of Lapis Lazuli, aiid on artificial Ultramarine. 249 



We cannot conclude this review more suitably than by a ver- 

 bal transcript of the following account from the BerlinerHand 

 und Spener'sche Zeitung, (10th April 1828,) No. St, and which 

 in substance seems to be from the distinguished inventor 

 himself. 



" Tubingen. — Prof. C. G. Gmelin, who for some time past 

 has been employed in the investigation of ultramarine, has 

 arrived at the conviction that sulphur is its colouring principle, 

 and particularly that there is no metal, properly so called, en- 

 tering into its composition. Gmelin had received some ultra- 

 marine from Paris eighteen months ago, but which, according 

 to the opinion of M. Seybold, the artist at Stuttgard, was 

 not of the best quality. In order, thei'efore, to obtain ultra- 

 marine of all kinds, and to determine by strict analysis what 

 proportions of its component parts are most favourable to the 

 production of its fiery colour, he addressed himself months 

 ago to Prof. Carpi at Rome. During a short residence he made 

 in Paris, in the spring of 1827, he expressed it as his opinion 

 to the chemists of that metropolis, especially to M. Gay- 

 Lussac, that ultramarine, with the investigation of which he 

 told them he was then engaged, m'ght be produced artifi- 

 cially. It is perhaps, therefore, his own fault if another (M. 

 Tunel of Paris, who wishes to keep his discovery a secret) has 

 anticipated him in this respect. The process by which, ac- 

 cording to M. G.'s inquiries, the production of ultramarine is 

 always successful, is the following : — Procure silica containing 

 water and alumina; calculate how much a given weight of 

 these earths will leave after being calcined. (By Gmelin's 

 investigations 100 parts of hydrous silica contained only 5Q, 

 and 100 parts of hydrous alumina only 32*4' parts of pure 

 earth.) Next, dissolve as much of the hydrous silica as can 

 be dissolved in caustic soda, and calculate the quantity of 

 earth used. Add now to 72 parts of this silica, (calcu- 

 lated as U'Q^ from water,) 70 parts of alumina (also calcu- 

 lated in a state free from water) ; add the latter to the sili- 

 cate of soda, and let it evaporate, stirring it all the time till 

 the residue presents a damp powder. (One may also take at 

 once 60 parts of dry caustic soda to 72 parts of alumina ob- 

 tained from alum, the latter being reduced to the dry state.) 

 This colourless mixture of silica, soda, and alumina, is the 

 foundation of the ultramarine, which is to receive its blue co- 

 lour. For this purpose, melt in an earthen crucible, well 

 closed, a mixture of two parts of sulphur and one part of an- 

 hydrous carbonate of scula, and when the mass is properly 

 incited, throw very small portions of the first mixture at once 

 into the middle of the crucible : as soon as the effervescence 

 K. S. \o\. 7. No. 10. April 1830. 2 K pro- 



