This latter consists of a series of bulbs arranged like a staircase, so as to permit the gas to come into the greatest possible contact with the standard solution of iodine in iodide of potassium, with which the condenser is filled, this solution ought not to be exposed to light.
When the apparatus is arranged as above, the atmospheric air is first driven out of the bottle by means of a current of hydrogen gas, introduced by the tube bent at right angles. When it is considered that the air is entirely expelled, the tap of this tube is closed. The funnel is now filled with hydrochloric acid, its tap is opened, and by means of the application of heat the acid is allowed to run down upon the iron without allowing any common air to enter. Hydrogen and sulphuretted hydrogen are formed which pass into the condenser.
Acid is thus added until all disengagement of gas ceases. The bottle is then heated till its contents boil, a little water having been first added by means of the funnel. After these operations, hydrogen is allowed to enter anew to sweep out all remaining gases. The iodised solution is then poured out, care being taken to rinse the bulb-tube thoroughly, and titrated with hyposulphite of soda, so as to find the remaining proportion of free iodine. The difference between the original amount of free iodine present in the solution, and the amount thus found, shows the proportion of iodine which has been converted into hydriodic acid, and which is proportional to the sulphur contained in the sample under examination.
Iron, Preparations of:—
Ferric Acetate. Fe2(C2H3O2)6. Syn. Peracetate of iron; Ferri sesquiacetas, L. Prep. Ferric carbonate, 1 part; acetic acid, 6 parts; digest three days and filter. A dark brownish-red, uncrystallisable liquid, very soluble and powerfully astringent. The calcined sesquioxide of iron of the shops, commonly sold as carbonate of iron, does not answer well for this or any of the sesqui-compounds, owing to its being with difficulty dissolved by acids, especially by the weaker ones.—Dose. (Of the last) 10 to 25 drops, in water or wine.
Ferric Albuminate. Syn. Ferri albuminas, L. Prep.
Precipitate a filtered solution of white of egg with another of ferric sulphate or persulphate of iron, wash the deposit in water, and dissolve it in alcohol holding potassium hydrate in solution.
This preparation is highly spoken of by M. Lassaigne as especially adapted by its nature, on theoretical grounds, for combining with the tissues of the body.
Ferric Citrate. Fe2(C6H5O7)2. Syn. Percitrate of iron, Citrate of Sesquioxide of i., Citrate of i.; Ferri citras.
Prep. By saturating a solution of citric acid in an equal weight of water with freshly precipitated moist hydrated ferric hydrate, evaporating at 150° Fahr. to the consistence of a syrup, and spreading on glass plates to dry.