GENERAL CHARACTERS. 
29 
of the tannin or on the anhydrides and phlobapheues 
resulting from the action of hydrochloric acid. This 
process of heating the tannins with alkali converts some 
of them into protocatechuic acid and either phloroglucol 
or acetic acid,—to this class belong the catechol tannins. 
Another class are converted into gallic and ellagic acids 
by the alkali, and they are found to be the pyrogallol 
tannins. The operation is carried out by taking 20 
grammes of the sample and boiling for three hours with 
150 cc. of potassium hydrate solution, specific gravity 
1.20 ; the liquid is then concentrated with constant 
stirring until it becomes pasty. It is then cooled and 
neutralized with dilute sulphuric acid, filtered from the 
potassium sulphate, and the filtrate treated with sodium 
bicarbonate until the acid is neutralized. The liquid 
is agitated successively with several portions of ether; 
the latter, after separation, is recovered by distillation, 
and its residue dissolved in water; from this solution 
protocatechuic acid is removed by lead acetate, filtered, 
and the phloroglucol, when present, removed from the 
filtrate by ether; the latter is evaporated, and the 
phloroglucol is recognized by its sweet taste, by ferric 
chloride, which imparts to its aqueous solution a deep 
violet-red color, and by bromine-water, which causes 
a separation of crystalline needles, with evolution of 
heat and a very irritating odor. 
With these various characters of the tannins our 
knowledge of them almost ceases. Except gallotannic 
and quercitannic acids the individuals have not been 
much studied, and the latter are only now in course of 
investigation by Bottinger. As recently as 1881, Dar- 
ton, who has had considerable experience in the assay of 
3* 
