1820.] extracted from Pijrites at Fahhin. 17 



An experiment made with lime seems to prove the contrary 

 of that made with potassium. I passed in a suitable vessel a 

 current of seleniuretted hydrogen gas through a portion of hme 

 water, taking care to exclude the atmospheric air completely. 

 The liquid became at first muddy, and deposited a small quantity 

 of red powder. The clear liquid remained colourless, though a 

 great excess of seleniuretted hydrogen gas was passed through. 

 it. The first precipitate was merely seleniuret of lime, whose 

 hydrogen had been oxidized by the air contained in tlie lime 

 water. The colourless liquid left in a phial, which I considered 

 us hermetically sealed, began, after two days, to become red at 

 the surface without any precipitation, and the colour increased 

 till it spread over the whole liquid. This eftect being at an end, 

 a brownish pelhcle of seleniuret of lime began to form on the 

 liquid, and small crystals of the same substance swam against 

 the sides of the phial. After three weeks, the liquid had again 

 become colourless. The explanation of this phenomenon is 

 easy. The hydroseleniuret of lime in contact with the air is 

 decomposed; but the resulting seleniuret remained combined 

 ■with the undecoraposed part, constituti^^g a seleniat.ed hydrose- 

 leniuret. This combination having at last reached its point of 

 saturation, the decomposition of the hydroseleniuret occasioned 

 the precipitation of seleniuret of lime, partly in the form of a 

 pellicle, and partly in crystals. The colourless liquid from which 

 this last vv-as deposited contained still hme in solution. This 

 proves that seleniuretted hydrogen can neutralize a greater quan- 

 tity of base than selenium alone. The same is the case with 

 sulphur. 



The best method of producing the hydroseleniurets is to dis- 

 solve seleniuret of iron in muriatic acid, and to make the gas 

 pass into a Woulfe's apparatus, in which the gases are dissolved, 

 or mixed with water. Seleniuretted hydrogen gas is absorbed 

 much more rapidly and completely than sulphuretted hydrogen 

 gas, and we do not lose so much "of it as of this last. 



The hydroseleniurets are decomposed by the contact of air, 

 and the selenium is deposited pure from those which have an 

 alkali for a base. It is generally deposited at the surface in the 

 form of a pellicle, which, on the upper surface, is smooth, 

 metaUine, and of the colour of lead. The under surfiice has a 

 deeper grey colour, and a crystallized texture. If the decom- 

 position takes place slowly, without agitation, in a vessel which 

 has more depth than breadth, the selenmm is deposited in crystal- 

 line vegetations on the part of the glass turned towards the light. 



The danger with which I conf^idered experimenis with sele- 

 niuretted hydrogen gas to be attended prevented me from 

 obtaining the hydroseleniurets in a dry state. The only base 

 with which I have made an experimentis ammonia; but" it did 

 not succeed to the degree that I expected. Into a small glass 

 filled with mercury, I passed dry ammoniacal gas till the vessel 



Vol. XV. N° I. B 



