The Triple Beam Balance

Click on the above image for a movie on how to use this balance

A. Look at the triple beam balance and note that:

• one beam measures from 0 - 10 grams in 0.1 g increments
• another beam measures from 0 - 100 grams in 10 g increments
• the third beam measures from 0 -600 grams in 100 g increments

B. Before using the instrument make sure that you have "zeroed" it:

• make sure that all weights are on zero. Observe carefully! Sometimes a weight "appears" to be on zero but it is not seated correctly. In this situation the weight is really a little to the left of the zero position. Jiggle each of the weights and make sure they each are seated in the notch which corresponds to zero.
• Once this is done, the balance should be "balanced" with the pointer at the far right of the instrument pointing to zero. If this is not the case, you must adjust the thumbscrew underneath the pan either clockwise or counter-clockwise until the pointer rests at zero.
• Once adjusted, the balance should maintain the thumbscrew setting as long as no one accidentally readjusts it. Practically this means that one should very rarely need to adjust the thumbscrew. But don't take it for granted -- always make sure that the balance reads zero before proceeding to weigh a sample.
• One weighs an object on the pan by counterbalancing it with the weights on the beams. When the weights match exactly - indicated by the pointer pointing to zero - the weight of the object is then read off of the beams.
• Practice weighing a variety of small objects - like your keys or coins or pencils - to become familiar with the balance and how it works.

C. Prepare to weigh

• Tare (or taring) the weighing container. This means weighing the empty container so that its weight can be deducted from the weight of the sample you want to weigh. (Some balances, but not these triple beam ones, allow you to "zero" the balance with the empty weighing container on them. This achieves the same purpose and it is also called taring.)
• In order to tare the weighing container do the following:
  • 1. Weigh the empty container

    2. Add to the container's weight the weight of the substance you wish to measure. You should perform this calculation in your notebook. Set the weights on the balance to this calculated total expected weight.

    3. Add the substance in small increments into the weighing container on the balance until the balance "balances."

D. Perform activities 1 and 2 as described below. There are 4 balances so work in 4 groups.

Activity 1: Weigh 5.5 g of sand onto a piece of weighing paper. Record the weight of the empty weighing paper and report it below and on the blackboard.

Activity 2: Weigh 43 g of sand into a beaker. Record the weight and size of the empty beaker and report it below and on the blackboard for class comparison.

Group Number	Weight of Paper	Paper + Sand Weight	Beaker Size	Weight of Beaker	Beaker + Sand Weight
Group 1
Group 2
Group 3
Group 4