To accurately perform the foam solution-concentration test, you must obtain refractive index readings from which components?

• A. water only
• B. foam concentrate only
• C. water, foam solution, AND foam concentrate
• D. foam solution only

Answer: (C)

The test relies on refractive index to determine how much foam concentrate is present in the solution, so you need reference readings for all parts involved. The refractive index of water sets the baseline, the refractive index of the foam concentrate defines how the concentrate behaves optically, and the refractive index of the foam solution shows how much concentrate is actually in the mixture. By comparing the foam solution reading to the established values for the water baseline and the concentrate, you can accurately determine the concentration of foam in the solution (and calibrate for temperature effects as needed). Measuring only one component wouldn’t give you enough information to interpret the mixture correctly.