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Page:Popular Science Monthly Volume 21.djvu/516

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502
THE POPULAR SCIENCE MONTHLY.

gen. By the hundred this is equal to 42·11 per cent of carbon; 51·46 per cent oxygen, and 6·43 per cent hydrogen. Its expression by symbols is C12H22O11. The amounts of carbon and hydrogen in cane-sugar are determined by igniting it with oxide of copper or other substance rich in oxygen. By this process the carbon is converted into carbon dioxide (carbonic acid), and the hydrogen into water, each of which substances is easily collected and weighed.

Indeed, this process is used for estimating carbon and hydrogen in all sugars. The oxygen is usually estimated by difference.

It has thus been shown that oxygen and hydrogen exist in sugar in the exact proportions necessary to form water. A materialistic definition of sugar would be forty parts of fine charcoal mixed with fifty-eight parts of pure water. Yet charcoal and water mixed in the above proportions are far from being sweet; a good illustration of the difference between chemical union and mechanical mixture. Pure cane sugar, when left to itself, has no tendency to change. When diluted with water, however, and brought in contact with a nitrogenous body it undergoes fermentation, and yields at first alcohol, carbonic dioxide, and other products, as will be shown subsequently.

Pure cane-sugar has the power of twisting the plane of polarized light to the right. For the purple ray or transition tint this torsion amounts to 73·8°, and for the monochromatic sodium-flame to 66·67°. These numbers represent its specific rotatory power.

I will give an explanation of what these terms and numbers signify further on. From this property the chemist is able to determine the amount of pure sugar in any sample submitted to him for examination, and containing no other optically active body. For, if, using the sodium-flame, he should find the rotation to be 33·34°, he would know at once that the sample contained only fifty per cent of sugar, and so on for other numbers. When cane-sugar is heated with an acid, or for a long time to a high temperature without one, it suffers a peculiar change which is called inversion. Inverted sugar has almost lost its power of crystallization, and has changed its deportment toward polarized light. It consists now of two distinct kinds of sugar, one of which turns the plane of polarized light to the left and is called lævulose, while the other turns it to the right and is called dextrose.

At ordinary temperatures, however, the lævo-rotatory power of inverted sugar is much greater than the other. This preponderance of lævo-rotatory power increases as the temperature falls, and diminishes as it rises. At 88° Cent., these two powers are equal, and the sugar exerts no influence whatever on polarized light.

These twin constituents of inverted sugar can be separated with lime, which forms with the lævulose a compound less soluble than with the dextrose, and from which the latter is separated by pressure. The lime compound is then decomposed by oxalic acid and the lævulose set free.