232 CHEMISTRY. 



hydride of the air unites with the lime gradually, thus lib- 

 erating the chlorine. In using this salt for bleaching the 

 gas is liberated by some acid which is applied. The arti- 

 cle to be bleached is first soaked in a solution of the chlo- 

 ride, and then in a dilute sulphuric acid. Here you have 

 chloride of lime and sulphuric acid brought together, and 

 the result is that the acid takes the lime and releases the 

 chlorine. What does the released chlorine do ? Being set 

 free in immediate contact with the cloth, it acts at once 

 upon the coloring matter. The operation is not all done 

 at once; but as strong solutions are apt to injure the cloth, 

 the solutions are made weak, and the articles are moved 

 back and forth from one solution to the other several times. 

 White figures are sometimes made on colored cloth by this 

 bleaching process. The figures are first stamped upon the 

 cloth with a mixture of tartaric acid and gum-water, and 

 then the cloth is soaked in the solution of the chloride. 

 You see what the result is. The chloride is decomposed 

 by the acid, and therefore the chlorine whitens only where 

 the figures are stamped. This bleaching powder is very 

 valuable because we have the bleaching gas condensed in 

 it, a form convenient for transportation, which would not 

 be true of either chlorine gas or chlorine water. 



323. Composition of Chloride of Lime. The name which 

 is so universally given to this preparation is a very incor- 

 rect one. It is impossible to have a real chloride of lime, 

 for the chlorine can not be made to unite with an oxide of 

 a metal, but will unite only with the metal itself. If there- 

 fore this salt be a chloride, it must be chloride of calcium, 

 the metal of which lime is the oxide. But it has been 

 found that it is composed only in part of this chloride. It 

 is a mixture of chloride of calcium, calcium hydrate, and a 

 salt called hypochlorite of calcium. This latter salt is a 

 compound of calcium with hypochlorous acid, an acid com- 



