Green and Blue Lltramarine. I 533 



sulphur and 16-91 sodium, which gave 7*084' sodium and 10"337 

 sulphur, or 17"421 monosulphide of sodium. This arrangement 

 of the sulphur, sodium, and oxygen has, according to Briinner's 

 results, some probability, but the 11 '306 per cent, sulphuric acid 

 can scarcely have been found. Besides, Briinuer does not seem 

 to have noticed, that in the decomposition of ultramarine by 

 hydrochloric acid sulphur is eliminated, which proves the pre- 

 sence either of a polysulphidc or of a hyposulphite of a metal ; 

 while on the supposition of monosulphide of sodium no sulphur 

 should precipitate, but should all be evolved as sulphuretted 

 hydrogen. 



Eisner and Rammelsberg found that the quantity of sulphur 

 was far more than sufficient to combine with the iron, and that 

 it must be present as sulphide of sodium. 



From the comportment of ultramarine with strong acids, 

 Gmelin considers that the sulphur is partially present as hypo- 

 sulphurous acid ; for this acid decomposes with a stronger acid 

 into sulphur and sulphurous acid, and the sulphurous acid coming 

 in contact with sulphuretted hydrogen evolved at the same time, 

 is decomposed into sulphuric acid, sulphui', and water. 



It might also be assumed that ultramarine contained a sul- 

 phide along with sulphate, but it is not then conceivable how a 

 sulphate as such should contribute to the colour, nor why the 

 blue compound should not also be formed under exclusion of 

 the air. 



I have considered it right to adduce these theories of the 

 coloui-ing principle of i;ltramarine, and I will now explain my 

 own, which I have formed from the results of my analyses. 



If we glance at the constituents of ultramarine, we see that 

 the chief quantities are silica, alumina, soda, and sulphur ; oxide 

 of iron, clay, sulphuric acid, and lime, are present in far smaller 

 quantities. I hold thein to be impurities, and in establishing a 

 formula do not consider them. 



The relation of ultramarine to oxidizing and deoxidizing agents, 

 the products formed from its decomposition by hydrochloric acid, 

 is a qualitative, and the results of the various analyses are quan- 

 titative indications, that in ultramarine, as Eisner has proved, the 

 colouring principle is a metallic sulphide united with a silicate. 

 The metallic sulphide in the blue is a higher one than in the 

 green ultramarine. 



I found that blue ulti'amarine contained pentasidphide and 

 green bisulphide of sodium, and that these were united witli a 

 silicate of constant composition, which has th(! greatest similarity 

 to that of a natural silicate, nejdiclinc. It consists of 



(2NaO) SiO'* + 3(AP O'-* SiO«). 

 The colouring compound in blue ultramarine contains 2 equi- 



