STERILIZATION 51 



ratus rises and steam penetrates all permeable objects. 

 When the steam escapes and air enters, moisture is 

 absorbed and the objects become dry. By this means 

 as much as two extra atmospheric pressures can be 

 run up, which will be equivalent to 34.5 C. or 74 F. 

 above the boiling point. After starting up steam the 

 apparatus should never be tightly closed at the safety 

 valve until all air is expelled. This method is particu- 

 larly adapted to the sterilization of dressings and 

 infected cast-off clothing. Hot air is suitable for 

 dried glassware and articles injured by moisture, and 

 can be used for domestic sterilization by exposing the 

 articles in the household oven. It is less efficient than 

 moist heat. This is due to the fact that organic sub- 

 stances are less easily coagulated in a dried condition. 

 Spores are more resistant also, as, for example, the 

 anthrax spore, which requires an exposure of three 

 hours at 140 C. or 284 F. dry heat. Hot, dry air 

 penetrates less easily than hot moisture. Burning is 

 the best of all methods, and should be used for every- 

 thing which can be spared, handkerchiefs, dressings, 

 and objects like magazines from the sick room. 



The two thermometric scales are explained as follows: 



F. = Fahrenheit, the ordinary scale used in this country. Water 

 just at the freezing point registers 32 F., while just at the boil- 

 ing point registers 212 F. The zero has no relation to physical 

 changes. 



C. = Centigrade, the French system. Water just at the freezing 

 point is C., and just at boiling point is 100 C. 



The 100 degrees in the Centigrade scale is equal to the 180 between 

 32 and 212 in the Fahrenheit scale. 



To change one system to the other proceed as follows: 



From Fahrenheit to Centigrade: Given degree F. 32-4-9X5 = 

 same degree in Centigrade scale. Example: 50 F. 32=18-4-9 = 

 2X5=10. Therefore 50 F. = 10 C. 



From Centigrade to Fahrenheit: Given degree C. -4-5X9+32 = 

 same degree in Fahrenheit scale. Example: 10 C. -4-5=2X9 = 

 18+32=50 F. 



