48 



STUDIES OX FERMEXTATIOX. 



twelve centimetres long (about i-in.), the one which is free 

 tapering off like the end of a pipe. In order to destroy all germs 

 which may exist in the flask, we must join the free end of the 

 copper tube to a platinum tube kept at a very high temperature, 

 after having carefully introduced into the flask a small quantity 

 of water, and expelled all the air by converting the water into 

 steam. Then as we allow the flask to cool, the air which re- 

 enters it will necessarily pass through the hot tube (Fig, 6). 

 We may cause the water in the flask to boil at a temperature 



Fig. 7. 



of more than 100° C. (212° F.) by fitting to the free end of the 

 platinum tube a glass tube bent at riglit angles, which we plunge 

 to any depth in a deep vessel filled with mercury (Fig. 7). 

 Whilst the water is boiling under pressure, we must separate the 

 tube which is plunged in the mercury ; the water in the flask will 



