Crossed Nicol prism

In thin sections natural graphite is translucent, strongly pleochroic, and uniaxial. It has a negative sign of birefringence and two extinctions per revolution under crossed Nicol prisms. The atomic number of carbon accounts for its low absorption coefficient for x-rays and electrons. 

When polymer solids are produced from their melts, the most common structures are these spherulites that can be seen by the naked eye and viewed as Maltese crosslike structures with polarized light and crossed Nicol prisms under a microscope. 

Recently, Sato and Hatano 67 69) found a new type of chiral lyotropic mesophase composed of Tween 80, sorbitan mono-9-octadecenoate poly(oxy-l,2-ethanediyl), and water, and discussed the ICD of achiral solute molecules intercalated into the lyotropic mesophase. As the concentration of Tween 80 is increased, three distinct phases are obtained micelle, neat phase, and reversed micelle, in that order. In the region of the volume ratio of Tween 80/(Tween 80 + water) of 0.40 to 0.63 under crossed Nicol-prisms, a focal conic texture was observed. This result indicates that the... 

C. Examine a portion of the sample with a polarizing microscope in polarized light under crossed Nicol prisms. The typical polarization cross is observed, except in the case of pregelatinized starches. 

When an isotropic crystal is placed between crossed Nicol prisms, there is extinction, which means that nothing is seen, and the field is perfectly dark. On the other hand, if an optically anisotropic, birefrin-gent crystal is similarly viewed, it will appear colored except at certain positions of rotation, usually 90° apart. At these positions, extinction occurs because the vibration directions of the light transmitted through the... 

FIGURE 5.13. Crossed Nicol prisms, (a) No crystal, (b) an isotropic crystal between the polarizer and the analyzer and (c) an anisotropic crystal which rotates the plane of plane polarized light to some extent as shown. 

Rotation of crystal between crossed Nicol prisms If a sample is dark at all angles of rotation, it is optically isotropic and is either a cubic crystal or amorphous. If a crystal appears alternately dark and light as it is rotated, it is optically anisotropic (triclinic, monoclinic, orthorhombic, tetragonal, trigonal. 

Crossed Nicol prisms An arrangement of two materials (calcite polarizing prisms or Polaroid discs) such that the first, the polarizer, transmits plane-polarized light that passes through the second, the analyzer, only if oriented in specific ways. 

Selection of optically pure crystals can be accomplished with the aid of a polariscope in which the thin plates of quartz are examined between crossed Nicol prisms in polarized light. These plates are sawed perpendicular to the optical axis of well formed natural crystals. Brasilian twins exhibiting bright interference patterns in crossed Nicol prisms must be broken out. Only optically pure areas are selected for further use, for example, for asymmetric adsorption and for asymmetric catalysis. Piezoquartz as plates of an oblique cut, called the "Cut of Curie", are used in radio electronics and can be identified by the sign of their optically rotation according to the method of Lemmlein According to this method, the etched plate of piezoquartz is... 

The study of birefringence in films of cyclolinear polyphenylsiloxane (CLPhS) gave the following results in a polarizing microscope with crossed Nicol prisms it was distinctly seen that the CLPhS films not subjected to external mechanical influences are on the whole optically inhomogeneous. The film consists of birefringent parts, the optical axes of which are oriented randomly over the entire sample. 

The mummy of Har-mose, the Singer of the eighteenth dynasty, who died about 1490 b.c. (cf Lansing and Hayes 1937) showed pulmonary anthracosis, emphysema, and an old pleural adhesion (Shaw 1938). The pulmonary lymph nodes were loaded with carbon pigment but no silica was detected with crossed Nicol prisms. 

Fig. 8. PhotomicrograiAs of a PDES sample in the transmitted light between crossed Nicol prisms (below) and the surface of the same sample in reflected light (above) at different stages formation of the mesophase at 305 K...

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