224 
BRITISH PHARMACEUTICAL CONFERENCE. 
The solution of acetate is titrated in a precisely similar manner against the 
cyanide solution ; and as the power of this latter has been already ascertained, 
a simple rule-of-three sum will show at once the proportion of copper in any 
given number of c. c. of the solution of cupric acetate. Analysis : About 1 
gramme of the astringent substance which it is desired to submit to experi¬ 
ment is boiled with 50 grammes of pure water, filtered, and filter washed with 
boiling water, so much water being added that filtrate and wash water toge¬ 
ther measure 100 c. c. ; 25 c. c. therefrom are taken for the experiment, mixed 
with 10 c. c. of the previously properly titrated solution of cupric acetate and 
10 c. c. (excess) of solution of ammonic carbonate, and the whole raised to 
the boiling-point. The precipitate which ensues is collected on a filter, and 
w 7 ashed with boiling distilled water. The filtrate serves to estimate the pro¬ 
portion of cupric oxide which has not entered into combination with the 
tannic acid. By determining, therefore, the quantity of copper in the filtrate 
by means of KCy, and deducting this from the quantity of copper known to 
be contained in 10 c. c. of the solution of cupric acetate, the quantity of 
copper which has combined with the tannic acid is ascertained. It only re¬ 
mains to fix the composition of the cupric tannate, in order to be able at once 
to calculate the percentage of tannic acid. 
I have given the volumetric determination thus in detail because it forms 
one of the principal features of Fleck’s process ; though, as I shall presently 
show, the estimation by volume cannot in any case be relied upon, save only 
when operating with purified tannic acid. 
From a series of experiments Fleck has determined that ‘00568 grm. copper 
correspond to 1 per cent, of pure tannin, and ‘00875 grm. copper to 1 per 
cent, of pure gallic acid. This latter relation, however correct, is valueless, 
since the whole of the colouring matter in the infusion combines with, and is 
precipitated by the copper salt, the which passing into solution on the addi¬ 
tion of the ammonic carbonate would be reckoned as gallic acid were we to 
attempt to estimate the percentage of that body. With respect to the cor¬ 
respondence between copper and tannic acid, the numbers I have obtained 
do not correspond with those of Fleck. I find that 1 gramme of commercial 
tannin dried at 100° C. combines with ‘3911 gramme of metallic copper=’489 
gramme of oxide, and the following are the analyses upon which this asser¬ 
tion is based:— 
In every case 10 c. c. of acetate solution were used, and by previous expe¬ 
riment, it was found that— 
10 c. c. acetate solutions 15‘34 c. c. cyanide. 
10 c. c. nitrate ,, == 2‘5 c. c. „ 
therefore 10 c. c. acetate „ = T227 grm. copper. 
A. *2195 grm. tannin took 4‘94 c. c. cyanide=6‘774 c. c. acetate consumed. 
C. T445 ,, ,, 7‘9 ,, ,, — 4‘85 „ „ ,, 
B. T745 ,, ,, 6‘4 ,, ,, =5‘83 ,, ,, ,, 
D. -191 „ „ 6.65,, „ =5-67 „ 
A. 1 gramme tannin=30‘86 c. c. cupric acetate 
„ =33 56 „ „ „ 
,, — 33 41 ,, ,, ,, 
„ =29-70 „ 
B. 1 
C. 1 
D. 1 
Mean=31‘88 „ ,, „ 
Therefore 1 grm. tannin=:31‘88 c. c. of acetate=‘3911 grm. copper=‘489 grm. 
CuO. 
The two following analyses show the same result by ignition of the tannate. 
‘1045 grm. cupric tannate gave on ignition ‘03425 grm. CuO ; 
•07025 tannin : ‘03425 CuO : 1: *487. 
