26 



A STUDY OF THE ABSORPTION SPECTRA. 



Angstrom units nearer the violet for the most concentrated solution, com- 

 pared with the 0.025 normal solution. This would mean that the value of 

 A had increased with increase in concentration. On account of the sharp- 

 ness of the edge of absorption it is possible to detect a change in the edge 



of 10 Angstrom units, and this would correspond to a change in A of about 

 20 per cent. One of the larger errors entering into the determination is 

 getting the depth of layer correct for their smallest values. The method 

 is very useful in showing the results over the whole spectrum. 



Potassium Dichromate. 



The spectrograms showing the variation of absorption of potassium 

 dichromate in water, keeping the depth of layer constant and changing the 

 concentration, are Plate 5, B, and Plate 6, A, B. The absorption is much 

 greater than for potassium chromate and the limits of the bands are much 

 more diffuse. The change of the absorption with change in concentration is 

 much greater than for potassium chromate. 



The concentrations for B, Plate 5 are, beginning with the strip next 

 to the scale, 0.333, 0.25, 0.16, 0.11, 0.083, 0.055, and 0.042 normal; the 

 depth of layer being 3 mm. The distance between complete absorption 

 and complete transmission is about 70 Angstrom units for the 0.3 normal 

 solution and over 200 Angstrom units for the 0.04 normal solution. The 

 limits of the absorption band beginning with the most concentrated solu- 

 tion are U 5340, 5320, 5300, 5240, 5200, 5140, and 5100. 



For Plate 6, A, the concentrations are 0.042, 0.031, 0.021, 0.014, 

 0.0104, 0.0068, and 0.0052 normal, beginning with the strip next the scale. 

 The depth of layer is 3 mm. In this case the edge of the absorption is very 

 diffuse, the distance between complete absorption and transmission being 

 over 200 Angstrom units. The limits of the band for the various concentra- 

 tions are U 5100, 4900, 4800, 4700, 4500, 4300, and 4200, approximately. 



The concentrations for Plate 6, B, are 0.0052, 0.0039, 0.0026, 0.0017, 

 0.00087, and 0.00065 normal, starting with the strip nearest the scale. 

 The limits of the red side of the absorption band are roughly M 4200, 4150, 

 4050, 4000, 3900. The violet edge of this absorption band makes its 



