LITMUS. 923 



Azoerythrm consists of C 22 H 19 O 22 (Kane), by abandoning 4 

 atoms of carbonic acid and 9 atoms of water, it will yield an 

 equivalent of alpha-orcein. 



Erythroleic acid, C 26 H 22 O 8 (Kane), is a purple substance, 

 distinguished for its semi-fluid consistence at the ordinary tem- 

 perature, and its solubility in ether and alcohol. 



Roccellic acid, C 16 H 16 O 4 (Liebig), one of the principles ex- 

 tracted by Heeren. 



Litmus. The cubical masses of commercial litmus being 

 reduced to powder and treated with boiling water give a deep 

 blue solution. The mass of insoluble matter, which is of a paler 

 blue than the original substance, is diffused through water and 

 reddened with hydrochloric acid. The whole is then thrown 

 upon a filter, and the red insoluble substance which remains is 

 washed with water until all excess of hydrochloric acid is re- 

 moved and then carefully dried. The mass when completely 

 dry is boiled in successive portions of alcohol, until every thing 

 soluble in that liquid is taken up. The deep red alcoholic 

 liquors are then distilled in a water-bath to dryness, and the 

 resulting solid material digested in warm sulphuric ether until 

 the latter no longer becomes coloured. The ethereal solutions 

 thus obtained, yield on distillation in a water-bath a fine crim- 

 son oily material which is nearly fluid. When purified, this 

 matter forms erythrolein, C 26 H 22 O 4 . This compound is 

 completely liquid at 100; its solutions in alcohol and ether 

 are of a fine red colour, and it tinges water pink, without how- 

 ever dissolving in any very sensible proportion. 



The substance from which the erythrolein has been removed, 

 and which is distinguished by its solubility is erythrolitmin, 

 C 26 H 22 O 12 -f HO ; it is of a bright red colour, sparingly soluble 

 in water, which it colours red. It dissolves of a blue colour in 

 potash, and combines with ammonia. 



The brownish red mass which resisted the action of alcohol, 

 yields its colouring material but very sparingly to water also j 

 but it may be dissolved in a large quantity of boiling water, and 

 gives by evaporation a deep blood-red mass, consisting of pure 

 colouring material, which has been named azolitmin,C ls H. lo NO lo ; 

 it differs only from alphaorcein and betaorcein in the pro- 

 portion of oxygen it contains. 



Another substance occasionally but rarely present in litmus is 



