Physical Properties of Water 269 



stopper fits the neck of the flask closely. Pass the end 

 of the side tube of the flask through the hole in the cork 

 fitted into the upper end of the piece of apparatus 

 shown, which is called a Liebig condenser. Arrange 

 the remainder of the apparatus as indicated. The flask 

 is placed upon a sand-bath a shallow tin dish on 

 which is spread a thin layer of dry sand. Note that 

 the rubber tube from the tap is connected to the lower 

 of the two small tubes projecting from the jacket of 

 the condenser, while the tube leading from the upper end 

 is placed near a sink. Fill the condenser with water 

 by gently turning on the tap, and arrange the flow of 

 water through the jacket so that a steady stream of 

 water issues from the end of the tube placed in the 

 sink. Boil the solution in the flask and, after rinsing 

 the receiver with the earliest portion of the distillate, 

 collect until about half the liquid has been turned 

 into vapour. If the rate of flow of the condensing 

 water is regulated properly, no escape of uncondensed 

 steam should be observed at the lower opening of the 

 condenser. 



Test the degree of purification effected by evapora- 

 tion of samples of the original solution and of the 

 distillate in the manner already described. Similarly 

 treat a sample of the liquid left in the still and note 

 the amount of solid residue as compared with that left 

 by the original solution. 



186. On the large scale, water is boiled in large 

 metal vessels frequently made of copper and the 

 steam passes through a long coil of tin pipe immersed 

 in a large vessel through which cold water is circulated. 

 A form of this apparatus is illustrated in Fig. 87. Tin 

 is chosen as the material for the construction of the 

 condensing worm, since, among the metals in common 



