62 CARBOHYDRATES AND THEIR [ch. 



(sp. gr. ri5, see Expt. 43) to tlie syrup and heat on a water-bath almost to dryness. 

 Pour the residue into about 100 c.c. of water and allow to stand. A microcrystalline 

 precipitate of mucic acid is formed showing the presence of galactose (see p. 50) as 

 a product of hydrolysis. 



Mucilages. 



The characteristic of these substances is that they swell up in water 

 and produce colloidal solutions which are slimy. 



Mucilages are widely distributed and may occur in any organ of the 

 plant. Sometimes they are confined to certain cells, mucilage sacs or 

 canals. They are distinguished from the pectic substances by the fact 

 that they do not gelatinize. Some of the best known examples of 

 mucilage-containing tissues are those in the root and flower of the 

 Hollyhock (AWiaea rosea): in succulent plants (Aloe, Euphorhia), in 

 bulbs {Scilla, Allium) and tubers (Orchis Morio): in seeds of Flax or 

 Linseed (Linum) and in fruits of Mistletoe (Viscum album). 



The mucilages vary in composition. They appear to be largely, if 

 not wholly, condensation products of various sugars (galactose, mannose, 

 glucose, xylose, arabinose), similar constituents to those of many gums 

 and hemicelluloses. On hydrolysis various mixtures of sugars are pro- 

 duced. Of the mucilages, that from linseed has been thoroughly 

 investigated. It has been found on hydrolysis to give sugars only, e.g. 

 arabinose, xylose, glucose and galactose. In this respect mucilages differ 

 from gums, since the latter have always some other accompanying sub- 

 stance in addition to sugars. 



Exjyt. 64. Preparation and properties of mucilage from Linseed {Linum) (Neville, 

 21). Take about 60 gms. of linseed and let it soak for 24 hrs. in 300 c.c. of water. 

 Then separate the slinie from the seeds by squeezing through muslin, and add to the 

 liquid about twice its volume of 96-98% alcohol. The mucilage is precipitated as 

 a thick slimy precipitate. Filter off the precipitate and wash with alcohol. By 

 washing with absolute alcohol and ether and finally drying in a desiccator, the 

 mucilage may be obtained as a powder. 



Add water to some of the mucilage. It swells up and finally gives an opalescent 

 solution. Make with it the following tests : 



(a) Add iodine. No colour is given. 



(6) Add a little Fehling's solution and boil. No reduction takes place. 



Expt. 65. Hydrolysis of Linseed mucilage. Put the remainder of the mucilage in 

 a round-bottomed flask and add 50 c.c. of 4 "/o sulphuric acid. Fit the flask with 

 an air condenser (see p. 45) and heat for at least four hours on a water-bath. 

 Cool and neutralize with barium carbonate. Filter off' the barium sulphate, and 



