A colorimeter is any device that measures the colour of a particular substance. It's a generic term that may refer to a range of devices such as a spectrophotometer, which is a specific type of colorimeter typically used to measure a solution's absorbance of a particular wavelength of light. This allows the concentration of a known solute in the solution to be calculated with considerable accuracy. This type of colorimeter is a standard piece of equipment in analytical chemistry.
Determine the wavelength of light that the solution absorbs most strongly. A colorimeter has a set of changeable filters that can show which colour of light to examine for the greatest accuracy. Set the colorimeter to this wavelength.
Calibrate the colorimeter. Turn the unit on and wait 30 minutes for the colorimeter to warm up before taking any measurements. Remove the container (cuvette) from its chamber.
Read the colorimeter. The meter is extremely sensitive, and you must use the correct measurement. Most models have a reflective surface under the needle and you should look at the needle so that you can't see its reflection in the mirror.
Fill the reference cuvette with the test solution as indicated by the colorimeter model you're using. Clean the reference cuvette carefully to ensure it doesn't have any smudges and place it in the chamber. Read the absorbance and adjust the colorimeter to show an absorbance reading of 0.
Put the test solution in the specimen cuvette and clean the outside of the cuvette. Place it in the chamber and read the absorbance of the test solution. You will typically record this value and use it in calculations to determine the solution's concentration.