THE VOLATILE PART OF PLANTS. 71 



In 100 parts, Arabic acid contains : 



Carbon 42.12 

 Hydrogen 6.41 

 Oxygen 51.47 



100.00 



By exposure to a temperature of 250, Arabic acid loses one molecule 

 of water, and becomes insoluble in water, being transformed into 

 Metarcibic Acid, (Fremy's Acide metagummique). 



Cerasin, The gum which frequently forms glassy 

 masses on the bark of cherry, plum, apricot, peach, and 

 almond trees, is a mixture in variable proportions of 

 Arabin, or the arabates of lime and potash, with cerasin, 

 or the metarabates of lime and potash. Cold water dis- 

 solves the former, while the cerasin remains -undissolved, 

 but swollen to a pasty mass or jelly. 



UIetaral>ic Acid, is prepared, as above stated, by exposing Arabic 

 acid to a temperature of 250 F., and its composition is Ci 2 H 20 O 10 . It 

 is likewise produced by putting solution of gum Arabic in contact with 

 oil of vitriol. On the other hand, metarabic acid is converted into Arabic 

 acid, by boiling with water and a little lime or alkali. Metarabic acid, 

 as well as its compounds with lime, potash, etc., are insoluble in water. 



BaSSOrin, C 12 H 20 O 10 , as found in Gum Tragacanth, has 

 much similarity to metarabic acid in its properties, being 

 insoluble in water, but swelling up in it to a paste or jelly. 



Vegetable Mucilage, C 12 H 20 O lfl , 



has the same composition, and near- 

 ly the same characters as Bassorin, 

 and is possibly identical with it. It 

 is an almost universal constituent 

 of plants. 



It is procured in a state of purity by soak- 

 ing unbroken flaxseed in cold water, with 

 frequent agitation, heating the liquid to 

 boiling, straining, and evaporating, until 

 addition of alcohol separates tenacious 

 threads from it. It is then precipitated by 

 alcohol containing a little cblorhydric 

 acid, and washed by the same mixture. On drying, it forms a horny, 

 colorless, and friable mass. Fig. 13 represents a highly magnified sec- 



