CHLORINE AND IODINE. 



13 of lead, which exist in 20*75 of nitrate of 

 lead. As the iodide of zinc is neutral, there 

 must be present in it just an atom of zinc, which 

 weighs 4*25. Thus it appears that dry iodide of 

 zinc is composed*of 



Zinc 4-25 

 Iodine 15 '5 



19-75 



These experiments leave no doubt that the atom 

 of iodine weighs 15*5. This is the number which 

 Dr. Prout fixed upon, though from erroneous data. 



It is obvious also from these experiments, that 

 hydriodic acid is a compound of 1 atom iodine, 

 and 1 atom hydrogen. For when hydriodate of 

 zinc is heated sufficiently, it is converted into 

 iodide of zinc. It is evident that the oxide of 

 zinc by this treatment is deprived of its oxygen, 

 and the hydriodic acid of its hydrogen. These 

 two substances combine together, and fly off in 

 the state of water. Consequently, the atoms of 

 hydrogen in the acid must be just equal to the 

 number of atoms of oxygen in the oxide. But 

 oxide of zinc contains only one atom of oxygen ; 

 consequently hydriodic acid contains only one 

 atom of hydrogen. 



From the experiments of Gay-Lussac, which 

 I have often repeated, we learn that when hy- 

 driodic acid gas is left in contact with mercury, 

 the whole of its iodine is gradually absorbed, and 



