Fleuiy.] 144 [Marcli20, 



the sulphide of silicium. Its bearings on the sciences of geology, 

 mineralogy ami metallui'gy are such as warrant me in giving you all 

 that is known of it ; it explains to us clearly, from whence our (juartz 

 comes and how the sulphurets of iron came to be embedded in the 

 same. 



Sulphide of silicium (Si S3) is a solid substance, white, infusible 

 and a little volatile, but it is easily carried along by a current of the 

 vapors of sulphide of carbon; at a very high temperature it sublimes 

 in the shape of silky needles. Nitric acid decomposes the sulphide of 

 silicium; in that case sulphuric acid is formed while silica remains in 

 solution in the nitric acid and the sulphur is left as a bulky preci- 

 pitate. 



Water decomposes the sulphide of silicium, sulphuretted hydrogen is 

 disengaged, while the remaining silica dissolves completely 

 IN the liquid. (Si S3-|-3 H0=3 HS-(-Si 03.) This silicious water 

 shows sometimes a remarkable stability, it can he preserved for months 

 without, forming a precipitate of silica, but when concentrated, the solu- 

 tion becomes gelatinous ; the same takes place when brought to the 

 boilino- jDoint, or when soluble alkaline salts are introduced Into the 

 liquid. When the silicious solution is completely evaporated in 

 vacuum, it leaves a transparent glass-like residuum of hydrated silica, 

 which is insoluble in water. This hydrate contains 16.7 per cent, of 

 water ; it consequently corresponds with the formula (Si 03-|-3 HO,) 

 andean part with about one half of its water ; it then contains nine^jer 

 cent., and its formula is represented by Si 03-|-2 HO which allies it 

 to certain opals. The sulphide of silicium presents the very curious 

 property of decomposing at the ordinary temperature under the influence 

 of a humid atmospihere and forming under this circumstance sulphur- 

 etted hydrogen and anhydrous silica in crystals. The silica that is 

 thus obtained is insoluble in water, hut soluble in the solutions of 

 potassa ; consequently it is not of the same nature as quartz. It can 

 be seen from this that the sulphide of silicium in its contact with 

 water, can produce phenomena which greatly add to our interest in 

 the natural history of rocks. 



Therefore, admitting the presence of large deposits of sulphide of 

 silicium in the interior of the earth, which are decomposed by 

 water, it is easy for us to explain all the phenomena of petrification, 

 and the silicious incrustations which we observe deposited on or- 

 ganic and inorganic matter in certain localities. By this decompo- 

 sition we can also explain the formation of silicious waters and such 

 sulphurous springs as contain silica in solution. It has been demon- 

 strated that the Geyser springs of Iceland, which are very rich in 

 silica, contain a considerable quantity of sulphuretted hydrogen ; they 

 contain therefore the two elements, resulting from the decomposition 



