DISINFECTION BY CHLORINE 109 



air. Instead of burning sulphur, liquid sulphurous acid 

 may now be bought. It is sold compressed in tins, with a 

 small metal pipe that can be cut off with a knife, thus 

 allowing the gas to vaporize slowly. 



Disinfection by Chlorine. — According to Koch, very large 

 quantities of chlorine are required to be effective, as much 

 as 15 pounds of bleaching-powder being necessary for 1,000 

 cubic feet, while to liberate the chlorine from this we should 

 need either 22 pounds -of hydrochloric acid or 7 pounds 

 of sulphuric acid. The sprinkling or spraying of infected 

 rooms with germicidal solutions is more frequent abroad, 

 and is a more scientific method to employ than the libera- 

 tion of gases, as we are not dealing with an unknown virus 

 any longer in the case of most diseases, but with number- 

 less small organized vegetable structures, the death of all 

 of which can be assured if they are brought into contact 

 with the proper reagents. 



Apart from the low specific disinfectant value of such 

 gases, they must in practice become diluted to an uncertain 

 extent, which increases continually during the operation ; 

 the process of diffusion by which they penetrate to various 

 parts of the room under treatment gives a disinfectant 

 atmosphere of varying and uncertain composition ; and the 

 presence of any slight mechanical obstacle, such as a little 

 dust or flue, may be sufficient to protect organisms from 

 being disinfected. A disinfectant spray, on the other hand, 

 has a known initial strength, which continually increases 

 during drying ; it is brought directly in contact with the 

 organisms on the surface to be disinfected ; and when 

 applied by a suitable apparatus, such, for instance as the 

 Equifex sprayer, it is projected on to the surface with a 

 sufficient velocity to penetrate obstacles which would pro- 

 tect against the action of a gas or vapour. 



Disinfection by Heat. — Hot air does not kill all organisms 



