DISTILLATION OF WATER. 



from escaping 1 , and to reconvert it into water. Now, as water is 

 converted into vapour by heat, so, on the other hand, vapour is 

 reconverted into water by cold. If, therefore, an apparatus be so 

 constructed that as the vapour rises from the boiling water it 

 shall be received into a close vessel where it is exposed to the 

 contact of a cold surface, it will be restored to the liquid form, and 

 being collected in that state, it will be so much pure water ; pure, 

 at least, so far as it has been separated from the substances which 

 it held in solution before it underwent the process of evaporation. 



32. The vapour of water is many hundred times lighter, bulk 

 for bulk, than water itself. It has resulted from accurately 

 conducted experiments, that a gallon of water evaporated at the 

 temperature of 212 will produce nearly 1800 gallons of vapour. 

 It follows, therefore, that when vapour is reconverted into water 

 by exposure to cold, a very great volume of it will produce a very 

 small volume of water. Thus, to produce a gallon of pure water, 

 we must have nearly 1800 gallons of vapour. 



33. It is for this reason that the conversion of vapour into water 

 has been called CONDENSATION, and the apparatus in which such 

 change is produced has been called a CONDENSEE. The vapour 

 is condensed, because it is reduced to a bulk 1800 times less, and 

 is, therefore, rendered 1800 times denser and heavier. 



The process by which water is first converted into vapour and 

 then restored to the state of water is called distillation, from a 

 Latin word DISTILLATIO, which signifies " falling in drops." The 

 conversion of the vapour into liquid in the condenser usually 

 proceeds so slowly that the liquid falls from the spout of the 

 condenser, not in a continuous stream, but in a succession of drops. 



34. In the industrial arts, and in chemical laboratories, where 

 water absolutely pure is needed in considerable quantities, its distil- 

 lation is conducted in an apparatus which is represented in fig. 1. 



This distilling apparatus, or alembic, consists of a copper boiler, 

 A., fixed in a brick furnace, having a dome-formed cover, B, 

 adapted to it, from which a bent tube, b c rf, proceeds, and is con- 

 nected with a spiral tube called a worm. This worm is inclosed in 

 a large cylindrical cistern, p qjr, constructed in metal, and which 

 is kept constantly filled with cold water. The lowest part of the 

 worm passes out of this cistern near its bottom, and terminates at 

 ft, over the mouth of a jar, c, intended to receive the distilled 

 water. An opening, , having a steam-tight stepper, is provided 

 in the boiler, through which the water to be distilled is introduced 

 into it. 



The vapour issuing from the boiler through the tube, bed, passes 

 into the worm, being first received by the vessel, o, where the 

 condensation begins. 



105 



