THE VOLATILE PART OF PLANTS. 75 



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

 pectic acid. 



Other ripe fruits, 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 fail in attempting to fol- 

 low them. 



Scheibler having shown that Fremy's metapectic acid of beets is 

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

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

 described. The 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, COOH, 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 



Formic acid, H, C O O H Pine needles, icd ants, guano. 



Acetic " C H, C O O H Vinegar and many vegetable juices. 



Propionic " C 2 H s COOH Yarrow-flowers. 



Butyric " C 3 H 7 C O O H Butter,limburgercheese,parsnip seeds. 



Valeric " C 4 H 9 C O O H Valerian root, old cheese. 



Caproic " C 5 H n COOH Butter, cocoanut oil. 



Oenanthylic " C H 13 C O O H (Artificial.) [fusel oil. 



Caprylic " C 7 H 1B COOH Butter, cocoanut oil, limburger cheese, 



Pelargonic " C 8 H I7 COOH Rose-geranium. 



Capric " C 9 II,,, COOH Butter, cocoanut oil. 



Umbellic " Cj H 21 C O O H Seeds of California laurel. 



Laurie " C u Hjg COOH Laurel oil, butter, bayberry tallow. 



Iridecylic M C u HjsCOOH (Artificial.) 



