402 COMPOUNDS OF HYDROGEN. 



namely, the compounds of hydrogen with sulphur and 

 selenium, with nitrogen and phosphorus, and with carbon. 

 With sulphur, hydrogen forms at least two compounds, one of 

 which, sulphuretted hydrogen gas, is a reagent of frequent ap- 

 plication, and considerable importance. 



Preparation. Of those metals which dissolve in dilute sul- 

 phuric acid, with the displacement of hydrogen, the protosul- 

 phurets dissolve also in the same acid, but the hydrogen then 

 evolved carries off sulphur in combination, and appears as 

 sulphuretted hydrogen gas. The protosulphuret of iron, which 

 is commonly employed in this operation, is obtained by depriv- 

 ing yellow pyrites or bisulphuret of iron of a portion of its 

 sulphur by ignition in a covered crucible ; or formed directly by 

 exposing to a low red heat a mixture of 4 parts of coarse sulphur 

 and 7 of iron filings or borings in a covered stone-ware or cast 

 iron crucible. The sulphuret of iron, thus obtained, is broken 

 into lumps, and acted upon by diluted sulphuric acid in a gas- 

 bottle, exactly as zinc is treated in the preparation of hydrogen 

 gas (page 257). Sulphuretted hydrogen is evolved without the 

 application of heat, and should be collected over water at SO or 

 90 ; or if collected in a gasometer or gasholder, the latter may 

 be filled with brine, in which this gas is less soluble than in 

 pure water. Sulphuretted hydrogen obtained by this process, 

 generally contains free hydrogen, arising from an intermixture 

 of metallic iron with the sulphuret. The gas may also be 

 evolved from the action of hydrochloric acid upon the sulphuret 

 of iron, but as it is then impregnated with the vapour of the 

 acid, and may also, like every gas produced with effervescence, 

 carry over drops of fluid, it should always be transmitted 

 through water, before being applied to any purpose as pure gas. 

 The reaction by which sulphuretted hydrogen is usually evolved, 

 is expressed in the following equation : 



Fe S and H O, S O 3 = H S and Fe O, S O 3 . 



Sulphuretted hydrogen, without any admixture of free hydrogen, 

 is obtained by digesting in a flask, used as a retort, with a gentle 

 heat, sulphuret of antimony in fine powder with concentrated 

 hydrochloric acid, in the proportion of 1 ounce of the former to 

 4 ounce measures of the latter. The gas of this operation, after 

 being passed through water and dried, may be considered as 

 pure. It may be collected over mercury, but is gradually de- 



