Dr. Stenhouse on Artificial Ultramarine. 4Sr 



The tannin of Divi-divi appears therefore essentially diflferont from 

 that of nut galls. 



Mr. Ilarvoj informs mo, that, a few^ years ago, some calico printers 

 endeavoured to employ Divi-divi as a substitute for galls, but the large 

 quantity of mucilage it contained rendered it unfit for this purpose. 

 It is at present employed pretty extensively in the tanning of leather, 

 as the presence of mucilage is not injurious to that process. The 

 price for which Divi-divi sells is about £20 per ton. 



XVL — On Artificial Ultramarine. By John Stenhouse, Ph.D. 



Till within the last twelve or fifteen years the only source of this 

 beautiful pigment was the rare mineral, lapis lazuli. The price of tho 

 finest Ultramarine was then so high as five guineas tho ounce. Since 

 the mode of making it artificially has been discovered, however, its 

 price has fallen to a few shillings the ounce. Artificial Ultramarine 

 is now manufactured to a very considerable extent on the continent, 

 but as far as I can learn, none has as yet been made in Great Britain. 

 The chief French manufactories of Ultramarine are situated in Paris; 

 and the two largest ones in Germany are those of Meissen in Saxony, 

 and of Nuremberg in Franconia. Three kinds of Ultramarine occur 

 in commerce, the blue, the green, and the yellow. The two first only 

 are true Ultramarines, that is, sulphur compounds ; the yellow is merely 

 chromato of baryta. 



Both native and artificial Ultramarine have been examined very 

 carefully by several eminent chemists, who, however, have been unable 

 to throw much light upon their true nature. Chemists have undoubt- 

 edly ascertained that Ultramarine always consists of silica, alumina, 

 soda, sulphur, and a little oxide of iron, but no two specimens, either 

 of the native or artificial Ultramarine, contain these ingredients in at 

 all similar proportions. In fact the discrepances between tlie analyses 

 are so great as to render it impossible to deduce from them any for- 

 mula for the constitution of Ultramarine; if indeed it does possess any 

 definite composition. The following are a few specimens of these 

 analyses, and others equally discordant might easily be added. 



Lapii LaxuU. By Clement amo Desobmbs. Lapit Laruli. By VARRERraAP. 



Soda, 23.2 .. . 9.09 



Alumina, 24.8 .. . 31.67 



Silica, 35.8 .. . 45.50 



Sulphur 3.1 .. . 0.95 



Carbonate of Lime, . . . 3.1 . . . 3.52 Lime. 



U.86 Iron. 



0.42 Chlorine. 



5.89 Sulphuric Acid. 



0.12 Water. 



