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.

    63/272 (page 45)
    103. The following precautions are to be attended to in the analysis of this grouwp.—In testing for ammonia, one error frequently committed is, that of allowing the glass rod to remain so long in the heated atmosphere of the test- tube, that on its removal a sensible evaporation takes place from its surface, which is mistaken for the white fumes which are formed when any volatile acid is brought in contact with ammonia. To avoid this error, the solution which is under examination should be heated until it approaches the boiling poimt, but should not actually be boiled, and the moistened glass rod should, immediately after its in- sertion into the test-tube, be withdrawn. If any fuming should then arise, it can only proceed from the presence of ammonia, which must be confirmed by the other appro- priate tests. Young students seldom continue the ignition for the expulsion of the ammoniacal salts sufficiently long ; consequently they find potash when it is not present, owing to the unexpelled ammonia giving precipitates with tartaric acid and bichloride of platinum. The attention of the student is therefore directed to paragraph 108. The detection of potash by tartaric acid requires, in the first place, that the solution be neutral or alkaline, not acid, and as concentrated as possible. The reagent must then be added in excess (if the fluid is alkaline the tartaric acid must be added until the solution is acid), and the fluid well agitated. The application of heat must be avoided, and time allowed for the appearance of the precipitate, as it becomes visible only after the lapse of some hours, when small quantities of potash are present. In testing for potash or soda by the blowpipe flame, it is necessary that the platinum wire should be perfectly clean. This can only be secured by directing the blowpipe flame upon it until it ceases to impart a colour; care should then be