196 SCIENCE OF COMMON THINGS. 



"Why distilled water Is Tery pure. Construction of a still. 



glass receiver contained in a vessel filled with cold 

 water y and is then condensed. 



Fig. 43. 



1298 Why is water obtained in this manner by distillation purer than 

 spring water f 



Because the non-volatile, earthy, and saline portions 

 contained in all spring waters do not ascend with the 

 vapor, but remain in the retort. By this means very 

 volatile bodies can be easily separated from less volatile 

 ones ; as brandy and alcohol from the less volatile 

 water which may be mixed with them. 



1J390 When the vessel used for generating the vapor is very large, what 

 is it called f 



A "still ;" and, for con- 

 densing the vapor, vats are 

 constructed, holding ser- 

 pentine pipes or " worms" 

 which present a greater 

 condensing surface than 

 if the pipe had passed di- 

 rectly through the vat. 



To keep the coil of pipe cool, the 



vats are kept filled with cold water. 



Fig (See Fig. 44.) 



In this figure a is a furnace, in 



which is fixed a copper vessel to contain the fluid. Heat being applied, 

 the steam rises in the head 6, and passes through the worm d, which is 

 placed in a vessel of water, the refrigerator. The vapor thus generated is 

 condensed in its passage, and passes out as a liquid by the external pipe 

 into a receiver. 



13OO What is the difference between drying by heat and distil'tmg f 



