Physical Properties of Water 265 



the gases thus held in solution we have already dealt, 

 and our next study will be the question of the solid 

 matter similarly present and the methods in general 

 use for its removal when required. 



EXPERIMENT 119. Let six drops of water from the 

 tap fall upon a carefully cleaned watch-glass. Place 

 the glass upon a tripod stand, a piece of fine wire gauze 

 being inserted under the glass. Heat the glass and its 

 contents with a Bunsen flame 

 of such a height that the tip V^^^^X 



of the flame just touches the 

 under surface of the gauze. 

 Continue the heating until the 

 water has almost entirely dis- 

 appeared, and at this stage 

 remove the burner. The hot 

 gauze will complete the evapor- 

 ation of the last traces of the 

 liquid. Examine the residue 

 at the bottom of the watch- ^ ^ 



glass. This consists of the 

 solid matter previously in solution in the water. Pre- 

 serve the glass for purposes of comparison with results 

 obtained in later work. 



183. To obtain a clearer idea of the relative 

 quantity of solids thus dissolved in the tap-water, 

 perform 



EXPERIMENT 120. Weigh a clean dry porcelain 

 dish to the nearest milligram. Into the dish intro- 

 duce, by means of a pipette, 25 c.c. of tap-water. 

 Place the dish upon a water-bath. (The usual labora- 

 tory apparatus may be replaced without loss of efficiency 

 by a beaker, of which the mouth is of such a size that 

 the dish will just rest upon it'.) Heat the water in the 



