16.2.1 Weighing

1. Take all the readings with the same balance and the weight box in a weighing tube or a small beaker.

   
   Figure 16.1: Chemical balance.

2. Always keep the weights on the right hand pan. If you are left handed, you may keep the weights on the left hand pan. The weights can be kept either on the balance pan or in the weight box and nowhere else.

   
   Figure 16.2: Weight box.

3. Lift the weights with forceps and never with hands. The dirt or sweat will increase the mass of the substance.

   
   Figure 16.3: Fractional weights.

4. Keep the doors of the balance closed while weighing. This will exclude dust, drafts, and even the disturbances due to your own breathing.

5. The beam is usually graduated into 10 mg numbered divisions on either side of the fulcrum. If the rider is placed on the 10th division, it balances its own weight (0.01g) on the opposite pan. If the rider is placed on the 1st division, it balances l/10th of its own weight or 0.001 g, on the 2nd it balances 0.002 g, on the 5th 0.005 g, etc., (by the principle of lever). Thus each division on the beam corresponds to 0.001 g or 1 mg.

   The space between two consecutively numbered divisions is further divided into five equal parts. Each of these small parts obviously corresponds to 0.001/5 = 0.0002 g or 0.2 mg. For example, if the balance is in equilibrium when the rider...