5 02 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 sym- 

 bols is CjjH^O^. 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 defini- 

 tion 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 differ- 

 ence 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 po- 

 larized 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 

 Icevulose, while the other turns it to the right and is called dextrose. 



At ordinary temperatures, however, the laevo-rotatory power of in- 

 verted sugar is much greater than the other. This preponderance of 

 laevo-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 laevulose 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 laavulose 

 set free. 



