SALT 267 



As when salt or other chloride is heated with sulphuric acid it 

 o;i\vs rise to hydrochloric acid, it follows that chlorine may be 

 obtained by heating a chloride with sulphuric acid and manganese 

 dioxide, and this also forms a convenient test for chlorides. 



Various Compounds of Chlorine. EXPT. 284. Pass 

 chlorine for some time through a boiling solution of caustic 

 potash. Allow the solution to crystallise, and examine the 

 crystals which first separate out. They will be found to con- 

 sist of potassium chlorate, which evolves oxygen when heated, 

 either alone or with a little manganese dioxide. 



We thus obtain potassium chlorate from chlorine and hot 

 potash, while some potassium chloride is also formed. The 

 chhu-'ifrx may be regarded as derived from an acid, which we 

 may call chloric acid, just as the chlorides are derived from 

 hydrochloric acid, and which differs from the latter acid . in 

 containing oxygen as well as hydrogen and chlorine. 



Of the chlorates, potassium chlorate is by far the most im- 

 portant, being largely employed in the manufacture of matches 

 and in pyrotechny. 



EXPT. 285. Pass chlorine through a cold solution of caustic 

 potash, and observe that you no longer obtain potassium 

 chlorate. 



In this case there results, as before, potassium chloride ; the 

 second product is, however, not potassium chlorate, but a com- 

 pound containing a smaller percentage of oxygen, and termed 

 potassium hypochlorite, which, by the action of acid, liberates 

 chlorine. By employing lime in place of caustic potash a some- 

 what similar mixture results, consisting of lime with a compound 

 of the chloride and hypochlorite. This also evolves chlorine 

 when acted upon by an acid, and is hence very largely employed 

 for bleaching, under the name of bleaching powder, which is 

 manufactured on the large scale by the method indicated above. 



CHIEF POINTS OF CHAPTER XVIII. 



Common Salt is a white soluble powder which forms crystals in 

 the form of small cubes, containing no w r ater of crystallisation. 

 When very strongly heated it melts. It imparts a golden -yellow 

 colour to the flame. When heated in a tube with strong sulphuric 

 acid, a gas with a powerful pungent odour and which forms fumes in 

 air is given off. This gas we provisionally called " salt gas." 



Properties of "Salt Gas." It neither burns nor supports com- 



