Abbe’ refractometer

Refractive index. The refractive index of a liquid is conveniently determined with an Abbe refractometer. This refractometer possesses the following advantages ... 

Fig. XI, 2, 5 is a drawing of the Hilger "Abbe refractometer, whilst Fig. XI, 2, 6 is a fine diagram showing the essential parts of the instrument.

The author is indebted to Messrs. Adam Hilger Ltd. for these two figures. A detailed description of the instrument will be found in their booklet, Instructions for the Use of the Abbe Refractometer," and to which the reader is referred for further particulars. 

D774 D1894-78 weighed samples D3420-80 D542 Abbe refractometer, 30°C... 

The refractive index is usually reported as n, where the tiny 25 is the temperature at which the measurement was taken, and the tiny capital D means we ve used light from a sodium lamp, specifically a single yellow frequency called the sodium D line. Fortunately, you don t have to use a sodium lamp if you have an Abbe refractometer. 

Fig. 3.12. An older Abbe refractometer. Thermostatted water enters and exits through the tubes on the front. The front housing also opens to allow sample to be placed between two analyzer plates.

Let us dwell on Figure 6.4 for a moment. The standards and sample solutions are introduced to the instrument in a variety of ways. In the case of a pH meter and other electroanalytical instruments, the tips of one or two probes are immersed in the solution. In the case of an automatic digital Abbe refractometer (Chapter 15), a small quantity of the solution is placed on a prism at the bottom of a sample well inside the instrument. In an ordinary spectrophotometer (Chapters 7 and 8), the solution is held in a round (like a test tube) or square container called a cuvette, which fits in a holder inside the instrument. In an atomic absorption spectrophotometer (Chapter 9), or in instruments utilizing an autosampler, the solution is sucked or aspirated into the instrument from an external container. In a chromatograph (Chapters 12 and 13), the solution is injected into the instrument with the use of a small-volume syringe. Once inside, or otherwise in contact with the instrument, the instrument is designed to act on the solution. We now address the processes that occur inside the instrument in order to produce the electrical signal that is seen at the readout. 

Just like refractive index, the °Brix scale is quite dependent on the temperature. Manual Abbe refractometers do not compensate for this temperature effect. Special correlation tables are used to adjust the readings to a standard temperature, 20°C. Digital refractometers, on the other hand, can operate over a fairly wide range of sample temperatures (+15 to +40°C) and automatically apply these temperature corrections. See Workplace Scene 15.2. 

Using the Abbe refractometer, read and record the refractive indexes of these solutions, the soft drink unknowns, and a control sample, if one is provided. 

In Figure 18.3, the optical system of Abbe Refractometer has been shown based on the critical angle principle. 

Figure 18.4. Abbe Refractometer Optical Path for Upper Prism.

Fig. 18.4, designates the optical path for the upper prism in Abbe Refractometer. When a ray of light passes from the liquid medium and enters the upper prism, it gets refracted by an angle 0 between the lower face of the prism and the normal, an angle P between the emerging refracted ray at the upper face and the normal, and finally an angle a between the reflected ray at the upper face and the normal. Thus, we have ... 

Now, based on the two constants, viz., A and N, for a specific prism and a measurable angle a it is convenient to determine the refractive index of the liquid n relative to air from Eq. (/ ). With the help of the Abbe refractometer the angle a lying between the normal and the critical ray emerging from the upper surface of the prism may be measured. By the aid of the two constants A and N (for a particular prism) the angle a has been converted into the refractive index directly and the scale of the instrument has been duly calibrated and printed accordingly. 

The telescope (F) of the Abbe refractometer is fixed (Figure 18.3) and the prism box (C) is directly attached to the scale. When C is made to rotate gradually the critical ray (E) falls on the cross hair (H) of the telescope (F). At this juncture the value of the refractive index of the liquid ( ) can be measured directly from the scale (G). 

Materials Required Abbe refractometer, volatile oil, xylene, capillary tubes ... 

Butryic acid (CH3CH2CH2COOH) is found to form micelles in an aqueous medium in a concentration range fairly suitable for measurements with the Abbe refractometer. 

Procedure Prepare precisely 2.5, 5.0, 7.5, 10.5, 15.0 and 20.0% solutions of butyric acid in water by measuring suitable volumes (from a stock solution of 25% w/v) with the help of a burette into six 50 ml volumetric flasks, and finally making up the volume with DW. Using Abbe refractometer measure the refractive indices of all the above six solutions besides the stock solution (25%) at 25°C. Measure also the refractive index of DW. 

Forty natural liquid honey samples from Middle Anatolia and surrounding areas, marked as a red circle in the map of Turkey (Fig. 23. 1), were collected directly from different beekeepers during the months of January and February in 2003. The honey samples, stored in glass jars, were kept in the dark at room temperature until analyzed. Moisture was determined by measuring the refractive indices at 200°C with a refractometer (Abbe Refractometer NAR2T) and the corresponding moisture content (%) was calculated according to AOAC method [10]. 

Determination of Wax + Lecithin. Weigh a 3-g sample and transfer it to a small, accurately tared, test tube. Add exactly 3ml of tetrachloro-ethylene and reweigh the tube with contents. Heat it in a steam bath to 90° while stirring vigorously and transfer to a water bath used to maintain the prisms of an AbbS refractometer at 50+0.5°. After... 

Refractive Index, 1.563-0.001 at 25° can be determined using an Abbe refractometer or other standard apparatus... 

The refractive index of experimental agents was measured at 25°C at 589 nm using an Abbe refractometer. The Abbe number was determined by measuring the... 

Refractive Index at 20° — 1.4495 0.0010. Determine it using an Abbe Refractometer... 

Abbe refractometer, 1033 Absorption bands, 1134, 1135, 1136 intensity of, 1135, 1138 Abstracting journals, 1126, 1127 Accidents, laboratory, 1130 Acetal, 320, 327 Acetaldehyde, 319,324 Acetals, 320, 1061 ... 

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