CHLORIDE OF LIME. 499 



plied so gradually as to prevent the heat, occasioned by the com- 

 bination, from rising above 62. When dried at 212, hydrate 

 of lime, I find, absorbs afterwards little or no chlorine; but 

 dried over sulphuric acid, without heat, it is, on the contrary, in 

 the most favourable condition for making chloride of lime. A 

 dry, white, purverulent compound is obtained, by exposing the 

 last hydrate to chlorine, which contains 41.2 or 41.4 chlorine, in 

 100 parts; but of this chlorine about 39 parts only are available 

 for bleaching, owing to 2 parts of that element going to the 

 formation of chloride of calcium and chlorate of lime. A slight 

 addition of moisture to hydrate of lime does not increase the 

 proportion of chlorine absorbed, and renders the compound less 

 stable. The above appears to be the maximum absorption of 

 chlorine by dry hydrate of lime, and is greater than it would be 

 advisable to attempt in the manufacture of bleaching powder, 

 owing to the occurrence of the partial decomposition adverted 

 to. Yet this proportion is considerably short of 1 eq. of chlo- 

 rine to 1 of hydrate of lime, which are 48-57 chlorine and 51.43 

 hydrate of lime, in 100 parts. The excess of lime appears to 

 be useful in adding to the stability of the compound. The 

 bleaching powder of commerce may ,contain, when newly pre- 

 pared, about 30 per cent of chlorine. As I have found it in 

 the shops of the apothecaries, the proportion of available chlo- 

 rine was more frequently below than above 10 per cent, so much 

 does it deteriorate by keeping. 



The same compound is obtained in solution by transmitting a 

 stream of chlorine gas through hydrate of lime suspended in 

 water. The lime then absorbs a full equivalent of chlorine, 

 and dissolves entirely. Ten parts of water take up the bleach- 

 ing combination from one part of dry chloride of lime, leaving 

 undissolved the hydrate of lime contained in excess. The solu- 

 tion has a strong alkaline reaction. It destroys most organic 

 matters containing hydrogen, including colouring matters. But 

 its bleaching action is not instantaneous, unless an acid be added 

 to it, which liberates the chlorine. Hence when Turkey-red 

 cloth, having a pattern printed upon it with tartaric acid thick- 

 ened by gum, is immersed for about one minute in this solution, 

 it comes out with the colour discharged where the acid was 

 present, but elsewhere uninjured. In this manner white figures 

 are produced upon a coloured ground. The solution of chloride 

 of lime also absorbs and destroy s contagious matters in the at- 

 mosphere, and is slowly decomposed by carbonic acid, with es- 



