Scientific Intelligence — Geology. 183 



from hence 100 species, which are partly identical with the 300 

 species from Barbadoes. The islands Car Nicobar and Comarta are 

 especially remarkable in this respect, and on the latter exists a hill 

 300' high, throughout which the Polycystina-clay occurs. A light 

 meerschaum-like clay and shale (tripoli, polishing shale) found there 

 and at other places is composed nearly altogether of these bodies, 

 mixed with many Spongolithes. These clays are generally traversed 

 by lignitiferous deposits, and by syenitic gravels. — Quarterly Jour- 

 nal of the Geological Society y vol. vii., No. 28, p. 118. 



6. Mr J, B. Guimefs Process for the Manufacture of Arti- 

 ficial Ultramarine. — Previous to the year 1828, all the ultra- 

 marine in use was obtained from the Lapis Lazuli^ a rare mineral 

 procured from Siberia. A common ultramarine thus obtained, 

 is, at the present time, sold at seven guineas per ounce, and the 

 price of a genuine and very choice article, is upwards of twenty 

 guineas per ounce. From its great costliness, the use of this pig- 

 ment is confined entirely to the artist. Several analyses of ultra- 

 marine were undertaken with the view of finding out a method of 

 making it artificially. These analyses shewed it to be a compound 

 of silica, alumina, sulphur, soda ; but the supposed colouring prin- 

 ciple for some time evaded all attempts at its detection. At last, 

 M. Guimet of Lyons, in the year 1828, aided by these analyses, 

 and encouraged by the offer of a prize of 6000 francs from the 

 Sociite d' Encouragement of Paris to the person who should suc- 

 ceed in the manufacture of artificial ultramarine, hit on the happy 

 idea of giving up further search for the hidden colouring principle, 

 and confined his attention to the combination of the several colour- 

 less ingredients which chemical analysis pointed out as the consti- 

 tuents of natural ultramarine. The result was the discovery of 

 artificial ultramarine. M. Guimet kept his process a secret, selling 

 his ultramarine at 42s. per pound. Gmelin, Persoz, and Robiquet 

 afterwards discovered the process, and published the mode of prepar- 

 ing this pigment, since which time its manufacture has extended in 

 Germany and in France, and has latterly been introduced into this 

 country. 



Ultramarine appears to be a compound of silicate of alumina and 

 silicate of soda, with sulphuret of sodium, and the colour is sup- 

 posed to be due to the reaction of the last constituent upon the for- 

 mer two. It may be prepared, according to Gmelin, by rapidly 

 igniting a mixture of equal parts of silica, carbonate of soda, and 

 sulphur, first adding a sufficient quantity of a solution of soda to 

 dissolve the silica. The result is a bluish-green mass, which, by 

 ignition in contact with air, becomes blue. Ultramarine is now sold 

 as low as fifteenpence per pound. It is applied to various purposes 

 in the arts, such as paper-staining, the azurage, or blue tinting of 

 writing papers, starch, ground white lead, &c., and has recently 

 been applied to the printing of cotton goods. It has superseded 



