194 PECTIN GLUCOSIDES 



These groups remain in combination with the original cellulose as lig- 

 no-cellulose. 



The same authors hold that the cellulose of cereal-straws, esparto 

 grass, etc., is not normal cellulose, but oxy-cellulose. These sub- 

 stances contain more oxygen than cellulose, and probably CO groups. 

 They yield furfural on treatment with hydrochloric acid and give a 

 characteristic rose-red colour on treatment with solutions of aniline 

 salts. The name hemi- cellulose has been proposed for another class of 

 cellulose, which occurs in many plants and which differs from 

 ordinary cotton cellulose in being much more readily hydrolysed both 

 by acids and by enzymes. 



Pectin Substances. This is the name given to the coagulable 

 substances present in many fruit juices, stems, roots, etc. They are 

 generally said to contain more oxygen in proportion to hydrogen than 

 is present in a true carbohydrate, but according to Tromp de Haas and 

 Tollens, 1 who analysed specimens of pectin derived from apples, cherries, 

 rhubarb, currants, plums and swedes, the ratio of oxygen Y to hydrogen 

 does not differ materially from the number (8:1) observed in true 

 carbohydrates. The percentage of carbon varies from 41 to 45 per 

 cent. Pectins by hydrolysis yield pentoses and hexoses. Tollens re- 

 gards them as consisting of carbohydrates in union with acids. 



Pectose is the parent member of the group ; it occurs associated, 

 or perhaps combined, with the cellulose as pecto-cellulose, and is in- 

 soluble. It is particularly abundant in unripe fruits. 



Pectin, a product of the hydrolysis of pectose, is soluble in water 

 and yields solutions which readily gelatinise. It is produced during 

 the ripening of fruits, etc., hydrolysis being brought about either by 

 the vegetable acids present or by an enzyme known as pectase. 



By further hydrolysis, effected by boiling water or alkalies, meta- 

 pectin, parapectic acid and pectic acid, are produced. The exact com- 

 position of these substances has not been determined, as recent work 

 has not corroborated the analyses of the earlier investigators. 



The Glucosides are compounds which, on hydrolysis with acids or 

 enzymes, yield glucose and one or more other products. They are glucose 

 ethers of alcohols, phenols, acids, etc., and have the general formula : 



B O CH 



JH 2 OH 

 where E is an organic radicle. 



1 Annalen, 1895, 286, 278. 



