74 HOW CROPS GROW. 



Mannite, C 6 H M O 6 , is abundant in the so-called manna of the apoth- 

 ecary which exudes from the bark of several species of ash that 

 grow in the eastern hemisphere (Ji'raxinus ornus and rotund ij'olia). It 

 likewise exists in the sap of our fruit trees, in edible mushrooms, and 

 sometimes is formed in the fermentation of sugar (viscous fermenta- 

 tion). It appears in minute colorless crystals and has a sweetish taste. 

 It may be obtained from dextrose and levulose by the action of 

 nascent hydrogen as liberated from sodium amalgam and water, 

 C 6 H 12 O 6 + H 2 = C 6 H 14 O 6 . 



Dulcite, CftHuOg, is a crystalline substance found in the common cow- 

 wheat (Melampyrum nemorostim) and in Madagascar manna. It is 

 obtained from milk-sugar by the action of sodium amalgam. 



The isomeres mannite and dulcite, when acted on by nitric acid, are 

 converted into acids which are also isomeric. Mannite yields saccharic 

 acid, which is also formed by treating cane-sugar, dextrose, levulose, 

 dextrin and starch with nitric acid. Dulcite yields, by the same treat- 

 ment, mucic acid, which is likewise obtained from arabin and other 

 gums. Milk-sugar yields both saccharic and mucic acid. Saccharic 

 acid is very soluble in water. Mucic acid is quite insoluble. Both 

 have the formula C 6 Hj O 8 . 



The Pectin-bodies. The juice of many ripe fruits, when mixed with 

 alcohol, yields a jelly-like precipitate which has long been known 

 under the name of pectin. "When the firm flesh of acid winter-fruits is 

 subjected to heat, as in baking or stewing, it sooner or later softens, 

 becomes soluble in water and yields a gummy liquid from which by 

 adding alcohol the same or a similar gelatinous substance is separated. 

 Fremy supposes that in the pulp " pectose " exists which is transformed 

 by acids and heat into pectin. 



Exp. 33. Express, and, if turbid, filter through muslin the juice of a 

 ripe apple, pear, or peach. Add to the clear liquid its own bulk of 

 alcohol. Pectin is precipitated as a stringy, gelatinous mass, which, 

 on drying, shrinks greatly in bulk, and forms, if pure, a white sub- 

 stance that may be easily reduced to powder, and is readily soluble in 

 told water. 



Pectosic and Pectic Acids. These bodies, according to Fremy, com- 

 pose the well-known fruit-jellies. They are both insoluble or nearly 

 80 in cold water, and remain suspended in it as a gelatinous mass. 

 Pectosic acid is soluble in hot water, and is supposed to exist in those 

 fruit-jellies which liquefy on heating but gelatinize on cooling. Pec- 

 tic acid is stated to be insoluble in hot water. According to Fremy, 

 pectin is changed into pectosic and pectic acids and finally into meta- 

 pectic acid by the action of heat and during the ripening process. 



EXP. 35. Stew a handful of sound cranberries, covered with water, 

 just long enough to make them soft. Observe the speedy solution of 

 the firm pulp or "pectose." Strain through muslin. The juice contains 

 soluble pectin, which may be precipitated from a small portion by 

 alcohol. Keep the remaining juice heated to near the boiling point in 

 a water bath (i. e., by immersing the vessel containing it in a larger 

 one of boiling water). Alter a time, which is variable according to 

 the condition of the fruit, and must be ascertained by trial, the juice 

 on cooling or standing solidifies to a jelly, that dissolves on warming, 

 and reappears again on cooling Fremy's pectosic acid. By further 



