THE FUNCTION OF TANNIN. 
271 
that either free, or in comparatively loose combination with 
it in the vegetable tissues, is an uncertain percentage of 
glucose. This latter may, in part at least, account on the 
one hand for the possibility of growing to some small extent 
moulds in solution of tannin, and, on the other hand, for the 
fact that solutions of tannin can be readily decomposed by 
means of moulds or bacteria into sugar (glucose) and gallic 
acid, and, it is said, under certain circumstances even further. 
Schiffs formula for this decomposition by a ferment is 
(a) C 34 Has 0 22 + 2 H 2 O = C 6 H 12 0 6 (glucose) -f 2 C 14 H 10 0 9 (tannic acid). 
(/>) C 14 H 10 0 9 + H 2 O = 2 C 7 H 6 0 5 (gallic acid). 
Scliiff is stated to have obtained tannic acid free from the 
glucose above referred to by a process consisting essentially 
in acting upon tannin, as extracted, by means of oxychloride 
of phosphorus, but this I take the liberty of very strongly 
doubting. 
Micro - chemistry. — The botanist who works out the 
chemistry of the cell-contents under the microscope is far 
more restricted in his power of producing chemical reactions 
than is the ordinary laboratory chemist. Any changes pro¬ 
duced by his reagents must be clearly optically recognisable, 
and hence, as a rule, he is confined to reagents which produce 
colour reactions, or changes of form ( e.<j ., b} 7- swelling), or 
which act as solvents. Thus, many of the metals, such as 
antimony, lead, barium, strontium, &c., produce tannin reac¬ 
tions which the macro-chemist can work upon, but a white 
precipitate is for micro-purposes useless, owing to the diffi¬ 
culty of recognising it. The most time-honoured reagent for 
tannin is a salt of iron, a reaction known even to Pliny.* 
The salts most commonly in use are chloride, acetate, and 
sulphate, but others have been recommended from time to time. 
"With any of these tannin takes either a green or blue colour, 
giving rise to the customary classification of the tannins into 
iron-blue or iron-green. The main micro-cliemical utility of 
iron-salts as reagents for tannin lies however in their indi¬ 
cating which of these two groups is present; otherwise they 
have several distinct disadvantages. The most important of 
these is that they indicate presence but not position. The 
solution of tannin diffuses so readily and rapidly that the 
* “ Die sehr cliaracterische Reaktion eines Gallapfeldekokts mit 
Eisen war sclion Plinius bekannt, und wurde in Altertkum verwendet 
urn Verfalscliungen des Griinspans mit Eisenvitriol zu entdecken, 
Es ist dies iiberliaupt die allererste chemisclie Reaktion.” Muller’s 
Poulsen’s “ Botanisclie Mikrocbemie,” 1881, p. 69.—Adulteration is 
no modern device of those who make haste to grow rich. It is probably 
as old as trade itself. 
