Qualitative analysis / by William Briggs and R.W. Stewart.

  • William Briggs
Date:
1913
Catalogue details

Licence: Public Domain Mark

Credit: Qualitative analysis / by William Briggs and R.W. Stewart. Source: Wellcome Collection.

    151/180 (page 135)
    tube with dilute sulphuric acid. If an evolution of gas occurs and the gas is found to be hydrogen, it affords a proof that the substance under examination is a metal. In order to settle this point, fill a rather larger test-tube with water and invert it in a basin of water ; now fill the test-tube containing the substance completely with dilute acid, and bring it mouth upwards under the lip of the inverted test-tube. Collect a tube full of the gas and apply a light to the mouth. If it is found to burn without luminosity, the conclusion may be drawn that the gas is hydrogen. Dilute sulphuric acid has, however, no action on the non-metals or on Cu, Ag, Hg, Pb, As, Sb, Bi; the action on Sn, Co, and Ni is slow. If, therefore, no hydrogen is evolved, the absence of an element must not be inferred. Note.—C02 will be evolved from carbonates, S02 from sulphites, II2S from sulphides, etc., in presence of dilute sulphuric acid, but these may be easily distinguished from hydrogen, and these salts are not likely to be mistaken for elements on account of the difference in their external appearance. D. Warm gently in concentrated nitric acid. In the case of the solid elements (both metals and non- metals) red fumes of the oxides of nitrogen are evolved. -This m&y be generally relied on as indicating the presence of an element, but it must be remembered that it may also occur with sulphides, which may by appearance (see A, c) be mistaken for metals, or with a few other substances, such as oxalic acid, which have no resemblance to the metals. E. Immerse the substance in a solution of copper sulphate to which one or two drops of dilute sulphuric acid have been added. Many metcds become coated with metallic coppei, and the deposit may be readily recognized by its colour,* either by the naked eye or with a lens. The formation of such a coating of copper may be taken as positive evidence of the * Note.—This deposit of copper looks black viewed through a blue solution, so the solution should be poured off in order that the colour may be examined.