APPARATUS, MATERIAL, AND REAGENTS. 33 



enables the temperature to be maintained with a 

 minimum variation. It consists of a cylindrical 

 copper vessel, with double walls, enclosing a wide 

 interspace for containing a large volume of water. 

 The roof of the 

 water - chamber is 

 oblique, so that the 

 wall rises higher 

 on one side than 

 on the other. This 

 admits of the inter- 

 space being com- 

 pletely filled with 

 water. At the 

 highest point is an 

 opening fitted with 

 a perforated caout- 

 chouc stopper, 

 through which a 

 glass tube passes. 

 The mouth of the 

 cylinder itself is 

 horizontal, and is 

 closed by a lid, 



which is also double-walled to contain water. In 

 the lid are four openings ; one serves for filling its 

 water-chamber, and the others for thermometers and 

 for regulating the air supply in the cavity of the cylin- 

 der. The cylinder is continued below by a cone, also 

 double-walled, and there is a perforated grating at 



3 



