56 
THE PHARMACEUTICAL JOURNAL. 
[July 16, 187C. 
If, then, 1 molecule of the acid is neutralized by 3 
mols. of soda, l mol. of the acid will be satisfied 
by 1 mol. of soda:— 
C 6 = 12 X 6 = 72 
H 10 = 1 X 10 = 10 
O s = 10 X 8 = 128 
3)210 
70 
70 grams of the acid would then be neutralized by 
40 grams of soda, or, which is the same tiling, by 
1000 c.c. of the yoL sol. of soda: therefore, 7 are 
neutralized by 100 c.c. 
Crystals of citric acid, exposed to the temperature 
of boiling water, lose 1 mol. of water, which is merely 
water of crystallization, and can be taken up again. 
Heated more strongly, the residual dry citric acid 
again loses a mol. of water and becomes transformed 
into an acid, which is chiefly interesting on account 
of its identity with the acid of the aconite and of va¬ 
rious species of the equiseta. It is soluble in ether, 
whilst citric acid is not:— 
H.C 6 H 5 0 7 - HjO = H s C 6 H s 0 6 . 
Citric acid. Aconitic acid. 
Acidum Gallicum. Gallic Acid. —Obtained by 
exposing crushed galls, in a moist state, to the air 
during a month or six weeks ; then pressing out the 
black residual liquid and boiling the cake in water, 
which extracts the gallic acid from it. On cooling, 
the acid crystallizes out from the solution. 
There is some difference of opinion as to the nature 
of the change which gives rise to the gallic acid in 
this way; it is probable, however, that under the in¬ 
fluence of the “ moulds ” which form upon the mass, 
the tannin present is broken up into gallic acid and 
glucose, and that the latter, as it forms, is almost en¬ 
tirely oxidized to C0 2 and H 2 0 :— 
C 27 H 22 0 17 -j- 4 H 2 0 = 3C 7 H 6 0 5 -j- C 6 H 12 0 6 ; 
Tannin. Gallic acid. Glucose. 
and then— 
C 6 H 12 0 6 -f- 0 0 2 = 6 C0 2 + 6 H 2 O ; 
possibly in a manner analogous to that by which the 
vinegar-plant promotes the oxidation of the alcohol 
in vinegar making. 
Minute silky needles, soluble in three times their 
weight of boiling water, but only in 100 of cold. In 
dispensing gallic acid, hot water should not, there¬ 
fore, be employed to dissolve it, or the acid crystal¬ 
lizes in large tufts on cooling. The aqueous solu¬ 
tion gives a deep bluish coloration with ferric salts, 
but, when pure, it does not precipitate the vegetable 
alkalies nor gelatine as tannin does. [§ The crys¬ 
talline acid when dried at 212° F., loses 9*5 per cent, 
of its weight.] This is only water of crystallization; 
but when heated to between 410° and 420°, it is 
wholly resolved into carbonic acid gas and pyrogallic 
acid, which sublimes in shining plates:— 
C 7 H 6 0 5 = C 6 H 6 0 3 -f* C0 2 . 
Acidum Hydrochloricum. —A solution of real hy¬ 
drochloric acid, H Cl, in water. 
On heating chloride of sodium (common salt) with 
sulphuric acid, it yields a colourless gas, which, if 
expelled into the air, forms a steamy fume, owing to 
the presence of moisture. This gas dissolves rapidly 
and readily when passed into water, forming the so¬ 
lution usually known as hydrochloric or muriatic 
acid, or spiiit of salt. The sp. gr. of the officiil 
liquid is 1T6, and it contains 31*8 per cent, of HC.. 
The residue left in the flask or retort is acid sulpliatt 
of sodium. 
Na Cl + H 2 S0 4 = NaHS0 4 + HC1. 
Hydrochloric acid and all other soluble chlorides 
give, with solution of nitrate of silver, a curdy white 
precipitate, consisting of chloride of silver, AgCl, 
soluble in excess of ammonia, but insoluble in nitric 
acid. 
[§ 11'48 grams mixed with half an ounce of dis¬ 
tilled water, require for neutralization 100 c.c. of the 
volumetric solution of soda.] 
1 mol. of HC1 (= 36-5) + 1 mol. of NaHO 
= NaCl + H 2 0. 
36*5 grams of hydrochloric acid gas would neutra¬ 
lize 1000 c.c. of the vol. sol. of soda, which contain 
40 grams or 1 mol. of NaHO. 3*65 grams of HC1, 
or 11*48 grams of the liquid, will, therefore, neutra¬ 
lize the same amount, viz. 100 c.c. of the vol. sol. of 
soda. 11*48 of the liquid contain accordingly 3*65 
of the gas :—what do 100 parts contain ? 
11*48 : 100 :: 3*65 : x. x = 31*8 per cent. 
Commercial hydrochloric acid is liable to many 
impurities; iron , recognized by the colour, and by 
giving, when diluted, blue precipitates with ferro- 
and ferri-cyanide of potassium ; arsenic, by giving, 
after dilution, a yellow precipitate with H 2 S, also 
by tarnishing copper-foil boiled in it; alkaline salts 
(NaCl, Na 2 S0 4 , etc.), by leaving a residue on eva¬ 
poration to dryness; sulphuric acid, by giving, with 
chloride of barium, a white precipitate ; sulphurous 
acid, by the last test in the B. P., which is identical 
with that explained under Acidum Aceticum ; chlo¬ 
rine or nitric acid would tarnish copper-foil, and 
would also dissolve gold-leaf. To ascertain if any 
gold has been taken up by the sample tested, add a 
few drops of a mixture of tin chlorides; purple of 
Cassius makes its appearance. 
Acidum Hydrocyanicum Dilutum. —The official 
preparation is a solution of real acid, containing 2 
per cent. It is prepared by distilling yellow prussiate 
of potash with sulphuric acid and w r ater, and col¬ 
lecting the distillate in a receiver containing distilled 
water. 
2K 4 (Fe"C 6 N 6 ) + 0H 2 SO 4 
Ferrocyanide of 
potassium. 
= K 2 Fe"(Fe"C 6 N 6 ) + 6HCN + 6KHS0 4 . 
Everitt’ssalt, or ferro- Hydrocyanic Acid sulphate 
cyanide of potassium acid. of potassium, 
and iron. 
At the end of the operation the retort contains a 
solution of bisulphate of potash, mixed with a pre¬ 
cipitate of the double ferrocyanide, wdiicli is generally 
green, from the action upon it of the air in the appa¬ 
ratus. The distillate is diluted with w 7 ater, till 100 
grains of it give, wdien mixed with excess of nitrate 
of silver, a precipitate of cyanide of silver, which, 
when w r ashed and dried, w r eighs 10’grains. 
HCN + AgNO, = AgCN + HNO a . 
27. 134. 
From this equation 27 grains of HCN give 134 
grains of AgCN ; so that if the 100 grains of dis¬ 
tilled liquid contain 2 grains, as they should, 10 (or 
more accurately, 9*926) grains of precipitate are ob¬ 
tained. 
