CHAPTER VIII. 

 CARBOHYDRATES. 



As the name indicates, we classify as carbohydrates a group of 

 substances containing carbon and the elements of water, i.e., and 

 H in the proportion of 1 : 2. 



We owe our knowledge of the constitution of the lower members 

 of this group, the crystalloid water-soluble sugars, largely to the in- 

 vestigations of EMIL FISCHER. The same difficulties which we 

 encounter in the study of all colloidal substances interfere with de- 

 termining the constitution of the higher colloidal members of this 

 group, the saccharocolloids. There is at present no means of positively 

 recognizing the purity and the individuality of the substance studied 

 or its derivatives. It is true 'that We may crystallize individual 

 colloidal carbohydrates, e.g., inulin, which as a rule naturally occurs 

 in crystals, but all we have said on page 71 concerning the crystalli- 

 zation of colloids in general applies to inulin. 



Because of their common occurrence, the most important sac- 

 charocolloids are the starches, vegetable and animal (glycogen), and 

 also cellulose. Next in importance come the various gums and pec- 

 tinous plant juices. Dextrins which are also usually colloidal are 

 really cleavage products of the starches. 



A host of individual facts have been derived from the enormously 

 extensive utilization of starches, as food, cereals and potatoes, for 

 fermented liquors, beer and brandy, as sizing, etc., and of cellulose 

 (in the textile industries and paper manufacture). It is only recently 

 that there has been manifested an effort to reach a general view- 

 point such as colloid science has made possible. (E. FOUARD.*) 



STARCH, obtained from starchy grains, is an amorphous white 

 powder which migrates in the electric current to the anode, it exhibits 

 an acid character chemically, since it adsorbs dissolved alkalis (with 

 the exception of NH 4 OH) and hydroxids of the heavy metals, 

 probably thus forming amylates. It does not adsorb acids or salts. 

 (A. RAKOWSKI.*) Since phosphoric acid is always present in native 

 starches and in the diastatic cleavage of phosphorus-containing 

 dextrins, we may assume with M. SAMEC that there is a carbohydrate 

 phosphoric acid complex probably an ester (amylophosphate). 

 Starch has a great reversible swelling capacity in water (pore swelling). 



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