1923] 



CAMP — CITRIC ACID AS A SOURCE OF CARBON 



227 



and sour stock fruit had a considerably higher acidity (the acid 

 being calculated as the anhydrous acid and not that with the 

 usual 1 molecule of water of crystallization). Grapefruit ran 

 from 0.8 to 1 .61 per cent acidity. The total sugar figures averaged 

 slightly lower than those cited by Colby ( '92) for California fruit. 

 All the above figures were calculated from simple titrations. 



TABLE II 



ACID AND SUGAR CONTENT OF CALIFORNIA ORANGES AND LEMONS 



Variety 



Average 

 for 



Per cent 

 citric acid 



Per cent 

 total sugar 



Navel oranges 

 Seedling oranges 

 Mediterranean 



Sweet (orange) 

 Lemons 



3 yrs. 

 2 yrs. 



3 yrs. 

 lyr. 



.96 

 1.29 



1.28 



6.72-8.4 



10.66 

 12.04 



9.30 

 1.56-2.70 



The hydrogen-ion concentration of the juice of citrus fruits, 

 ?ted from thoroughly macerated pulp, was given by Haas 



('17) 



P H 2.2 for lemons 



and 3.8-3.9 for 

 )f lemons varied 



oranges. Bartholomew ( '23) stated that the P H of 



from 2.2 to 4.4 during the course of growth, and that the average 



for a large number of determinations on mature lemons was 2.31. 



In discussing either the total or actual acidity of citrus fruits the 



the fruit must be 



The duId of 



these fruits consists of numerous small iuice sacs, each of which 



has a definite covering or skin 



consisting 



> 



according to Reed 



('14), of 10 



of small living cells, and inside of this 



of broken-down 



These sacs may be easily separated from each other under a dis- 

 secting microscope without breakage and the consequent loss of 

 acid. Reed ('14) pointed out that while the acidity of the juice 

 contained in the juice sacs was extremely high, indeed high enough 

 to destroy oxidases, yet the living cells of the wall of these juice 

 sacs contain large amounts of oxidase in an active condition. 

 From this he drew the conclusion that the acid is retained within 

 the juice sac by a semi-permeable membrane. The living tissues 

 are not required, therefore, to sustain any such high acidity as is 

 found in the extracted iuice. 



