518 
PHARMACEUTICAL MEETING. 
isinglass, and add to it about 1 grm. of powdered alum. To ascertain the 
quantity of tannin which 1 c. c. of this solution represents, dissolve 2 grins, of 
tannic acid accurately in 1 litre of water for a standard solution, of which every 
10 c. c. will therefore contain *02 grm. of tannic acid. Measure now 50 c. c. of 
this latter solution, containing T grm. of acid, into a beaker, dilute it somewhat 
with water, and drop in from a burette the aluminous solution until the falling 
of a drop on the surface no longer produces the characteristic ring of tannate of 
gelatine, then allow the precipitate to settle; next take a drop out carefully by 
the end of a glass rod, drop it on to the surface of a black glass plate, and there 
test it for excess of either tannin or gelatine, by bringing in contact with it a 
drop of either solution, and observing whether any cloudiness occur at the junc¬ 
tion of the two drops; when the exact point has been ascertained at which the 
gelatine no longer produces a precipitate, which requires some practice to hit 
exactly, the number of cubic centimetres of gelatine solution consumed cor¬ 
respond to T grm. of tannic acid. 
Mulder does not appear to have tried this process with such substances as 
catechu and kino, at least I can find no notice of it anywhere, and this is its 
weak point, for with this class of bodies, the precipitate, even with the addi¬ 
tion of alum, certainly will not settle, and I failed to obtain by it even an ap¬ 
proximative analysis,—with such the antimony process to be next noticed will be 
found to answer much better; but with everything of the nature of wood, barks, 
roots, leaves, etc., the exact point of precipitation may be ascertained within 
half a c. c., and the percentage calculated without the slightest difficulty. 
In operating, I prefer to extract the soluble portions with hot water, and to 
pour off the clear liquor without filtering, as the small particles thus remaining 
in the solution appear to assist considerably in accelerating the subsidence of the 
precipitate. 
The Antimony process —About four years ago, Dr. B. W. Gerland published 
a process in the ‘ Chemical News ’ for the estimation of tannin, which he con¬ 
sidered as an improvement upon all others up to that date, and it certainly upon 
trial appears to answer remarkably well; he effects the precipitation of the 
tannin by means of a volumetric solution of tartar emetic, in presence of some 
ammoniacal salt, such as the chloride. Now although tartar-emetic will give a 
precipitate of tannate of antimony, even in pure solutions of tannin, a consider¬ 
able time must elapse before the precipitate manifests at all, and it never sub¬ 
sides, let the solution stand ever so long ; but the addition of chloride of ammo¬ 
nium acts even more remarkably than does alum with solution of gelatine, for 
the tannate of antimony instantly forms, and subsides as a dense white curdy 
precipitate, leaving the supernatant liquor quite clear, and ready to be tested 
for excess of either tannin or antimony. 
In preparing the volumetric solution. Dr. Gerland calculates the proportion 
of oxide of antimony necessary to combine with 1 gramme of tannic acid, taking 
3(C,3 HsOi,) =: 636 as the formula for the latter, and the composition of the 
precipitated tannate of antimony SbOy, 3 (CigHgOj 2 ) = 789, consequently by 
dissolving 2-611 grms. of emetic tartar, dried at 100° C. in a litre of water, a 
solution is obtained, 1 c. c. of which (containing *002611 grm.) will exactly pre¬ 
cipitate 005 grm. of tannic acid. 
Now, for my own part, I prefer to standardize the antimony solution in the 
same manner as with gelatine, by dissolving a known weight of tannin in a 
litre of water, ascertaining the number of c. c. required to exactly precipitate 
100 c. c. of the tannin solution, and by this means arriving at the precipitating 
power of the tartar-emetic in hand; for according to Strecker’s more recent 
analyses C 27 H 22 OJ 7 — 618 is the correct equivalent to be given to tannin, and 
* ‘Cheii'ita News,’ vol. viii. p. 54. 
