WATER 



57 



heat to the flask, and reject the first portion of water that is dis- 

 tilled. Distil about 25 or 30 cc. of water. 



Tests, (i) Thoroughly clean out your porcelain evaporating 

 dish, if necessary using a little white sand for scouring, rinse 

 with distilled water, and 

 then by placing the evap- 

 orator upon a sand-bath, 

 evaporate some of the 

 distilled water to dry- 

 ness. Carefully regulate 

 the heat so that as the 

 water evaporates there 

 will be less and less heat. 

 This is to prevent the 

 breaking of the evapo- 

 rating dish by too much 

 heat at the close. Ex- 

 amine the evaporating 

 dish. See if there is 

 any residue. (2) Evapo- Fig. 29. Distillation of water, 



rate to dryness a similar amount of ordinary water, and observe 

 the residue. 



Questions, (i) Why do the contents of flask A become cloudy 

 after boiling and cooling ? (2) Why was the residue obtained by 

 one test and not by the other ? (3) What became of the residue 

 when the water was distilled ? (4) How could you distil water 

 on a larger scale for drinking purposes, if necessary to do so ? 



60. Physical Properties. When water cools, it 

 reaches its maximum density at 4 C ; below this point, 

 it expands, and hence ice has a lower specific gravity 

 than water. All natural waters contain more or less im- 

 purities in the form of mineral and vegetable matter and 

 gases. Pure water can be prepared only by distillation. 

 When a substance, as salt, is dissolved in water, a solu- 



