268 M. Balard on the Nature of the [Oct. 



able to demonstrate that the bleaching compounds are truly 

 saline compounds of a peculiar acid, formed of chlorine and 

 oxygen. It is the properties of this acid which I have been 

 able to separate that form the subject of this paper. 



2. Mode of preparing Chlorous Acid. — In projecting a plan 

 for the separation of this acid, it was obvious that this would 

 be simple, if we could obtain a metal which would form with 

 the chlorine a compound soluble in water, and the oxide of 

 which, at the same time, would form with chlorous acid a com- 

 pound insoluble in this liquid. The same object might also 

 be effected if we could find a metal which would form with 

 the chlorine an insoluble compound, and the oxide of which 

 would unite with the chlorous acid and form a soluble com- 

 pound. All the metallic chlorides are, however, soluble 

 in water, except the chlorides of silver, lead, and proto- 

 chloride of mercury. It was necessary to chose one of these 

 three : Economy pointed out lead or mercury. But when 

 a solution of acetate or nitrate of lead is poured into that 

 of a decolourizing chloride, a precipitate of chloride of lead 

 is immediately formed, which is susceptible of being altered 

 by the chlorite. If the liquid is separated it becomes brown, 

 by being changed into peroxide, and disengages a strong 

 odour of chlorine. This is obviously produced by the de- 

 composition of chlorous acid. 



Again, when solutions of chloride of lime or soda are treated 

 with proto-nitrate of mercury, a great quantity of proto- 

 chloride of mercury is precipitated, and the supernatant 

 liquid possesses strong bleaching powers, which soon dis- 

 appear, and we find in the liquid a notable portion of deuto- 

 chloride of mercury, and the precipitate soon becomes red 

 and changes into a chloride of an oxide. 



Since neither the salts of lead or mercury would answer 

 the end in question, it was necessary to have recourse to 

 those of silver. These also present obstacles which it is 

 necessary should be pointed out : 



If we precipitate by neutral nitrate of silver, a solution of 

 chloride of lime containing a slight excess of alkali, a great 

 quantity of chloride of silver falls down, together with some 

 oxide of silver, which communicates a gray colour to the 

 precipitate. The supernatant liquor possesses very strong 

 decolourizing powers, which disappear with effervescence 



