GREGG] A STUDY OF WATER 89 



minutes, taking now some bright new shingle nails and putting 

 two or three in each bottle, and then corking up tightly. In the 

 course of a day the nails in the unboiled water will show rust, 

 while the others will show little if any rust. Have you noticed 

 that fish in an ordinary aquarium sometimes keep their mouths 

 steadily near the surface? Why is this and when does it occur, 

 answered in terms of the length of time the fish have been in the 

 water? Have you noticed that sometimes when water "looks 

 good" it may *'smell bad?" Explain. 



(e) It is worth while to give the pupil a concrete demon- 

 stration of the power of water to carry particles in suspension, 

 and especially some idea of the relation of velocity to the size 

 of particle that can be carried. The cut here presented shows 

 the means by which the gross facts can be set forth interestingly 

 and luminously, provided access may be had to a water supply 

 through a faucet and under pressure. 



{B) is a glass tube four or five feet long and about an inch 

 and a half in diameter, and is held in a vertical position by a 

 suitable device. Inserted in the lower end of the tube (C) is a 

 stopper having a hole into which is thrust a short tube such 

 that it can take on a rubber tube {G) leading from the faucet 

 (£). A handful or two of sand, gravel and fine dirt are thrown 

 clown into the tube and a stopper like the one at (C) inserted in 

 the top {A) and connecting by a rubber tube (F) with the basin 

 {D). Turning the water on slowly so as to produce a current 

 through {G), (B) and (F), the finer particles of dirt in the tube 

 are now carried up. Now doubling the velocity of the current 

 by turning the faucet so as to have the water rise from (C) to 

 (A) in half the time it did at first (the amount of turning neces- 

 sary should have previously been determined), note that the larg- 

 est particles now carried up are about four times the diameter 

 of the particles carried up at first. Increase the velocity to three 

 times that at first and the largest particles will now be about 

 nine times the diameter of those at first carried up. Stop the 

 flow of water and watch the stratification of the particles as they 

 settle. What sizes drop first? What later? Why? 



2. Kinds of water. — (a) Prepare some soap solution by dis- 

 solving a small piece of soap in a bottle of hot water. Get a 

 sample of water that is called "hard" water and into a small 

 quantity of it put a little of the soap solution. Notice how the 

 mixture curdles and does not form good soap suds. 



(b) Take an equal amount of ''soft" water, such as clear 

 rain water, and put into it, a similar amount of soap solution as 



