ON ORGANIC COLOURING MATTERS. 495 



oxygen, and all of them dissolve several colouring matters. Yet, not only dry, 

 but moist chlorine may be passed through solutions of the colouring principle of 

 false alkanet root [anchusa thictmna), in the solvents mentioned, without bleaching 

 occurring. 



On the other hand, solutions of blue litmus, in chloroform and bisulphuret of 

 carbon, are bleached instantaneously by dry chlorine. I took the greatest precau- 

 tions in these trials to exclude moisture. Paper was dispensed with. A solu- 

 tion of blue litmus was dried up in a glass tube, and desiccated in a current of 

 air. The chloroform, or sulphuret of carbon, was repeatedly rectified over 

 chloride of calcium, and finally distilled into a bulb communicating with the 

 outer air, through a narrow tube filled with the same hygrometric salt. The 

 bulb was then sealed, and placed within the tube containing the litmus at the 

 commencement of the experiment. Chlorine was ultimately passed over the 

 colouring matter for some minutes, in order to make certain that the gas was too 

 dry to act unaided on the coloiu-. The tube was then sealed, full of chlorine, and 

 shaken till the bulb broke. The blue colour immediately disappeared, and the 

 liquid became of a pale yellow tint. 



The tincture of alkanet in chloroform or sulphuret of carbon retained its 

 bright red colour, if kept in darkness ; but less than an hour's exposure in the 

 open air, though the sky was clouded, sufficed to turn the scale in favour of 

 bleaching, and the colour disappeared. 



From these results it appears that, contrary to Davy's view, chlorine can 

 bleach though oxygen be absent, for chloroform contains none ; and that neither 

 of the elements of water is essential to its bleaching action, for sulphuret of car- 

 bon is devoid of both. The further conclusion seems unavoidable, that neither 

 water nor any other liquid is essential to the decolorising action of chlorine, 

 otherwise than as enabling the gas and the colour to come within the sphere of 

 chemical action, by dissolving both. This function, water probably performs 

 better than any other liquid, in virtue of its solvent power for most substances 

 exceeding that of almost all other fluids. 



A similar conclusion, mutatis mutandis, may be extended to oxygen, sulphur- 

 ous, hydrosulphuric, and hydrochloric acids, but with this qualification, that 

 specific differences may be expected to occur with all the gases named, as to 

 their action on any one coloiu-ing matter, and with different colouring matters, as 

 to their deportment with any one of the gases. 



VOL. XVI. PART IV. 6 L 



