Answer:
Emulsion test is used to check the presence of lipids in a sample. This test is based on the dissolution property of the fat molecule. The property of fat is that it is soluble in non-polar solvent like ethanol but are not soluble in polar solvent like water.
So in the emulsion test first the sample is dissolved in ethanol. As ethanol is a non-polar solvent fat is dissolved in it. Then water is added in that solution of ethanol and fat which dilutes the ethanol concentration.
As lipids are not dissolved in water it comes up and gives the solution a cloudy white emulsion which proves that the sample contains lipids. Therefore to determine if the sample contains lipids I will do the emulsion test.