THE VOLATILE PART OP J>LAKTS. 



75 



heating, the juice may lorm a jelly which is permanent when hot— 

 peotic aold. 



Other ripe fruita, as quinces, strawberries, peaches, grapes, apples, 

 etc., may be employed for this experiment, but In any case the time 

 required for the juice to run through these changes cannot be pre- 

 dicted safely, and the student may easily fall in attempting to fol- 

 low them. 



Soheibler having shown that Fremy's metapeotlo acid of beets Is 

 arable acid, it is probable that Fremy's pectin, pectlc acid and pectosic 

 acid of fruits, are bodies similar to or identical with the gums already 

 described. "Hie pectin bodies of fruits have not yet been certainly ob- 

 tained In a state of purity, since the analyses of preparations by vari- 

 ous chemists do not closely agree. 



The Vegetable Acids. — Nearly every family of the 

 vegetable kingdom, so far as investigated, contains one 

 or more organic acids peculiar to itself. Those of more 

 general occurrence which alone concern us here are few 

 in number and must be noticed very concisely. 



The vegetable acids rarely occur in plants in the free 

 state, but are for the most part united to metals or 

 to organic bases in the form of salts. The vegetable 

 acids consist of carboxyl, OOOH, united generally to 

 a hydrocarbon group. They are monobasic, dibasic or 

 tribasic, according as they contain one, two or three 

 carboxyls. 



The Monobasic Acids, to be mentioned here, fall into 

 two groups, viz. : Fatty acids and Oxyfatty acids. 



The Fatty Acids constitute a remarkable " homolo- 

 gous series," the names and formulae of a number of 

 which are here given: 



Found in 

 Pine needles, red ants, guano. 

 Vinegar and many vegetable juices. 

 Yarrow-flowers. 



Butter,llmburger cheese,parsnlp seeds. 

 Valerian root, old cheese. 

 Butter, cocoanut oil. ■ 

 (Artificial.) [fusel oil. 



Butter, cocoanut oil, limburger cheese, 

 Kose-geranium. 

 Butter, cocoanut oil. 

 Seeds of California laurel. 

 Laurel oil, butter, bayberry tallow. 

 (Aitlflclal.) 



