APPENDIX 



1. Observations of Quantity of Matter. Balances. The delicate 

 structure of balances makes it necessary that they should be used 

 with great care. They should be periodically inspected, and all dirt 

 removed. The knife-edges and planes, when made of steel, must be 

 kept free from rust. When balances are fitted with a case, they may 

 t be kept free from oxidation by drying the air in the case with strong 

 hydrogen sulphate or calcium chloride. These substances must be 

 periodically renewed. It is obvious that freedom from chemical 

 fumes is essential to their preservation, hence they should be placed 

 in a room cut off from the working chemical laboratory. In addition, 

 a balance should always be placed in a good light, and on a steady 

 table or bracket. For physical observations the large open balances 

 illustrated are very suitable, and are readily adapted for weighing 

 bodies in liquids. It must be remembered that large masses tend to 

 strain the beam, and sudden or uneven movements may diminish the 

 accuracy of the suspension. For this reason the beam should be 

 placed in suspension with a steady movement, and stopped from 

 swinging when the pointer is in the centre of the scale. Of course, 

 alteration of the masses in the pans must only take place when the 

 balance is at rest and supported. Before using a balance it should 

 be dusted, if necessary, and made to swing, in order to test its ac- 

 curacy of adjustment. If it swings equally on each side of the scale, 

 or if it swings nearly equally, it is ready for use. It is better to 

 allow for a little inequality of swing than to constantly alter the 

 adjustment. Sometimes it is difficult to get the balance to swing. 

 In that case, blow one of the pans very gently. Do not weigh 

 bodies when hot, as the surrounding air becomes heated and ascends, 

 thus making an upward current irom the pan used. Most substances 

 should not be allowed to touch the pans, for fear of injury to them. 



