52 JUNIOR GRADE SCIENCE 



the body be immersed in any other liquid, then the loss of weight is equal 

 to the weight of an equal volume of that liquid. It does not matter 

 what substance the thing is made of ; the amount of loss of weight 

 depends upon the volume of the part immersed, and not upon the 

 material. 



This principle explains many interesting facts. For instance, a 

 ship made of iron, and containing all kinds of heavy things, is able 

 to float in water although the material of which it is made is denser 

 than water. This is because the ship and all its contents only weigh 

 the same as the volume of the water displaced by the immersed part 

 of the hull. Or, the ship as a whole weighs less than a quantity of 

 water the same size as the ship would weigh. 



Now, too, it can be seen why some solids float and some sink. When 

 an object weighs more than an equal volume of water it sinks. 

 When an object weighs less than an equal volume of water it floats. 

 When an object weighs the same as an equal volume of water it 

 remains suspended in the water. 



A balloon rises in the air because the gas in it, together with the car 

 and tackle, weigh less than an equal volume of air. If the balloon 

 were free to ascend it would rise to a height where its weight would 

 be equal to the weight of an equal volume of the air around it. 



23. APPLICATION OF THE PRINCIPLE OF ARCHIMEDES 

 TO THE DETERMINATION OF VOLUMES AND 

 DENSITIES. 



i. Accurate determination of the volume of a small body. (a) Using the 

 method described in Section 22, iii., find the loas of weight of a small 

 glass stopper when weighed in air and in water. Since the loss of weight 

 is equal to the weight of the water displaced it follows that the loss of 

 weight in grams gives the volume in cubic centimetres, because one gram 

 of water has a volume of one cubic centimetre. 



(6) Find the volume, by the displacement of water in a graduated cylinder. 

 Compare with the previous result. 



ii. Density of glass. Find the density of the stopper from the results 

 of the last experiments. 



iii. Relative density of liquids. Determine the loss of weight of the 

 stopper already used when weighed in methylated spirit. As the volume 

 of spirit displaced by the stopper is the same as the volume of water dis- 

 placed by it, the loso of weight in spirit represents the same volume of 

 liquid as the loss of weight in water. Find the relative density of the 



iv. Density of a cork. As a cork floats in water, a sinker must be used. 

 Obtain a piece of lead sufficient to sink the cork. Suspend the cork in water 

 as in previous experiments, and weigh. Place the cork on the pan of the 



