362 Memoir upon Ultra-marine. 



J 7th, The analysis of ultra-marine appears to us more dif- 

 ficult than that of a stone composed in an analogous manner, 

 although it is very attackable by the acids and alkalis. The 

 disunion of its principles is not complete until the most de- 

 cisive action of each of the reagents generally employed. 



The quality of the ultra-marine we employed (which we 

 could not regard as perfectly pure), and the variation which 

 we found in its constituent principles, determined us to study 

 their nature better than their quantities. We assigned a 

 distinct portion of ultra-marine to the investigation of each 

 of these principles, and, after uniting our results, we came 

 to the conclusion that 100 parts of ultra-marine are com- 

 posed of, 



Silex - - 35-8 



Alumine - - 34-8 



Soda - - 23-2 



Sulphur - - 3'1 



Carbonated lime - 3*1 



100-0 



We always experienced losses of about five per cent., and 

 sometimes more. 



The carbonated lime which we found is not essential to 

 the composition of ultra-marine, no more than the iron met 

 with in ultra-marine of the first quality, produced from lazu- 

 lite a little saturated with sulphurated lime. We do not 

 even always meet with sulphur in this substance. 



The following is the manner in which we recognised the 

 nature of the four substances, which to us appear to be es- 

 sential to ultra-marine: 



Thirty grammos (one ounce) of fine ultra-marine, heated 

 with sulphuric acid, left a residue weighing 14 - 0. The li- 

 quor evaporated presented some crystals of alum*, and plenty 

 of sulphate of soda in long needles. 



• It is probable that the alkali which had caused this sulphate of alumine 

 to crystallize was potash arising from the ultra-marine; we do not, however, 

 assert this as a fact, because we could not protect this salt from the ammo- 

 r.iacal vapours which might be in the laboratory. 



All 



