Cambridge Philosophical Transactions, Vol. XVIII., Plate 3. PLATES 3-23 ILLUSTRATING PROFESSOR LIVEING'S PAPER (pp. 298-315), On the effects of Dilution, Temperature, and other circumstances, on the Absorption Spectra of solutions of Didymium and Erbium salts. These plates are all reproductions, enlarged to double the size, of photographs of some of the spectra from which the conclusions in the text have been deduced. In the processes of enlargement and reproduction some of the fainter details visible in the original negatives have (perhaps unavoidably) been lost but they present the salient features of the changes in the spectra produced by the variations of circumstance. The references to these plates in the text applied to the original negatives and were printed before the reproductions were ready. The latter, being positives, are reversed, and in order that the references may be easily intelligible it has been necessary to place the red ends of the spectra on the left hand. The figures at the top of each plate are the approximate wave lengths of the bands in the spectra beneath them, and sufficiently indicate the range of the spectrum photographed. PLATE 3. Absorptions of solutions of didymium chloride in four degrees of dilution in thicknesses inversely as the dilutions. The most concentrated solution contained 1407 grams per litre, and the absorbent thickness of this solution was 38 mm. It will be noticed how very nearly identical these four spectra are. shews a number of faint bands which have not come out in the reproduction. nearly identical in all four spectra as are the stronger bands here reproduced. The original photograph 4 2 Cambridge Philosophical Transactions, Vol. XVIII., Plates 4, 5. PLATE 4. Absorptions of solution of didymium sulphate in four degrees of dilution. saturated solution 38 mm. thick half-strength 76 mm. thick quarter-strength one-eighth strength The diffuse bands at about à 380, 375 and 364, are quite visible in the original photograph, but have nearly disappeared in the reproduction PLATE 5. Absorptions by solution of erbium nitrate in four degrees of dilution, the strongest containing 566 grams of the salt to the litre. The increasing diffuseness of the bands with increased concentration of the solution is seen in this series; the weak band about X441 seeming to be washed out when the solution is concentrated while that about 449 is much broader and the details within it obliterated. 2 1 596 2 1 596 Cambridge Philosophical Transactions, Vol. XVIII., Plates 6, 7. PLATE 6. Absorptions by solutions of didymium nitrate, concentrated, and extremely dilute. The most concentrated had 6111 grams of the salt per litre; the other was part of the same solution diluted to 455 times its bulk. There is very little difference between these two spectra except that the band in the yellow is broader with the stronger solution, and those at 1476 and 427 more washed out. stronger solution 1/45.5 strength 305 mm. thick PLATE 7. Absorptions by solutions of didymium chloride of concentrations equivalent to those of the nitrate used for plate 6: the stronger containing 462-9 grams of the chloride per litre. There is no definite difference between these two spectra. |