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.

    259/272 (page 241)
    silicates (for instance, the members of the felspar family) may not only be recognised, but the relative quantity of potash, soda, and lithia approximatively determined. The process adopted in these cases will be most readily understood by an example. Bunsen selects the discrimina- tion of the following minerals :—Orthoclase and its varieties, Sanidine and Adularia; Leucite, Labradorite; Albite and Oligoclase, Anorthite, Nepheline, Hauyne, and Lasurstein ; Petalite, Lepidolite, and Triphane. These are divided into two groups—those containing lithia, and those which-do not contain that alkali. It is first ascertained to which of the two groups the sample belongs, by exposing it with gypsum in the melting-space side by side with a specimen of pure potash, and viewing the two flames through the indigo prism. If the sample contains lithia, its flame at that part of the prism at which the soda colour vanishes appears red against the cornflower-blue of the potash. With thicker layers of indigo, the red of the lithia gradually lessens in intensity, while the cornflower-blue of the potash passes through violet into red, which, with a certain thickness of the indigo layers, is quite like the colour of the lithia. If no lithia is found, the sample belongs to the first group; in the other case, to the second. The individual minerals of the first group are recognised by comparing them with each other according to their relative proportions of potash and soda. A standard series of felspathic minerals is selected, and arranged according to the soda they contain. Bunsen uses the following series, and distinguishes them by the numbers placed over the analyses : . ie