442 MR. SCHUNCK ON RUBIAN AND ITS PRODUCTS OF DECOxMPOSlTION. 
supernatant liquid becomes almost colourless. Ammonia changes the colour of a 
solution of rubian to blood-red ; the colour is not changed by boiling ; and by super- 
saturating the ammonia with acid either before or after boiling, no precipitate is 
formed. Lime and baryta water give dark red precipitates in a solution of rubian, 
which are soluble in pure water, forming dark red solutions. Magnesia turns the 
solution dark red; the solution contains magnesia. The carbonates of lime and 
baryta produce no perceptible effect on a solution of rubian ; they do not change its 
colour, nor do they take up any rubian. Hydrate of alumina, when placed in a solu- 
tion of rubian, acquires a brownish-yellow colour. If sufficient alumina be taken, the 
liquid is rendered almost colourless. Hydrated peroxide of iron acts in a similar 
manner. Oxide of copper also removes most of the rubian from its solution. Alkaline 
solutions of rubian do not reduce the oxides of silver and copper on the addition of 
salts of these oxides, but they reduce salts of gold to the metallic state. When heated 
on platinum foil, rubian melts, swells up very much, burns with a flame and gives a 
carbonaceous residue, which does not entirely disappear on being further heated, but 
leaves a quantity of ash. When heated gradually in a tube it begins to undergo de- 
composition, accompanied by loss of water at a temperature of about 130° C., and is 
converted into another substance, which I shall describe further on. When heated 
to a still higher degree in a tube or retort, it gives fumes of an orange colour, which 
condense on the colder parts of the vessel to a crystalline mass, consisting chiefly 
of alizarine. 
Rubian cannot be considered as a colouring matter in the ordinary sense of the 
word. It imparts hardly any colour to mordanted cloth, when an attempt is made 
to dye with it in the usual way, the alumina mordant only acquiring a slight orange, 
the iron mordant a light brown colour. 
Composition of Ruhian .- — In determining the composition of rubian, I found it 
necessary to take into consideration the fact of its leaving when burnt a considerable 
quantity of ash. This ash consists almost entirely of carbonate of lime. The amount 
of ash is not uniform in different specimens ; it is greatest when the rubian has been 
purified by means of sulphuric acid, but I have never been able to obtain it in a state 
in which it burns without any residue. Even after being precipitated with basic 
acetate of lead and again separated from the oxide of lead, rubian leaves some ash on 
being burnt, so that it appears as if the lime which it contains were an essential con- 
stituent, or at all events, that it follows it into the lead compound, from which it 
cannot be removed by means of water or alcohol. 
The following results were obtained on analysis : — 
I. 0*3880 grm. rubian, which had been purified by means of sulphuric acid, dried 
at 100° C., gave, when burnt with oxide of copper, 0*7210 carbonic acid and 0*1745 
water. 
II. 0*4780 grm. of the same preparation, burnt with oxide of copper, gave 0*8865 
carbonic acid and 0*2180 water. 
