This research revealed that metal ions with different charges could significantly affect the viscosity of aqueous sodium carboxylmethylcellulose (CMC) solution. On the basis of an Ostwald viscometer, an improvised apparatus using a dropping ball for examining the viscosity of liquids/solutions has been developed. The results indicate that the colloidal size of CMC aggregations is changed mainly by the metal cation charge. The improvised apparatus was introduced to high school students in a lesson on viscosity and intermolecular interaction where the students could examine the viscosity of several solutions and compare it with an aqueous sodium CMC solution. Although there are some limitations, the results show that the apparatus can be useful in helping high school students to understand the concept of viscosity.