160 INTRODUCTION TO GENERAL SCIENCE 



c. Take some cold water and add ice to it. What is its 

 temperature ? Add some salt, and record the lowest tempera- 

 ture which you can obtain. 



d. Take some ice water, remove the ice, and add some 

 ammonium nitrate. What was the lowest temperature which 

 you obtained ? 



e. Take some cracked ice and add ammonium nitrate to it. 

 What was the lowest temperature obtainable? 



/. If there is gas in the laboratory, hold the platinum wire 

 coiled into a small spiral, by means of the forceps, in the gas 

 flame. Shut off the gas and turn it on again with the plati- 

 num still in the gas. The gas should ignite. 



116. USES OF WATER 



Water is used for drinking, cleansing, and agriculture. 

 Aside from drinking purposes, water owes its usefulness to the 

 fact that it readily dissolves many substances. Thus in 

 cleansing, water and soap dissolve the dirt, while in agricul- 

 ture water holds in solution the plant food which comes from 

 the soil. See Section 115, Solution and its Effects. In 

 Section 208, Simple Household Remedies, we will take up a 

 consideration of drinking water, while in Section 196 we will 

 study the analysis of water. Section 146 treats of the im- 

 portance of water in agriculture. 



On account of its mobility and noncompressibility, water is 

 useful as a means of conveying pressure which may be util- 

 ized in water motors and hydraulic elevators. Waterfalls 

 can be used to turn wheels and produce mechanical energy, 

 which may be changed into electrical energy capable of being 

 used at a great distance. 



Water is taken as the standard of density, and the density 



