Differential scanning calorimetry (DSC) produces thermograms which should be satisfactory for purity analyses using the van't Hoff equation. Using mixtures characterized by accepted alternate methods the precision and accuracy of the DSC method have been explored. The single most important variable has been found to be the thermal resistance of the cell sample-encapsulation package. Sample size and heating rate are also important in the accuracy of the determination. This is due to a combination of thermal resistance and response rate of the DSC instrument. When all variables are properly controlled a precision of ± 3% of the component in lowest concentration can easily be obtained. Eutectic formation was found to cause serious errors only when the eutectic melted near the principal component peak. © 1970.