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.

    54/272 (page 36)
    baryta. He filters, and to the filtrate he adds oxalate of ammonia, to test for lime; he obtains a precipitate with oxalate of lime, although lime is absent, because he has not added sufficient quantity of the chromate of potash to preci- pitate all the baryta: thus, by the imperfect addition of are- agent, he arrives at a wrong conclusion. This fruitful source of error, viz., imperfect precipitation, may be avoided, by adding to the filtrate a little more of the reagent with which the precipitation was effected. If this produces no further precipitate, the substance has been fully precipitated. Should a further precipitate be produced, it must be removed by filtration before attempting to throw down any other sub- stance. The student must also carefully distinguish between the terms precipitate and filtrate, and be very particular in thoroughly washing the precipitates which require further examination. The wash-water must not be collected with the filtrate, if this last should be required for further examination. But all these precautions will have been attended to in vain should the experiments be performed in dirty apparatus, this being sufficient of itself to nullify all satisfactory results. 83. SYSTEMATIC COURSE OF QUALITATIVE ANALYSIS.— A qualitative investigation may be made with a two-fold view, viz.—either, lst, to prove that a certain definite body is or is not contained in a substance (e. g. lime in a mineral water) ; or, 2d, to ascertain all the constituents of a chemical compound or a mixture. A few simple experi- ments enable us to determine the first; but if we wish to discover all the constituents of a chemical compound or a mixture, if we intend to prove that, besides certain bodies examined further ; the fluid for other substances, the precipitate for the detection of the several substances which may have been precipitated, or for the confirmation of any one substance.