Melting Point Apparatus

Melting Point Apparatus

A melting point apparatus is a laboratory device that is used to determine the melting point of an element with great precision and accuracy. The temperature at which the state of a substance changes from solid to liquid is said to be its melting point. Melting of a substance is generally obtained by heating it. It is one of the most important and basic parameters to know about the nature of a substance, determine its purity, and characterize organic and inorganic compounds. Pure elements generally have a sharp and high melting point, whereas impure and contaminated elements have a low melting point and take a comparatively longer time to meltdown completely. The higher melting point of a substance implies that there exist high magnitude intermolecular forces. Most of the melting point apparatuses are able to display the initial as well as the final melting point of an element. Also, some of them are equipped with a mechanism that can record and display the melting point curve and determine the average value of the melting point.

Working Principle of Melting Point Apparatus

A melting point apparatus typically works on the principle of reflectance and transmittance of light falling on and passing through the sample. The change in light transmission is easily visible; therefore, the working of a melting point apparatus is not much complicated. The melting process of a substance can be categorized into five stages, namely, moistening, sintering, collapse, meniscus, and clear point. The moistening point is the initial stage of melting an element. In the collapse stage, the substance is mostly solid and contains a small amount of molten material. At the meniscus point, a major portion of the sample gets melted, but it still contains some of the solid particles. The substance is said to be fully melted once it reaches the clear point or clear stage. The intensity of light passing through the sample varies throughout the stages of the melting process of the substance and is easy to notice. The percentage of light intensity shining through the capillary tubes containing the sample is recorded and compared to determine the difference in optical properties, thereby allowing the user to estimate the melting point of the sample substance.

Working of Melting Point Apparatus

The standard method used by melting point devices to determine the temperature at which an object melts is the capillary technique. To determine the melting point of a sample with the help of the melting point apparatus, the sample is placed into multiple capillary tubes. The capillary tubes are then placed in the heating block. The sample is individually analysed and the average of the measurements is obtained to determine the exact melting point of the substance. The first step of this technique is the preparation of the sample. The substance is placed in a vacuum desiccator for one day to ensure that the sample does not contain moisture and is properly dried. The dried sample is then crushed into fine powder. This is done because coarse and non-homogenous grains of the sample would receive an uneven amount of heat, and the device will not be able to provide accurate measurements. A compact layer of approximately 2-4 mm in height of the properly ground sample is then placed into three or more thin glass capillary tubes. The powdered sample placed in the capillary tubes should be closely packed. This can be done by gently tapping the tube against a rigid surface. The capillary tubes are then placed into the heating block of the melting point apparatus that provides the necessary temperature to melt the sample. The temperature of the heating block can be varied according to the density of the sample. The temperature at which the sample undergoes the five stages of melting is observed and recorded. During the process, some of the samples do not get liquified, but instead, they undergo sublimation and get converted to gaseous form directly. This must be recorded manually. The internal mechanism of the device records the temperature at which the sample begins to liquefy and the temperature when the substance gets fully melted. This temperature interval is said to be the melting range of the substance.

Working of Melting Point Apparatus

Uses of Melting Point Apparatus

1. Melting point apparatus is typically used in the research and development domain to study the structure and characteristics of certain solid substances.

2. Melting point apparatus tells about the purity of a substance, which is why it is prominently used by the quality control department of various industries.

3. It is used by the pharmaceutical and medical industries for drug testing.

4. Perfume industries make use of melting point apparatus to manufacture scents having different fragrances.

Safety Measures While Using Melting Point Apparatus

1. The device should be operated only within the specified restricted temperature range.

2. Do not move or carry the machine when in use and connected to the supply.

3. Make use of safety wearables and tools such as protective gloves, safety goggles, crucible tongs, etc., to handle the hot samples.

4. Keep the device and sample away from flammable and combustible objects to prevent fire hazards and accidents.

Advantages of Melting Point Apparatus

1. The melting point apparatus delivers fast and accurate results.

2. It is compact and portable.

3. The accuracy and precision rate of a melting point apparatus is significantly higher than the traditional methods of calculating the melting point of a substance.

4. It is suitable to calculate the melting point of both pure and contaminated substances.

Disadvantages of Melting Point Apparatus

1. The melting point apparatus can only be used to determine the melting point of solid substances.

2. The device is specifically designed to observe the conversion of sample substances from solid to liquid form. If the sample substance undergoes sublimation or deposition, it is required to be noted manually.


  1. Stan Lukezic
    • Milind Vaidya
  2. vishal Singh

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