196 AGRICULTURAL CHEMISTRY 



vegetables. They are jelly-like substances, which are 

 soluble in hot water, and are commonly known as fruit 

 jellies. When treated with dilute acids, digestive fluids, 

 and other reagents, the pectin bodies are converted into 

 dextrose sugars and other products. Potatoes, turnips, 

 beets, and all fruits contain pectin. In unripe fruits, and 

 in some uncooked vegetables, the pectin is in the form of 

 acid bodies which are insoluble and indigestible. In the 

 last stages of ripening, the pectin of fruits and vegetables 

 undergoes a change to soluble forms. Soluble pectin is 

 considered to have the same food value as the soluble 

 carbohydrates. 



Experiment 57. Pectose from potatoes. Reduce a small clean 

 potato to a pulp. Squeeze the pulp through a clean cloth into a 

 beaker, add 10 cc. H 2 O, and heat on a sand-bath to coagulate the 

 albumin. Filter, add a little hot water if necessary. To the filtrate 

 add a little alcohol. The precipitate is the pectose material. 



Questions, (i) Is the pectose from the potato soluble? (2) 

 Is pectose coagulated by heat? (3) Is it soluble in alcohol? (4) 

 In what ways does pectose differ from sugar? (5) In what ways 

 does it resemble sugar? 



259. Nitrogen- Free Extract. In the processes of chem- 

 ical analysis of plants and foods, the chemist determines the 

 water, ash, crude protein, ether extract, and crude fiber, 

 and classes the remainder in one group or division called 

 nitrogen-free extract. Wheat, for example, contains : 



Per cent. 



Water 9.25 



Ash 2.95 



Crude protein 13.25 



Ether extract 2.20 



Crude fiber 2.25 



Total 29.90 



TOO 29.90 = 70.10 per cent, nitrogen-free extract. 



