furnished in large glass containers boxed with straw, called carboys. In handling these carboys it is usually advisable to have trunnions on which they can be rocked (Fig. 216), though, with careful handling, this expense may be avoided. There is no uniformity in the commercial strength of the different strong acids, the usual custom being to furnish an acid of the greatest concentration feasible. It is useful to memorize the following strengths and specific gravities: While the pharmacopoeial concentrated acids vary in strength, the same standard demands that diluted acids contain 10 per cent. of absolute acid, except diluted acetic acid (6 per cent.) and diluted hydrocyanic acid (2 per cent.). A very convenient method of estimating the strength of acids is by their specific gravity. As an illustration, it will be noted above that the specific gravity of sulphuric acid is 1.83. Water, which is the only likely adulterant, has, of course, the specific gravity of 1.00, and if sulphuric acid is diluted with water, the specific gravity will fall to a point somewhere between 1.83 and 1.00. The only official liquid acid whose specific gravity is not a criterion of strength is acetic acid (see p. 672). The antidote for acids is mild alkali, such as calcined magnesia or lime liniment, this being a good illustration of a chemical antidote acting on an acid to form a neutral and inert salt. Too much emphasis cannot be placed on the word "mild," for while it is true that con centrated sodium hydrate or other strong alkali would form with the acid a neutral salt, yet the action of the same alkali is as dangerously caustic as is the acid for which it is intended as an antidote. Most inorganic acids are prepared by the action of sulphuric acid on a salt of the acid which is desired. Sulphuric acid possesses a greater affinity for metals than most other acids, hence when a salt of the acid is treated with sulphuric acid, a sulphate is formed and the acid is liberated. Reviewing the manufacture of official acids, we see how often this rule applies: Hydrochloric acid, made from sodium chloride and sulphuric acid. Hydrobromic Nitric Chromic Carbonic Exceptions to this method are: Phosphoric acid, made by oxidation of phosphorus with nitric acid. 66 66 A liquid composed of 31.9 per cent., by weight, of absolute Hydrochloric Acid [HC 36.18], and 68.1 per cent. of water. It should be kept in glass-stoppered bottles. A colorless, fuming liquid, of a pungent odor, and an intensely acid taste; the fumes and odor disappear on diluting the Acid with 2 volumes of water. Specific gravity: about 1.158 at 25° C. (77° F.). Miscible, in all proportions, with water or alcohol. On distilling it, at first a stronger acid passes over, until, at 110° C. (230° F.), a liquid containing 20.13 per cent. of the absolute acid remains (specific gravity, about 1.098 at 25° C.), which distils unchanged, leaving no residue. Hydrochloric Acid, even when highly diluted, shows an intensely acid reaction with blue litmus-paper. Heated with manganese dioxide it evolves chlorine. With silver nitrate T.S. it yields a white, curdy precipitate, insoluble in nitric acid, but readily soluble in ammonia water. If 10 Cc. of the Acid be evaporated from a platinum or porcelain dish, and dried at 110° C. (230° F.), no appreciable residue should remain (limit of non-volatile impurities). Tests for Identity.-Tests for HCl and non-volatile impurities just given. Impurities.-Non-volatile impurities (just given), bromine, iodine, free chlorine, arsen, sulphuric acid, sulphates, sulphurous acid, and heavy metals. Details in Part V. Assay.-Details in Part V. Remarks. This is an aqueous solution of hydrochloric acid gas, containing 31.9 per cent. of absolute acid, and having a specific gravity of 1.16. Its two synonyms-spirit of sea-salt and muriatic acid-suggest its origin, the word muriatic being derived from the Latin murias, which means brine. As mentioned above, it is prepared by distilling a mixture of salt (sodium chloride) and sulphuric acid. ACIDUM HYDROCHLORICUM DILUTUM. Diluted Hydrochloric = Acid. Diluted Hydrochloric Acid should contain 10 per cent., by weight, of absolute Hydrochloric Acid [HCI 36.18] and 90 per cent. of water. It should be kept in glass-stoppered bottles. Recipe.-Hydrochloric Acid, one hundred grammes. Mix them. 100 Gm. Distilled Water, two hundred and nineteen grammes 219 Gm. Specific gravity: about 1.049 at 25° C. (77° F). It does not fume in the air and is without odor, but otherwise it should conform to the reactions and tests given under Acidum Hydrochloricum. Assay.-Details in Part V. Diluted hydrochloric acid is prepared by mixing 100 Gm. of hydrochloric acid (U. S. P.) with 219 Gm. of water. It will be noticed that the preparation strictly follows the rules of dilution performed by alligation. The problem is to reduce a 31.9 per cent. acid to a 10 per cent. acid. Following general rules of alligation, we get: Summed up, we find that 10 Gm. of the official strong acid (31.9 per cent.) and 21.9 Gm. of water (0 per cent.) gives 31.9 Gm. of the diluted acid (10 per cent.). Then, by proportion: If to make 31.9 Gm. diluted acid we require 10 Gm. of strong acid; then to make 319 Gm. diluted acid we require 319 31.9 × 10 or 100 Gm. stronger acid. Hydrochloric acid, always in diluted form, is used in indigestion. Dose. Of the diluted acid, 1 Cc. (15 minims). ACIDUM HYDROBROMICUM DILUTUM. Diluted Hydrobromic Acid. A liquid composed of not less than 10 per cent., by weight, of absolute Hydrobromic Acid [HBr 80.36] and about 90 per cent. of water. It should be kept = in amber-colored, glass-stoppered bottles, protected from light. A clear, colorless, and odorless liquid, having a strongly acid taste. Miscible, in all proportions, with water or alcohol. On distilling it, water and weak acid first pass over; when the temperature of 126° C. (258.8° F.) is reached, an acid of 48 per cent. remains, which may be distilled unchanged. Diluted Hydrobromic Acid strongly reddens blue litmus-paper. Silver nitrate T.S. causes a yellowish-white precipitate, which is insoluble in diluted nitric acid, but slowly soluble in an excess of stronger ammonia water, and readily soluble in solutions of sodium thiosulphate or potassium cyanide. If copper sulphate T.S. be added to the Acid, a deep red color is produced upon the addition of sulphuric acid. The Acid should not become colored on keeping. Tests for Identity.-Given above. Impurities. Non-volatile impurities (test same as under hydrochloric acid). Sulphuric acid, barium, heavy metals, free bromine, iodine, arsenic, hydrochloric acid, and chlorides. Details in Part V. Assay.-Details in Part V. Remarks. This official acid is a liquid containing 10 per cent. of absolute hydrogen bromide, and since an unstable chemical, should be dispensed as fresh as possible by the pharmacist. Hence efforts have been made to devise a simple method for its extemporaneous manufacture. The ordinary method of manufacture is by treatment. of potassium bromide with sulphuric acid by the following reaction: From this equation it will be seen that the product of the reaction other than hydrobromic acid is potassium sulphate. This dissolves in water with the hydrobromic acid, and to separate the acid from the sulphate solution the tedious process of distillation is necessary. This led investigators to attempt the separation of the second reaction product from the acid by precipitation, in which case the acid could be obtained by simple filtrations of the liquid from the precipitate. There are very few insoluble potassium salts, the best known being the bitartrate,-cream of tartar,-and this is utilized. in the Fothergill process of making hydrobromic acid. In this, instead of using sulphuric acid with potassium bromide, tartaric acid. is employed, and, on standing, the bitartrate crystallizes out, the reaction being: The above equation implies the molecular proportion of 119 Gm. potassium bromide and 150 Gm. tartaric acid in making 80 Gm. hydrobromic acid. Then to make 1000 Gm. 10 per cent. hydrobromic acid (containing 100 Gm. absolute acid) will require 100 x 119, or 148 Gm. potassium bromide and 100 X 150, or 187 Gm. tartaric acid. 80 These proportions do not agree with the original recipe of Dr. Wade, who planned an acid each dram of which would contain the equivalent of 10 grains of bromine; nor with Dr. Fothergill's recipe, which was a cumbersome one, adapted to the Imperial system of measures; nor with the simpler recipe of Professor Maisch. The latter recipe consists of 80 grains of potassium bromide dissolved in 6 fluidrachms water; 100 grains tartaric acid dissolved in 2 fluidrachms water; the solutions mixed and then chilled, in order to facilitate the separation of the cream of tartar. The difficulty in striking an exact recipe is due to the uncertainty of the amount of cream of tartar precipitated, and in the metric recipe given above, the total amount of water used should be 900 Cc. Moreover, not more than 100 Cc. should be made at a time, since the product is not very stable. It must be said that the product of this process is not absolutely pure acid; it always contains some potassium bromide and potassium bitartrate. Diluted hydrobromic acid is used as a sedative. Dose.-4 Cc. (1 fluidrachm). = ACIDUM HYDRIODICUM DILUTUM. Diluted Hydriodic Acid. A solution of Hydriodic Acid [HI 126.9], containing not less than 10 per cent., by weight, of the Absolute Acid, and about 90 per cent. of water. It should be kept in amber-colored, glass-stoppered bottles, protected from the light. Recipe.-Potassium Iodide, one hundred and thirty-five gram Dissolve the Potassium Salts in two hundred and fifty cubic centimeters of Distilled Water with the aid of heat, and the Tartaric Acid in four hundred cubic centimeters of Diluted Alcohol. Having poured the Solution of Tartaric Acid into a bottle of about one thousand cubic centimeters capacity, add the solution of Potassium salts and shake the mixture briskly. Place the bottle in a bath of ice-water for several hours, and having inserted a pledget of cotton tightly in the throat of a funnel, transfer the contents of the bottle to the funnel. When all the liquid has passed through, wash the bottle and crystalline precipitate with Diluted Alcohol in successive small portions until one thousand grammes of clear solution have been obtained. Evaporate the liquid at a moderate temperature, on a water-bath, until all of the Alcohol has been dissipated, and add sufficient Distilled Water to make the product weigh one thousand grammes. A clear, colorless liquid, odorless, and having an acid taste. Miscible, in all proportions, with water or alcohol. |