814 
THE PHARMACEUTICAL JOURNAL AND TRANSACTIONS. 
[April 22, 1871. 
CHEMICAL NOTES TO THE PHARMACOPOEIA. 
BY WILLIAM A. TILDEN, B.SC. LORD. 
DEMONSTRATOR OE PRACTICAL CHEMISTRY TO THE 
PHARMACEUTICAL SOCIETY. 
Ferri Peroxidum Humidum. —Solution of persul¬ 
phate of iron is diluted with distilled water and 
poured with constant stirring into solution of soda. 
The brown precipitate which forms is collected, 
washed thoroughly to free it from sulphate of sodium, 
drained and preserved in the moist state. (See Ferri 
et Ammo-n. Cit.) 
This preparation is employed as an antidote to 
arsenic; an insoluble ferrous arseniate together with 
ferrous hydrate being probably formed :— 
2 Fe 2 6HO+As 2 0 3 = Fe 3 2 As 0 4 -f Fe 2 H 0 -f 5 H 2 0. 
To be effective it must be freshly prepared, since 
ferric hydrate loses the elements of water even when 
preserved, as in this case, in contact with excess of 
water. The hydrates form a class of salts which are 
by most chemists regarded as compounds of the ra¬ 
dicle H 0 with the metals. Some of them are, how¬ 
ever, so readily resolved into the corresponding ox¬ 
ides and water, that they may possibly be only mole¬ 
cular combinations. For example, ferric hydrate 
may be written Fe 2 (HO) G or Fe 2 0 3 , 3H 2 0. With 
the exception of the hydrates of the alkali metals, 
they are, as a general rule, insoluble in water. 
Graham, however, prepared soluble modifications of 
many of them, such as ferric and aluminic hydrates, 
by submitting solutions of the chlorides to dialysis. 
In the case of ferric chloride, a red transparent liquid 
remains on the dialyser. It is probable that tliis 
contains the real hydrate, Fe 2 GHO, capable of ex¬ 
isting only in solution, and that all the solid forms 
which we obtain as precipitates are in reality oxyhy- 
drates. 
Ferri Peroxidum Hydratum. 
Fe 2 0 2 (H0) 2 or Fe 2 0 3 , H 2 0. 
Moist hydrate of iron is dried at a temperature of 
212° until it ceases to lose weight. 
This seems to be one of the most stable and defi¬ 
nite of the hydrates of iron. [§ Heated to dull 
redness in a test-tube, it gives off moisture.] The 
residue is Fe 2 0 3 : this test shows that it has not 
been dried at too high a temperature. When such 
is the case, the preparation ceases to be easily so¬ 
luble in acids. 
A brown ferric oxyhydrate is commonly sold in 
the shops under the name of “carbonate of iron.” 
This is generally prepared by precipitating a solution 
of ferrous sulphate with carbonate of sodium, and 
exposing the resulting ferrous carbonate freely to the 
nir during washing. It then absorbs oxygen and 
loses carbonic anhydride. It generally retains a 
minute quantity of unchanged ferrous carbonate, and 
so effervesces when treated with acids. 
Ferri Phosphas.— [§Pliosphate of iron, Fe 3 2P0 4 , 
partially oxidated.] 
A solution of sulphate of iron is mixed with a 
solution of phosphate and acetate of sodium. The 
precipitate is collected and washed, to free it from the 
acetic acid and sulphate of sodium which are retained 
in solution. The use of the acetate of sodium and 
the nature of the reaction are explained under ferri 
arsenias, which is prepared in a manner precisely 
similar. 
[§ A slate-blue amorphous powder insoluble in 
water, soluble in hydrochloric acid. The solution 
yields a precipitate with both the yellow and red 
prussiate of potash, that afforded by the latter being 
the more abundant (because the salt is essentially 
ferrous); and when treated with tartaric acid and an 
excess of ammonia, and subsequently with the solu¬ 
tion of ammonio-sulphate of magnesia, lets fall a 
crystalline precipitate.] 
This precipitate is MgNH 4 P0 4 6 H a O ; the ar¬ 
seniate gives an analogous compound of similar ap¬ 
pearance, MgN H 4 As O 4 0 H 2 O. [§ When the salt 
is digested in hydrochloric acid with a lamina of 
pure copper, a dark deposit does not form on the 
metal.] This test shows that it is not the arseniate. 
[§ 2 grains dissolved in hydrochloric acid continue 
to give a blue precipitate with red prussiate of potash 
until 25 cubic centimetres of the volumetric solution 
of bichromate of potash have been added.] This 
would indicate the presence of ‘895 gram of ferrous 
phosphate in the 2 grams, or 41*7 5 per cent. 
One molecule of red chromate will convert two 
molecules of ferrous into ferric phosplmte. Ferric 
phosphate has the formula Fe 2 '' 7 2 P 0 4 ; it is not now 
used in medicine. 
The syrup of phosphate of iron of the Pharma¬ 
copoeia is a solution of ferrous phosphate in dilute 
phosphoric acid with sugar, but the proportion of 
phosphoric acid ordered is too large. 
The deepening of colour to which tins prepara¬ 
tion is liable is often referred to change in the sugar, 
under the influence of the acid present; it generally 
arises, however, from the phosphate of iron, owing 
to having been imperfectly washed, retaining small 
quantities of acetic acid or an acetate. As oxygen 
is absorbed, ferric acetate is generated, and betrays 
itself by its deep brownish-red colour. 
Ferri Sulphas. —Iron wire is dissolved in dilute 
sulphuric acid, aided by a gentle heat; and when 
the effervescence caused by the escape of the hydro¬ 
gen ceases, the liquid is filtered and set aside to 
crystallize— 
Fe -f H 2 S0 4 = FeS0 4 + H 2 . 
Undiluted sulphuric acid has scarcely any action 
upon iron in the cold; but, when water is added, 
hydrogen gas is freely evolved. The same is the case 
with zinc. 
In former Pharmacopoeias the green vitriol of 
commerce was employed as the source of the sul¬ 
phate of,iron. It was ordered to be redissolved in 
water, a small quantity of sulphuric acid added, and 
the solution digested upon some iron wire. In this 
way the brown rusty ferric oxysulphate, which is 
always present, is reduced to the ferrous state by 
the hydrogen which the iron wire evolves from the 
sulphuric acid. Thus— 
Fe 2 (S0 4 ) 2 0 + H a S0 4 + Fe 
= 3Fe S0 4 + H 2 0. 
The common green vitriol of commerce, being pre¬ 
pared from pyrites, generally contains more or less 
copper ; this may be removed by digesting it in so¬ 
lution upon scraps of iron ; but it is far better to 
prepare pure sulphate of iron for medicinal pur¬ 
poses by the official process. 
Sulphate of iron should be in pale greenish-blue, 
