To test the cryoscopic method for determination of purity, the impurity concentrations of duplicate specimens taken from four prepared lots of benzene were determined on the basis of the van't Hoff law of freezing-point lowering and on the assumption that the phases in equilibrium were composed of pure solid benzene and of liquid benzene containing all of the impurities in ideal solution. The adiabatic calorimeter method was used in conjunction with automatic temperature controls and platinum resistance thermometry. Three of the four lots contained weighted amounts of pure n-heptane as an impurity, known only to the preparer, which were added to portions of the first lot which had been purified to better than 99.999 mol % by a fractional crystallization technique.

The mean impurity concentration determined by the calorimetric method for duplicate specimens from the lot of purified benzene was found to be 0.0006₆₀ mol % with deviations of ±27% from the mean of the two specimens. The results of the duplicate specimens from each of the three lots containing added impurity did not deviate by more than ±2% from their means which were 0.088₃, 0.20₆, and 1.0₉ mol % impurity. These mean values deviated by −4, +2, and −7%, respectively, from the values calculated from the known amount of n-heptane impurity that was added to each lot. These results demonstrate that the cryoscopic determination of purity by calorimetry yields accurate values.