138 TEXTILE FABRICS. [ V. 



tincture is not precipitated by a tincture of acetate of lead, 

 but a solution of subacetate gives a large precipitate. Its 

 solution in ammonia, by exposure to the air, becomes purplish- 

 red. By continued boiling in "water it is converted into 

 picroerythrin. Heated on platinum foil, it fuses and burns 

 without residue ; heated in a glass tube, it yields first an oily, 

 then a crystalline sublimate of orcin. Erythric acid is the 

 basis, and, according to Schunck, the only basis of all the 

 coloring-matters of the lichens. Its composition is Cg^H^gOj^. 



Picroerythrin is a product of the decomposition of erythric 

 acid, and is the cause of the bitter taste of an extract of 

 lichens. A hot solution of the acid, evaporated, leaves a 

 brown glutinous mass, which becomes solid and crystalline, 

 has a bitter taste, and leaves white picroerythrin when ex- 

 tracted by cold water. Its composition is G^JI^O^q ; and it 

 is formed from the acid by its taking up the elements of 5 eq. 

 water. 



Extraction of Color from OrcJiil. — Chandois (Ch. Gaz. vii.) 

 exhausts the lichens by repeated washings with water, and 

 separates the coloring-matter from this liquid by means of 

 ammonia or alkali. 



N^ew Mode of Testing Indigo. — Reinsch's new process 

 (Jahrbuch fiir Pract. Pharm.) for testing the coloring power 

 of indigo is said to give accurate results, with greater facility 

 than the usual methods. It consists in the use of a standard 

 solution, made by triturating 1| gr. finely-powdered Bengal 

 indigo, of best quality, with 4 or 5 drops of very concentrated 

 fuming sulphuric acid, and when the mass has become uni- 

 formly brown, adding 15 gr. more of the same acid. The 

 rubbing is to be continued until the mixture turns green, when 

 another 15 gr. of acid is added, and the whole diluted with 

 150 gr. water. Two uniform cylinders having been previously 

 graduated into 20 equal divisions, one is to receive 15 gr. of 

 the above solution, or more if necessary, to give a light-blue 

 liquid by filling the glass with water. The other cylinder is 

 similarly filled, to determine whether the contents of the two 

 are alike in shade. This being so, one is emptied, and then, 



