TANNIC ACID IN WINE. 195 



into ulmic acid, or some similar substance. Up to 

 this time gallic acid has not been sought in that solu- 

 tion of tannic acid which has been rendered deep 

 brown, by being heated during exposure to the air, 

 otherwise it might perhaps have been discovered. 

 Here, also, it can only be the sugar of the tannic 

 acid which gives rise to a humus-like substance, 

 which, in this case, combines with a portion of 

 the tannic acid, and is thereby precipitated. What 

 therefore is called apothema of tannic acid, is a humus- 

 like substance combined with tannic acid. Berzelius 

 has given the following method of analysis : Let the 

 dissolved tannic acid which has become brown by the 

 action of heat be precipitated with sugar of lead, 

 washed with water, the precipitate dissolved in water 

 and decomposed by means of sulphuretted hydrogen. 

 The tannic acid remains in solution in the water, and 

 in the sulphide of lead a dark-coloured substance is 

 deposited, which is best removed by the use of 

 ammonia, when it yields a dark-coloured solution, and 

 after evaporation deposits a blackish brown sub- 

 stance almost tasteless, and soluble in water. This 

 solution cannot be precipitated by means of solution 

 of gelatine, unless an acid be added, which gives rise to 

 a brown gelatinous precipitate. I regain the term 

 apothema, although the substance is really of the 

 nature of humus. Erom all that has been said, the 

 following inferences may be deduced : 



a. That the yellow colour of old Port wine is the 



