The ordinary hydrochloric acid used for dissolving tin generally contains a little sulphuric acid, but the quantity is too small to produce more than a faint white turbidity in the solution of the tin crystals.
To determine the actual proportion of tin present in a sample of tin crystals, or of the liquid muriates, the following volumetric process may be used. A standard solution of tin is first made up by dissolving 500 gr. of pure tin (grain-bar) in pure hydrochloric acid, an operation which may be facilitated by putting it into contact with a platinum crucible. The liquid is then made up with distilled water to exactly 10,000 grain-measures. Every 20 grain-measures of the solution will contain consequently 1 gr. of tiu.
A standard solution of iodine is then prepared by weighing out 127 gr. of pure iodine and 180 gr. of pure potassium iodide. They are then dissolved in 10,000 grain-measures of water, without applying heat, and the solution is preserved in 6-oz. stoppered bottles.
To find the value of this iodine solution, 100 grain-measures of the standard tin-liquor, con taining of course 5 gr. of tin, are measured off into a beaker, and mixed with bicarbonate of soda in excess, and with sufficient double tartrate of potash and soda to keep the liquid from precipi tating. A little weak starch paste is then added, and the iodine-solution is dropped. in from a burette, till a faint but permanent blue tinge is seen in the glass. The number of degrees on the burette consumed show how many grain-measures of the iodine solution represent 1 gr. of metallic tin.
For the actual teat of the crystals, a known quantity is weighed out, put into a beaker, and dis solved in distilled water, with the aid of a drop or two of hydrochloric acid, so as to give a perfectly clear solution. Bicarbonate of soda and double tartrate of potash and soda are added as before. The starch-paste is then added, and the iodine solution is dropped in as before, till the blue colour appears. From the number of grain-measures consumed, as shown on the burette, the percentage of tin in the crystals is readily calculated.
Next come what may be called mixtures of muriate of lin with other acids, their properties being thus modified. The following are specimens in extensive use :—
.Amaranth Spirit.—Mix 95 lb. hydrochloric acid at 32° Tw. with 5 lb. oil of vitriol, and dissolve in it 4 lb. II oz. of tin. Used for dyeing reddish-violet with the woods on woollens and worsteds.
Yellow and Orange 5 lb. 11 oz. of double muriate at 80° Tw., mix separately 2 lb. oil of vitriol and 2 lb. water, and when cold, stir it into the double muriate. The more tin there is in the double muriate, the more the cloth will show a greenish reflection, if held up to the light and looked at along the surface. For woollens or worsteds.
Scarlet Finishing Spirit.—Take 3 pints muriate of tin at 54° Tw., and 2 oz. oxalic acid. Dissolve, before mixing, in hot water enough to set the whole at 40° Tw. Used for fioishing grain starlets which have been grounded with nitrate of tin. Some dyers prefer to substitute tartaric acid for a part, or even for the whole, of the oxalic acid. In soft woollen goods, the strength of the muriate of tin may be raised to advantage at 70°-80° Tw. A spirit thus prepared acts well for cochineal orange, maize, &c.
On the Continent, nitro-muriate of tin (see below), is generally used for dyeing cochineal and lac acarlets, &c., on woollens.
Plum Spirit.—Take 2 gal. muriate of tin at 70° Tw. In another vessel, mix sulphuric acid and water till the mixture stands at 28° Tw. when cold. Add of this 1 gal., and stir well. This mordant is used for dyeing plums, reddish-violets, and brownish-purples on wool.
Oxalate of Tin.—In the strict sense of the words, this is not a commercial article, but the name, generally shortened into "Ox. Tin," is given to mixtures of muriate of tin with sulphuric and oxalic acids in different proportions. The following, which is largely in use, may serve as an example :— Muriate of tin at 80° Tw., 6 gal.; sulphuric acid at 42° Tw., 3 gal. ; oxalic acid, 2 oz. a gal. These spirits are used for finishing royal blues, topping blacks, where " bloomy " reflection is required, and as a scarlet or orange spirit with cochineal, lac, fiavine, young fustic, &c.