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.

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    ammoniacal salts which have been employed in their preci- pitation ; if a residue remains, it must be examined for potash and soda. 598. THE SOLID SUBSTANCE UNDER EXAMINATION IS NEITHER A PURE METAL NOR AN ALLOY, BUT CONTAINS ORGANIC MATTER. 599. The presence of fixed organic matter* interferes with the detection of many substances. Thus, in the pre- sence of tartaric acid, which is a fixed organic acid, the oxides of aluminum, chromium, and iron, and many other metallic oxides, are not precipitated by the alkalies; alka- line citrates prevent the precipitation of acids, by bases, with which the acids form insoluble salts under ordinary circumstances ; a soluble salt of baryta will not produce a precipitate, even in a solution of a sulphate, if an alkaline citrate be present, unless the sulphate is present in the proportion of three or more equivalents for every one of the citrate. It is therefore necessary, after precipitating the fifth and sixth groups by hydrochloric acid and sul- phuretted hydrogen, to destroy the fixed organic matter, when it is present, which will have been ascertained in the preliminary examination. or this purpose, the filtrate from the sulphuretted hydrogen precipitate, or the solution which has failed to give a precipitate with this reagent, is evaporated to dryness, and ignited} until all the organic matter has been destroyed, the residue must then be dis- * Organic substances are termed fixed when they cannot be distilled or volatilized without decomposition. + Many substances, especially alumina and oxide of iron, after ignition dissolve with very great difficulty even in the concentrated mineral acids. The residue may therefore require protracted boiling in acids, although the original substance dissolved in water or dilute acid very readily.