Define Observation or Inference for half and full saturation Test?
1. Starch is precipitated by half saturation with ammonium sulfate whereas dextrin is not precipitated. This test can be used to detect dextrin.
2. Starch and dextrin are both precipitated with ammonium sulfate. When colloids are dissolved in water, they get hydrated with water. A salt like ammonium sulfate has greater affinity for water and hence on addition to a solution of colloid, it precipitates the colloid from solution. The degree of hydration is proportional to the surface area of the colloid, which in turn is inversely proportional to the size of the colloidal molecule. Thus, starch being a larger molecule compared to dextrin, is precipitated even by half saturation with ammounium sulfate while dextrin is precipitated only when fully saturated with ammounium sulfate.