Volume 1

Allen's commercial organic analysis : a treatise on the properties, modes of analysis, and proximate analytical examination of the various organica chemicals and products employed in the arts, manufactues, medicine, etc. with concise methods for the detection and estimation of their impurities, adulterations, and products of decomposition.

  • Alfred Henry Allen
Date:
1911-1917
Catalogue details

Licence: Public Domain Mark

Credit: Allen's commercial organic analysis : a treatise on the properties, modes of analysis, and proximate analytical examination of the various organica chemicals and products employed in the arts, manufactues, medicine, etc. with concise methods for the detection and estimation of their impurities, adulterations, and products of decomposition. Source: Wellcome Collection.

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    live treatment of the subject is contained in Kayser’s comprehensive “Handbuch der Spectroscopic.” Microspectroscope.— For observing the absorption-spectra of organic substances a pocket spectroscope will often suffice, but it is far better to employ a microspectroscope, furnished with a proper comparison stage and reflecting prism, so as to allow of the spectrum of the colouring matter under examination being viewed in juxtaposi¬ tion with the spectra of standard specimens of known origin. Fluorescence of organic bodies is a qualitative character often of much value. It is absolutely necessary that the liquid to be observed should be perfectly clear, as the presence of minute suspended particles may lead to fallacious conclusions. As a rule, the phenomenon of fluorescence may be observed by filling a small test-tube with the fluorescent liquid, holding it in a vertical position before a window, and observing the liquid from above against a dark background. Another plan is to make a thick streak of the liquid on a piece of polished jet or black marble, or on a glass plate smoked at the back, and to place the streaked surface in front of, and at right angles to, a well-lighted window. Either of these methods is superior to the polished tin plate sometimes recommended. The background should be black, not white. In some cases, the following method of observing fluorescence may be advantageously employed. A cell is made by cementing a piece of barometer-tube about 3/4 in. in length, and having an internal diam¬ eter of 1/6 in., to a glass microscope-slide, by means of black sealing- wax. The open end of the cell must be well polished. On introduc¬ ing a clear solution of any fluorescent substance, covering the cell with a piece of thin glass, placing the slide on the stage of a microscope, illuminating the tube at the side by means of strong daylight, and looking down and observing the axis of the cell by a low microscopic power, the liquid will appear more or less turbid and of a colour dependent on the nature of the fluorescent substance in solution. If no fluorescent substance be present, the field will appear perfectly black, as no light is reflected either from the apparatus or the liquid. For a sensitive method of detecting fluorescence see Francesconi and Bargellini, Atti dei Lined 1906, [5] 15, No. 3. When desired, the spectrum of the fluorescent light can be observed by the micro¬ spectroscope. In some instances the spectrum thus obtained shows remarkable and characteristic bands.