Balance scales are used to compare unknown weights to known weights. To prepare a set of known weights, obtain a set of gram weights (e.g., grams, decigrams, centigrams), and some wire or pieces of metal foil.

Place the known weights, one at a time, onto the scale, and balance each one by putting sections of wire or rolled foil onto the other side of the scale. When the scale is
balanced, you have your own weight that is equal to the weight you used to make the new one. Label it by putting a mark on it. (If you put a sticker onto your weight to label it, it will weigh more!) You can now use your wire and/or foil weights in place of the known gram weights.

Amounts of absorption can be measured with a balance scale. To do this, obtain pieces of different materials, such as sponges, blotters, cloths, and paper towels.

Make weighing papers, and put one in each balance scale. Balance the scale, then weigh each of the sample materials, and record the dry weight on a table.

Now saturate each material with water. Shake off any excess water, and weigh each piece of material when it is wet. Compare the dry weight with the wet weight.

Compare different brands of paper towels to see which absorbs more. You can test other materials, such as napkins and facial tissues, for absorbency.

This is applicable to geologic study, because the porosity of rock and the absorbency of soils can be tested. After determining the dry weights, soak some rocks in water for an hour or so, and then weigh them to see how much water their pores held. Check the dry weight of some different soil types, then make a paste by adding small amounts of water to them, stirring as you go, until they will hold no more. Weigh the soil samples and see which types absorbed the most water.