. Practical physical chemistry . ascertained more exactly, and the prismfixed. 122 PRACTICAL PHYSICAL CHEMISTRY We have now to determine the angular devia:tion ofdifferent spectral lines of known wave-length, by illuminatingthe slit with different incandescent substances, bringing thecross-wire of the telescope into coincidence with the differentlines of the spectra, and reading off on the graduated scale andvernier of the instrument the angle of deviation for the differentlines. The angles so read off are plotted as abscissse againstthe wave-lengths of the particular lines as ordinates, and a
. Practical physical chemistry . ascertained more exactly, and the prismfixed. 122 PRACTICAL PHYSICAL CHEMISTRY We have now to determine the angular devia:tion ofdifferent spectral lines of known wave-length, by illuminatingthe slit with different incandescent substances, bringing thecross-wire of the telescope into coincidence with the differentlines of the spectra, and reading off on the graduated scale andvernier of the instrument the angle of deviation for the differentlines. The angles so read off are plotted as abscissse againstthe wave-lengths of the particular lines as ordinates, and asmooth curve drawn through the points so plotted. In thisway we obtain a map from which the wave-length of anyother line can then be obtained, by determining the angulardeviation (the prism always being in the same position) of theparticular line, and reading off from the curve the corre-sponding wave-length. Instead of determining the angular deviation of the differentlines, one may make use of a fixed scale. This is contained. Fig. 41. in a third tube, D (Fig. 41), and is seen in the telescope byreflection from the face of the prism, the scale being illuminatedby a small gas flame or electric lamp placed opposite the end OPTICAL MEASUREMENTS 123 of the tube. Too strong an illumination should be avoided,otherwise difficulty will be found in seeing the weaker spectrumlines. To adjust this scale, place a sodium flame in front of theslit of the collimator, and turn the telescope until the D lineis seen in the centre of the field of view; illuminate the scale,and focus it quite sharply on the face of the prism; thenadjust the position of the scale so that the sodium linecoincides with some definite scale mark—say 100. Theposition of other spectral lines is then read off on the scale,and the scale numbers are plotted against wave-lengths. Experiment.—Construct a Spectrum Map, and determinethe Wave-lengths of the Chief Lines of the Spectra of Hydrogenand of Helium. The spectrome
Size: 1991px × 1255px
Photo credit: © Reading Room 2020 / Alamy / Afripics
License: Licensed
Model Released: No
Keywords: ., bookcentury1900, bookdecade1910, bookpublisherlondonnewyorklongm
