438 Dr, Thomas Thomson, on [Dec. 



the quantity of water disengaged . The precipitated chloride 

 of silver in the Wolfe's bottle being washed, dried and fused, 

 gave the quantity of chlorine driven off. Finally, the vo- 

 lume of gas extricated was determined. It was always oxy- 

 gen gas. 



The matter in the retort was washed out as far as possible 

 with water, and what the water would not dissolve was dis- 

 solved by nitric acid. The portion dissolved by the water 

 was found to be pure chloride of calcium. What was dis- 

 solved by the nitric acid was lime, silica, alumina, kc, for 

 the porcelain retort was always acted upon, and usually lost 

 from 12 to 13 grs. of its weight. 



The experiments made were numerous, because I wished 

 to try the nature of bleaching powders of different strengths 

 and of different ages. The following are the general results : 



1. The water from 200 grs. of the strongest bleaching 

 powder was 41*55 grs., or 20*77 per cent. When the 

 strength of the bleaching powder was inferior, the quantity 

 of water diminished. I tried some very weak powder, con- 

 taining more than half its lime uncombined ; the quantity 

 of water which it contained was only 13*35 per cent. 



2. When the bleaching powder was newly made, and of 

 the strongest quality, the oxygen disengaged bore a constant 

 ratio to the chlorine. This chlorine had partly escaped in 

 the form of gas, and continued partly united to calcium in 

 the residue in the retort. For every atom of chlorine con- 

 tained in the powder, a corresponding atom of oxygen was 

 disengaged. 



This result was verified by numerous repetitions. It 

 proves sufficiently that if the bleaching powder contains a 

 combination of oxygen and chlorine, it can only consist of 

 a combination of one atom of chlorine and one atom of 

 oxygen. The simplest explanation would be to consider 

 bleaching powder as a compound of one atom lime and one 

 atom chlorine. When heat is applied the chlorine displaces 

 the oxygen of the lime, and forms chloride of calcium. 

 But the researches of Balard demonstrate that there really 

 exists a compound of one atom chlorine and one atom oxy- 

 gen. It is clear, therefore, that bleaching powder is in 

 reality a mixture of chloride of calcium, and chlorite of 

 lime. 



