ULTRAMARINE. 137 



6t a roller, in warm water. This water becoming turbid 

 is thrown away, and fresh substituted, which is soon per- 

 (Jeived to acquire a fine blue tint. When this is suffici- 

 ently loaded with the colouring matter, it is put by to 

 settle, and more water is taken, which likewise assumes 

 a blue colour, but less intense than the former. This is 

 repeated, till the water acquires only a dirty grey hue. 

 From these waters a powder is deposited, which is so 

 much the more beautiful, in proportion as the lapis lazuli . 

 was more rich, and according to the order in which the 

 water affording it was employed. The gangue of the 

 ultramarine remains behind in the cement. 



We employed in our researches ultramarine of various The finest ul- 



qualities ; but that used in the experiments from which we tramarme em- 

 Ilia, . ■ . • » . . pioyed in this 



have deduced the approximate proportions of its consti- analysis. 



tuent principles was of the greatest beauty. Only two Only a or 3 per 



or three per cent, of this was obtained from a very fine 9^'^^' afforded 



lapis lazuli ; yet still it was not perfectly pure, though it 



was at least fifteen or twenty times as pure as the stone 



from which it was taken. 



The following are the results of our labours: 



1. The specific gravity of ultramarine is to that of 'Vcific gr^- 

 water as 2360 to 1000. '^'^^* 



2. This substance, as afforded by the preceding pro"- Action of fire 

 cess, contains oily or resinous matters decomposable by 



fire : their coal burns completely in contact with air : the 

 ultramarine grows red, and as it cools resumes its former 

 beautiful colour. In this operation it loses a little in 

 quality, and requires levigation to reduce it to the state 

 of finenesss and softness it at first possessed. 



3. With a more violent fire, perhaps of 1500° of the Fused Into a 

 centigrade thermometer [2532*^ Fahr.] the ultramarine black enamel 

 fuses into a black enamel, if the cement mixed with it 



have not been completely burnt away; but, if this have 

 been done, into a transparent and almost colourless glass. _ qj. colour- 

 In this fusion it loses twelve per cent, of its weight. less glass. 



4. Treated in the fire with borax, it readily gives a very \\rith borax- 

 transparent glass; and sulphur is evolved, with a little 

 carbonic acid, the quantity of which varies according to 



the quality of the ultramarine. 



5. Exposed to the action of the galvanic pile, the oxj- Volta's pile ; 

 VoL.XV.— Oct. 1806. T gensting 



