534 M. E. Breunliii on the Constitution of 



valents of silicate to 1 equivalent of pentasulpliide of sodium, 

 and that in green 1 equivalent of silicate to 1 equivalent of 

 bisulphide of sodium. I will endeavour in what follows to de- 

 velope the probability of this constitution. 



Metallic Sulphide. — In the ultramarine analysed, I found for 

 the quantity of sulphur liberated as sulphuretted hydrogen in 

 the decomposition by hydrochloric acid S«, for the quantity pre- 

 cipitated as milk of sulphur S6, the following numbers : — 



I. II. III. IV. V. 



Tj, „ . rS« 1-9 2-2 1-3 1-4. 2-2 



Blue ultramarme^g^ 7-1 8-4 4-8 58 8-6 



which is almost in the proportion of 1 to 4. 



VI. VII. 



S« . 3-6 3-9 



{^ 



Green ultramarine ^ ^i o.^ ^.7 



No. VI. was pure green. In it Sa : S6 as 1 : 1. No. VII. 

 was bluish-green. 



The sulphur is united with sodium. The quantity of sodium 

 coiTCspouding to S« was calculated (the weight of soda corre- 

 sponding to this quantity of sodium was calculated and sub- 

 tracted from the amount of soda found by the analysis) . 



Na S« is the monosulphide of sodium. Na + Sa + S6 is the 

 polysulphide of sodium, which in green ultramarine is Na S^, 

 and in blue Na S^. All the properties of blue and of green 

 ultramarine, as well as their formation, justify this mode of the 

 arrangement of the sulphur. 



The sulphuric acid found in the solution after decomposition 

 of ultramarine by hydrochloric acid, is not forn.cd, as was above 

 shown, by the decomposition of a hyposulphite. It is united 

 with lime, and rather hinders the formation of the colour than 

 otherwise. 



That the sulphur in the form of a hyposulphite cannot contri- 

 bute to the constitution of the colour, is evident from the fact, 

 that, at the temperatui-e at which ultramarine is formed, a hy- 

 posulphite could not exist, but would be resolved into sulphur 

 and a sulphate. Lastly, Ijesides the oxygen in the silica, the 

 alumina, the oxide of iron, and the soda, there is no more pre- 

 sent in ultramarine. The agreement of the analyses shows this. 

 The sulphur can only contribute to the formation of the blue or 

 green colour in the form of polysulphide of sodium. 



On bringing hydrochloric acid in contact with ultramarine, 

 one of its chief constituents, the polysulphide of sodium, is de- 

 composed, sulphuretted hydrogen is evolved, and sulphur preci- 

 pitates. On the addition of excess of concentrated acid, persul- 



