3 CO Memoir upon Ultra-mar inc. 



this mixture is well made it is allowed to cool, and then 

 bruised, or ground with a pestle or roller in warm water. 

 This water soon gets dirty; it is then thrown away and new 

 water made use of, which soon assumes a verv fine blue co- 

 lour: when it is sufficiently saturated it is allowed to stand 

 "some time, and then several other washings are taken from 

 the lapis lazuli, until the last water is no longer of a blue 

 colour. These washings afterwards deposit a hluc powder, 

 beautiful in proportion to the richness of the lazuli. The 

 matrix of the ultra-marine remains blended with the 

 mastic. 



In our researches we. employed ultra-marine of various 

 qualities ; but that which was the foundation of our estimate 

 of the proportions of its constituent parts, was the most beau- 

 tiful we could procure; we only got it at the rate of two or 

 three per cent, from a beautiful lazuli : nevertheless it was by 

 no means completely pure, but it was at least fifteen or twenty 

 times more so than the lazuli from which it was procured. 



The following are the results of our labours : 



1st, The specific gravity of ultra-marine is to that of wa- 

 ter : : 2360 : 1000. 



2d, This substance, such as the process yields, contains 

 oily or resinous matters, which are decomposed by fire ; 

 their charcoal is completely burnt by the contact of the 

 air; the ultra-marine becomes red, and upon cooling re- 

 sumes its former fine colour: in this operation it. loses a 

 little of its quality, and it is only by means of attrition 

 that it is brought back to this state of fineness and softness 

 which it had at first. 



3d, In a more violent heat, which may be to 1500 

 decrees of the centigrade thermometer, the ultra-marine 

 melts into a blajk enamel, if the mastic which is mixed 

 with it is not completely burnt; and it melts into transpa- 

 rent glass, almost colourless, if the mastic is completely 

 burnt. In this fusion it loses 1 2 per cent, of its weight. 



4th, Treated in the lire with borax, it easily gives a very 

 transparent glass; sulphur is liberated, and a little carbonic 

 acid, the quantity of which varies according to the quality 

 of the ultra-marine. 



5 th, E»- 



