DISTILLATION 



earthenware vessel ; these nro very convenient when the operation is not to be con- 

 ducted on a very large scale, and only at a moderate temperature. They are now to 

 be obtained of all manufacturers of stone-ware articles. More commonly the worm 



619 



620 



is of copper, tin, or copper lined with silver, and in some rare cases where the liquids 

 to be distilled act upon both copper and silver, of platinum. (Fig. 620.) 



A tube of the shape shown in Jig. 621 is found more convenient than the worm, on 

 account of its exposing a larger surface, and also because it can be placed into a vessel 

 of a prismatic form which occupies but little space : the water employed for condensa- 

 tion enters at the bottom and passes out at the top. 



621 



622 



& 



v 



a 



3 



D 



cr is represented in jig. 622. It consists of two conical vessels of 

 metal, of unequal size, the smaller being fixed within the other, ;ind the space between 

 them closed at the bottom. These are placed in a tub filled with <<>!. 1 water, which 

 comes in contact with the inner and outer surfaces of the cones, win In the space 

 between is occupied by the vapour to bo condensed. This condenser i* subject to the 

 objection which applies to the common worm, that it cannot bo easily anil efficiently 

 cleaned. 



To obviate this, Professor Mitscherlich has proposed a very simple modification in 

 its form, in which the inner cone is moveable,so that, when taken out, the intervening 

 space between it and the outer cone can bo cleaned, and then the inner cone replaced 

 previously to commencing an operation. 



