226 LECTURE XII. 



capric acid C^U^O^ palmitic acid C 16 H 32 O 2 , stearic acid C^U^O^, have 

 only been found to occur in combination with glycerin as fats (gly- 

 cerides). 



2. Acids of the acrylic series ; general formula C K H 2n _! COOH. 

 Angelic acid, C 5 H 8 O 2 , has been detected in certain plants (especially 



in the root of Angelica Archangelica] in the free state. 



Oleic acid, C 18 H 34 O 2 , occurs in the form of fat (olein) in combination 

 with glycerin. 



3. Acids of the lactic series ; general formula C w H (2n+1 _ w) (OH) m COOH. 

 To this group belongs carbonic acid, H 2 CO 3 , which is produced by all 



plants ; also glycolic acid, C 2 H 4 O 8 , which has been found in unripe grapes ; 

 and lactic acid, C 3 H 6 O 3 , which is probably produced, by the fermentative 

 action of Bacteria, from sugar and other carbohydrates. 



4. Acids of the succinic series ; general formula C M H 2n (COOH)* 

 Oxalic acid, C 2 H 2 O 4 , is frequently present, combined with sodium or 



potassium, in solution in the cell-sap of plants, especially in the leaves of 

 the Wood-sorrel, the Dock, and their allies. It is even more commonly 

 found precipitated in the form of crystals of calcium oxalate. 



Succinic acid, C 4 H 6 O 4 , has only been found in a few plants, but is 

 probably widely distributed. It may be readily obtained from amber 

 which is a fossil resin. 



a. Amidated acids of the succinic series : 



Aspartic or asparaginic acid (succinamic acid) C 4 H 7 NO 4 and gluta- 

 minic acid, C 5 H 9 NO 4 , have not been found in the free state in plants, but 

 they commonly occur in extracts of plants as products of the decom- 

 position of asparagin and of glutamin respectively. 



b. Hydroxy-acids of the succinic series. 



Malic acid, C 4 H 6 O 5 , very commonly occurs in plants, especially in 

 unripe fruits. 



Tartaric acid, C 4 H 6 O 6 , is probably (at least dextrotartaric acid) of 

 universal occurrence in plants, and is usually associated with oxalic, 

 malic, and citric acids. 



These acids occur either free, or in combination with potassium, or 

 calcium, or with organic bases. 



5. Tribasic acids derived from the paraffins. 



Citric acid, C 6 H 8 O 7 , occurs in the free state in many fruits, and is 

 occasionally met with, in potatoes for example, in the form of acid salts 

 of potassium or calcium. 



6. Acids of the maleic series ; general formula, C n H 2n _ 2 (COOH) 2 . 



Fumaric acid, C 4 H 4 O 4 , has been found in a considerable number of 

 plants. 



