November 12, 1870.3 THE PHARMACEUTICAL JOURNAL AND TRANSACTIONS. 
3S3 
then left in the form of vesicular masses, made up of 
thin glistening scales. The amount of tannin ob¬ 
tained varies from 30 to 00 per cent, of the weight of 
the galls employed. 
Tannin is uncrystallizable, very soluble in water 
and in rectified spirit, and gives a yellowish-white 
precipitate with solution of gelatine. [Contrast these 
with the characters of gallic acid.] It is almost in¬ 
soluble in pure ether, but in a mixture of ether and 
water readily dissolves. 
It is soluble in about six times its weight of glyce¬ 
rine ; in less if warmed. It gives precipitates with 
almost all metallic solutions, and with most of the 
alkaloids. If free from adulteration, it is completely 
soluble in rectified spirit, and burns without leaving 
a residue. 
The amount of tannin dissolved in a liquid, e. g. a 
vegetable infusion, is usually estimated by ascertain¬ 
ing the amount of a solution of gelatine of known 
strength, wliicli is precipitated by a given quantity 
of it. .... . 
Tannin is a “ glucoside,” that is, when boiled with 
acids, or when under the influence of the peculiar 
ferment contained in galls, it splits up, yielding glu¬ 
cose among the products of its decomposition. [See 
gallic acid.] There are several varieties of tannin ; 
this from oak galls (gallotannic acid) is distinguished 
by giving a bluish-black precipitate with ferric salts; 
another kind from catechu (mimotannic acid) gives a 
greenish compound with ferric solutions. 
Acidum Tartaricum. H 2 C 4 H 4 0 6 . Acid tartrate 
of potash is first boiled with chalk until the effer¬ 
vescence has ceased and the liquid is neutral. There 
is then formed a precipitate of tartrate of calcium, 
and a solution of neutral potassic tartrate. 
2(KHC 4 H 4 0 6 ) + CaC0 3 
Acid tartrate of Carbonate of 
potassium. calcium. 
= K„C 4 H 4 0, + CaC 4 H 4 0 6 + H.0,C0 2 . 
Neutral tartrate Tartrate of Carbonic 
of potassium. calcium. acid. 
To the liquid is added a solution of chloride of 
calcium; this causes a further precipitation of tar¬ 
trate of calcium:— 
K 2 C 4 H 4 0 6 + CaCL 
= CaC 4 H 4 0 6 + 2 K Cl. 
The mixed precipitates are collected, drained, 
washed, and decomposed by digestion with diluted 
sulphuric acid:— 
CaC 4 H 4 0 6 + H 2 S0 4 = H 2 C 4 H 4 0 6 + CaS0 4 . 
Most of the sulphate of calcium produced is re¬ 
moved by filtration; the tartaric acid crystallizes 
from the concentrated solution. 
Tartaric acid is recognized by blackening, when 
heated, with an odour like that of burnt sugar. It 
gives a white crystalline precipitate (KHC 4 H 4 0 6 ) 
with solution of acetate of potash. Admixture of 
oxalic acid would be detected by the solution giving 
a precipitate with one of sulphate of lime ; alum or 
any sulphate, by forming a precipitate with chloride 
of barium ; sulphate of lime, by giving a precipitate 
with oxalate of ammonia, also by leaving a residue 
when burned with free access of air. 
7 grams (Jy of a gram-molecule) of tartaric acid 
require, for neutralization, 100 cubic centimetres of 
the volumetric soda. 100 c.c. vol. solution contain 
of a gram-molecule, or 4 grams of NaHO. 
Tartaric acid utters an example of isomerism. There 
are three (or perhaps four) acids all represented by 
the same chemical formula, being of the same com¬ 
position, but differing from one another in chemical 
and physical properties. Dextrotartaric acid, the 
common kind, rotates a ray of polarized light to the 
right; kevo-tartaric acid to the left; and racemic 
acid, which is formed by the union of the two former, 
is inactive. Bodies which thus have the same compo¬ 
sition, but exhibit characteristics which show that 
they are not identical, are said to be isomeric. The 
differences are considered to be due to a difference of 
constitution, or manner of arrangement of then - con¬ 
stituent atoms. The particular kind of isomerism 
exhibited by the modifications of tartaric acid is 
sometimes called physical isomerism or allotropy. 
The related bodies are convertible one into the other, 
and differ chiefly in mechanical, slightly in chemical 
properties. 
Oxalic Acid. —Appendix I. The oxalic acid of 
commerce is made in two ways. Sometimes sugar 
is boiled with slightly diluted nitric acid: nitrous 
fumes are evolved, and on cooling, the oxalic acid 
crystallizes out. Saccharic acid, C 6 H 10 O 8 , is formed 
at first, and is afterwards converted into oxalic acid, 
but the reactions cannot be shown in any simple or 
probable equation. A large quantity is now made 
by roasting sawdust (impure cellulose) with a mix¬ 
ture of caustic potash and soda. The resulting alka¬ 
line oxalate is boiled with lime, which gives insoluble 
oxalate of calcium, and this is converted into the 
acid by digesting with diluted sulphuric acid. 
[§ Test. It is entirely dissipated by a heat below 
350° F.] The commercial acid almost invariably 
leaves a small residue of sodic carbonate. Oxalates 
oive a white precipitate with chloride of calcium, 
which is not dissolved by the addition of acetic acid: 
when heated they give oft carbonic oxide, C O, and 
leave a residue of carbonate of the metal. Neutral 
ammonium oxalate, heated gently, gives up water 
and furnishes a white, nearly insoluble, slightly 
volatile residue of oxamide. 
(N H 4 ) 2 C 2 0 4 — 2 H 2 O = (NH 2 ) 2 C 2 0, 
Oxalate of ammonium. Oxamide. 
Oxalic acid is resolved by heating it gently with 
glycerine into formic acid and carbonic acid gas. 
C 2 H 2 0 4 = CH.O, + C0 2 . 
The glycerine takes no obvious part in the decom¬ 
position; but without it a much higher temperature 
is requisite. Oxalic acid and oxalates, heated 
with strong sulphuric acid (q. v.), evolve carbonic 
monoxide and dioxide gases. The latter may be 
separated from the former by passmg tlie im.jed 
^ases through solution of potash. The 0O 2 is an 
sorbed the C O left untouched. 
Oxalic acid is dibasic and therefore gives two: 
series of salts, neutral and acid. 
H 2 C 2 0 4 , 2H.O. 
k 2 c 2 o 4 , 
hkc 2 o 
h 2 o. 
h, a. 
Crystallized oxalic acid 
Neutral potassic oxalate . 
Acid potassic oxalate ) 
(Binoxalate of potash) ) 
But it also gives another class of compounds 
formed by the union of the normal acid oxalates. 
with oxalic acid. 
Quadroxalate of potash ) K H C 2 0 4 ] 2 H 2 O. 
(Salt of sorrel) ) H 2 0 2 O 4 ) 
The antidote to oxalic acid is chalk or whiting. 
