418 JOURNAL OF THE SOCIETY OF COSMETIC CHEMISTS in phase, some onc-half out of phase, and others out of phase in varying de- grees in between. Each of the individual wavelengths will, therefore, pass the top analyzer in a differential amount where they summate, giving a single color or wavelength. Figure 7 is a black-and-white representation of this phenomenon. For a color interpretation of the summation of retardation, refer to Michael Levy's birefringence chart (9,). There are two types of birefringence which occur in an anisotropic mate- rial: intrinsic and form (9,, 3, 11). Intrinsic birefriengence is a function of the anisotropic polarizability (nonisometric molecular orientation) of electron orbits, and not dependent upon any particular morphology. Form birefrin- gence, however, occurs when crystallites of one refractive index are immersed in a medium of another refractive index. Intrinsic birefringence occurs on a molecular level, whereas form birefringence occurs more on a macromolecular or structural level. The measured quantity, numerical birefringence. is the stunmarion of the intrinsic birefringence and form birefringence (2, $, 4). EXPERIIVIENTAI. Apparatus Microscope: A Reicherr Zeropan research microscope is outfitted for po- larization as follows (Fig. 8(A)): (1) 100 W ouartz-iodine lamp house* (2) strain free, 0.95 N.A., dual- dial•hra•m condenser * ($) calibrated-rotating polarizer and analyzer * (4) 25 X. 0.60 N.A. Neofluar N.A.* obiective, checked to be strain free (5) KPL 8 X Pol Occular*, modified to contain a measuring reticle (6) 360 ø rotating stage* (7) Gips Rot i Ord Compensator* (Fig. 8(B) ) and (8) Ehringhaus Compensator with ouartz plates* (Fig. 8(B) ). 1totaru Device: This device enables a hair fiber to be rotated 360 ø on its own axis for microscopic viewing and to evaluate structure and measure di- mensions (Fi N. 8(C)). Two 25x75 mm glass micro slides (i.e., Corning 2948++). one cut longitudinally with a standard •lass cutter, are needed to make ] reuseable device. The 3 pieces are held together with an epoxy resin glue. It is necessary to use only high quality •lass is all parts of the svstem as any inherent strain present will cause '%ack•round" birefringence. A capillary tube ~ 0.5 mm i.d. ~ 1.0 mm o.d.. and 75-90 mm long (i.e., Scientific Products B4195-2'*), to which a short piece of plastic tubing (Comln• Silastic©$ medical grade tubing 0.035 in. i.d.) is attached, holds the hair for rotation. The capillary tube is filled with immersion oil, n, = 1.515, of a light to medium viscosity (Carl Zeiss ImmersionsoelP). The holdinz channel is fillod with oil of the same refractive index, but of a higher viscosity to damp- en tube movement (i.e., Ziess EinschluBmittel W15*). With a coverslip in place (Coming 22 x 40 mm Number 1-%$), a nearly homogenous refractive *Reicherr Division of American Optical Scientific Instruments, Buffalo, N.Y. 14215. *Carl Zeiss, Inc.. New York, N.Y. 10018. •Corn•ng Glass Works, Scientific Glassware and Equipment Dept., Corning, N.Y. 14830. **Scientific Products, McGaw Park, Illinois.

POLARIZATION MICROSCOPY !:. PLASTIC COVER: SLIP HAIR ?-': CAPIL 'LAB.:'•:'TU BE ............ • ':•:•t'""•:: " .ROTARY:DEVICE • 25min. . ..• . •lmm:: :'CApIE..-LAB't e '.'l•':::•:teW:' 419 Figure 8. Reicherr Zeropan microscope apl•aratus for determination of numerical bire- fringence in hair: (A) microscope with (a) polarizer, (b) strain free condenser, (c) rotary stage, (d) rotary device, (e) strain free Neofluar obiective , (f) analyzer, (g) com,pensator, (h) quartz-iodine light source (B) detail of quartz first order red (i) and Ehringhaus rotary quartz (j) compensators. [Note slow xvave axis orientation (k).] (C) detail of hair rotary device