DESCRIPTION OF PLATES. 



With the exception of the plates representing changes in temperature of the solution, 

 the times of exposure and the width of the slit are the same for each strip of the plate. The 

 current through the Nernst glower was kept constant. In the case of the uranyl salts a 

 much longer exposure is often made in the ultra-violet and violet, in order to bring out the 

 uranyl bands as strongly as possible, and this will be noted in the description. In some 

 strips ultra-violet wave-length spark lines will be found, these being photographed without 

 the solution in the path of the light, and only for purposes of measurement. In exposures 

 to the spark of this kind, the film holder was never moved between the photographing 

 of the absorption spectra of the solution and that of the spark spectra. In some instances 

 the strips are not uniformly exposed. This was due in many cases to the formation of 

 precipitates. A great deal of trouble of this kind was encountered, especially with the 

 uranous salts, in the high temperature work, and in the spectrophotography of chemical 

 reactions. In referring to the strips, the first or lowest strip will be that at the bottom of 

 the plate the one that is nearest the scale of wave-lengths. The scale of wave-lengths 

 is in Angstrom units, the whole number standing for so many hundred Angstrom units. 



Plate 1. A. Lithium Chromate in Water. Depths of cell and concentrations, starting 

 with the lowest strip: 0.25 normal, 3mm.; 0.25 normal, 24 mm.; 0.46 nor- 

 mal, 24 mm.; 1.0 normal, 24 mm.; 1.5 normal, 24 mm.; and 2.0 normal 

 24 mm. 

 B. Lithium Bichromate in Water. Depths of cell and concentrations, start- 

 ing with the lowest strip: 0.25 normal, 3 mm.; 0.25 normal, 24 mm.; 0.46 

 normal, 24 mm.; 1 .0 normal, 24 mm.; and 2.0 normal, 24 mm. 

 Plate 2. .4. Calcium Ferricyanide in Water. Depth of cell kept constant, 24 mm. Con- 

 centrations, starting with the lowest strip, 0.031, 0.058, 0.125, 0.175, 

 and 0.25 normal. 

 B. Calcium Ferrocyanide in Water. Depth of cell kept constant, 24 mm. Con- 

 centrations, starting with the lowest strip, 0.25, 0.46, 0.66, 1.0, 1.5, and 

 2^0 normal. 

 Plate 3. A. Aluminium Chromate in Water. Depths of cell, 3, 24, 24. and 24 mm. Con- 

 centration could not be determined on account of hydrolysis. 

 B. Calcium Chromate in Water. Depth of cell constant, 24 mm. Concentra- 

 tion somewhat less than 0.01 normal. 

 Plate 4. A. Copper Bichromate in Water. Depths of cell and concentrations, starting 

 with the lowest strip: 3 mm., 0.044 normal; 24 mm., 0.044 normal; 24 mm., 

 0.08 normal; 24 mm., 0.117 normal; 24 mm., 0.175 normal; 24 mm., 0.26 

 normal; and 24 mm., 0.35 normal. 

 B. Potassium Nickel Chromate in Water. The depth of cell was kept constant 

 at 24 mm., and the concentration could not be determined on account of 

 hydrolysis. 

 Plate 5. A. Neodymium Chloride in Butyl Alcohol. Depth of cell 10 em. and concen- 

 tration 0.024 normal, strip 1, and in Butyl Alcohol, depth of cell 3 cm. 

 and concentration 0.04 normal, strip 2. 

 B. Neodymium Chloride in Glycerol and Ethyl Alcohol, concentration con- 

 stant, 0.5 normal. Depth of cell constant, 18 mm.; starting with the 

 lowest strip the following numbers represent the percentage of the solvents : 

 10, 15, 20, 40, 60 glycerol. 

 90, 85, 80, 60, 40 ethyl alcohol. 

 Plate 6. A. Neodymium Chloride in Isopropyl Alcohol. Depth of cell 30 mm. Con- 

 centration, 0.0266 normal. 



B. Neodymium Nitrate in Tertiary Butyl Alcohol. Concentration, 0.2 normal. 



C. Neodymium Chloride in Water and Alcohol. The lower strip represents 



about 8 per cent water and shows both sets of bands. Concentration, 

 0.5 normal. The other strips show the effect of adding hydrogen peroxide. 



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