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III. On Rubian and its Products of Decomposition. By Edward Schunck, F.R.S. 
Received April 19, — Read June 10, 1852. 
PART II. 
Action of Alkalies and Alkaline Earths on Rubian. 
In the first part of this paper I have described, in general terms, the effect produced 
on rubian by alkalies. It is only the fixed alkalies that are capable of effecting the 
decomposition of rubian. Ammonia produces no perceptible change in a watery 
solution of this substance, except that of altering its colour from yellow to blood- 
red. This blood-red colour remains unchanged even after long-continued boiling, 
and the solution still contains rubian, for on supersaturating the ammonia with acid, 
the solution again becomes yellow, and not the slightest precipitate is produced. The 
fixed alkalies, on the other hand, act very differently. On adding caustic soda to a 
solution of rubian, the colour of the solution first changes to blood-red. On boiling 
the liquid, however, its colour soon changes again from blood- red to purple. This 
alteration in colour indicates the formation of alizarine. If the boiling be continued, 
there is deposited, as the liquid becomes more concentrated, a dark purple powder, 
which consists mainly of a compound of alizarine and soda, and separates in conse- 
quence of its insolubility in caustic lye. After the liquid has been boiled for some 
time, then, provided the quantity of soda employed be sufficiently large, the rubian is 
entirely decomposed. On now adding sulphuric acid in excess, a quantity of orange- 
coloured flocks, exactly like those produced by the action of acids on rubian, is pre- 
cipitated, while the liquid becomes almost colourless. These flocks are separated 
by filtration and washed with cold water, until the sulphate of soda and sulphuric 
acid are entirely removed. They now consist mainly of four substances, viz. 
\st, Alizarine ; 2ndly, Rubiretine; Srdly, Verantine-, and 4thly, a substance which 
has not hitherto been observed, and to which I shall give the name of Rubiadine. 
In order to separate these substances from one another, I adopt almost the same 
method as that employed for the separation of the products of decomposition with 
acids. The mixture is first treated with boiling alcohol, which dissolves the greatest 
part, leaving undissolved however a considerable quantity of a dark brown fioccu- 
lent substance. This substance invariably accompanies the other products of the 
action. It is, however, as its properties and composition show, a secondary product 
of decomposition, the formation of which I shall explain presently. To the dark 
yellow alcoholic solution, after filtration from this flocculent substance, there is 
added acetate of alumina, which produces a dark red precipitate. This precipitate. 
