52 



A MANUAL OF BACTERIOLOGY 



sterilised by the steam at 100 C. which fills this 

 space. 



Here again an inexpensive substitute may be devised ; 

 the ordinary kitchen steamer may be utilised. 



Autoclave (Fig. 4). This is useful, but it is expensive 

 and not a necessity, as the steam steriliser, with the 

 expenditure of a little more time and trouble, will serve 

 almost every purpose for which the autoclave is employed. 



It consists of a strong boiler 

 of brass or gun-metal with 

 a removable lid, which is 

 attached to the boiler by 

 means of screw-bolts. The 

 lid is provided with a safety 

 valve, a gauge for indicating 

 the pressure and temperature, 

 and a stopcock to relieve the 

 pressure if required. A small 

 quantity of water is placed 

 in the bottom, and the media 

 or apparatus to be sterilised 

 having been introduced, the 

 lid is screwed down. It is 

 heated by means of one or 

 more Bunsen burners, which 

 are turned down when the 

 required temperature has been 

 reached. The temperature usually employed is about 

 115 to 125 C. When sterilising media care should 

 be taken that the vessels are not too full, and that the 

 autoclave is allowed to cool down below 100 C. before 

 opening the stopcock, or some of the contents may be lost 

 by violent ebullition. While the temperature is rising, 

 the stopcock should always be left open until steam is 

 being freely generated so that the air may be expelled. 



FIG. 4. Autoclave. 



