GREGG] A STUDY OF WATER 91 



quantity of stuff in solution and in suspension with that in the 

 well water. 



( c) So also a sample of tap water, if it is at hand. 



4. Purification of water. — If water is to be purified at the 

 point where it is delivered for use, one or more of the following 

 methods are employed : 



(a) Filtering may be impressively illustrated by taking sev- 

 eral ordinary flower pots that will hold a quart or more, each, fill- 

 ing them each with a different grade of material, from very fine 

 sand to course gravel, and then pouring a pint or less of very mud- 

 dv water in each and collect the water as it comes through the hole 

 in the bottom of each vessel. What makes the difference in the 

 clearness of the waters that come through? Can you make use 

 of what you learned in experiment 1(e) to explain it? Examine 

 a commercial filter if one is available. 



(b) Even though the water that comes through the fine sand 

 is clear, we are not yet sure that it may not have live germs in it. 

 What can we do to kill the germs and still preserve the water? 

 Yes, if we boil the water long enough we can kill all the germs 

 that may be there. 



(c) But even now the water may still have minerals in solu- 

 tion, and to get perfectly pure water we must distill it. Nine 

 and ten year old boys will be glad to make a distilling apparatus, 

 if the teacher will encourage them and show them pictures of 

 how distilling apparatus may be made. The books on physics 

 will describe the process. But better than the practice of purify- 

 ing the water at the point of delivery is that of purifying it at its 

 source. Here the pupil may be sent to the books and to various 

 wells and cisterns, to see how they can best be arranged so as 

 to guarantee reasonably pure water. If a city waterworks is 

 accessible, of course an excursion to such a place would next be 

 in order. Our experiments up to this point should help make 

 the processes clearer. 



(b) HYGIEXIC CONSIDERATIONS AND CONCLUSIONS. 



Do you think it makes much difference what kind of water 

 one drinks? Why should we be particular about this matter?' 

 What is the objection to taking a drink with a cup that some one 

 else has just taken a drink with? What is the advantage of the 

 drinking fountain ? Are there any disadvantages ? What should 

 be done with a boy or girl who persistently "fingers" the cup of 

 a drinking fountain? About how much water do you drink in a 

 day? Suppose we all keep track of it for a week and then 



