Melting Point Determinations: Sample Melting

What should you observe through the eyepiece as you watch your solid sample through the Mel-Temp eyepiece? You may see the sample shifting slightly (wiggle) or small amounts of condensation form on the interior walls of the capillary tube near the solid. These are not signs of melting.

The initial melting point temperature is recorded when you begin seeing the small granules of the sample becoming a liquid. The final melting point temperature is recorded when the entire sample is observed to be a liquid. You may also see color changes as the sample chemically changes due to the elevated temperature. This is the reason for never using a capillary sample more than once: the sample may have become an entirely different substance as a result of the first melting point determination.

The photos below are of a solid at various stages of melting in the Mel-Temp apparatus taken over a 30 second time interval. This is what you will see as you peer into the Mel-Temp eyepiece. Note the two additional locations to the right and left of the sample capillary that may be used for additional samples.

.

1. The first photo is of the room temperature sample.
2. In the second photo, the temperature has been increased and liquid is observed near the top of the solid. (...record this temperature...it is the lower temperature limit)
3. More liquid and a slight darkening of the remaining sample is observed in photo number 3.
4. The entire sample has melted (...record this temperature...it is the upper temperature limit)