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



alkaline-earth tartrates. So long as free tartaric acid is present the 

 loss of malic acid is accounted for by the vital processes of the plant, 

 but as soon as there is no longer free tartaric acid present, malic 

 acid will combine with potassium and other bases which may con- 

 tinue to enter the fruit by influx of sap. It would appear that 

 though the fruit was held on the vines at Sandusky until long 

 overripe, the sugar apparently increased to the last and the malic 

 acid decreased. 



The total acidity of the first sample of Catawba is nearly twice 

 the sugar content. Norton also shows the same relation, bub all 

 the other varieties show a much higher ratio of sugar to acid in the ' 

 first samples. These two varieties develop their sugar content rap- 

 idly during the later period of growth and decline in acid content 

 with marked rapidity. Note in this connection the ratio of loss of 

 acid to increase of sugar in Table 2. The acid content of the Catawba 

 sample when harvested was only 22 per cent of the acid shown in 

 the first sample, and the last frosted sample of Catawba showed only 

 about one-sixth of the acid contained in the first sample. Though 

 the Norton crop at Sandusky did not fully ripen, the acid of the 

 last sample was not quite 30 per cent of the first sample. The sugar 

 of the last sample of these two varieties at Sandusky was approxi- 

 mately ten times that of the first sample. Clinton and Cynthiana 

 do not show anything like such extremes, though varieties of about 

 the same season and composition when ripe. Delaware, Ives, and 

 Concord do not show these striking contrasts. 



The results for cream of tartar are somewhat abnormal and should 

 be checked by further complete analyses of the fresh fruit. It 

 would appear that cream of tartar should increase in the fruit of the 

 grape until fully ripe, or, more correctly, until all free tartaric acid 

 disappears, but the evidence on this subject, to which there was access, 

 is not conclusive. Certainly the results of the analyses of fresh juice 

 thus far made do not fully support this presumption. Only the sam- 

 ples of Norton taken at Sandusky show a notable increase of cream 

 of tartar at maturity. Ives and Clinton show also a slight increase. 

 Delaware at Charlottesville shows a slight increase, but all other 

 varieties show a decline of this substance. These results raise the 

 question as to whether the cream of tartar can be wholly recovered 

 by the method of extracting the juice followed in this laboratory. 

 It is undoubtedly true that this substance is deposited as crystals 

 when the juice is fully saturated, and especially will this be more 

 pronounced as the acid content declines and the sugar content in- 

 creases. The temperature of the sample might affect the results to 

 a slight degree because of the varying solubility of cream of tartar 

 at different temperatures. 



