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.

    139/272 (page 121)
    of ammonia in excess, and heat applied; by this means the CADMIUM, if present, will be precipitated. As this method for detecting and separating cadmium from copper is not a safe one if only small quantities of cadmium are present, we give the following method by Fresenius:—To one por- tion of the acetic solution add hydrosulphuric acid in excess. The formation of a yellow precipitate denotes CADMIUM. If, on account of the presence of copper, the sulphide of cadmium cannot be distinctly recognised, allow the precipitate produced by the hydrosulphuric acid to subside, decant the supernatant fluid, and add to the precipitate a solution of cyanide of potassiwm until the sulphide of copper is dissolved. If a yellow residue is left undissolved, capmivm is present ; in the contrary case, not.* 308. If a black residue remain after boiling the mixed sulphides in nitric acid, it must be collected upon a filter, to separate it from the other members, and specially ex- amined for protoxide of mercury by one of the two follow- ing methods:— Ist. After having dried the black mass thoroughly in a water bath, mix it with dry carbonate of soda, and proceed with the examination for mercury in the way described in paragraph 321. 2nd. Dissolve the black mass m as small a quantity of AqUA REGIA as possible, then add ammonia in slight excess, and then a slight excess of hydro- chloric acid ; examine the solution, thus prepared, for mer- cury by means of copper wire, in the way described at paragraph 319. 309. The following precautions must be attended to in analysing this group :—The means, both for separating and detecting the members of the first section, are so simple and positive, that no difficulty will be experienced by the * See Appendix B.