46 A MANUAL OF BACTERIOLOGY 



space of nearly an inch between them, and furnished 

 with a door. The joints should be brazed, riveted, or 

 folded, not soldered. The outer skin at the bottom should 

 have a large hole cut in it in which a loose piece of sheet 

 iron or copper should be inserted to protect the inner 

 skin from oxidation and may be renewed as it " burns " 



away. The top is perforated 

 with a couple of holes, through 

 one of which a chemical thermo- 

 meter, registering to 200 C., is 

 inserted in a cork, while through 

 the other some form of mercurial 

 regulator can be introduced if 

 required, but is not usually 

 needed. In the hot-air steriliser 

 all thin- glass vessels and cotton- 

 wool are sterilised by heating to 

 a temperature of about 150 C. 

 by means of a Bunsen or a small 

 ring burner under the steriliser, 

 which is supported on a suitable 

 iron stand. If the steriliser is 

 placed on a table or other 

 wooden support, a piece of sheet 



FIG. 3. Steam steriliser. . , 



iron, asbestos cardboard or 



uralite should be laid over the wood to protect it from 

 the heat. An inexpensive substitute for the hot-air steri- 

 liser may readily be devised, any iron box or even a 

 biscuit- tin being used for the purpose. 



Steam steriliser (Fig. 3). This consists of a cylindrical 

 or rectangular vessel of tinplate, galvanised iron, or 

 copper, covered on the outside with a layer of felt or 

 asbestos, having a false perforated bottom supported a 

 few inches above the true bottom, and provided with a 

 movable lid. In the steam steriliser or " steamer " the 



