Chem ical^Appa ratus. 109 



distillation of spirits is represented in fig. 14. 

 It consists of a boiler covered by a metal head, 

 A, usually of copper, for collecting the vapour, 

 which is made to pass through a spiral tube called 

 a worm, immersed in a tub of cold water, B, for 

 the purpose of condensing the spirit, which 

 comes out at the pipe C in a fluid form. 



3. By the retort and receiver (see fig. 15.) we 

 perform the lateral distillation. Those that have 

 the neck of the retort descending into the lower 

 parts of the receiver are more useful than those 

 in which the neck of the receiver is inserted in 

 the retort. Some have contrived them with an 

 opening in the back for the mixture of bodies 

 that emit elastic steam : this hole is stopped 

 during the process, but not very tight, so that if 

 the vapour is very elastic it may find its way, and 

 the vessel be preserved. The conical receiver is 

 accounted best. It is dangerous to restrain the 

 steam too tight, and therefore in luting the re- 

 tort and receiver do not screw them too tight. 

 When a degree of heat capable of softening glass 

 is required, the retort may be coated over with 

 clay and sand, which do not contract with heat : 

 for very intense heat, we must have a retort of 

 the same materials with the crucibles. In many 

 operations of the retort we have occasion to mix 

 two substances in order to obtain a third or 

 new product, which is to rise in vapour upon 

 mixture. In this operation the neck of the re- 

 tort must be kept very clean and dry. In sub- 



