Immersion refractometer

The proof content is determined by the use of a standardized hydrometer with a standardized thermometer. The alcohol content can also be determined by the use of an immersion refractometer, a pycnometer, or a density meter. 

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. 

Modifications of existing differential refractometers have been made for precise evaluation of dn/dc at high X0, which has been particularly necessary where values at other wavelengths are not known. The apparatus of Jennings et al.64) is based on the immersed prism technique of Debye (also used in the commercial Shimadzu-... 

It can be concluded that if nx n2 light can be seen, whereas if nx = n2 no light can be seen. The immersion liquid is adjusted so that this last condition is fulfilled. The refractive index of the immersion liquid is then determined at the same temperature by means of an Abbe refractometer. The value found is equal to the refractive index of the glass. 

The most precise type of refractometer is the immersion refractometer. It contains a prism fixed at the end of an optical tube containing an objective lens, an engraved scale reticule, and an eyepiece. It also contains an Amici compensating prism (see below). In use, the instrument is dipped into a beaker of the liquid clamped in a water bath for temperature control. A mirror in the bath or below it reflects light into the bottom of... 

Essential features of an immersion refractometer. The behavior of tiie critical ray is shown in detail, since diis represents the basic principle of almost all refractometers. 

The most commonly used form of refractometer is the Abbe refractometer, shown schematically in Fig. 11. This differs from the immersion refractometer in two important respects. First, instead of dipping into the liquid, the refractometer contains only a few drops of the liquid held by capillary action in a thin space between the refracting prism and an illuminating prism. Second, instead of reading the position of the critical-ray boundary on a scale, one adjusts this boundary so that it is at the intersection of a pair of cross-hairs by rotating the refracting prism until the telescope axis makes the required angle 8 with the normal to the air interface of the prism. The index of refraction is then read directly from a scale associated with the prism rotation. 

The Abbe refractometer is less precise ( 0.0001) than the immersion refractometer and requires somewhat less exact temperature control ( 0.2°C). For this purpose water... 

The alcohol content of the distillate may be checked by determining the immersion refractometer reading and obtaining the percentage of alcohol from Table A6. 

Determine by the immersion refractometer at 20° the refraction of the distillate obtained in the determination of alcohol. If, on reference to the table under A6, the refraction shows the percentage of alcohol agreeing with that obtained from the specific gravity, it may be assumed that no methyl alcohol is present. If, however, there is an appreciable quantity of methyl alcohol, the low refractometer reading will at once indicate the fact. If the absence from the solution of refractive substances other than H2O and the alcohols is assured, this difference in refraction is conclusive of the presence of methyl alcohol. 

Scale Readings on Zeiss Immersion Refractometer at 20°, Corresponding to Each Per Cent by Weight of Methyl and Ethyl Alcohols... 

Rack, vacuum, 4 ft long, 3 ft high A inch rods 3,4 ft rods, 4, 3 ft rods Receiver, udder type Refractometer, Abbe Ring, cork, 250 mL Rings, cork, 50 mL Sacks, paper, to get dry ice in Stopcock, straight, 2 mm Stopper, rubber, 1 hole. No. 3 Stopper, rubber, 1 hole. No. 7 Strip, terminal, 3 port minimum Support rack, stirring motor rack 10/30 Thermometer, 5 cm immersion, -10 to 150 C Towel to crush dry ice in Transformers, variable Traps, vapor... 

In evaluating Debye s factor H (equation 16), the refractive index increment of the solute must be accurately known. This determination is conveniently carried out with the differential refractometer of P. P. Debye (1946), in which the solution is contained in a hollow glass prism of triangular cross section, immersed in a cell containing the pure solvent. The deflection of a light beam passing through the system is a nearly linear function of the refractive index difference n — n0, which may thus be measured to about 0.000,003. 

In general, these methods have changed very little since the nineteenth century, so that the older references still have value. Wiley and Hobson s review [9] covers refractometer methods and immersion methods, whereas Brown, McCrone et al. [10, II] deal with dispersion staining. Billmeyer [12], Ellis [13], and Schael [14] deal specifically with polymer films, where it must be borne in mind that, as in the case of fibers, birefringence may result from the processing conditions. 

There is a considerable difference between the values of the index of refraction of H2O and D2O, 1.33250 and 1.32796 (at 25°C, Na D-line), respectively. This difference can be used for a rapid, although not very precise ( 0.4 atom percent of D) deuterium analysis of water samples by means of a simple immersion refractometer (Muller et al. 1969). 

Methods—Refractometric. A rapid method for determination of alcohol in wines by refractive index was developed by Newton and Munro (1933). Use of their formula for the immersion refractometer determination of alcohol was found inapplicable to... 

Nicholls also gives a useful table for specific gravity and immersion refractometer readings of dilute mixtures of acetone and water, which is reproduced below. If from the specific gravity of a dilute pure aqueous... 

The B.P. requires the final distillate to comply with purity tests for freedom from methanol and / opropyl alcohol. The refractive index of the distillate, when determined with an immersion refractometer, should not differ by more than 0 00007 (equivalent to 0 2 on the immersion refractometer scale) from that corresponding to the specific gravity of the distillate (see table). If it differs by more than 0 00007 the process B must be used... 

---