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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    that the observation is made with sodium light, a without the brackets is the angle of rotation as read off. Remembering the definition of specific rotation we have this general formula as applied to solutions: , ioo X iooa io4a [a]= ixc -rr in which / expresses the length of the observation tube in millimeters and c the concentration or strength of the solution in grams per ioo cubic centimeters. For many substances this rotation is so characteristic and so easily observed that it constitutes a good test of purity or identity. With the specific rotation known the following relation enables us to find the amount of active substance in solution: io4q C~[a]-l The following are some specific rotations which have importance from the stand- point of physiological chemistry, the temperature being 200 C. in each case: Cane sugar, [a]x) = -|- 66.50 c = 10 to 30 Milk sugar (+H20), [a]D = + 52.5° c= 3 to 40 Malt sugar (+H,0), [a]D = + 137.0° c— 2 to 20 Glucose, [oi]d = -\- 53-0° c = 20 Levulose, [a]o = — 93.00 c= 10 to 20 Invert sugar, [a]x> = —■ 20.20 c = 15 The protein substances, dextrin, glycogen and a number of other compounds to be referred to later have also a high rotating power, which finds application in investigations. THE POLYSACCHARIDES. We have here a very important group of bodies, some of which appear to have an extremely complex structure. Formerly these com- pounds were assumed to be simpler than the sugars and were repre- sented by the general formula C6H10O5. The action of water in producing glucose was assumed to consist merely in the addition of one molecule as shown by the formula: CJJttO, + H,0 = CiHfflO» But this view is no longer held; the starches, cellulose bodies and certain gums belonging to the group have been shown to exist in the form of large and probably very complex molecular aggregations, and the formula (C6H10O5)n is now usually employed to indicate this fact. These polysaccharides are related to the real sugars by several reactions. By certain treatment most of them may be converted more or less readily into maltose, glucose or fructose, and besides this they yield the ester derivatives characteristic of polyhydric alcohols. In their natural condition they are mostly insoluble in water and other solvents. It is customary to make three classes of these compounds, of which the starches or amyloses, as the most important, will be treated first.
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