JUICE OF THE CONCORD GRAPE. 



351 



The increase of organic and saline constituents was deter- 

 mined by expelling the moisture at 100° Centigrade. The 

 juice was pressed, out with a small iron hand-press, and the 

 specific gravity and per cent of grape-sugar and acid deter- 

 mined by the customary analytical methods. 



The juice collected June 17 was examined, and found in a 

 thin, watery condition, and by certain test showed the purple 

 coloring-matter to be present even at that early period. 



The fruit upon the vines began to change in color the 15th 

 of August, commencing in the stems, and soon passing to 

 the berries ; and Aug. 30 the color had increased to such an 

 extent as to give a bluish-purple precipitate with a solution 

 of basic sugar of lead. 



The table shows, that, at the time when the first coloring 

 occurred, a great change was taking place in the growth of 

 the grape. The free acid, which had reached its highest 

 point the first week of August, lost fifty per cent before Aug. 

 30. Grape-sugar began to increase rapidly when the free 

 acid decreased. Aug. 2 all the acid was in solution ; and the 

 decrease was due to its being changed into insoluble com- 

 pounds of lime and potassa in crystalline form, and not, as 

 claimed by Liebig and others, to the change of the acid into 

 grape-sugar. 



The mineral constituents show no less change during 

 growth, as will be seen by the following table : — 



