ANNALS 



OF 



PHILOSOPHY. 



JUNE, 1820. 



Article I. 



On the Bleaching Powder, v.suallij called Oxymuriate of JLime. 

 By Thomas Thomson, M.D. F.R.S. 



IN a preceding number of the Amiah of Philosophy, vol. xiii. 

 p. 182, I stated very briefly the result of a set of experiments 

 which I had made on Mr. Tennant's bleaching powder. In these 

 experiments I employed nitrate of silver to determine the quan- 

 tity of chlorine contained in the soluble part of the salt ; but this 

 method is not capable of detecting the whole of the chlorine, at 

 least without precautions which 1 neglected. This was shown 

 in a satisfactory manner by M. Gay-Lussac in the observations 

 with which he favoured me on my mode of analysis (Ann. de 

 Chim. et de Phys. x. 425, and xi. 108). When nitrate of silver 

 is dropped into a solution of chloride of lime, the nitric acid 

 unites with the lime, while the chlorine and the silver are preci- 

 pitated in the state of chloride of silver. But the silver existed 

 in the nitrate in the state of an oxide, while in the chloride of 

 silver it is in the metallic state. What then has become of the 

 oxygen of the oxide of silver 1 If after dropping nitrate of silver 

 into the solution of chloride of lime till no farther precipitation 

 take place, we pour off the supernatant liquid, and decompose it 

 by the application of a moderate heat, o.xygen gas is disengaged, 

 and if the residual matter be dissolved in water acidulated with 

 nitric acid, we shall find that a portion of chloride of silver 

 remains behind. From this experiment, for which I am indebted 

 to''Gay-Lus.sac, it is obvious that nitrate of silver does not preci- 

 pitate all the chlorine. We see likewise the reason of this, and 

 Vol. XV. i\° VI. 2 C 



