104 



WATER 



is called temporarily hard. If the water is not rendered 

 soft by boiling it is called permanently hard. Was the 

 water you used temporarily or permanently hard, or was 

 it soft? 



Since hard water requires more soap than soft water, 

 in order to produce suds, the use of hard water for cleans- 

 ing is more expensive than the use 

 of soft water. Water which is tem- 

 porarily hard contains carbon diox- 

 ide, as well as a solid. When we 

 boil it the heat drives off the gas 

 and the solid collects on the sides 

 and bottom of the dish ; thus both 

 are removed on account of the heat 

 and the water becomes soft. How 

 could you show that carbon diox- 

 ide is driven off from temporarily hard water? 



We wash our clothing to remove the visible dirt so 

 that the clothing will be neat and clean. At the same 

 time we remove the invisible dirt which is usually more 

 harmful than the visible. The invisible dirt is composed 

 chiefly of material which has been left by the perspira- 

 tion when it evaporated, particles of dead skin and 

 bacteria. Since the perspiration comes from our bodies 

 it is of great importance that we keep our skin clean 

 not alone visibly clean but really free from anything 

 which can be washed off. The mouths of the tubes 

 through which the perspiration comes, called pores. 



