ROCELLA TINCTORIA. 137 



and nitric acid, above 277°. It is soluble in all proportions 

 in alcohol and water ; difficultly so in ether, its solution giving 

 an acid reaction. The alkaline earths throw it down of a 

 purplish color ; the acetates of lead, copper, zinc, and silver, 

 purplish-red. Sulphate of alumina does not throw it down, 

 but upon adding a little ammonia, a brilliant carmine-lake 

 is precipitated. The chlorides of tin do not precipitate it, 

 but impart a rich carmine tint to the liquid. Its formula 

 is C,JI,,0,,. 



AlJcanet. — Bolley gives (Schweizer Gewerbebl. 1847) a 

 method of preserving the tincture of alkanet, which is valua- 

 ble, since alkanet is a costly dye, and its tincture produces a 

 peculiar violet of the fastest character. The method consists 

 simply in the addition of a very little pure muriatic acid to the 

 tincture, a few drops being sufficient for large quantities. Its 

 action is supposed to be its neutralizing a little ammonia, 

 which is the cause of the tincture spoiling ; but it is more 

 probable that it combines with the substance from which the 

 ammonia is produced by decomposition. 



Rocella Tinctoria{Orcliil^ Cudbear). — Schunck's examination 

 of this lichen is described in Ann. d. Chem. u. Pharm. Ixi. 64, 

 &c. The cut lichen is boiled in water . for some time, in a 

 spacious vessel, and the yellowish-brown liquid strained. On 

 cooling, white flocks and crystals separate, and when filtered 

 off, washed and dried, are gray. Dissolved in boiling alcohol, 

 a slight-brownish residue remains, and the cooling solution 

 deposits a white crystalline substance, Heeren's erythrin, 

 Kane's erythrilin, and Schunck's erythric acid. It is the 

 most important constituent of the lichen, as it produces the 

 color for which the lichen is gathered. 1ft) lichen yields 

 about 50 grains. 



It is white, tasteless, soluble in alcohol and ether ; 1 pt. 

 dissolves in 240 pts. boiling water, but the greater part se- 

 parates on cooling ; it is also more soluble in boiling than in 

 cold alcohol ; its solution reddens litmus ; it is soluble in 

 caustic and carbonated alkalies, in lime and barytic water, 

 and is again precipitated by acids in a gelatinous form. It8 



m2 



