Pasteur Oven

Pasteur Oven, or dry sterilizer, is used for sterilizing dry glassware, paper, cotton, and metal objects that fear rust. It represents a metal cabinet having double walls and sheathed with asbestos (see figure). In the upper wall are openings for ventilation and a thermometer, by which the t° of the hot air inside the oven is measured. The air circulating between the double walls is heated by gas or kerosene burners placed under the bottom of the oven. There are ovens with electric heating and automatic temperature regulators. Inside the cabinet are arranged sliding shelves for the ware. All glass objects subjected to sterilization must be completely dry, otherwise they may burst. Test tubes and flasks are plugged with cotton before sterilization; cups and pipettes are wrapped in paper. The beginning of sterilization is considered from the moment when the t° in the Pasteur oven reaches 150–160°. Sterilization continues at 150° for 2 hours, at 160° for 1 hour. If the t° reaches 180°, the cotton and paper carbonize and crumble. Upon completion of sterilization, the flame is extinguished and the fall of t° is awaited. If the not-cooled apparatus is opened, the glass may burst from a jet of cold air. The ware and cotton remain wrapped in the same paper, which is removed only before their use.