the protoxide of manganese is thus formed, which is decomposed 

 by baryta, and the barytic salt in its turn decomposed by sulphuric 

 acid. 



Two other acids of sulphur have recently been discovered, called 

 respectively the sulpkuretted hypesulphuric acid, SgO^, and bisul- 

 phuretted hyposulphuric acid, Sfi^, 



SELENIUM. 



A very rare substance, much resembling sulphur in its chemical 

 habitudes. It is a reddish brown solid body, having an imperfect 

 metallic lustre, and a sp. gr. of 4-3; — melts at about 212°, and boils 

 at 650°. It forms, an oxide and two acids. 



PHOSPHORUS. 



Exists in bones and urine ; — prepared from bones, in which it exists 

 as phosphate of lime, by calcining, and then adding sulphuric acid 

 and water ; the sulphate of lime is precipitated, and the phosphoric 



