Editing Polarization (waves) (section)

=== Chemistry ===
We have seen (above) that the birefringence of a type of crystal is useful in identifying it, and thus detection of linear birefringence is especially useful in [[geology]] and [[mineralogy]]. Linearly polarized light generally has its polarization state altered upon transmission through such a crystal, making it stand out when viewed in between two crossed polarizers, as seen in the photograph, above. Likewise, in chemistry, rotation of polarization axes in a liquid solution can be a useful measurement. In a liquid, linear birefringence is impossible, but there may be circular birefringence when a chiral molecule is in solution. When the right and left handed [[enantiomers]] of such a molecule are present in equal numbers (a so-called [[racemic]] mixture) then their effects cancel out. However, when there is only one (or a preponderance of one), as is more often the case for [[organic molecules]], a net circular birefringence (or ''[[optical activity]]'') is observed, revealing the magnitude of that imbalance (or the concentration of the molecule itself, when it can be assumed that only one enantiomer is present). This is measured using a [[polarimeter]] in which polarized light is passed through a tube of the liquid, at the end of which is another polarizer which is rotated in order to null the transmission of light through it.<ref name="Hecht2002" />{{rp|360–365}}<ref name="VollhardtSchore2003">{{cite book|first1=K. Peter C.|last1=Vollhardt|first2=Neil E.|last2=Schore|author-link2=Neil E. Schore|title=Organic Chemistry: Structure and Function|year=2003|edition=4th|publisher=[[W. H. Freeman]]|isbn=978-0-7167-4374-3|pages=[https://archive.org/details/organicchemistry00voll_0/page/169 169–172]|url=https://archive.org/details/organicchemistry00voll_0/page/169}}</ref>