Classical optics numerical techniques

Sulfoxides were first prepared in optically active form in 1926 by the classical technique of diastereomeric salt formation followed by separation of the diastereomers by recrystallization16 17. Sulfoxides 1 and 2 were treated with d-camphorsulfonic acid and brucine, respectively, to form the diastereomeric salts. These salts were separated by crystallization after which the sulfoxides were regenerated from the diastereomers by treatment with acid or base, as appropriate. Since then numerous sulfoxides, especially those bearing carboxyl groups, have been resolved using this general technique. 

Because of the particle sizes involved, classically the optical microscope has been the instrument of choice especially for lyophobic colloids. Excellent books and manuals are available (Bradbury 1991 Cherry 1991 Schaeffer 1953) on the numerous variations of optical microscopy, and we do not go into all the details. Our purpose here is merely to point out some very elementary principles that make this method ideally suited for direct examination of colloids. We also use this introduction as a first step in pointing out modern techniques that fall under the class of microscopy but use principles (e.g., electron tunneling see Vignette 1.8) and radiation (e.g., electron or x-ray) other than those used in optical microscopy. 

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