What is the primary function of sodium sulphite when used in x-ray processing?

Sodium sulphite serves as a preservative in x-ray processing solutions, primarily to prolong the life of the developer by protecting it from oxidation. When x-ray film is developed, the developer solution contains various chemicals that facilitate the reduction of exposed silver halide crystals. As the developer ages, it can become less effective due to the oxidation of the active ingredients. Sodium sulphite helps to slow down this oxidation process, thus ensuring the developer remains effective for a longer period.

While some might consider sodium sulphite to have roles in other areas, its primary and most significant function revolves around its preservative qualities, making it essential for maintaining the efficacy of the developer solution over time. This function is critical in both film developing and in maintaining the quality and consistency of x-ray images produced.