L. TECHNOLOGY. 429 



foreign substances it retains. On redissolving these crystals, 

 and removing all traces of aniline by means of alcohol, indi- 

 gotine of the utmost purity will be obtained. The aniline 

 here used is an organic basis produced by the decomposition 

 of indigo by heat, or, better, by the simultaneous action of 

 hydrate of potash and heat. 14 (7, CC, i., 72. 



IMPROVED TREATMENT OF INDIGO FOR DYEING. 



Mr. J. de Werveirne, of Ghent, employs a composition for 

 dyeing with indigo which, he says, essentially expedites the 

 operation, can be used cold, and yields a greater amount of 

 dye from the same quantity of indigo. This is prepared as 

 follows : To each pound of indigo are to be added one pound 

 of amorphous zinc powder, one pound of madder, 750 grains 

 of protochloride of tin, and one pound of slacked lime ; the 

 resulting mass then to be completely dissolved in 112 gallons 

 of cold water. 13 (7, 1871, vl, 403. 



COMPOSITION OF ULTRAMARINE. 



Some discussion has arisen as to whether ultramarine is, on 

 the whole, a chemical combination, and if so, in what condi- 

 tion of combination its sulphur exists. This problem has at- 

 tracted the attention of many authors, and among others that 

 of Professor Stein, who has lately published a memoir on the 

 subject in Dingler's Polytechnic Journal. In this he states 

 that a majority of authors look upon the sulphur combined 

 with soda in ultramarine as mono-, di-, or penta-sulphuret. 

 A few persons, among them himself at an earlier period, be- 

 lieved in the existence of hyposulphuric acids, together with 

 the sulphide of sodium, and still fewer thought it probable 

 that the sulphur was combined with aluminium. As the re- 

 sult of his more recent observations, Dr. Stein has come to 

 the conclusion that in blue ultramarine the acid is sulphuric 

 and not hyposulphuric, and that sulphide of aluminium alone 

 exists, without any sulphuret of sodium. The sulphide of 

 aluminium may exist in two modifications, one of which is an 

 amorphous black powder, and the other is a connected color- 

 less or yellowish mass of crystalline character. The former 

 occurs at a low temperature, and can be readily transformed 

 into the second modification by heating to the melting point. 



The blue color of ultramarine, according to Dr. Stein, which, 



