STEAM DISINFECTION 625 



For the reasons given above, disinfection by dry heat 

 is often impracticable ; on the other hand, moist heat is 

 more effective, is found to work well in practice, and is 

 now generally adopted. In the household, for articles 

 which cannot be burnt, brisk boiling for an hour or so will 

 suffice. 



Steam disinfection. For public disinfectors, steam under 

 pressure i.e. at a pressure greater than that of the atmo- 

 sphere is employed. Steam under pressure has not such 

 a deleterious action on articles, with the exception of 

 leather, as dry heat, while its penetrating powers are far 

 greater. By " saturated steam " is meant steam at the 

 temperature at which it can condense, and the tempera- 

 ture of the condensation point rises as the pressure increases. 

 By " superheated steam " is meant steam at a temperature 

 higher than that at which it can condense ; therefore 

 superheated steam has to be cooled down into the state of 

 saturated steam before condensation ensues. If super- 

 heated steam is used for disinfection, it loses heat by 

 conduction, and the rise in temperature of the articles 

 treated approximately corresponds to the fall in tem- 

 perature of the steam. With saturated steam, on the 

 other hand, immediately it is cooled an enormous amount 

 of latent heat is set free by the change in state from the 

 gaseous to the liquid condition, therefore saturated steam 

 is a far more efficient disinfectant than superheated steam. 

 These considerations should always influence the choice 

 of a steam disinfecting apparatus for efficient working. 



The Equifex disinfector is worked with saturated steam 

 at 10 Ib. pressure (239 F.). The chamber consists of a 

 cylinder of mild steel, made without steam jacket, so as 

 to avoid risk of superheating. The cylinder is lagged with 

 non-conducting composition and wood, to reduce loss of 

 heat by radiation, and, as usually supplied, is furnished 

 with separate doors for infected and disinfected articles 



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