Determining the Melting Point of a Solid
A particular substance will have a distinctive temperature at which it changes from a solid to a liquid. This temperature range is called a melting point. The melting point is the temperature at which the first drop of liquid forms until the temperature at which the sample has formed a transparent liquid. Both temperatures are reported in the melting point (for instance 57-59 deg C).
Preparing the sample
1. Select a new closed-ended capillary tube. They are kept in a clear plastic container next to the melting point apparatus.
2. Push the open end of the tube into your dry, solid sample. You should try to get a 1 mm high portion in the tube.
3. Pack the sample firmly into the closed end of the tube by dropping the tube, closed side down, through a long glass tube. Each time the sample bounced against the bench top, the sample will pack down some more.
Loading sample and measuring melting point
4. Check to make sure the apparatus is cool (the temperature is at least 20 degrees or more below the expected melting point). Carefully slide the packed tube into one of the sample ports of the melting point apparatus. Don't force it, since the tube will break off (and clog that port). You can have as many as 5 samples in the apparatus simultaneously.
5. Turn on the power, and adjust the power to the heating coil. A low setting will have a slower rise in temperature and max out at a fairly low temperature. A higher setting will rise faster through the low temperatures, and slow down and max out at a higher temperature. Your goal is to control the rate of temperature increase such that as the sample is melting, the temperature is only rising about 1 or 2 degrees per minute.
6. Look through the magnifying glass to see your sample in the hot oil bath. Ignore shifting and settling of the sample, and watch until an actual drop of liquid forms (record 1st temp) and then when it has completely formed a liquid (record 2nd temp).
Clean up
7. Turn the power off on the melting point apparatus.
8. Dispose of used melting point tubes in the container marked for them ("Used"), or in the white "broken glass disposal bucket" under the balance table.