834 
THE PHARMACEUTICAL JOURNAL AND TRANSACTIONS. 
[May 6,1871. 
Gently warm tlie globe, to expel a few gas bub¬ 
bles; on cooling, the potash solution will rise to the 
widened part of the tube, after which the trough 
must be raised so that the tube dips into the mer¬ 
cury. 
The absorption of the carbonic acid by potash pro¬ 
duces a partial vacuum, indicated by the rise of 
mercury in the long tube, which at the same time 
shows that all the joints are air-tight. 
The column of mercury must remain stationary 
for some time at a height of 15 in. above the surface 
of the mercury in the trough, when the liquid in the 
retort will be under a pressure of only half an atmo¬ 
sphere. 
Then heat the retort and well cool the globe. 
The use of an air-pump supersedes the potash 
apparatus. A T tube is introduced instead, one leg 
of which is connected with the air-pump, to draw 
out the air before and after the distillation, the 
second leg connects the globe, and the third is at¬ 
tached to a long tube dipping into mercury. 
The success of the operation entirely depends 
upon the absolute perfection of the joints, for which 
india-rubber is the best material. Vulcanized corks 
and tubes are first boiled in a weak solution of 
caustic soda, they are then well dried and immersed 
in molten tallow ; after several hours they are taken 
out and well cleaned with a cloth. Corks and tubes 
thus prepared make perfectly air-tight joints, they 
do not become hard and brittle, but preserve their 
elasticity. India-rubber melts at about 150° C. 
(302° F.). In case the heat applied during the dis¬ 
tillation exceeds this temperature, the connection at 
the tubulus of the retort must be made with a sound 
cork, which is made air-tight by soaking it in molten 
wax or paraffin, and by painting a solution of caout¬ 
chouc in chloroform over the part above the tubulus. 
Many organic substances, partially decomposed 
by distillation under ordinary pressure, such as 
glycerine, may be volatilized without decomposition, 
provided the receiver is well cooled to prevent the 
tension of the vapours from exerting any pressure.— 
Commentar znr osterreichisclien Pharmacopce. 
Cpgtors for ^fohnfs. 
CHEMICAL NOTES TO THE PHARMACOPOEIA. 
BY WILLIAM A. TILDEN, B.SC. LOND. 
DEMONSTRATOR OF PRACTICAL CHEMISTRY TO THE 
PHARMACEUTICAL SOCIETY. 
Ferri Sulphas Exsiccata.— FeS0 4 H 2 0. 
Sulphate of iron dried at a temperature which is 
gradually raised to 400°, loses six out of the seven 
molecules of water which it contains. This last 
molecule is only expelled by a much stronger heat; 
but if a solution of the salt be mixed with sulphate 
ot potassium or ammonium, a double salt is produced 
in which the alkali sulphate replaces this seventh 
molecule of water. 
Thus FeS0 4 , K 2 S0 4 , GH„0. The sulphates of 
magnesium, zinc and copper form double compounds 
of a similar formula. Heated to redness, sulphate 
of iron leaves a residue of red ferric oxide, Fe 2 0 3 . 
Ferri Sulphas Granulata.—A solution of freshly 
prepared sulphate of iron is filtered into rectified 
spirit. The salt being insoluble in spirit is precipi¬ 
tated in small granular crystals. Some experiments 
made by a student in the laboratory of tlie Society 
showed that this preparation is of the same composi¬ 
tion as the ordinary sulphate of iron, having lost 
none of its water of crystallization. It is supposed 
to resist oxidation longer than the crystallized salt. 
To retard such change, it has been recommended to 
keep in the bottle containing sulphate of iron a small 
piece of camphor wrapped in paper. 
Ferrum. — [§Wrought iron in the form of wire or 
nails free from oxide.] 
Chemically pure iron is almost unknown. The 
Pharmacopoeia orders wrought iron to be employed 
for preparing the ferruginous compounds, because in 
that form it is practically least contaminated with 
foreign substances. The impurities contained in iron 
wire are chiefly minute quantities of carbon (average 
•3 per cent.), silicon, phosphorus and sulphur. When 
ordinary iron is dissolved in dilute hydrochloric or 
sulphuric acid, the evolved hydrogen possesses ail 
odour which is due to the presence in it of minute 
quantities of the hydrogen compounds of these ele¬ 
ments. A small quantity of carbon also floats un¬ 
dissolved. This is much more noticeable when cast 
iron is used. Other substances are usually present, 
but in proportions smaller still, and interfere in no 
way with the employment of the iron for pharma¬ 
ceutic purposes. 
Iron filings are objectionable, as they are not only 
usually very dirty, but contain particles of other 
metals. 
Ferrum Redactum. — [§ Metallic iron, with a va¬ 
riable amount of magnetic oxide of iron.] 
Hydrated peroxide of iron contained in a gun- 
barrel is heated to redness in a current of pure and 
dry hydrogen gas. The greater part of the iron is 
thus reduced to the metallic state:— 
Fe 2 0 3 , HoO + 3H 2 =: Fe 2 -f 3H 2 0 + H 2 0 
A small quantity of it, however, does not lose the 
whole of its oxygen, and thus a certain proportion of 
magnetic oxide of iron is retained in the product. 
3 Fe 2 0 3 , H 2 O + H 2 = 2 Fe 3 0 4 + H 2 0 + 3H 2 0 
At the end of the process, the current of hydrogen 
is continued until the tube is cold. If exposed to 
the air whilst still hot, the pulverulent iron becomes 
red-hot from the rapid reabsorption of oxygen, and 
the product is spoiled. 
[§ A fine greyish-black powder, strongly attracted 
by the magnet, and exhibiting metallic streaks when 
rubbed with firm pressure in a mortar. It dissolves 
in hydrochloric acid with the evolution of hydrogen.] 
This hydrogen should be odourless, that is, free from 
sulphuretted hydrogen, the evolution of winch indi¬ 
cates the presence of a little sulphide. “ As the hy¬ 
drated peroxide of iron of the Pharmacopoeia is made 
by precipitation from a solution of persulphate of 
iron with caustic soda, this, as produced by manu¬ 
facturers, generally retains a small portion of sul¬ 
phate, which is not completely washed out in the 
process, and this sulphate is afterwards reduced to 
sulphide by the hydrogen during the conversion of 
the oxide to reduced iron. Tlie liability to such a 
result would be obviated if the oxide used in the 
process were directed to be obtained from chloride of 
iron by precipitation with ammonia.”— Redwood. 
Strong ignition of the oxide before use would also 
probably effect the same object. 
[§ 10 grains added to an aqueous solution of 50 
grains of iodine and 50 grains of iodide of potassium, 
