72 STUDIES ON APPLES. 



the action progressed and the concentration increased, the odor of cara- 

 mel appeared, but if the volume was kept constant the solution re- 

 mained nearly colorless. There was nearly always left a black residue 

 which consisted in part of pectic acid. This was soluble in alkali, from 

 which acid threw it down in brownish flocks. From the reaction prod- 

 uct, sulphuric acid was removed by barium carbonate. The filtrate was 

 concentrated to a sirup and treated with alcohol, which yielded an 

 abundant precipitate. The filtrate from the alcohol precipitate, evap- 

 orated to dryness, consisted largely of sugar, recognized by the crys- 

 talline form of the compound with sodium chlorid, reducing propert} 7 , 

 and by a weak fermentation. The presence of sugar explained the 

 formation of the black substance, a material of the nature of humic 

 acid. Boiling with sulphuric acid also gave rise to a peculiar odor, 

 like that of ben zoic acid. 



This author notes that pectins disappear during the ripening of 

 fruits; for example, pears containing much pectin when stored in the 

 fall } 7 ielded only 0.5 gram from 100 pears in the spring. It is sug- 

 gested that the pectins may form malic acid when they disappear as 

 pectins. 



Fremy" now published an elaborate paper on the pectin bodies. 

 Pectose was considered to be a substance analogous to starch. Pectin 

 was prepared by boiling a fruit marc or a root marc with malic or 

 citric acid, and also by precipitating a ripe fruit juice with alcohol. 

 Its properties are given neutral, soluble in water, insoluble in alcohol, 

 not colored by iodin, not precipitated by neutral lead acetate, and 

 inactive to polarized light. 



Boiling pectin with water gave parapectin, which only differed 

 from pectin in being precipitated by neutral lead acetate. Boiling 

 pectin with dilute acid gave metapectin, like pectin and parapectin 

 except that it was slightly acid and precipitable by barium chlorid. 

 Prolonged boiling with acids gave parapectic acid; the action of pectase 

 (an enz}^m analogous to diastase) on pectin gave soluble poctosic acid 

 which gelatinized. Alkalis converted pectin into pectic acid, soluble 

 in alkalis and precipitating on adding acid. Heating poetic acid to 

 200 C. gave pyropectic acid. The author noted great difficulty in 

 obtaining pure pectin. Further changes and other pectin bodies were 

 described in an unsatisfactory way. The methods employed were not 

 .described and practically no experimental data were given. The work 

 of Chodnew received no notice. The formation of sugar by the acid 

 hydrolysis of pectins is denied, since, though the solutions are reducing, 

 the} 7 are not active to polarized light and are not fermentable. 6 A list 

 of pectins with proposed formulas is contained in the paper. 



J. pharm. chim., 1847, [3] 12: 13; Comptes rend., 1S47, 24: 1046; Ann. Chein. 

 (Liebig), 1847, (>4: 383. 



6 The fact that pentoses undergo alcoholic fermentation with difficulty was discov- 

 ered later. See W. E. Stone, Amer. Chem. J., 1891, 13: 73. 



