494 DR GEORGE WILSON ON THE ACTION OF THE DRY GASES 
sulphurous acid, which yielded a result so interesting, that I mention it particu- 
larly. A piece of blue litmus-paper was exposed for three hours to a current of 
dry air, and then sealed up in the narrow tube in which it had been dried. The 
sealed bulb, containing the paper, was placed in a tube immersed in a mixture of 
pounded ice and salt, and carefully dried sulphurous acid transmitted through 
the arrangement. As soon as a sufficient quantity of the gas had assumed the 
liquid form, at the low temperature to which it was exposed, the open ends of the 
tube were sealed, and it was shaken till the bulb within broke, and allowed the 
paper and the liquefied gas to come in contact with each other. The paper was 
instantaneously soaked through, and completely wetted, but its blue colour re- 
mained totally unaltered, whilst an aqueous solution of sulphurous acid would 
have instantly reddened it. The liquidised gas acquired no colour itself, even 
after a fortnight’s contact with the litmus-paper. It appeared to wet it without 
dissolving anything from it. 
The retention of the blue tint on the part of the paper was, however, only 
temporary. In an hour and a quarter it had become dark purple, and the blue 
slowly faded, till, in twenty hours, the paper was bright red. No indication of 
bleaching action appeared. 
1 attribute the final reddening to the production of water, generated out of its 
elements in the litmus or paper, or both, by the influence of the sulphurous acid. 
For, if anhydrous liquid sulphurous acid possessed the power, per se, of redden- 
ing vegetable blues, there seems no reason why its action should be so long de- 
layed, when it wetted the coloured paper so readily. And it could not owe its 
reddening power to water present in it, ready formed from the first, otherwise 
it would have reddened instantaneously. 
I set aside, therefore, as at least unproven, and, further, as not probable, the 
dogma, that the mere passage of an elastic fluid, such as chlorine, from the state 
of gaseity to that of liquidity, is the whole cause of its accelerated action on 
colours, when dissolved in water. It seemed to me, indeed, that the acceleration 
of action was as much owing to the water liquefying the colouring matter as to its 
 liquefying the gas, and that one might venture, in the spirit of the elder chemists’ 
motto already quoted, to infer, that any liquid which dissolves alike the gas and 
the colouring matter, would be as efficacious as water in determining the destruc- 
tion or modification of the colour. But, I have learned by experiment, that this 
also is too general a conclusion, and that it is quite possible for a liquid to dissolve 
simultaneously a colouring matter and a gas, and yet not exhibit the results 
which it would present if water were the solvent of both. 
So far as this branch of the inquiry is concerned, I have been compelled, by want _ 
of leisure and opportunity, to limit myself almost entirely to chlorine. This gas 
is dissolved by chloroform, by bisulphuret of carbon, and by the volatile oils of the 
type of spirit of turpentine (C’ H’). None of these liquids, when pure, contain 












