208 VETERINARY HYGIENE 



to the solution; this is important as an aqueous solution of this 

 poisonous salt has neither colour nor smell. 



BLEACHING POWDER (" Chloride of Lime," Chlorinated Lime, 

 Calx Chlorinata). The exact chemical composition of bleaching 

 powder, which is sold for disinfectant purposes as " chloride of 

 lime," is not known, beyond the fact that it consists of calcium 

 chloride and calcium hypochlorite. The common commercial 

 product oftens contains impurities, especially an excess of calcium 

 chloride. It is made by passing chlorine gas over slaked lime; 

 when the chlorine has been apparently taken up, excess of the lime 

 is added for safety before the bleaching powder is removed. It 

 occurs as a white or greyish powder with a distinctive unpleasant 

 smell. It is poorly soluble in water, but mixes with it to form 

 a cream. Bleaching powder possesses powerful oxidising and 

 deodorant properties, and owes its germicidal action to the libera- 

 tion of nascent chlorine gas and nascent oxygen. The utility of 

 bleaching powder therefore depends upon the amount of " available 

 chlorine " it contains, and this should not be less than 30 per cent. 

 This amount is specified as the minimum when the powder is used 

 as a disinfectant under the regulations of the Ministry of Agri- 

 culture. Bleaching powder is unstable, and is liable to decompose 

 with reduction in the amount of nascent chlorine; if kept in the 

 damp and exposed to light and air the decomposition is more rapid. 

 This explains the necessity of standardising its strength. It is 

 used either as a solution poured on to the substance to be disinfected 

 or by generating chlorine gas from it for aerial disinfection. Being 

 very destructive to organic matter, it is of the greatest value in 

 veterinary practice for the cleansing and disinfection of stable floors 

 and the like. It speedily dissolves sputum and other albuminous 

 material, and its use is therefore indicated on anthrax-infected bed- 

 ding and manure, and for disinfecting premises and equipment 

 following an outbreak of foot-and-mouth disease. Unfortunately 

 it cannot be used about dairies or in byres where milking is done 

 owing to its liability to taint the milk. A 10 per cent, mixture of 

 the powder with water may be depended upon to destroy anthrax 

 spores if the available chlorine is 30 per cent. It should be mixed 

 immediately before use, and this should be done by making the 

 powder into a thick cream with water and then diluting to the 

 desired strength. A 1 per cent, solution may be used to wash 

 clothes, and in this strength is germicidal, but it is doubtful if it 

 would destroy anthrax spores. Such a mixture may be used for 

 the disinfection of soiled rugs and bandages, and it possesses an 

 additional advantage in that it removes stains by its bleaching 



