. Biological stains; a handbook on the nature and uses of the dyes employed in the biological laboratory. Stains and staining (Microscopy); Stains and Staining; Dyes. 56 Biological Stains. A A ^i ^M j£! P Ni -^x -tv Z2^~> Slivered Prism P 1 PHOTOlitTE-R- PEC'TKOntTLR- Fig. 1. Schematic diagram of Hilger-Nutting spectrophotometer. Specimen holder with dye dissolved in a suitable solvent is placed at Ei while a similar cell with solvent alone is placed at Ej. Both are equally illuminated from the same light source. Through the partially silvered prism, P, the upper and lower portion of the ph
. Biological stains; a handbook on the nature and uses of the dyes employed in the biological laboratory. Stains and staining (Microscopy); Stains and Staining; Dyes. 56 Biological Stains. A A ^i ^M j£! P Ni -^x -tv Z2^~> Slivered Prism P 1 PHOTOlitTE-R- PEC'TKOntTLR- Fig. 1. Schematic diagram of Hilger-Nutting spectrophotometer. Specimen holder with dye dissolved in a suitable solvent is placed at Ei while a similar cell with solvent alone is placed at Ej. Both are equally illuminated from the same light source. Through the partially silvered prism, P, the upper and lower portion of the photometer field is illuminated through the specimen while the central portion is illuminated through solvent alone. This latter illumination may be varied by the rotation of the analyzer, Nj, which is actuated by a graduated circle C, reading with the index I. By this means the illumination of the several portions of the field is maintained equal and absorption values read off of circle C. The spectrometer of the constant deviation type serves to isolate particular portions of the spectrum by means of a graduated drum D which through a screw actuates the prism table sup- porting prism B. This visual type of instrument, as explained above, is now rarely used, having become obsolete on account of the greater efficiency of the photoelectric cell in comparison with the eye. The eye is badly subject to fatigue after continuous use, and even at its best has low sensitivity at the violet end of the spectrum. The photo- electric cell, on the other hand, is not so subject to fatigue, can make readings over a longer wavelength range, and even into the ultra-violet, if special equipment for that purpose is provided. For these reasons more rapid readings can be made, and it is pos- sible to obtain the exact point of maximum absorption much more quickly than with the eye. A photoelectric instrument such as the General Electric Recording Spectrophotometer, is even more automatic, as it has a
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