8 ELEMENTS OF LABORATORY WORK 



Additional Exercises and Qicestions. 



1. Assuming that the density of brass is 8 that is, that 1 cubic 

 centimetre contains 8 grams of matter find the volume of a given piece 

 of brass by weighing and calculating. Compare the result with that 

 obtained by measuring the volume of water displaced by the brass. 



2. Compare the densities of lead and tin by weighing, and determin- 

 ing volumes by displacement of water. 



3. Suggest methods of finding both the apparent and real density of 

 porous bodies. 



4. How would you find the density of copper sulphate a substance 

 which dissolves in water ? 



5. Mention the various precautions which must be taken during 

 observations of density. 



6. What hypothesis can you suggest in explanation of the difference 

 in density observable among various kinds of matter ? 



7. Principles of Systematic Measurement, We have dis- 

 cussed in the preceding sections concrete quantities of dif- 

 ferent kinds quantity of matter, quantity of length, quantity 

 of area, quantity of volume, and quantity of density. 



By direct observation we have been able to decide when 

 two given quantities of the same kind are equal. -We have 

 then seen how many times a given standard quantity is to be 

 taken to make up a quantity equal to the quantity being 

 measured that is, we obtain numerical values, or numbers 

 expressing the magnitude of any concrete quantity. All that 

 we can say of any quantity is that it is equal to so many 

 times a quantity of the same kind selected as a standard, 

 and all that we can directly observe is equality, or inequality, 

 in quantity. 



The standard quantity of matter, or the unit of mass, now 

 used in all physical measurements is called a gram. 



The standard quantity of length, or unit of length, now 

 used is called a centimetre. 



For convenience in exact weighing, sets of weights are 

 used i.e. various pieces of brass and aluminium, carefully ad- 

 justed by the maker, so as to contain certain multiples and 

 fractions of the quantity of matter in a gram, and arranged as 

 follows : 



