360 CHANGES OF ORGANIC MATTER IN THE PLANT. 



^ Sugar-cane stem 16-18 per cent. 



Sugar-beet 10-14 " 



Sorghum 10-11 " 



Indian corn 5-7 " 



Sugar maple 8 " 



947. Products free from nitrogen. II. Vegetable acids. Of 



these the most widely distributed are oxalic, tartaric, citric, and 

 malic acids. 



948. Oxalic acid (C 2 H 2 O 4 ) occurs in almost every plant, the 

 amount in some reaching as high as 4 per cent. Most of it is 

 combined with calcium or with potassium, a part remaining un- 

 combined. According to Miiller, 1 the fresh leaves of sugar-beet 

 contain 4 per cent of this acid, of which one third is in solution. 



949. Tartaric acid (C 4 H 6 O 6 ) occurs free, and also combined 

 with potassium in the juice of the grape and many other fruits. 



950. Citric acid (C 6 H 8 O r ) occurs in the amount of 6 to 9 

 per cent in the juice of lemons and allied fruits, and is asso- 

 ciated with other acids in most of our subacid fruits, such as 

 currants, cherries, etc. 



951. Malic acid (C 4 H 6 O 5 ) occurs free, or combined with cal- 

 cium, in the juices of many fruits and in the sap of many plants. 

 It imparts the sour taste to our most common fruits. 



952. Products free from nitrogen. III. Fats, or Glycerides. 

 According to Ebermayer most of the fats which occur in plants 

 are mixtures (not compounds) of the following three kinds of 

 fats in different proportions : Tristearin or stearin, tripalmatin 

 or palmatin, triolein or olein. The oils in most seeds, however, 

 are free, fatty acids ; namely, stearic, palmitic, and oleic. 



The fats are regarded as compound ethers formed from the 

 triatomic alcohol glycerin, whence they have been sometimes 

 termed Glycerin ethers. The following formulas exhibit one view 

 as to their constitution : 



Tristearin . l j 



Tripalmatin .......... f 3 3 



Triolein ........... (CH0) 



3 5 



Stearic acid .......... ^18^36^2 



Palmitic acid ......... C 16 H 32 0. 2 



Oleic acid .......... C t 18 Hg 4 0. 2 



(Glycerin ......... C 3 H 5 (OH) 3 ) 



1 Quoted by Ebermayer, Chemie der Pflanzen, p. 320. 



