516 
PHARMACEUTICAL MEETING. 
ganate of potash to both beakers, till precisely the same rose-tinted colour is 
produced in each. The volumes V and of permanganate consumed, are, of 
course, proportional to the quantity of tannin contained in the liquors, and the 
amount of one being known, the other can be calculated without any difficulty. 
He then proceeds to enumerate certain bodies, which in dilute solutions appear 
to have no action upon permanganate, but •which in the concentrated state act 
slowly; such are citric and tartaric acids, sugar, gum, fats, theine, caffeine, qui¬ 
nine, etc., and to eliminate the action of such substances, states that it is only 
necessary to have the solution sufficiently dilute, so that they may be present in 
ess than one-half per cent. 
Now all this reads very well, and if we were operating on pure tannic acid, 
nothing could be more simple; but unfortunately for it this is never the case, 
and to attempt to use permanganate with deeply coloured infusions is absolutely 
impossible, while to dilute the liquor to such an extent as to nullify the effect of 
the colour, is only practicable in a very few cases; imagine the rose tint visible 
in infusion of catechu! But this is not all, other organic matter than that 
operated upon is present in the solution, and to say that it has no action because 
it is at first imperceptible, is not chemical analysis, nor could any such results be 
accepted as accurate. 
Commailes process *—The next process 1 would mention, is that of Com- 
maile, published a short time since. It is based upon facts noticed by M. IVIillon 
in the 12th vol. 3rd series of the ‘ Annales de Chimie,’ that many organic sub¬ 
stances comport themselves in various manners, when their solution is heated 
with iodic acid, in presence of a small quantity of hydrocyanic acid. Some are 
not affected, whether HCy be absent or present, others only when absent, while 
the class of astringent matters are acted on only when a small proportion of 
hydrocyanic acid is present with them. 
To operate, take a known weight of substance, boil with water and filter, add 
a few drops of H Cy, and boil again gently for a quarter of an hour with a slight 
excess of IgOg; all the iodine set at liberty disappears. Cool, decolorize with 
animal charcoal, and estimate the iodic acid remaining in the liquor. 
This latter may be done in several ways;—1, as argentic iodide by reducing 
the iodate with sulphurous gas; 2, as argentic iodate ; 3, by means of a standard 
solution of indigo in sulphuric acid ; 4, by a standard solution of iodide of potas - 
sium ; and by these methods he has proved that 1 gramme of tannic acid 2-32 
grms. of iodic acid, and 1 grm. of gallic acid^r 2-366 of the same. 
Great credit is due to M. Commaile, for the manner in which these results 
are worked out, and the original paper well repays perusal, it appears to answer 
in practice pretty well, several results being fairly coincident, but the whole is 
too bulky, and the necessary decolorization with charcoal almost fatal, for un¬ 
less it be removed it is impossible to work, and to get rid of it entirely is a very 
difficult job. 
Handtke’s p>rocess f is a volumetric one, depending on the precipitation of the 
tannin by solution of peracetate of iron, some acetate of soda being added to 
cause the separation of the precipitate. Prepare a solution of peracetate of 
density 1*14, and to 16 grms. of this liquid add 8 grms. of acetic acid^and 16 
grms. of acetate of soda, with sufficient water to fill a litre measure; this’ is used 
as a volumetric solution, the termination of the operation being known by the 
liquid ceasing to form a precipitate. M. Handtke, however, practically con¬ 
demns this himself, by stating that the solution of peracetate will not keep, and 
further, that it is only available for substances such as are used in tanning, for 
the astringent matters of coffee, tea, and other leaves and flowers, do not form 
a permanent precipitate. 
* ‘Comptes Eend;is,’ tome lix. p. 398. 
t Jourii. fill- Prak. Cliem. b. 82, p. 3465. 
