404 MR. SCHUNCK ON RUBIAN AND ITS PRODUCTS OF DECOMPOSITION. 
of decomposition to which it gives rise may therefore be explained in the satne manner 
as in the case of riibian. 
Of its products of decomposition with acids I oidy obtained alizarine in quantities 
and of the degree of purity requisite for analysis. It had the usual composition of 
that substance, as the following analysis will show : — 
0’2500 grm. of the crystallized substance lost, on being heated in the water-bath, 
0*0460 water =18*40 per cent. 
0*2800 grin, of the dry substance gave 0*7110 carbonic acid and 0*1030 water, 
corresponding in 100 parts to — 
Carbon 69*25 
Hydrogen .... 4*08 
Oxygen 26*67 
Rubihijdran . — This substance, like rubidehydrau, bears a great resemblance to 
lubian, the body from which it is derived. It is obtained on evaporation of its solu- 
tions as an uncrystalline, transparent mass like gum, having a dark brownish-yellow 
colour and a bitter taste. When quite dry it is brittle and may be easily pulverized, 
but on exposure to tlie atmosphere at the ordinary temperature it rapidly attracts 
moisture and becomes soft, a property by which it may be distinguished from rubian 
and rubidehydran. On being heated in a tube it gives less crystalline sublimate than 
rubian does. Its watery solution, on being boiled with the addition of sulphuric or 
muriatic acid, becomes muddy, and slowly deposits a quantity of yellow flocks mixed 
with some brown resinous drops. The liquid must be boiled for a considerable time 
in order to effect the entire decomposition of the rubihydran contained in it and make 
it appear colourless. The flocks on being collected on a filter are found to consist 
chiefly of rubiretine, verantine, and rubiadine, with only a very small quantity of 
alizarine, while the filtered liquid contains sugar. The products of decomposition 
with acids are therefore the same as those of rubidehydran, the only difference being 
in the relative proportions of the products formed. It is not decomposed; when 
treated with boiling phosphoric, oxalic, tartaric or acetic acids. If a watery solution 
of rubihydran be boiled with caustic potash or soda, the colour of the solution, which 
was red on the first addition of alkali, changes to reddish- or yellowish-brown, but 
only a few purple flocks are deposited. This circumstance also serves to distinguish 
this substance from rubian and rubidehydran, the watery solutions of which, when 
mixed with caustic alkali and boiled, deposit an abundance of the purple compound 
of alizarine and alkali. Nevertheless the rubihydran is completely decomposed by 
the caustic alkali, for on adding an excess of acid to the liquid a quantity of yellow 
or light brown flocks are precipitated like those produced by the action of acids, 
while the liquid becomes almost colourless. When chlorine gas is passed through 
the watery solution, it produces exactly the same effects as in watery solutions of 
rubian or rubidehydran. It is the behaviour to chlorine, which more than any other 
