228 HISTORICAL INTRODUCTION TO CHEMISTRY CHAP. 



muriate of potash." On heating it, oxygen was liberated 

 more easily and in much larger quantity than from nitre ; 

 100 grains of salt gave 75 cubic inches or nearly 37 grains 

 of oxygen ; the salt could therefore be used very conveni- 

 ently for the preparation of oxygen and has been employed 

 for that purpose ever since. On account of the readiness 

 with which its oxygen was set free and the brilliancy of its 

 detonation with charcoal, Berthollet predicted that "the 

 powder which I propose to prepare with this salt, will have 

 remarkable properties " ; the experiment was carried out 

 shortly afterwards but produced a disastrous and fatal 

 explosion. The acid from which the oxidised muriate is 

 derived was prepared by Gay-Lussac in 1814 (Ann. de 

 Chimie, 1814, 91, 107-110). He described the acid (ibid, 

 p. 9) as CHLORIC ACID, and its salts CHLORATES. 



Berthollet (1788) prepares bleaching solutions, contain- 

 ing alkaline hypochlorites. By passing chlorine into a 

 cold aqueous solution of a mild or caustic alkali, Berthollet 

 obtained a liquid which possessed all the bleaching qualities 

 of chlorine-water, .and decomposed slowly (like chlorine- 

 water exposed to sunlight) with liberation of oxygen gas. 

 When the liquid was heated, these properties disappeared 

 and nothing was left but the chloride and chlorate. The 

 bleaching properties are due to the presence of a salt 

 (derived from an unstable HYPOCHLOROUS ACID), which 

 contains less oxygen than the chlorate and is distinguished 

 as a HYPOCHLORITE. Hypochlorite solutions were used by 

 Berthollet as a convenient source of chlorine in the 

 experiments in which he laid the foundations of the 

 bleaching industry (Ann. de Chimie, 1789, 2, 151-190). 



Tennant (1799) prepares bleaching powder. A some- 

 what similar compound, prepared by the direct union of 

 chlorine with lime, and widely known as BLEACHING 

 POWDER, was introduced by the English chemist Tennant in 

 1799 as a substitute for hypochlorite of potash or soda. 



