FRUITS AND THEIR COMPOSITION. 311 



yet on filtering it will be found that what passes through above 

 contains scarcely a trace of a mucilaginous substance. Hence, 

 it is doubtful whether mucilages exist which are actually solu- 

 ble in water, and whether they occur in wine. Artificial dex- 

 trin is, however, an exception, as it forms with water a perfectly 

 clear fluid, which can be filtered. We will here call attention to 

 an easy method of distinguishing between solution of gum- 

 arabic and of dextrin ; the first cannot be heated, even for a 

 minute, over an open fire without scorching, while the latter can 

 be completely boiled down without fear of burning. 



Tannin. Several kinds of tannin occur in plants, which can ; how- 

 ever, be finally reduced to two modifications, viz : pathological and 

 physiological tannin. The first occurs in large quantity in nut- 

 galls, especially in the Chinese variety, also in sumach (the twigs 

 of Rhus Coraria) and in many other plants. Pathological tan- 

 nin is characterized by splitting under the influence of dilute 

 acids as well as by fermentation into gallic acid and grape-sugar. 

 Furthermore, it completely precipitates glue from its solutions, but 

 is not suitable for the conversion of the animal skin into techni- 

 cally serviceable leather which will withstand putrefaction. Be- 

 sides, only the gallic acid obtained from pathological tannin 

 yields pyrogallic acid by dry distillation. 



Physiological tannin is chiefly found in materials used for tan- 

 ning ; it cannot be split by dilute acids or fermentation, does not 

 yield gallic acid, and the product of dry distillation is not pyro- 

 gallic acid, but pyrocatechin or oxyphenic acid ; it converts the 

 animal skin into perfect leather. 



There can be but little doubt that physiological tannin is the 

 variety found in fruits or fruit-juices. Generally speaking, a 

 content of tannin in wine is not exactly a desirable feature, as 

 it is readily decomposed. It can only have an advantageous 

 effect when the wine contains an excess of albuminous substances 

 which the tannin removes by entering into insoluble combinations 

 with them. This may be the reason why wine containing tannin 

 is considered more durable, because if it contained albuminous sub- 

 stances in large quantity it would be still more readily subjected 

 to changes. Under such circumstances a small addition of tan- 

 nin to the wine may be of advantage, though instead of tannin it 



