266 ELEMENTARY GENERAL SCIENCE CHAP. 



this gas is actually the second constituent of the hydrochloric 

 acid gas, i.e., chlorine. In the case of the burning taper the 

 effect is due to the fact that the taper consists of two con- 

 stituents, viz., carbon and hydrogen, and that, whereas both 

 burn in air to form oxides, only one, the hydrogen, can combine 

 with the chlorine, forming hydrochloric acid gas (hence the 

 acidity of the water), while the carbon, being incapable of com- 

 bining with the chlorine, gets deposited as soot. In the case of 

 the burning phosphorus the white fumes consist of the compound 

 of phosphorus and chlorine, i.e., a chloride of phosphorus, and, 

 similarly, hydrochloric acid gas may be called hydrogen chloride, 

 and common salt sodium chloride. 



We have seen above that hydrogen can combine with chlorine ; 

 indeed, so great is their tendency to unite that a mixture of 

 hydrogen and chlorine explodes even if exposed to a bright 

 light as direct sunlight or burning magnesium and combines 

 gradually in diffused daylight, the mixture being seen to lose the 

 green colour imparted to it by the chlorine. If the combination 

 is effected in the eudiometer described on page 240, it is found 

 that 1 volume of hydrogen combines with 1 volume of chlorine 

 to form 2 volumes of hydrochloric acid gas, so that in this case 

 there is no contraction during the formation of the compound. 

 Also, if a concentrated solution of hydrochloric acid be decom- 

 posed by the electric current in the voltameter, equal volumes of 

 hydrogen and chlorine result, although at the commencement of 

 the experiment more hydrogen seems to be obtained, this being 

 due to the solution of the chlorine. 



Summary of Results. We may summarise our results thus : 

 Chlorine obtained from hydrochloric acid and manganese dioxide 

 is a very heavy, yellowish-green gas, with an irritating, choking 

 smell. It is soluble in water, the solution having an odour 

 similar to that of the gas. It possesses powerful bleaching 

 properties. Though it does not burn itself, it is capable of 

 supporting the combustion of many bodies, with the formation of 

 chlorides. Of these, sodium chloride is ordinary table salt, and 

 hydrogen chloride is hydrochloric acid gas, which consists of 

 equal volumes of hydrogen and chlorine united without con- 

 traction, this union occurring directly in daylight. The weight 

 of a litre of chlorine [which may be found by weighing a flask 

 full of (1) air or hydrogen, (2) chlorine, and allowing for the 

 weight of air or hydrogen in (1)] is about 3 '18 grams, so that it 



3 '15 grams, so tnat it 

 is about 35 '5 times as heavy as hydrogen. 





