ACIDS AND ALKALIES 633 



infection. That which has been most commonly used is 

 sulphurous acid, applied either direct from burning of 

 sulphur (in which case it will also contain S0 3 if there is 

 sufficient moisture to hold the sulphur dioxide in solution) 

 or by the use of the liquefied gas. It produces a slow 

 superficial disinfection of a weak and uncertain character 

 even under laboratory conditions. Such experiments 

 avoid, however, to a far greater extent than is possible in 

 practice the difficulty of diffusion, and the unequal diffusion 

 of sulphurous acid in air and its small power of penetration 

 make it less efficient in practice. To obtain even the 

 poor efficiency which is its maximum possible it is neces- 

 sary for the air to be damp and the room most carefully 

 sealed, and in these conditions it is often more injurious 

 to the objects under treatment than to the bacteria against 

 which it is directed. One of the most efficient methods of 

 applying sulphurous acid disinfection is by means of the 

 Clayton apparatus. The gas is generated by burning 

 sulphur in a current of air at a high temperature, and 

 contains, in addition to S0 2 , traces of higher oxides of 

 sulphur. It is also a very efficient vermin-killer, destroying 

 rats, cockroaches, bugs, fleas, flies, etc. 



Alkalies and soaps. The degree of alkalinity of a solu- 

 tion affects, but does not by itself altogether determine, 

 its germicidal power, which is also dependent on the nature 

 of its metal. The hydrates of thallium, lithium, barium, 

 calcium, potassium, sodium, and ammonium have widely 

 different efficiencies, roughly in the order named. For 

 practical purposes only those of potassium, sodium, and 

 calcium need be considered. 1 They exhibit notably the 

 characteristic of all disinfectants in that they work much 

 more vigorously in hot than in cold solution. It is to the 

 hydrates or alkaline carbonates of potassium and sodium 



1 See Forrest and Hewlett, Journ. Roy. Army Med. Corps, February 

 1904. 



