DENSITY 



33 



solution, fill it with the solution ; when it stands at the mark 

 after suspending in the beaker of water at 15° C. for a few 

 minutes, dry and weigh. 



Like liquids, solids differ in their density. Wood floats on 

 water, but iron sinks. Compare the densities of glass and 

 water. Weigh a piece of stout glass rod. Immerse it in the 

 water in a half-filled burette, and read off the increase in the 

 height of the water. The increase will be an amount of 

 water equal in volume to the glass rod. From this calculate 

 the relative density of the glass. 



Solids weigh less when immersed in water than in air ; the 

 loss in weight is found to be equal 

 to the weight of water displaced. 

 Weigh the glass rod under water, by 

 suspending it to the arm of the 

 balance by a hair, as figured. The 

 loss in weight will be found to be 

 equal to the weight of water it dis- 

 placed, as found in the previous 

 experiment. This provides an exact 

 method for determining the relative 

 density of solids. Weigh the solid 

 first in air and then in water, and 

 compare its weight in air with the loss in weight, i.e. the weight 

 of an equal volume of water. 



It is obvious that the loss in weight of a solid when immersed 

 in a liquid will depend upon the density of the liquid, for the 

 loss in weight is equal to the weight of an equal volume of the 

 liquid. Hence this method also provides a means of deter- 

 mining the density of liquids. For example, to determine the 

 relative density of the salt solution, compare the loss in weight 

 of the glass rod when immersed in the salt solution with its 

 loss in weight when immersed in water, i.e. the weight of equal 

 volumes of salt solution and water. 



This principle is adopted in the rough determination of 



3 



Fig. 19. 



