Qi6 Dr. Schweigger-Seiilel ofi the Blue Colouring-matter 



was chiefly the sulphur it contained which, combined with the 

 iron, produced the colouring matter of the stone*. This view, 

 however, was refuted by Clement and Desormes, who proved 

 that the ultramarine contained sulphur, but no ironf; which 

 conclusion Avas confirmed by the experiments of R. Phillips, 

 on the methods of ascertaining the degree of purity of the 

 ultramarine^. Clement and Desormes at the same time men- 

 tioned a considerable proportion of soda in the ultramarine, 

 which also seemed to contain some potash §. These two che- 

 mists, however, express no opinion as to the cause of the blue 

 colour. Thenard, indeed, does not deny the possibility of a 

 coloured body being produced by the combination of colour- 

 1-ess bodies, but adds that the loss of 0*8 per cent, experienced 

 by MM, Clement and Desormes in their analysis, might 

 lead to the supposition that it was just the colouring substance 

 which had escaped them||. Phillips expresses the opinion 

 that the lazure-stone perhaps owes its colour to a peculiar 

 substance not metallic, and recommends this part of the sub- 

 ject to the attention of chemists % 



With this difference of views on the nature of the colouring- 

 matter in the lazure-stone, scarcely any result could be ex- 

 jiected from the experiments instituted for producing ultra- 

 marine artificially; indeed they were all unavailing. An in- 

 teresting accident, however, had led to a probable hope of the 

 result ultimately turning out advantageously. M., Tassaert, 



* Compare Scherer's Journal (1800), vol. iv. p. 659, and more at large 

 vol. V. p. 709 ; also Ann. de Chimie, xxxiv. p. 54, and Von Crcll's Chem. 

 Ann. 1801, p. 467: he notices the following snbstances as appearing acci- 

 dentally in various quantities in the lazure stone, — carbonate and sulphate 

 of lime, and at times even barytes. 



f Gehlen's Journ.fur Chcm. u. F/u/s. vol. i. p. 214 — 221, and A7m. de 

 Chim. March 1806, toni. Ivii. p. 317 — 364. Compare also Jouni. des Mines, 

 xvii. (No. 100) p. 322; and this (Schweigger's) Journal, vol. xiii. p. 489; 

 vol. xiv. p. 331, and vol. xli. p. 235. 



J Vol. xli. of this (Schvi'eigger's) Journal, p, 233— 241. Comp. also An- 

 nals of Philosophy, No. 51, 5uly 1823, p. 31. The methods of examination 

 are given here with mountain blue, prussian blue, indigo, smalt, and oxide 

 of cobalt, although we may venture (as Phillips says at p. 2.39) to declare 

 an ultramarine as genuine, which in a few minutes" (developing sulphurous 

 acid gas, especially on being heated)" loses its colour when an acid is poured 

 on it, leaves an insoluble dirty white residue, and forms a colourless so- 

 lution. 



§ They at least saw crystals of alum, like Guyton de Morveau. They 

 found no sulphurous acid gas, and even carbonate of lime does not always 

 appear; but always sulphur in connection with soda, alumina and silica, 

 which therefore must be considered as the essential components of the 

 ultramarine. 



II See his Traite de Chimie, V A. tom. ii. p. 208; and Schweigger's 

 Jiinrnal, vol. xli. p. 236. 



^ In this (Schweigger's) Journal, vol. xli. p. 239. 



super- 



