406

ELEMENTS OF MATERIA MEBICA.

Monis.

Real sulphuric acid....., l .,

Water .................. i ..

Strengest (ep. gr. 1-845.)Eq. Wt. Per Cent.

.... 40 ........ 81-6

.... 9 ........ 18-4

Oil of Vitriol

1

49

100-0

Commercia! (sp. gr, 1-8433.)Atoms. Eq. Wt. Per Cent.

1 ........ 40 ........ 78

1J ........ 1125 ........ 22

51-25

100

Characteristics. —Free sulphuric acid or the soluble sulphates are reeognisedby a Solution of any of the barytic salts, which throws down a heavy white pre-cipitate {sulphate of baryta) insoluble in acids or alkalis. If this precipitate beignited with chareoal, it is decornposed and converted into sulphuret of barium,whieh, on the addition of hydrochloric acid, evolves hydrosulphuric acid, knownby its odour and its blackening paper rnoistened with acetate of lead. If sulphu-ric acid be heated with organic matter, sulphurous acid is given out: this may beknown by its odour, and by its occasioning the formation of the blue iodide ofstarch, when mixed with iodic acid and starch. Oil of vitriol is reddened byveratria, salicin, piperin, oil of bitter almonds, phloridzine, &c.

To determine whether sulphuric acid be free or combined with a base, Dr. Christison(Treaiise on Poisons, 3d ed. p. 142.) recommends tiie liquid to be boiled with pure carbonateof lead. If free sulphuric acid be present, sulphate of lead will be formed, which, beinrr inso-luble in diiute nitric acid, may be thereby disting-nished from carbonate of lead; and it is as.sumed that no suiphate of lead will be formed if there is only a natural sulphate present," because carbonate of lead and the neutral sulphates do not deeompose eaeh other." Butthis test is liable to objection : alum, sal enixum, sesquisulphate of iron, and other supersul-phates, react on carbonate of lead like free sulphuric acid ; and, farthermore, neutral sulphateof ammonia is decornposed at a boiling temperature by carbonate of lead.

Impurities. —Pure oil of vitriol should be colourless: the presence of organicmatter, as cork, communicates a brownish or black colour. The acid of com-merce usually contains traces of sulphate of lead: this may be detected either byadding water, when the white sulphate is preeipitated; or by the addition of hy-drosulphuric acid to the diiute sulphuric acid, when a very slight change of colouris observed, owing to the formation of sulphuret of lead. " What remains Vi. e.sulphate of lead] after the acid has been distilled to dryness does not exceed the_1 part of its weight."

4U 0 ^ ö

Oil of vitriol frequently, or usually, contains an oxide ofnitrogen. Accordingto A. Rose it is generally the binoxide of nitrogen. A Solution of the protosul-phate of iron detects the binoxide of nitrogen, nitrous acid, or nitric acid, by thereddish brown or brownish black colour which it gives rise to, " if a sufficientquantity of pure sulphuric acid be added to the liquid to be examined " (A. Rose.)Permanganate of potash is an excellent test of binoxide of nitrogen or nitrousacid in sulphuric acid, diluted with about six parts of water. If either of thesesubstances be present, the permanganate is decolourized. The effect is not pro-duced by the presence of pure nitric acid in diluted sulphuric acid. Hence itdistinguishes binoxide of nitrogen and nitrous acid from nitric acid.

Latterly, in consequence of the high price of Sicilian sulphur, sulphuric acidhas been extensively manufactured from iron pyrites, in which arsenic is usuallycontained; and in consequence the oil of vitriol of commerce has been found tobe contaminated with arsenious arid. Dr. G. O. Rees [London Medical Gazettefor Feb. 5, 1841.) found 22-58 grains of this acid in twenty fluid ounces of oil ofvitriol; and Mr. Watson 1 states that the smallest quantity which he has detectedis 35j grains in twenty fluid ounces. The tests for this dangerous contamina-tion are Marsh's test and sulphuretted hydrogen. 2 In the application of thesethe acid must be previously diluted with distilled water.

Physiological Effects. «. On Vegetables. —In the concentrated state sulphu-

' London Medical Gazette for Fol). 1841. Mr. Watson states that a man had nearly lost, his life in cnnse-qnence of the Inhalation of arseninrelted hydrogen, prodnced in the manufacture of hydrochloric acid, by thediluted, unpurified, pyritea sulphuric acid acting lipon the iron retort employed.

5 See the article Mrsentous Jicid, in a subseqnent part of this work, where füll directions will be given fort>*e application of these tests.