The Thiele tube, named after the German chemist

Johannes Thiele Johannes Thiele may refer to: *Johannes Thiele (zoologist) *Johannes Thiele (chemist) Friedrich Karl Johannes Thiele (May 13, 1865 – April 17, 1918) was a German chemist and a prominent professor at several universities, including those in ...

, is a

laboratory glassware Laboratory glassware refers to a variety of equipment used in scientific work, and traditionally made of glass. Glass can be blown, bent, cut, molded, and formed into many sizes and shapes, and is therefore common in chemistry, biology, and anal ...

designed to contain and

heat In thermodynamics, heat is defined as the form of energy crossing the boundary of a thermodynamic system by virtue of a temperature difference across the boundary. A thermodynamic system does not ''contain'' heat. Nevertheless, the term is ...

an oil bath. Such a setup is commonly used in the determination of the

melting point The melting point (or, rarely, liquefaction point) of a substance is the temperature at which it changes state from solid to liquid. At the melting point the solid and liquid phase exist in equilibrium. The melting point of a substance depen ...

of a substance. The apparatus resembles a glass

test tube A test tube, also known as a culture tube or sample tube, is a common piece of laboratory glassware consisting of a finger-like length of glass or clear plastic tubing, open at the top and closed at the bottom. Test tubes are usually placed in ...

with an attached handle.

Operation

Oil is poured into the tube, and then the "handle" is heated, either by a small flame or some other heating element. The shape of the Thiele tube allows for formation of

convection Convection is single or multiphase fluid flow that occurs spontaneously due to the combined effects of material property heterogeneity and body forces on a fluid, most commonly density and gravity (see buoyancy). When the cause of the c ...

currents in the oil when it is heated. These currents maintain a fairly uniform temperature distribution throughout the oil in the tube. The side arm of the tube is designed to generate these convection currents and thus transfer the heat from the flame evenly and rapidly throughout the heating oil. The sample, packed in a capillary tube, is attached to the thermometer, and held by means of a rubber band or a small slice of rubber tubing. The Thiele tube is usually heated using a microburner with a small flame.

Melting point determination

A sample in a sealed capillary, attached to a

thermometer A thermometer is a device that measures temperature or a temperature gradient (the degree of hotness or coldness of an object). A thermometer has two important elements: (1) a temperature sensor (e.g. the bulb of a mercury-in-glass thermometer ...

with a rubber band, is immersed in the tube. Heating is commenced, and the temperature ranges at which the sample melts can then be observed. During heating, the point at which melting is observed and the temperature constant is the melting point of the sample. A more modern method uses dedicated equipment, known as a

melting point apparatus A melting-point apparatus is a scientific instrument used to determine the melting point of a substance. Some types of melting-point apparatuses include the Thiele tube, Fisher-Johns apparatus, Gallenkamp (Electronic) melting-point apparatus and ...

. A slow heating rate at the melting point is needed in order to get an accurate measurement. Record the temperature on the thermometer when the sample starts to melt and record the temperature again when all of the sample has melted (this gives you the melting point range, which is what is usually quoted in chemical literature).

Boiling point determination

A sample in a

fusion tube A test tube, also known as a culture tube or sample tube, is a common piece of laboratory glassware consisting of a finger-like length of glass or clear plastic tubing, open at the top and closed at the bottom. Test tubes are usually placed in s ...

is attached to a thermometer with a rubber band, and immersed in the tube. A sealed capillary, open end pointing down, is placed in the fusion tube. The Thiele tube is heated; dissolved gases evolve from the sample first. Once the sample starts to boil, heating is stopped, and the temperature starts to fall. The temperature at which the liquid sample is sucked into the sealed capillary is the boiling point of the sample.

References

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