POTASSIUM SALTS. 27 



appearance at the concentration 0.0026 normal, and has a limit at about 

 X 3200. For 0.0017 normal the limit is 3300, and for 0.00087 normal, 

 X 3400. The middle of this absorption band for 0.00087 normal would 

 thus be about X 3800. The ultra-violet band which appears at 0.0017 

 normal has limits upon its red side of X 3100; for 0.00087 normal, X 3000; 

 and 0.00065 normal, X 2900. 



Plate 5, A, tests Beer's law. Starting with the strip nearest the 

 numbered scale the concentrations are 0.33, 0.25, 0.16, 0.11, 0.083, 0.055, 

 and 0.042 normal; the corresponding depths of cell being 3, 4, 6, 9, 13, 

 18, and 24 mm. The limit of absorption is at X 5350. Beer's law is found 

 to hold. 



Plate 7, A, and B, contains spectrograms in which Beer's law is tested 

 for more dilute solutions. The concentrations and depths of cell are given 

 in the general description of the plates. In A the limit of absorption is at 

 X 5000, in B at X 4200. In both cases Beer's law holds. The edge of the 

 absorption band in this case is quite broad. 



Potassium Ferrocyanide in Water. 



Potassium ferrocyanide has a color very similar to that of potassium 

 ferricyanide. It is practically insoluble in all solvents except water. Its 

 spectrum has been mapped out for concentrations ranging from 0.5 to 

 0.00078 normal, and Beer's law has also been tested between these limits. 



The methods of exposure have been the same in all the spectrograms 

 taken of the potassium salts. The time of exposure to the Nernst glower 

 was 80 seconds, the current being 0.8 ampere and the slit width 0.08 mm. 

 When there was any transmission in the ultra-violet, exposure was made 

 for 120 seconds to the spark. 



The mapping of the spectrum was done by keeping the depth of cell 

 constant at 3 mm. and gradually changing the concentration of the solution. 

 Plate 8, A and B, shows the variation of the absorption of light with varia- 

 tion in the concentration. Starting with the strip at the top of A, the con- 

 centrations were 0.5, 0.375, 0.25, 0.17, 0.117, 0.083, and 0.062 normal. 

 The corresponding limits of absorption were XX 3950, 3920, 3890, 3840, 3790, 

 3750, and 3700. The region between complete transmission and complete 

 absorption was quite wide, being almost 100 Angstrom units. This is in 

 marked contrast with the sharp edge of the absorption band for concen- 

 trated solutions of potassium ferricyanide. 



Starting with the upper strip of spectrogram B, the concentrations 

 were 0.0625, 0.0469, 0.0312, 0.0208, 0.0144, 0.0103, and 0.0078 normal. 



The corresponding limits of absorption in this case were XX 3700, 3640, 

 3600, 3500, 3400, 3300 and 3150. For dilutions greater than this there is 

 almost complete transmission throughout the whole violet region. 



Two spectrograms (Plate 9, A and B) are given to show that Beer's 

 law holds for solution of potassium ferrocyanide. Starting with the upper 

 strip of A, the concentrations were 0.5, 0.375, 0.25, 0.17, 0.117, 0.083, 

 and 0.062 normal. The corresponding concentrations in spectrogram B 

 were 0.0625, 0.0469, 0.0312, 0.021, 0.0144, 0.0103, and 0.0078 normal. 

 The depths of layer starting at the top of either A or B were 3, 4, 6, 9, 13, 18, 



