6 LABORATORY EXERCISES 



3 rings of the beam are made of metal (brass or plated iron), so 

 that they shall have little friction against the beam. A con- 

 venient length for the beam is 18 cm. (7+ in.). 



b. Rules for Weighing: 



1. Put the object to be weighed on the left-hand pan, the weights 

 on the right. Handle the weights with forceps if possible. 



2. Do not drop the weights on the pan, but set them down care- 

 fully. 



3. Do not leave the balance beam swinging when the balance is not 

 in use. 



4. Do not weigh an object directly upon the pan. Put a dish or a 



piece of paper on the left-hand pan, 

 counterpoise, or balance, it exactly with 



weights or shot placed in the right-hand 

 pan, and then put the object in the 

 balanced pan or paper. 



5. Learn just what weights ought to 

 be in your case, and see that all are 

 there before you begin weighing. When 

 you have balanced the object you are 

 weighing, count up what weights are 



gone from your case; these should be the ones on the balance pan. 



Finally, take off all the weights used, set them in a row on a clean 



piece of paper, and count them up to see if you added them correctly 



before. 



6. Record all your weights while you are at the balance. Do not 

 try to carry the number "in your head" until you return to your desk. 

 Put down all your weights in grams and decimals (tenths or hun- 

 dredths). 



7. Label all your figures at once, so that you will know to what object 

 or material they belong. 



8. When you are through weighing, return all weights to their proper 

 places in the case, and leave the case and the balance in good condition. 



c. Weight of a Given Volume of Water. In a graduated 



