54 Domestic Science 



Since weight is directly proportional to mass, it 

 is unnecessary to adopt a special system of units of 

 mass, and mass is consequently generally expressed 

 in the same units as weight, viz. pounds and kilograms. 

 To avoid confusion, however, it must be clearly under- 

 stood that the term pound, when used as a unit of 

 weight, denotes a force, while when used as a mass unit, 

 it indicates only a definite quantity of matter. 



31. Practice in the use of the balance will be 

 provided in the experiments which follow. 



EXPERIMENT 14. Examine carefully the box of 

 weights supplied with a balance such as that shown in 

 Fig. 20. This usually contains the following weights : 



50 g., 20 g., 20 g., 10 g. ; 5 g., 2 g., 2 g., 1 g. 

 0-5 g., 0-2 g., 0-2 g., 0- 1 g. ; 0'05 g., 0'02 g., 0'02 g., 0*01 g. 

 With a balance and box of weights of this character, 

 bodies weighing up to 100 grams may be weighed, 

 and the error involved in weighing should not usually 

 be greater than that of the smallest weight, O'Ol g. or 

 10 mg., if the balance is in good order. 



Turn the arrestment so that the pans of the balance 

 are set swinging. This is called " putting the balance 

 into action ". Note the number of divisions over which 

 the end of the pointer swings on each side of the centre 

 division of the scale. The lengths of swing gradually 

 lessen till the beam comes to rest. To avoid the waste 

 of time involved in waiting till this occurs it is sufficient 

 to note whether the number of scale-divisions passed 

 over on each side of the centre is approximately the 

 same. Thus, if the reading on the right of the middle 

 of the scale be 7 divisions, that on the left 6' 5, followed 

 by another on the right of 6 divisions, the balance is 

 in good working order and needs no special adjustment 



