172 HISTORICAL INTRODUCTION TO CHEMISTRY CHAP. 



posited and hydrogen liberated, without any change of 

 volume. Dalton writes : 



"From the experiments of Austin, Henry, etc., it has 

 been established, that sulphuretted hydrogen undergoes no 

 change of volume by electrification, but deposits sulphur. 

 I have repeated these experiments, and have not been able 

 to ascertain whether there was increase or diminution. The 

 residue of gas is pure hydrogen " (New System, II. 452). 



The gas therefore contains its own bulk of hydrogen. 

 The proportion of sulphur as well as of hydrogen can be 

 deduced from its behaviour when exploded. 



" When mixed with oxygen, in the ratio of 100 measures 

 to 50 of oxygen (which is the least effective quantity), it 

 explodes by an electric spark ; water is produced, sulphur 

 is deposited, and the gases disappear. If 150 or more 

 measures of oxygen are used, then after the explosion over 

 mercury, about 87 measures of sulphurous acid are found 

 in the tube, and 150 of oxygen disappear, or enter into 

 combination with both the elements of the gas " (New 



System, II. 452). 



' 



In the first case the hydrogen present in the gas is found 

 to require (like pure hydrogen) half its volume of oxygen for 

 combustion ; in the second case an additional volume of 

 oxygen is required to burn the sulphur, and rather less 

 than an equal volume of sulphurous anhydride is pro- 

 duced. The quantity of sulphur in the gas is therefore 

 about the same as in an equal volume of sulphurous 

 anhydride. 



Metallic sulphides. The fact that sulphur combines with 

 the metals was known from the earliest period of alchemy. 

 The compounds which result are similar in many respects 

 to the oxides ; they were described by Lavoisier and 

 his colleagues as SULPHURETS, but this name has now 

 been abandoned in favour of the name SULPHIDES. 



