8 BULLETIN 335, U. S- DEPARTMENT OF AGRICULTURE. 



methods have been carefully checked in this laboratory and at the 

 Bureau of Chemistry and found to give more reliable results than 

 the methods given in Bureau of Chemistry Bulletin 107, Revised. 

 For the items reported as " Fixed acid other than tartaric," the fol- 

 lowing formula was used: Total acid as tartaric — [(total alkalinity 

 X (X0075) +free tartaric acid] = fixed acid other than tartaric expressed 

 as tartaric. This result is practically the same as the "Sauerrest" 

 of the German chemists. 1 



This formula gives those acids present other than tartaric, but as 

 it is known that almost the total quantity of these acids in the grape 

 consists of malic acid, 2 the result may be interpreted as this acid for" 

 the considerations involved in this report. To actually convert this 

 result to malic acid, multiply the figures given in the table by 0.8934. 

 It was not possible, with the conditions under which this work was 

 done, to determine the minute quantities of other acids present, such 

 as succinic and glycolic acids. 



The total acid percentage is practically the same in the green fruit of 

 Concord in both juice and whole-fruit samples, and this relation con- 

 tinues so nearly throughout the entire period that either result may 

 be taken as fairly expressing the content. The total acid is decid- 

 edly higher in the juice sample of green Catawba than in the whole 

 fruit for the first three samples taken; then the acid content of both 

 samples becomes about what may be expected of check samples. 



The results for total tartaric acid in the juice and whole fruit are 

 not so uniform as for total acid. Yet for the Concord samples, both 

 at Sandusky and Charlottesville, there is a degree of uniformity 

 which is striking, considering the difficulty of sampling which has 

 been mentioned. The Catawba samples show much difference in 

 the green fruit, but the later samples approach uniformity. 



There is a striking dissimilarity in the percentage of tartaric acid 

 for the Concord samples at Sandusky and Charlottesville through- 

 out the period of investigation. Those taken at Sandusky show 

 much less variation than the Charlottesville samples and the former 

 show approximately the same amount at the close of the season as 

 for the partly colored samples first taken, while the Charlottesville 

 samples show a very marked decline in tartaric acid for both the 

 juice and fruit samples. Further investigation of this point is neces- 

 sary before offering any critical discussion. 



It would appear that the crushed fruit invariably yields decidedly 

 the greater part of the free tartaric acid content when pressed. The 

 rapid diminution of the percentage of this acid as the fruit ripens is 

 shown for both the juice and fruit samples. These results support 



i Babo and Mach, Kellerwirtschaft, 4th ed., 1910, 2: 629. 

 2 Babo and Mach, Weinbau and Kellerwirtschaft, loe. cit. 



