When a chemical is dissolved in a solvent, the concentration of the solution can be measured by the amount of the solute divided by the volume of the solution. The most common concentration measurement is moles of solute per liters of solution, called the molarity (moles/liter). If you take a solution and saturate it 50%, you are doubling the amount of solvent in the solution. This is doubling the denominator of the fraction, so you are dividing the concentration by a factor of 2. In other words, you are cutting the concentration of the new solution in half.