256 ELEMENTARY GENERAL SCIENCE CHAP. 



using iron in place of copper. By this means we obtain a dark 

 gray solid, iron sulphide, another example of a large class of 

 compounds, which consist of a metal and sulphur united together, 

 and known as the metallic sulphides. 



EXPT. 268. Place a very small quantity of the iron sulphide 

 in a test-tube and add a little hydrochloric or sulphuric acid. 

 Note that it effervesces and that a gas is evolved. 



Sulphuretted Hydrogen. It has in this way been found that 

 by the action of acid upon some metallic sulphides we obtain a 

 gas with a peculiar odour, resembling that of rotten eggs. We 

 must now collect and examine this gas. 



EXPT. 269. Fit up a flask with cork, delivery tube, and 

 thistle funnel, as for the preparation of hydrogen, and in the 

 flask place some iron sulphide. Pour down the thistle funnel 

 some hydrochloric acid diluted with about twice its volume of 

 water (see that the thistle funnel dips below the liquid). 

 Collect the gas over water in the usual way. 



EXPT. 270. In a jar of the gas place a lighted taper. Note 

 the extinction of the taper and the combustion of the gas with 

 the smell of sulphur dioxide and also the formation of a pale 

 yellow deposit on the inside of the jar. 



EXPT. 271. Apply a light to the gas issuing from the de- 

 livery tube and over the flame hold a cooled vessel, e.g., a flask 

 of water. Observe that drops of liquid condense on the sides 

 of the flask and that a yellow deposit is also formed. By 

 collecting this on the end of a wire and burning it, satisfy 

 yourself that it is sulphur. 



The liquid may also be collected in the manner described in 

 Expt. 244, and as in that case it will be here again found that 

 its physical properties prove it to be water. 



Hence the gas contains hydrogen (since water produced from 

 it contains hydrogen, which could only have come from the gas, 

 not being present in the air) and also sulphur, as shown by the 

 formation of a sulphur deposit or of sulphur dioxide. It cannot 

 be proved to contain any other element, and we may hence call 

 it hydrogen sulphide, or, as it is generally termed, sulphuretted 

 hydrogen. When the gas burns in a plentiful supply of air, 

 sufficient oxygen is at hand to combine with both the hydrogen 

 and sulphur, and hence sulphur dioxide is produced by the 

 combustion ; but if there is an insufficient supply of oxygen, or 



