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 tlu-ough, and completely wetted, but its blue colour re- 

 mained totally unaltered, whilst an aqueous solution of svilphurous 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, jyer 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 o-aseity 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 



