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 tinctoria), 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 colour. 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 colouring matter, and with different colouring matters, as 
to their deportment with any one of the gases. 
VOL. XVI. PART IV. 2 6 
