Prop. Commercial sulphuric acid (oil of vitriol) is a colourless, odourless, and highly corrosive liquid, the general properties of which are well known. Its sp. gr. at 60° should never be greater than 1·848, or less than 1·840. (Miller and Odling give the sp. gr. of the pure and concentrated acid as 1·842; Abel and Bloxam, as 1·848; Apjohn gives it as 1·846, and Hardwich about 1·845.) It is immediately coloured by contact with organic matter. It attracts water so rapidly from the atmosphere when freely exposed to it, as to absorb 1-3rd of its weight in 24 hours, and 6 times its weight in a few months. When 3 volumes are suddenly mixed with 2 of water, the temperature of the mixture rises more than 180° Fahr. Its freezing point appears to be about 60° below that of water (Miller and Odling give that of the rectified acid as -30° Fahr.; Apjohn and Abel and Bloxam, -29°). It boils at about 620° Fahr. (620·6°, Odling; 620°, Hardwich and Fownes; 617°, Apjohn; 590·6°, Abel and Bloxam). It exhibits all the properties of the acids in an exalted degree. Its salts are called sulphates.
In the following table is given the quantity of anhydrous sulphuric acid contained in sulphuric acid at 60°F. (15·5°C.).
| Hydrated Sulphuric Acid. | Sp. Gr. | Anhydrous Acid. | Hydrated Sulphuric Acid. | Sp. Gr. | Anhydrous Acid. |
| 100 | 1·8485 | 81·54 | 76 | 1·6630 | 61·97 |
| 99 | 1·8475 | 80·72 | 75 | 1·6520 | 61·15 |
| 98 | 1·8460 | 79·90 | 74 | 1·6415 | 60·34 |
| 97 | 1·8439 | 79·09 | 73 | 1·6321 | 59·55 |
| 96 | 1·8410 | 78·28 | 72 | 1·6204 | 58·71 |
| 95 | 1·8376 | 77·40 | 71 | 1·6090 | 57·89 |
| 94 | 1·8336 | 76·65 | 70 | 1·5975 | 57·08 |
| 93 | 1·8290 | 75·83 | 69 | 1·5868 | 56·26 |
| 92 | 1·8233 | 75·02 | 68 | 1·5760 | 55·45 |
| 91 | 1·8179 | 74·20 | 67 | 1·5648 | 54·63 |
| 90 | 1·8115 | 73·39 | 66 | 1·5503 | 53·82 |
| 89 | 1·8043 | 72·57 | 65 | 1·5390 | 53·00 |
| 88 | 1·7962 | 71·75 | 64 | 1·5280 | 52·18 |
| 87 | 1·7870 | 70·94 | 63 | 1·5170 | 51·37 |
| 86 | 1·7774 | 70·12 | 62 | 1·5066 | 50·55 |
| 85 | 1·7673 | 69·31 | 61 | 1·4960 | 49·74 |
| 84 | 1·7570 | 68·49 | 60 | 1·4860 | 48·92 |
| 83 | 1·7465 | 67·68 | 59 | 1·4760 | 48·11 |
| 82 | 1·7360 | 66·86 | 58 | 1·4660 | 47·29 |
| 81 | 1·7245 | 66·05 | 57 | 1·4560 | 46·58 |
| 80 | 1·7120 | 65·23 | 56 | 1·4460 | 45·68 |
| 79 | 1·6993 | 64·42 | 55 | 1·4360 | 44·85 |
| 78 | 1·6870 | 63·60 | 54 | 1·4265 | 45·03 |
| 77 | 1·6750 | 62·78 | 53 | 1·4170 | 43·22 |
Pur. “Free from colour and odour. Sp. gr. 1·843. 100 gr. are saturated by 285 gr. of crystallised carbonate of soda.” (Ph. L.) “What remains after the acid is distilled to dryness does not exceed 1⁄400th part of its weight. Diluted sulphuric acid is not discoloured by sulphuretted hydrogen.” (Ph. L. 1836.) “Diluted with its own volume of water, only a scanty muddiness arises, and no orange fumes escape. Sp. gr. 1·840.” (Ph. E.) “The rectified acid (ACIDUM SULPHURICUM PURUM—Ph. E. & D.) is colourless; dilution causes no muddiness; solution of sulphate of iron shows no reddening at the line of contact when poured over it. Sp. gr. 1·845.” (Ph. E.) Sp. gr. 1·846—Ph. D.; 1·843—B. P.; 1·842—Ure.
Tests.—See Sulphate.
Uses, &c. “The uses of sulphuric acid are so numerous that it would be impossible to mention all of them, sulphuric acid being to chemical industry what iron is to the mechanical. Sulphuric acid is employed in preparing a great many other acids—among them, nitric, hydrochloric, sulphurous, carbonic, tartaric, citric, phosphoric, stearic, oleic, and palmitic. Further, sulphuric acid is used in making superphosphates, soda, sulphate of ammonia, alum, sulphates of copper and iron, in paraffin and petroleum refining, silver refining, manufacture of garacine, garanceux, and other madder preparations, manufacture of glucose from starch, to dissolve indigo, &c.[216] In the diluted state it is used in medicine. When swallowed, it acts as a violent corrosive poison. The antidotes are chalk, whiting, magnesia, carbonate of soda, or carbonate of potash, mixed with water, or any bland diluent, and taken freely, an emetic being also administered.
[216] Wagner.
Estim. The strength of sulphuric acid is most correctly ascertained by its power of saturating bases. In commerce, it is usually determined from its sp. gr. The quantity of sulphuric acid present in a compound may be determined by weighing it under the form of sulphate, as explained in a former part of this volume. See Acidimetry.
Concluding Remarks. According to most of our standard works on chemistry, British oil of vitriol, when purified and brought to its maximum strength by distillation, is a definite chemical compound, having the formula H2SO4, and designated normal sulphuric acid by Odling. Marignac, however, asserts that the distilled acid always contains an excess of water, and that the true monohydrate can only be obtained by submitting fuming sulphuric acid (‘Nordhausen s. a,’) to congelation. According to this chemist, the true monohydrate readily freezes in cold weather, and remains solid up to 51° Fahr. Two other definite hydrates of sulphuric acid are generally recognised by chemists, viz.—Bihydrated sulphuric acid (‘glacial s. a,’), having a sp. gr. of 1·78; freezing at about 40° Fahr. (47°, Miller); and boiling at about 435° (Apjohn; 401° to 410°, Odling): Terhydrated sulphuric acid, having a sp. gr. of 1·632, and the boiling-point 348° Fahr. See also Sulphuric acid, Nordhausen (below).
Sulphuric Acid, Al′coholised. Syn. Acidum sulphuricum alcoholisatum, L.; Eau de rabel, Fr. Prep. (P. Cod.) To rectified spirit, 3 parts, add, very gradually, sulphuric acid, 1 part. It is generally coloured by letting it stand over a little cochineal. Refrigerent, and, externally, escharotic.—Dose, 1⁄2 fl. dr. to water, 1 pint; as a cooling drink in fevers, &c.