280 BALARD'S RESEARCIFES CONCERNING THE 
distillation. The red 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- 
cifie 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, hut not sour. 
