56 



JUNIOR GRADE SCIENCE 



centimetres. From this will be obtained the volume, and therefore the 



mass of water displaced. 



(c) Fill the divided glass cylinder with water up to a certain mark. 



Notice the level of the water. 



Draw lines at equal distances apart across a narrow strip of paper and 



fix the paper inside a test tube, as in Fig. 44. Float the test tube in 



water in the graduated jar and put mercury or shot into it until a 

 certain mark upon the strip of paper inside 

 it is on a level with the surface of the water. 

 Notice the number of cubic centimetres of 

 water displaced when the test-tube is thus 

 immersed. 



Then take out the test-tube, dry it, and weigh 

 it together with the mercury it contains. The 

 total weight of the test-tube and contents will 

 be found equal to the weight shown by the 

 number of cubic centimetres of water displaced. 

 Repeat the experiment with the test-tube im- 

 mersed to a different mark. 



Float the test-tube and mercury in spirits of 

 wine and milk in succession. Notice that in 

 the former case it sinks deeper than the mark, 

 while in the other not so deep. 



FIG. 44. The weight of the 

 test-tube and contents is equal 

 to the weight of water dis- 

 placed. 



(d) Place the loaded test tube or a hydrometer (1) in milk, (2) in water, 

 (3) in a mixture of milk and water. Observe the depth to which it sinks 

 in each case. 



Water displaced by solids. If a solid one cubic centimetre in size 

 sinks in water it pushes aside one cubic centimetre of water to make 

 room for itself. If its size is two cubic centimetres, it makes two cubic 

 centimetres of water rise above the level the water had at first. What- 

 ever the size of the solid it must have room, and this room is obtained 

 by displacing an amount of water of exactly the same size. 



Floating bodies. A solid which sinks in water or any liquid, 

 displaces a volume of liquid equal to its own volume. When a solid 

 floats, the case is slightly different. Part of the solid is in water and 

 part out of the water, and, of course, only the part immersed is pushing 

 the water aside in order to make room for itself. In the case of a 

 floating object, therefore, the volume of liquid displaced is equal to the 

 volume of the part of the solid below the surface. 



When any object is floating in water, a certain volume of it is under 

 water, and a certain volume is above the surface. The depth at which 

 it floats depends upon its density. A rod of heavy wood sinks deeper 

 in water than a rod of light wood of the same size. The water displaced 

 by the heavy wood has therefore a greater volume, and consequently 

 a greater weight, than that displaced by the light wood. But there is 

 one important fact which applies to both cases and should be kept 

 well in mind. It is that the weight of the water displaced by the 



