iMR. SCHUNCK ON RUBIAN AND ITS PRODUCTS OF DECOMPOSITION. 
69 
The products formed by the action of caustic baryta on rubian do not differ from 
those resulting from the action of caustic soda. On adding caustic baryta to a solu- 
tion of rubian and boiling for some time, the rubian is entirely decomposed ; the 
decomposition, as might be supposed, requiring a rather longer time for its com- 
pletion than in the case of caustic soda. After the process is finished, the products 
of decomposition are found for the most part in combination with baryta in the shape 
of a purple powder, while the liquor still retains a red colour. The purple powder is 
placed on a filter and slightly washed with cold water. On passing carbonic acid 
through the filtered liquid, the latter loses its red colour, and a yellow flocculent 
substance is precipitated together with carbonate of baryta. The liquid, after being 
boiled in order to decompose the bicarbonate of baryta, and then filtered, is evapo- 
rated over sulphuric acid at the ordinary temperature, when it leaves a substance of 
a light brown colour, which resembles the sugar produced by the action of acids on 
rubian, but is not quite so deliquescent. This substance, as I shall presently show, 
is in fact a baryta compound of sugar. The mixture of yellow flocks and carbonate 
of baryta is now added to the purple powder before mentioned, and the whole is 
treated with muriatic acid in order to extract the baryta. The acid leaves undissolved 
a quantity of orange-coloured flocks, which consist, as before, of alizarine, rubiretine, 
verantine, and rubiadine, as well as of some of the dark brown flocculent substance, 
insoluble in boiling alcohol, and are separated from one another in the manner just 
described. If sulphuric acid be employed instead of carbonic acid for separating the 
baryta from the red liquid, and the excess of acid be neutralized with carbonate of 
baryta, the liquid on evaporation gives a substance exactly similar to that obtained 
in the other case, being also a compound of sugar and baryta, but differing from the 
latter in containing only half the quantity of baryta. The identity of the alizarine 
and rubiretine obtained by the action of alkalies, with those produced by the action 
of acids on rubian, is proved by the following analyses. 
0-2255 grm. crystallized alizarine obtained by means of caustic soda, lost on being 
heated in the water-bath, 0-0405 water =17‘96 per cent. 
0-1820 grm. of the dry substance, burnt with chromate of lead*, gave 0-4610 car- 
bonic acid and 0-0770 water. 
These numbers correspond in 100 parts to — 
Carbon 69*07 
Hydrogen 4*70 
Oxygen 26-23 
I. 0-2610 grm. rubiretine, prepared by means of caustic soda, and dried at 100° C., 
gave 0-6565 carbonic acid and 0-1250 water. 
* In order to avoid repetition, I may state that all the organic analyses given in this paper, in which the 
material used for combustion is not especially mentioned, were performed with chromate of lead. 
MDCCCLIII. L 
