2.24 Dr. Sclnmck onRubian and its Products of Decomposition. 



whole of the rubian is converted, the liquid becoming colourless. 

 Caustic soda turns the colour of the solution from yellow to 

 blood-red, and on neutralizing the alkali with acid, a clear yel- 

 low solution is again obtained. By boiling the solution to 

 which the soda has been added, the colour changes from blood- 

 red to purple ; and on now supersaturating the alkali with acid, 

 a reddish yellow precipitate falls, while the 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 supersaturating 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 per- 

 ceptible 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 solution 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 decomposition, accompanied by loss of water at a tem- 

 perature 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 Rubian. — 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 



