on a Substance possessing the Properties of Tannin. 313 
but oxalic acid when formed in any considerable quantity, 
seemed absolutely to prevent the formation of this substance ; for 
whilst abundance of the former was obtained from gum arabic, 
tragacanth, manna, and guaiacum, not any of the latter could 
be produced. 
Common liquorice appears at first to be an exception, but 
from the smallness of the quantity and the colour of the 
precipitate which it produced with solution of isinglass, I am 
almost convinced that the tanning substance was formed by the 
action of the nitric acid on a portion of uncombined carbon, 
In sulphuric acid, that a great quantity of beautifully crystallized white benzoic acid 
was sublimed during digestion; and as it is produced in so very pure a state by this 
single and simple operation, I would recommend a trial of the process to those who 
prepare benzoic acid for commerce; but I am not certain whether this mode may prove 
more economical than those which at present are employed. 
When dragon’s blood, however, was treated in the same manner with sulphuric acid, 
I could not obtain a particle of benzoic acid ; nor did I succeed much better when I had 
recourse to lime, according to Scheele’s process; for although a considerable quantity 
of the substance was thus rendered soluble in water, yet by the addition of muriatic 
acid I obtained only a slight appearance of benzoic acid accompanied by a copious 
precipitate of red resin, notwithstanding that the solution had acquired a powerful 
and peculiar balsamic odour. 
But in a former part of this Paper I have stated, that when dragon’s blood was 
dissolved in nitric acid, and afterwards evaporated to dryness, it yielded about 6 per 
cent, of benzoic acid. Now if this had been originally present in dragon’s blood in the 
state of benzoic acid, some stronger evidence of it might reasonably have been ex- 
pected in each process, but this not being the case, I am inclined to consider it as pro- 
duced, and not educed, by the action of the nitric acid on the original principles of the 
dragon’s blood ; and I am also persuaded that similar but more general effects take 
place when benzoin or any of the balsams are subjected to the diffeient processes by 
which benzoic acid is ob ained ; so that to me, this last seems to be as much a chemical 
product, as the oxalic, the acetous, and other of the vegetable acids. 
The succinic acid also appears to be a product and not an original ingredient of 
amber. 
MDCCCV. 
Ss 
