1823.] Mr, R, Phillips on UUrammine, 33 



Pon considere que toutes les autres pierres doivent leur couleiir 

 a. une matiere colorante. On pourrait soutenir, a la verite, 

 que la silice, J'alumine, la chaux, la soude, quoiqu' incolores, 

 sont susceptibles de former uii compose colore ; mais il faut 

 avouer qu'il serait fort extraordinaire qu*il n'y eut qu'un compose 

 de ce genre parmi ces pierres ; et cependant c'est a cette conse- 

 quence qu'on serait conduit en admettant qu'il n'existe point de 

 principe colorant particulier dans le lazulite : aussi M. Vauquelin 

 croit-il que cette pierre contient de Toxide de fer." 



Although in the 34th vol. of the Annales de Chimie, Guy ton also 

 attributes the colour of ultramarine to iron, I need hardly again 

 state, that ultramarine contains no oxide of iron, and, therefore, 

 the opinion of the last-mentioned chemists, although meriting the 

 highest attention, cannot be considered as well founded. Indeed 

 the lapis lazuU examined by Klaproth contained only 3 percent, of 

 oxide of iron, and this, supposing it capable of affording a blue 

 colour, could hardly be admitted to yield the intense blue of the 

 lapis la:zuli. 



When any coloured earthy substance occurs, the first and 

 most natural supposition is, that the colour is owing to the pre- 

 sence of a metallic oxide. There is however great difficulty in 

 admitting this colouring matter to be a metallic oxide; for 

 when it is destroyed by an acid, we may suppose one of several 

 cases to happen, first, that the loss of colour is the result of 

 the mere act of solution, as when we obtain a colourless solution 

 by dissolving peroxide of mercury in nitric or muriatic acid : 

 this, however, can hardly be the case with the colouring matter 

 of ultramarine ; for we do not by the addition of potash repro- 

 duce a blue substance ; whereas from pernitrate of mercury, 

 the oxide is precipitated possessing its original colour. 



It raay be supposed that the solution of ultramarine in acid is 

 attended with the evolution of oxygen, and consequent loss of 

 colour ; but in this case one of three things would happen ; 

 first, that oxygen would be evolved in the state of gas, as when 

 peroxide of manganese is heated in sulphuric acid ; secondly, 

 that carbonic acid would be formed and evolved with efferves- 

 cence, as when peroxide of manganese is decomposed and dis- 

 solved by binoxalate of potash ; or, thirdly, that when put into 

 muriatic acid, chlorine would be evolved ; the fact, however, is, 

 that no one of these circumstances occurs. 



On the other hand, it is possible that the peculiar colouring 

 matter of the ultramarine may acquire oxygen during solution, 

 and thus lose its usual appearance ; to this, however, there is 

 one experiment in direct opposition ; viz. that sulphurous acid 

 which readily absorbs oxygen, but does not impart it, destroys 

 the colour of ultramarine as completely as nitric acid, which might 

 be supposed to oxidize it. 



When nitric acid is added to ultramarine, the colour is 

 quickly destroyed, and a slight smell of sulphuretted hydrogen is 



AVa? Series f v o l . v i . d 



