NATURE OF THE BLEACHING COMPOUNDS OF CHLORINE. 283 



with the metal, which it converts into a liquid of deep yellow colour, 

 which is acid but does not decolorize ; it appears to be perchloride of 

 iron ; it does not seem to be mixed with chlorate. We might be tempted 

 to suppose that the action of chlorous acid on other metals is compara- 

 ble to that which it exerts upon iron ; but this is not the case. The 

 greater number of the other metallic substances, put into contact with 

 chlorous acid, cannot decompose it, and I am yet entirely ignorant of 

 the cause of the peculiarity of iron in this respect. 



Tin filings may remain in contact with weak chlorous acid for 

 several days, without causing it to undergo any sensible decomposition, 

 and without losing their metallic lustre. The same is the case with 

 zinc, with fragments of antimony, bismuth, and lead. But the presence 

 of another acid renders these metals capable of effecting this decompo- 

 sition. 



The nature of the acid employed for this purpose is not a matter of 

 indifference. This acid must form a compound, soluble in water, with 

 the oxide of the metal employed. Thus with zinc and tin, sulphuric 

 acid causes the decomposition of the chlorous acid most rapidly ; with 

 antimony, sulphuric acid and even nitric acid does not answer, but 

 tartaric acid succeeds extremely well in causing its oxidation ; lastly, 

 chlorous acid, which alone or mixed with sulphuric acid scarcely acts 

 upon lead, exerts an intense action upon it when mixed with a little 

 nitric or even acetic acid. 



In this re-action, induced by the presence of these acids mixed with 

 the chlorous acid, the metal, in order that it may saturate them, must 

 decompose the acid, and not the water ; for in combining with the 

 oxygen, it is chlorine, and not hydrogen, which it sets at liberty. How- 

 ever when in operating with chlorous and sulphuric acid on zinc or 

 tin, the gas obtained contains a little hydrogen, which indicates that 

 in some cases it is at the expense of the water itself that the oxidation 

 occurs. 



If concentrated chlorous acid be used, the action is not at first 

 more energetic, but it becomes so at the end of a certain time. During 

 its spontaneous decomposition chlorous acid forms chloric acid, the 

 mode of action of which is the same as that of sulphuric, nitric, and 

 other acids, as I determined by direct means. 



Gold and platina do not appear to suffer any action by chlorous 

 acid, either alone, or mixed with nitric and sulphuric acid ; but copper, 

 mercury, and silver decompose it, and each with a peculiar mode of ac- 

 tion. Copper filings put into contact with chlorous acid are partly 

 dissolved : the solution after some time is found to contain chloride 

 of copper. There is also formed at the same time a green powder, 

 which appears to be merely oxichloride of copper, and it disengages 

 chlorine mixed with a very small proportion of oxygen. 



