EXPERIMENTS AND PRACTICAL WORK 77 



water, and sea-water. Eecord the relative quantity of 

 residue in each case, and taste that from sea-water. 



Expt. 174. Softness of Rainwater. Show that soap- 

 suds are easily formed in rain-water; rain-water is there- 

 fore called soft. 



Expt. 175. How to make Rain-water Hard. Get a 

 quart of rain-water; through a glass tube or bit of small 

 bamboo breathe into it so as to supply it with carbon 

 dioxide; add J lb. of marl or powdered chalk; allow it 

 to soak for twenty-four hours, stirring and breathing 

 into it occasionally. Test with soap, and note that 

 soapsuds are not so easily formed as in the case of 

 the rain-water. 



Expt. 176. Water also contains Gases. Shake up a 

 vessel of water, put over a fire, and observe that bubbles 

 of air pass off long before the water boils. 



Expt. 177. Weight of Water. Discover by experi- 

 ment the weight of 1 gallon of water. 



Expt. 178. Formation of Water by Combination of 

 Oxygen and Hydrogen. Invert a tumbler over a burn- 

 ing candle, and observe drops of water formed by the 

 combination of the oxygen of the air and the hydrogen 

 of the candle. 



Expt. 179. Presence of Sewage Matter. Shake a 

 mixture of water and a little stable manure in a bottle; 

 observe the dark appearance. Pour into a dilute solu- 

 tion of permanganate of potash, and observe that the 

 sewage destroys the colour of the permanganate. 



Expt. 180. Contamination of Ponds. Make a draw- 

 ing of a pond, showing how the water in it may get 

 contaminated. 



Expt. 181. The Best Means of purifying Water for 

 Drinking Purposes. Boil some water, and note that 

 water should never be drunk unless it has been boiled. 



