280 balard's research-es concerning the 



distillation. The I'ecl oxide of mercury seemed to me to present all 

 these advantages. Its alkaline power is strongly marked. I had no 

 fear that chlorite of mercury could be compared, with respect to its 

 instability, to chlorite of silver, which does not decompose so readily, 

 merely on account of the insolubility of the chloride. Although solu- 

 ble in water, the chloride of mercury [bichloride] loses much of its 

 solubility by combining with oxide, and thus forming an oxichloride ; 

 and this state of combination would retard to a certain point the de- 

 composition which the chlorous acid would readily produce in other 

 circumstances. My attempt was followed by success : by employing 

 this substance, I obtained in fact chlorous acid in larger proportion 

 and more concentrated. 



This operation may be conveniently performed as follows : the spe- 

 cific gravity of red oxide of mercury does not allow of its being sub- 

 jected to the action of chlorine in a Woulfe's apparatus ; it is much 

 more convenient to pour the red oxide of mercury reduced to a fine 

 powder by trituration, and mixed with about twelve times its weight of 

 distilled water, into bottles filled with chlorine gas. 



By strong agitation the absorption of chlorine takes place rapidly, and 

 operates as quickly as if the gas were treated with an alkaline solution. 

 It has happened to me during this operation, that bottles which were 

 perfectly stopped have broken in my hands, on account of the almost 

 perfect vacuum which is produced in this case. If the proportion of 

 red oxide of mercury employed is insufficient, the powder deposited at 

 the bottom of the bottle is white, and the colour of the gas indicates 

 the presence of chlorine. If the red oxide of mercury, on the con- 

 trary, is in slight excess, it colours the deposit spoken of red, and the 

 chlorine then disappears completely. It appeared to me to be preferable 

 to operate with a slight excess of oxide of mercury, to prevent the 

 chlorous acid from being mixed with free chlorine. When the ab- 

 sorption of the chlorine is complete, the matter contained in the bottle 

 should be thrown upon a filter, upon which there remains the greater 

 part of the oxichloride formed : the liquor which filters, subjected to 

 distillation in vacuo, furnishes weak chlorous acid, but it may be 

 brought to greater state of concentration by subjecting the first products 

 to a second distillation. 



§ 3. — Properties of the Aqueous Solution of Chlorous Acid. 

 The chlorous acid diluted with water, obtained as above stated, has 

 the following properties : it is a transparent liquid and slightly yellow- 

 coloured when it, is concentrated. Its smell is penetrating, and quite 

 distinct from that of chlorine and the deutoxide of chlorine of Davy. 

 It more nearly, however, resembles the first than the second. Its taste 

 is extremely strong, but not sour. 



