36 THE GEAPE. 



vegetable albumen nor vegetable gluten ; too little 

 was obtained even from a large quantity of juice to 

 allow of a satisfactory analysis. 



The action of heat applied to the juice does not 

 cause vegetable albumen to coagulate, for free tartaric 

 acid retards the coagulation of albumen ; acetic acid, 

 potash, &c., have the same effect. The same cause 

 prevents grape juice from becoming turbid by boiling. 

 Grape juice evaporated to the consistency of an ex- 

 tract, and mixed with alcohol, gave no insoluble albu- 

 minous precipitate, for tartaric acid renders albumen 

 soluble even in boiling alcohol. And if this extract of 

 grape juice be mixed with water and with sufficient 

 carbonate of ammonia to saturate the tartaric acid, 

 the alcohol only produces a deposit consisting prin- 

 cipally of salts. 



According to the method of "Will and Yarrentrapp, 

 the two following results were obtained by M. Vlaan- 

 deren with respect to the quantity of nitrogen found 

 in the residuum of clear filtered grape juice, dried at 

 230 F., 110 C. : 



a. 1-128 gave 0'031 platinum. 



b, 1-150 gave 0*0295 platinum. 



This gives a. 0*39 per cent., and b. 0.36 per cent, 

 nitrogen. 



If we take the mean proportion, or 0*375, and 

 compare it with albumen or gluten, reckoning the 

 nitrogen in the organic elements at 15 -5 per cent., 

 we get, albuminous substances in the extract of grape 



