MAPPING ABSORPTION SPECTRA OF VARIOUS SALTS. 33 



In strip 1, B, plate 2, cd is 6 and the middle of the edge of absorption is at 

 about X 4150, the edge of the band being about 300 Angstrom units wide. The 

 edge of the absorption is very wide and diffuse, resembling the absorption of 

 potassium ferrocyanide. No direct comparison of the absorption in the two 

 cases can be made, as the value of cd is much larger in the case of the calcium salt. 



The Chromate and Bichromate of Lithium. 



The absorption spectrum of an aqueous solution of lithium chromate is 

 given in A, plate 1, and of lithium bichromate in B, plate 1. In the case of 

 lithium chromate a changejn cd of 0.75 to 0.0 produces an increase in width of 

 the absorption of over 200 Angstrom units; the edge of the band being at about 

 X 4850 for cd = 0.75. This is approximately the position of the edge of the 

 absorption band of potassium chromate for a corresponding value of cd. For 

 lithium bichromate, the edge of the absorption for strip 1, cd = 0.75 is about 

 X 5350. The values of cd here are much larger, and the absorption is, therefore, 

 much greater than in the case of potassium bichromate previously investigated. 



Aluminium and Calcium Chromates. 



The absorption spectrum of an aqueous solution of aluminium chromate 

 is given in A, plate 3. The depths of cell are 3, 24, 24, and 24 mm. Starting 

 with the lowest strip the solution used in strip 1 was the same as in strip 2. 



In B, plate 3, is given the absorption of an aqueous solution of calcium 

 chromate, the depths of cell being 24 mm. and the concentrations 0.025, 0.033, 

 0.046, 0.066, 0.1, 0.15, and 0.2 normal. For a value of cd of 0.6 the edge of the 

 absorption is at about X 4670. For corresponding values of cd it seems, there- 

 fore, that the absorption of calcium chromate is less than the absorption of 

 lithium or potassium chromate, and that the presence of calcium does not 

 increase the width of the absorption bands. 



Potassium Nickel Chromate and Copper Bichromate. 



The absorption of these two salts is an example of the absorption of salts 

 in which both the anion and the cation are colored. A, plate 4, represents the 

 absorption of an aqueous solution of copper bichromate, the depths of cell 

 being 3, 24, 24, 24, 24, 24, and 24 mm. and the concentrations 0.044, 0.044, 

 0.08, 0.117, 0.175, 0.26, and 0.35 normal. B gives the absorption of an aqueous 

 solution of potassium nickel chromate. A is seen to show the edge of the red 

 copper band. For a value of cd of 0.13, the edge of the absorption in the blue 

 is about X 4900, which is seen to be about the same as that for potassium 

 bichromate. The absorption of salts having both ions colored does not seem 

 to be at all different from what one would expect if the absorption was addi- 

 tive. Of course, these experiments are very largely qualitative, and it is 

 expected that a rigorous examination along quantitative lines will be made 

 with the radiomicrometer. For photographic methods the above salts are 

 not at all well suited, since the limits of absorption and transmission are very 

 large and ill defined. 



The Absorption op Solutions op Certain Erbium Salts. 

 On account of the slight solubility of the erbium chloride in the higher 

 alcohols and other organic solvents, very few solutions could be made of 

 sufficient concentration to show the erbium absorption bands. Several of 

 3 



