So also are the large retorts used in canning factories for sterilization of tin cans of food? The autoclave is essentially a double walled metal chamber fitted with a door which can be closed very tightly.
There is a safety valve to permit the escape of the steam should be pressure get too high There are usually two gauges, one to shoe pressure of steam in the outer jacket and another to show the pressure in the inner chamber.
There are valves to hold the steam in the jacket and to send it into the sterilizing chamber. There is an exhaust valve to let the steam escape from the inner chamber. There should also be a thermometer to show the temperature within the chamber, but some autoclaves are made without thermometers.
The steam is often generated by a gas-heated boiler arranged beneath the autoclave, though in some large laboratories and hospitals steam from the main boiler room is piped directly to the apparatus.
Articles to be sterilized in the autoclave are usually exposed to a pressure of 15 pounds of steam (that is, to a temperature of about 121 °C.) for twenty to thirty minutes.
The time required depends upon how bulky the material is, larger articles naturally requiring longer to heat through, and also how closely the material is packed into the chamber. In order to be sterilized, every part of the material must be heated to the sterilizing temperature for the necessary length of time.
Both the hospital and the laboratory find constant use for the autoclave; in the hospital for the sterilization of sponges and dressings and other materials for the operating rooms and wards, and in the laboratory for bacteriological culture media and many other things.
Practical points concerning the operation of the autoclave. The efficient operation of the autoclave is a very important matter, particularly in hospitals where this apparatus is depended upon to sterilize the dressing and other materials used in surgical and obstetrical work.
Often nurses have the responsibility of operating the hospital autoclaves.