Cane sugar, optical activity

In the early nineteenth century, the French physicist Jean Baptiste Biot (1774-1862) studied the behavior of a great many substances in a polarimeter. Some, such as turpentine, lemon oil, solutions of camphor in alcohol, and solutions of cane sugar in water, were optically active. Others, such as water, alcohol, and solutions of salt in water, were optically inactive. Later, many natural products (carbohydrates, proteins, and steroids, to name just a few) were added to the list of optically active compounds. What is it about the structure of molecules that causes some to be optically active and others inactive ... 

The French physicist Jean Baptiste Biot (1774-1862) then found that some liquids are optically active (that is, have the power of rotating the plane of polarization). For example, turpentine was found to be levorotatory, and an aqueous solution of sucrose (cane sugar, C12H22O11) was found to be dextrorotatory. The substances that were found to be optically active in solution were all organic compounds, produced by plants or animals. 

It is a singular fact that heinihedral fomis of this kind generally occur in the case of bodies which are optically active, that is wbidi possess tlie power of deviating the plane of polaiizatiou. They are accordingly found (Fig. 343) in tlie case of cane-sugar, which also possesses this optical property. 

The above formulae do not apply when a third optically-active substance is present e.g. glucose in the presence of cane sugar and invert sugar). For such mixtures the copper reducing power must also be determined, as described below. 

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