A text-book of physiological chemistry for students of medicine / by John H. Long.

  • John Harper Long
Date:
1909
Catalogue details

Licence: Public Domain Mark

Credit: A text-book of physiological chemistry for students of medicine / by John H. Long. Source: Wellcome Collection.

Provider: This material has been provided by the Augustus C. Long Health Sciences Library at Columbia University and Columbia University Libraries/Information Services, through the Medical Heritage Library. The original may be consulted at the the Augustus C. Long Health Sciences Library at Columbia University and Columbia University.

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    This osone on reduction with nascent hydrogen yields a sugar, not glucose, but d-fructose, or levulose: CH2OH.(CHOH)3.CO.CHO + H2 = CH2OH(CHOH)3.CO.CH2OH. Glucose and levulose (cf-fructose) yield the same glucosazone; we are therefore able by this reaction to pass from one sugar to the other. The ready fermentation of glucose will be shown later in the dis- cussion of fermentation reactions in general. The production of glu- cose from cane sugar will also be explained. The specific rotation of glucose in 20 per cent solution is given by the formula [a]z> = 53°, and increases slightly with the concentration. gJ-Fructose, fruit sugar, levulose, is a ketohexose similar to d- glucose in some respects but very different in others. It occurs in honey and sweet fruits, but is not easily separated in a pure state because it is very soluble and does not readily crystallize. The prepa- ration of glucose from ordinary starch has been referred to above. In like manner fructose may be obtained from certain less common starches, especially from inulin by hydrolysis with very weak acid. In pure condition this sugar has no technical importance. The various reduction and fermentation reactions are shown by fructose as well as by glucose, but the quantitative relation between copper hydroxide and fructose is not quite the same as with glucose. As they yield the same osazone the phenyl hydrazine test can not be employed to distinguish between them. The most characteristic prop- erty of fructose is found in its optical behavior. While the specific rotation of c?-glucose is about 53° to the right, that of d-fructose is, at 200 C, and for a strength of 20 per cent, about 93° to the left. Because of this behavior the sugar is commonly called levulose. An- other reaction which may be applied is this: Experiment. Dissolve resorcin in 20 per cent hydrochloric acid and heat a little of this solution with the levulose solution to be tested. A red color results. At the same time a precipitate forms which may be dissolved in alcohol with a red color. One-tenth gram of resorcin to 5 cc. of the acid is sufficient. ^-Galactose. This is the third hexose of importance, but it is not a natural substance. In the inversion of milk sugar by weak acids galactose is formed along with glucose, and it results also from the action of acids on several gums. The sugar is readily soluble in water, fermentable and dextro-rotatory like glucose. It forms a char- acteristic osazone. It reduces Fehling's solution but not in the same proportion as glucose. On reduction it yields dulcitol, which shows its chemical relations most characteristically. On oxidation it yields galactonic and mucic acids. J-Talose is an unimportant aldose of artificial origin.
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