226 ANNALS OF THE MISSOURI BOTANICAL GARDEN 



[Vol. 10 



carefully washed with 26 per cent alcohol to free it from them 

 and the occluded sugar. 



Unless oxalic acid is present in large amounts it does no harm, 

 but where the amount is so great as to utilize large quantities 

 of permanganate the calcium precipitation should be used and 

 carried out first in an excess of acetic acid. The precipitate of 

 calcium oxalate should be filtered off, the washings and filtrate 

 neutralized, and the regular procedure followed. 



It is quite possible that the autoclave may be satisfactorily 

 made use of in connection with the calcium precipitation. A 

 number of experiments were tried with precipitations in varying 

 amounts of solution, 25, 50, and 100 cc, and it was found that the 

 amount of citric acid remaining in the solution was approxi- 

 mately proportional to the volume. Whether this would vary 

 in the presence of additional substances has not been determined. 



OCCURRENCE OF CITRIC ACID 



Citric acid is commonly known as the constituent acid of citrus 

 fruits. Numerous writers have given figures for the acid content 

 of these fruits, but the figures usually represent titrations of total 

 acid, calculated as citric acid, as is the case in most of the work 

 done on the acidity of fruit juices. However, in the case of citrus 

 fruits the percentage of acid is so high and the presence of citric 

 acid so well known that these figures are fairly accurate. It is 

 probable, however, that other acids occur in small quantities in 

 fruits of the citrus type. 



Colby ( '92) gave figures for the analyses of California oranges 



crops for 2 or 3 years. The figures in 



and lemons covering the 



table ii, taken from his work, give the percentage of total sugar 

 and acid, calculated as citric, in the juice of certain varieties. 

 Chace, Wilson and Church ('21) stated that California lemons 

 contained 3 to 4 per cent of citric acid in the whole fruit (including 

 rind). Gray and Ryan ( '21), in some work on the effects of vari- 

 ous sprays on oranges, gave some figures indicating from 0.7 to 

 1.5 per cent of citric acid in normal, unsprayed oranges. Collison 

 ('13) gave figures on Florida oranges and grapefruit of various 

 varieties. According to these, the good marketable oranges 

 varied from 0.35 to a little more than 1.0 per cent of citric acid 



