DISINFECTION 327 



of vapour it is termed saturated steam. But if it is at that 

 same pressure further heated, it becomes practically a gas, 

 and is called superheated steam. The former can condense 

 without cooling; the latter cannot so condense at the same 

 pressure. Saturated steam condenses immediately it meets 

 the object to be disinfected, and gives out its latent heat ; 

 superheated steam acts by conduction, and not uniformly 

 throughout the object. Its advantage is that it dries moist- 

 ened objects. As a disinfecting power, superheated steam 

 is much less than saturated steam. There is one further 

 term which must be defined, namely, current steam. This 

 is steam escaping from a disinfector as fast as it is admitted, 

 and may be at atmospheric or higher temperatures. The 

 disinfecting temperature which is now used as a standard is 

 an exposure to saturated steam of nf C. for fifteen minutes. 

 A number of different kinds of apparatus have been in- 

 vented to facilitate disinfection to this standard on a large 

 scale. Most sanitary authorities of importance are now 

 supplied with some form of steam disinfector, though many 

 are unable to go to the expense of high-pressure disinfectors. 

 Professor Delepine has pointed out ' that a current of steam 

 at low pressure may completely disinfect. Whilst such 

 simple current-steam machines have thus been demonstrated 

 as efficient bactericides, for all practical purposes it is im- 

 portant to have disinfectors capable of giving temperatures 

 considerably above 100 C., of simple construction, having 

 steam power of uniform temperature and rapid penetration, 

 and containing, when in action, a minimum of superheated 

 steam. In addition to these characters of a first-rate steam 

 disinfector, two other important points should be borne in 

 mind, namely, the air must be completely ejected from the 

 disinfection chamber before the results due to steam are 

 obtained, and some sort of automatic index giving a record 

 of each disinfection is indispensable. 



1 Journal of State Medicine, December, 1897, p. 561. 



