282 CHEMICAL HISTORY OF THE GRATIOL A. 
oxalite of lime, chloride of sodium, silica, and woody fibre 
Vauquelin, Bulletin de Pharmacie, t. i. p. 481.) 
It may be observed that Vauquelin has not mentioned 
tannic acid among these principles, and yet it exists in the 
gratiola. This was because, at the time Vauquelin under- 
took his task, men had extremely vague ideas of the con- 
stitution of organic substances, and on the characters they 
could offer in their reciprocal combinations. Although 
science has not as yet had the last word on the subject, it is 
at least permitted to us, in a host of instances, to dissect 
nature in a better manner, and thus be able to discover 
laws and substances she so obstinately conceals from us. 
The whole of the tannic acid that exists in the gratiola is 
found in theresinoTdsubstan.ee obtained by Vauquelin, and 
it exists in combination with othe rprinciples, among which 
is found one at least which ought to take its place near 
digitaline. In fact, if we dissolve in alcohol the resinoi'd 
matter of Vauquelin ; if we add it to the liquid sulphate of 
iron, until it becomes tinged with blue ; if we add to this 
mixture as much hydrate of lime as is necessary to saturate 
the free sulphuric acid, and decompose the excess of sul- 
phate of iron that was used ; if we mix the alcoholic liquor 
with the water, for the purpose of afterwards filtering it 
(after having bleached it by means of animal charcoal, if 
necessary ;) then, if the liquor is evaporated in vacuo, or 
rather in a situation where the aqueous vapor shall be con- 
stantly carried off by concentrated sulphuric acid, we shall 
obtain as a residuum a white matter; but still a compound 
substance. 
This substance, by the addition of water, is partially dis- 
solved, and gives an excessively bitter taste to the liquid. 
The intention in adding the water is to remove the mineral 
saline particles that are often, if not always, mixed up with 
the bitter principle of the gratiola, in this first part of the 
operation. 
What remains after being washed in water is a substance 
