264 



ELEMENTARY GENERAL SCIENCE 



CHAP. 



oxide, forming the water, while the copper with the other part of 

 the " salt gas " formed the green substance. 



FIG. 132. Composition of Hydrochloric Acid Gas. 



EXPT. 282. To further investigate this acid gas collect a 

 tube full over mercury, and quickly introduce into it a piece 

 of clean sodium. Allow it to stand, and observe that the . 

 volume of the gas becomes ultimately reduced to one-half the 

 original volume (correction being made for the difference in 

 pressure), while further, the sodium gets covered with a white 

 powder which you may satisfy yourself is salt. 



Test the gas left with a lighted taper and see that it has the 

 properties of hydrogen. 



We have thus found that from hydrochloric acid gas, 

 sodium abstracts something and leaves one-half the original 

 volume of hydrogen. Hence, also, salt consists of sodium with 

 something and this same material with hydrogen forms hydro- 

 chloric acid gas. The name given to this material is Chlorine, 

 and we shall now endeavour to obtain this element from the 

 hydrochloric acid gas. 



Preparation and Properties of Chlorine. EXPT. 283. 

 In a fairly large flask (Fig. 133) put some manganese dioxide 

 (a black powder which also occurs naturally in compact masses 

 known as pyrolusite). Through the thistle funnel pour in suf- 

 ficient hydrochloric acid (i.e. the strong acid used in the 



