DRY HEAT 3! 



To USE THE HOT-AIR OVEN. 



1. Place the crates of test-tubes, metal cases con- 

 taining plates and pipettes, loose apparatus, etc., inside 

 the oven, taking particular care that none of the 

 cotton- wool plugs are in contact with the walls, other- 

 wise the heat transmitted by the metal will char or 

 even flame them. 



To prepare a wire crate for the reception of test-tubes, etc., 

 cover the bottom with a layer of thick asbestos cloth; or take 

 some asbestos fibre, moisten it with a little water and knead it 

 into a paste; plaster the paste over the bottom of the crate, 

 working it into the meshes and smoothing the surface by means of 

 a pestle. When several crates have been thus treated, place them 

 inside the hot-air oven, close the door, open the ventilating slide, 

 light the gas, and run the temperature of the interior up to about 

 1 60 C. After an interval of ten minutes extinguish the gas, open 

 the oven door, and allow the contents to cool. The asbestos now 

 forms a smooth, dry, spongy layer over the bottom, which will 

 last many months before needing renewal, and will considerably 

 diminish the loss of tubes from breakage. 



Copper cylinders and large test-tubes intended for the reception 

 of pipettes are prepared in a similar manner, in order to protect 

 the points of these articles from injury. 



2. Close the oven door, and open the ventilating 

 slide, in order that any moisture left in the tubes, etc., 

 may escape; light the gas below; set the electric alarm 

 to ring at 1 00 C. 



3. When the temperature of the oven has reached 

 100 C., close the ventilating slide ; reset the alarm to 

 ring at 175 C. 



4. Run the temperature up to 1 7 5 C. 



5. Extinguish the gas at once, and allow the appa- 

 ratus to cool. 



6. When the temperature of the interior, as recorded 

 by the thermometer, has fallen to 60 C. but not 

 before the door may be opened and the sterile articles 

 removed and stored away. 



NOTE. Neglect of this precautionary cooling of the oven to 

 60 C. will result in numerous cracked and broken tubes. 



