284 HISTORICAL INTRODUCTION TO CHEMISTRY CHAP. 



(2) A grain of potassium burning in oxygen was found 

 (after igniting the calx to decompose the peroxide) to pro- 

 duce an absorption amounting to J cubic inch. By ab- 

 sorbing i J cubic inches of chlorine the oxide was converted 

 into chloride ; exactly half a cubic inch of oxygen was 

 regenerated, but " there was no separation of moisture," 

 provided that the chlorine had been properly dried. 



(3) Similar phenomena were observed in the action of 

 chlorine on the peroxide, the whole of the absorbed oxygen 

 being regenerated without liberating any water. But when 

 chlorine was admitted to " a white sublimate of hydrate " 

 formed by the action of moisture on the peroxide "it 

 instantly became transparent from the evolution of water ; 

 and on heating the glass in contact with the sublimate, its 

 opacity was restored, and water driven off." (A.C.R. IX. 



4143)- 



Caustic potash was, therefore, a binary compound of 

 oxide of potassium with water, corresponding with slaked 

 lime, or a ternary compound of potassium, oxygen and 

 hydrogen. It is therefore described as POTASSIUM HYDROXIDE. 

 Similar experiments show that caustic soda is correctly des- 

 cribed as SODIUM HYDROXIDE. 



SUMMARY AND SUPPLEMENT. 

 A. THE COMPOSITION of AMMONIA. 



Priestley, in 1/73, showed that ammonia was inflammable 

 and in 1775 decomposed it by sparking. This method was used 

 by Berthollet in 1785 to determine the composition of the gas. 

 He found that 



ammonia gave hydrogen + nitrogen 



2 vols. 3 vols. i vol. 



The action was shown by St. Claire Deville, in 1865, to be 

 incomplete and reversible. 



2NH 3 ZT 3H 2 + N 2 



(Am- (Hydro- (Nitro- 

 monia.) gen.) gen.) 



