226 
BRITISH PHARMACEUTICAL CONFERENCE. 
In analysing astringent substances by this process it would appear at first 
sight, since both the colouring matter and gallates are dissolved by the am¬ 
monia salt, that we might adopt either the gravimetric or volumetric method 
of procedure, either weighing the washed and dried precipitate, or estimating 
the excess of a previously-known quantity of copper ; but this latter method, 
however, unfortunately, does not work in practice, and I am surprised that 
Dr. Fleck should lay such stress upon it, since the results obtained by it are 
so obviously erroneous. The action of the alkali upon gallic acid, when 
oxygen is present, produces, as is well known, dark brown-coloured products 
of the nature of ulmic acid ; and though in this instance the change proceeds 
but slowly, it is more than sufficient to entirely mask the termination of the 
reaction, since the liquor, instead of being colourless, is more or less yellow, 
which causes the original solution to possess a green colour instead of blue. 
Again, the cyanide does not appear to decompose the cupric gallate in the 
same proportion as the acetate, since the volume of cyanide which is sufficient 
to discharge the blue colour is invariably found to be less than calculation 
would indicate, and thus the percentage is unduly raised. Moreover, the 
cyanide has the property of combining chemically with gallid acid, as I have 
prepared a beautiful white crystalline salt by the agency of these two bodies 
in presence of ammonia, the which, though I have not had time to analyse, 
I am assured contains cyanogen. This fact would also doubtless tend to affect 
the real volume of cyanide used, and vitiate the results. 
If we now proceed to analysis by weight, we shall find the results highly 
satisfactory. There will, of course, be always the one drawback, that we 
cannot estimate mimotannic acid ; and, further, that where many commercial 
analyses have to be conducted, estimation by weight is not sufficiently rapid. 
Nevertheless, I was greatly pleased to find that the percentages obtained by 
this method were, in nearly every instance, corroborated by the old gelatine 
process. 
Valonia. 
*279 grm. gave *1208 tannate 
= 
•08112 tannin 
ZZ 
29-7 per cent. 
Mimosa. 
*2521 
„ „ -1255 
55 
= 
•0968 
55 
383 
55 
Sumach (Palermo) . 
*2785 
„ „ *0928 
55 
zzz 
•0623 
55 
ZZZ 
22-3 
55 
„ (another variety) 
•4502 
„ „ *0639 
55 
zz 
•0429 
55 
zz 
95 
55 
Kermes Oak . . . 
•5608 
„ „ *085 
55 
•057 
55 
10-1 
55 
French Coppice Bark 
•4991 
,, „ *0331 
55 
zzz 
•0222 
55 
zzz 
4.4 
55 
Aleppo Galls . . . 
•16945 
„ „ -152 
55 
zzz 
•102 
55 
zzz 
60-1 
55 
Divi-divi .... 
•246 
„ „ -122 
55 
= 
•0819 
55 
= 
307 
55 
In the accompanying table, the numbers are compared with those obtained 
by gelatine and by volumetric copper :— 
Gallotannic Acid. 
Percentage By Volume, 
by Weight. By Gelatiue. showing error. 
Valonia. 
29*7 
. . 29 . . 43-13 
Sumach (Palermo) . 
•I 
22-3 
20*0 
. . 20 - 2 . .{<£»} 
Sumach (unground) 
• 
( 9-5 \ 
1 9-1 1 
•• 9 5 • • { 1 ^ 0 } 
Kermes Oak . . . 
• 
10-1 
. . 10’4 . impossible to see 
the reaction. 
Divi-divi .... 
• 
30-7 
. . 29-8 — 
French Coppice Bark 
• 
4.4 
4-5 . . 10-8 
Pomegranate Boot Bark 
• • • 
. . 9-0 . . — 
Aleppo Galls . , . 
•1 
58-2 
601 
[ . . 61-0 . . 68-0 
Myrobalans . . . 
• 
. . 38-0 . . — 
Mimosa. 
•1 
f 38-3 
38-4 
•. . 37-0 , . 51T 
