DISINFECTANTS. 371 



Ozone, 8 , the allotropic form of oxygen, is much more 

 powerful in its action, and attempts to apply it as a disinfectant 

 have been made. The cost of its production by the silent 

 electrical discharge, and the fact that only about 2 % of the air 

 can be converted into ozone, render the success of these 

 attempts doubtful, especially as ozone would probably first 

 attack the oxidisable organic matter before the micro- 

 organisms. 



Hydrogen peroxide, H. 2 0. 2 , is an excellent disinfectant, and 

 though a powerful germicide has no influence upon enzymes, 

 e.g., those of digestion. 



When air is brought into contact with oil of turpentine in 

 the presence of water, hydrogen peroxide is formed. Advan- 

 tage is taken of this in the preparation of " Sanitas," a 

 preparation made from terpenes and possessing a characteristic 

 odour. 



Sulphur dioxide, SO. 2 . This gas, of well-known properties, 

 is a powerful disinfectant and deodoriser. It is poisonous and 

 very irritant when breathed, 5% in air producing fatal results. 



It dissolves in about -^ of its volume of water, yielding a 

 weak solution of the unstable sulphurous acid, H a SO 8 . 



It acts in presence of water as an acid, and therefore unites 

 with ammonia, amines, organic bases, &c. It decomposes 

 sulphuretted hydrogen or ammonium sulphide and reduces 

 many organic substances, generally producing colourless com- 

 pounds. Hence its use in bleaching wool, &c. 



By pressure it can be condensed to a liquid and is now 

 commercially obtainable in glass siphons (under a pressure of 

 about three atmospheres), each of which will yield about 

 500 litres of the gas. 



The usual plan of generating the gas is by burning sulphur 

 in air. The sulphur is either in the form of "candles," i.e., 

 cylinders provided with a wick, or a cheaper method is to use 

 roll sulphur placed in metal dishes and moistened, when every- 

 thing is ready, with the very inflammable and volatile carbon 

 disulphide ; the ready ignition of the sulphur can thus be 

 ensured. According to the Local Government Board's direc- 

 tion, l^lb. of sulphur should be used for an ordinary room ; 

 this probably would yield air containing about 2 % of SO 2 . 



BB 2 



