Differential Thermal Analysis.  In differential thermal analysis the sample together with a reference standard is placed in an oven and the two subjected to an identical temperature program. During the temperature program the difference between the temperature of the sample and that of the reference standard is continuously measured and recorded. Any phase change experienced by the sample will be cause a temperature difference between the sample and the standard and the temperature at which the phase change takes place can be identified.    

Further Information on this Topic can be found in the books of R.P.W. Scott by following the listed links