MISCELLANEOUS 213 



Bleaching Powder, or " chloride of lime," Ca(OC])Cl. This 

 substance may act in two ways : 



1. By evolving hypochlorousacid, HCIO, which is a powerful 

 oxidising agent and readily destroys putrescible matter and 

 bacteria. The liberation of hypochlorous acid is eflfected by 

 the carbon dioxide of the air : 



2Ca(0Cl)Cl + CO, + H,0 = 2HC10 + CaCl, + CaCO,. 



2. By evolving chlorine, which is a powerful disinfectant. 

 The evolution of chlorine occurs when bleaching powder is 

 acted upon by any acid — e.g., dilute sulphuric acid : 



0a(0Cl)Cl + H3SO, = CaSO, + 11,0 + CI 



If a building is to be disinfected by means of chlorine about 

 2 lb. of bleaching powder for each 1000 cubic feet of space should 

 be placed in an earthenware bowl or vessel, and then a pre- 

 viously cooled mixture of 1 J lb. of oil of vitriol and a gallon 

 of water poured upon it, and the windows and doors closed as 

 quickly as possible. This will yield gas enough to form nearly 

 0"5 per cent, of the atmosphere in the room, and this is suffi- 

 cient to kill micro-organisms, though possibly some spores may 

 escape destruction. 



Sulphur Dioxide, SO,, is a much-used disinfectant. It gives 

 rise to the well-known smell of burning sulphur, and is soluble 

 in water, forming a solution of sulphurous acid, H^SOg. It is 

 a strong reducing agent, and acts upon many organic sub- 

 stances, producing colourless compounds, and is therefore 

 often used for bleaching wool, straw, (fee. By strong pressure 

 it can be liquefied, and liquid sulphur dioxide, under a 

 pressure of three or four atmo-^phsres, is now commercially ob- 

 tainable in glass siphons or in metal cylinders. In this form 

 it can very conveniently be used for disinfecting purposes, 

 but the gas is usually made by burning sulphur in air. The 

 sulphur should be either in the form of " candles " — i.e., short 

 cylindrical cakes provided with a wick — or roll sulphur, which 

 can be readily set on fire if placed in metal dishes just pre- 



