82 HOW CEOPS GEOTV. 



pectose, are subjected to the joint action of a moderate 

 heat and an acid, the starch they contain is slowly altered 

 into dextrin and sugar, while the firm pectose shortly soft- 

 ens, becomes soluble in water, and is converted into pec- 

 tin. It is precisely these changes which occur in the bak- 

 ing of apples and pears, and in the boiling of turnips, car- 

 rots, etc., w^th water. In the ripening of fruits the same 

 transformation takes place. The firm pectose, under the 

 influence of the acids that exist in all fiuits, gradually soft- 

 ens, and passes into pectin. 



Exp. 33. — Express, and, if turbid, filter tliron^li musiin tlie juice of a 

 ripe apple, pear, or peach. Add to tlie clear liquid its own bulk of al- 

 cohol. Pectin is precipitated as a stringy, gelatinous mass, which, on 

 drying, shrinks greatly in bulk, and forms, if pure, a white substance 

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

 water. 



Exp. 34 — Reduce several white turnips or beets to pulp by grating. 

 Inclose tlie pulp in a piece of muslin, and wash by squeezing in water 

 until all soluble matters are removed, or until the water comes off nearly 

 tasteless. Bring the washed pulp into a glass vessel, with enough dilute 

 elilorhydric acid, (1 part by bulk of commercial muriatic acid to 15 

 parts of water,) to saturate the mass, and let it stand 48 horn's. Squeeze 

 out the acid liquid, filter it, and add alcohol, when pectin will separate. 



The strong aqueous solution of pectin is viscid or gummy, 

 as seen in the juice that exudes from baked apples or pears. 



PcctOSic and Pectic acids. — Under the action of a fer- 

 ment occurring in many fruits, assisted by a gentle heat, 

 pectin is transformed first into pectosic, and afterward into 

 peotic acid. These bodies compose the well-known fruit- 

 jellies. They are both insoluble in cold water, and remain 

 suspended in it as a gelatinous mass. Pectosic acid is 

 soluble in boiling water, and hence most fruit jellies be- 

 come liquid when heated to boiling ; on cooling, its solu- 

 tion gelatinizes again. Pectic acid is insoluble even in 

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

 or roots containing pectose is acted on by alkalies or by 

 ammonia-oxide of copper. The latter agent, (a solvent 

 of cellulose,) converts pectose directly into pectic acid, 



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