AGRICULTURAL CHEMISTRY. . 127 



the flesh of unripe fruits, and of the roots just mentioned. Its prop- 

 erties in the pure state are quite unknown, since we have no method 

 of separating it from the associated cellulose. Nearly the entire mass 

 of green fruits and of these roots consists of pectose, which is rec- 

 ognized to be a special organic body by the products which it yields 

 when submitted, either naturally or artificially, to the action of vari- 

 ous chemical or physical agents. 



Pectin is prepared from pectose in a way analogous to that by which 

 cellulose or starch yields dextrin, viz: by the action of heat, acids, and 

 ferments. When the fruits or roots that contain pectose are subjected 

 to the action of gentle heat and an acid, the cellulose they contain is 

 more or less changed into dextrin and sugar, and at the same time tho 

 firm pectose begins to soften, and in a little time becomes soluble in 

 water, being converted into pectin. In the baking or roasting of apples 

 and pears, and in the boiling of turnips and beets, it is precisely this 

 transformation that occttrs. When fruit ripens, either on the tree or, 

 as happens with winter apples and pears, after being gathered, the 

 same metamorphosis takes place. The hard pectose, under the influ- 

 ence of the acid (or ferment) that exists in greater or less quantity 

 in the fruits, gradually softens and passes into pectin. If the clear 

 juice of ripe pears be mixed with alcohol the pectin, which cannot 

 dissolve in the latter liquid, is separated as a stringy gelatinous mass, 

 that, on drying, remains as a white body, easily reducible to a fine white 

 powder. The concentrated solution of pectin in water has a viscid 

 or gummy consistence as seen in the juice that exudes from baked 

 apples. 



Under the further action of heat, acids, and ferments, pectin itself 

 undergoes other transformations. We shall only notice its conver- 

 sion into pectosic and pectic acids. These bodies, chiefly the first, 

 together with sugar and flavoring matter, compose the delicious fruit 

 jellies, which, as is well known, are prepared by gently heating for 

 some time the expressed juice of strawberries and raspberries, or the 

 juice obtained by stewing apples, pears, grapes, currants, gooseberries, 

 plums, &c. They are both insoluble in cold water, and remain sus- 

 pended in it as a gelatinous mass. Pectosic acid is soluble in boiling 

 water, and hence most fruit jellies become liquid when heated to 212°. 

 On cooling, its solution gelatinizes again. Pectic acid is insoluble 

 even in boiling water. It is also formed when the pulp of fruits or 

 roots containing pectose is acted upon by alkalies or by ammonia- 

 oxyd of copper. This reagent (which dissolves cellulose) converts 

 pectose directly into pectic acid that remains in insoluble combina- 

 tion with oxyd of copper. 



Our knowledge of the composition of the bodies of the pectose 

 group is very imperfect, from the difficulty or impossibility of pre- 

 paring them in a state of purity. Below is a table of their composi- 

 tion according to the most recent investigations: 



Pectose Unknown. 



Pectin C 32 H 20 23 + 4 HO. 



Pectosic acid C 39 IL 28 -f- 3 HO. 



Pecticacid C 32 IL O.B+2HO. 



