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.

    164/272 (page 146)
    and lime, when in combination with oxalic acid. When the student looks for acids as well as bases, he must examine the precipitate produced by ammonia, accord- ing to Table 5. Baryta, strontia, and lime, when in combination with hydrofluoric and boracic acids, may also be precipitated by ammonia in minute quantities ; but asa suf- ficient quantity of the bases will always remain in solution, and be precipitated in their proper place, and as the acids will be found in the examination for acids, we have not in- cluded these salts in the table. | 351. Precautions to be observed in examining for the Third Group.—If chromic acid and baryta are both present in a solution, a substance insoluble in acids is sometimes found on dissolving the precipitate produced by ammonia, or that produced by sulphide of ammonium; the insoluble sub- stance is sulphate of baryta. A sulphur acid appears to be formed when chromic acid is reduced by sulphide of hydro- gen, which becomes converted into sulphuric acid after some time. __ 352. The precipitate produced by sulphide of ammonium is very difficult to filter; the filtrate will frequently come through the filter twrbzd for some time ; there is no remedy for this but to pass it through the filter until it is perfectly clear. The student must not mistake between a turbid filtrate and one which is perfectly clear but colowred. A filter can only remove what is heldin suspension by a liquid, as in the first case; it cannot remove what is dissolved, as in the second case: when the filtrate is coloured, consult the next para- graph. The precipitate must be carefully washed with water containing a little sulphide of ammonium, in order to prevent the precipitated sulphides from oxidizing.. If the wash-water comes through of a deep-brown colour, it must be treated as directed in the next paragraph.