Manual of qualitative analysis / by Robert Galloway.

  • Galloway, Robert.
Date:
1861
Catalogue details

Licence: Public Domain Mark

Credit: Manual of qualitative analysis / by Robert Galloway. Source: Wellcome Collection.

    255/272 (page 237)
    soda at 2300° C, at a temperature, therefore, much less than that of many lava streams. Besides these determinations of volatility, the flame can be used for many valuable blowpipe experiments, among which is the quantitative determination of soda in the pre- sence of lithia and potash. For the qualitative determination of soda in its volatile salts, it is enough to hold a small bead in the melting-space, and to illuminate with it a crystal of bichromate of potash. When the rays of the soda-flame are incident on this salt, it appears perfectly colourless, transparent, and with an adamantine lustre, But the following reaction is more delicate, and better suited to approximative quantitative determinations. A piece of paper about a centimetre square is coated with red iodide of mercury, and placed upon a small holder d (fig. 1), which is moveable on an arm ce, also moveable, attached to the chimney. When the least quantity of soda, sulphate of soda, or chloride of sodium is introduced into the melting- space of the flame, the red iodide becomes white, with a faint tinge of fawn colour. The glaring contrast of these colours is apparent when the paper is lit up by being placed close to the red-hot wire and bead, and the wire then placed in the flame, that the bead only reaches the melting-space. Potash, lithia, and lime do not prevent this reaction. If the soda compound is dissolved in water, the experiment is made as follows: The capillary platinum wire d, fig. 3, is bent to a loop, and this is beaten out so as to form a small ring. If this be dipped in the substance under examina- tion, a drop of the liquid in the form of a lens adheres to it. If this drop is evaporated, without boiling, in the neigh- bourhood of the flame, as much solid substance remains as is necessary for the reaction. With solutions of various