8i Mr, R. Phillips on Ultramarine. fJuLY, 



perceptible ; it might, therefore, be supposed that the colouring 

 matter is the sulphuret of some pecuhar metal. To try whether 

 the colour could, upon this supposition, be reproduced, I added 

 sulphuretted hydrogen both to the solution and the colourless resi- 

 duum, but no restoration of colour was effected by this or any other 

 mode which I could devise. The only remaining supposition with 

 respect to the metallic nature of this colour to which 1 shall allude, 

 is the possibility that it may be in the metallic state. This, however, 

 can hardly be the case, for if the colour be lost by oxidation^ 

 then when acetic acid produces the effect, hydrogen must be 

 evolved from the decomposition of water ; but this does not occur. 



Although it is possible, as M. Thenard has stated, that colour- 

 less bodies may, by combining, form a coloured compound, I 

 confess I rather incline to the opinion, that lapis lazuli owes its 

 colour to a peculiar non-metallic substance ; and I recommend 

 the subject as worthy of the attention of chemists. 



I shall now briefly state the methods of detecting various sub- 

 stances, which may possibly be employed for adulterating ultra- 

 marine. 



Although we may almost venture to pronounce ultramarine to 

 be genuine, which, in a few minutes, loses its colour when put 

 into an acid, leaving insoluble matter of a dirtv-white colour, and 

 affording a colourless solution, I shall nevertheless mention certain 

 bodies which it is probable may be mixed with ultramarine, and 

 the methods by which they may be detected. 



Blue Verditer. — If this carbonate of copper be mixed with 

 ultramarine, it may be ascertained by heating the suspected 

 colour on a piece of silver or platina foil in a spirit lamp. If 

 there be any verditer present, the mixture will become almost 

 immediately greenish, and eventually black. The degree of 

 alteration of colour will of course depend upon that of the adul- 

 teration. 



Genuine ultramarine loses its colour totally by being put into 

 an acid, no effervescence is excited, a deposit remains of dirty- 

 white colour, and a colourless solution is obtained which gives 

 only a slight and colourless precipitate with ammonia ; so that 

 verditer, or any other cupreous compound, may also be detected 

 by putting the colour into an acid. If a blue or green solution 

 be obtained, and if ammonia added to it in excess gives a deep- 

 blue solution, or if a drop of the acid solution leave a deposit of 

 copper upon iron, it follows that some preparation of copper was 

 present; and if the admixture of verditer be considerable, the 

 evolution of carbonic acid will be evident. 



Prussian Blue. — Genuine ultramarine suffers no change of 

 colour by being heated, but if it contain prussian blue, its colour 

 will be much darkened by heat ; if also the genuine colour be 

 boiled in a solution of potash, its intensity and brilhancy is 

 rather increased than diminished ; but if it contain any admix- 

 ture of Prussian blue, the colour will become browner, and the 



