1909.] OF VARIOUS SALTS IN SOLUTION. 199 



with decrease in concentration the transmission gradually moves 

 towards the ultra-violet, and for dilutions greater than 0.0078 normal 

 there is transmission throughout the whole spectrum. Beer's law 

 was found to hold. 



A 2-normal aqueous solution of potassium chromate 3 mm. in 

 thickness, shows complete transmission of wave-lengths greater 

 than A 4950. Decreasing the concentration causes the transmission 

 to move gradually towards the violet and for a o.oi normal solution 

 a transmission band appears at A 3100, or, in other words, there 

 appears an absorption band whose center is about A 3700. As the 

 concentration decreases this absorption band fills up, the violet edge 

 of the transmission band gradually pushes out into the ultra-violet, 

 and for dilutions greater than 0.0005 normal there is complete 

 transmission throughout the spectrum. Beer's law was found to 

 hold for potassium chromate throughout the above ranges of con- 

 centration, except in the more concentrated solutions between 2 

 normal and 0.25 normal. 



Potassium dichromate in water was found to have a much 

 greater absorbing power than the solutions previously described. A 

 one-third normal concentration absorbed all wave-lengths shorter 

 than A 5350. As the concentration is decreased the transmission 

 extends farther and farther out into the violet. For a 0.0026 normal 

 concentration a transmission band appears in the violet, thus giving 

 an absorption band whose center is about A 3800. As the concen- 

 tration is further decreased transmission becomes greater and 

 greater in the violet and ultra-violet, and is practically complete for 

 a 0.0006 normal concentration. Beer's law has been tested between 

 the above ranges of cencentration and has been found to hold. 



In photometric measurements of Beer's law, the equation defin- 

 ing the quantities to be measured is : 



Jq is the intensity of the light that enters the solution (neglecting 

 any loss due to reflection), / the intensity of the light as it leaves 

 the solution, c the concentration in gram molecules of the salt per 

 liter of solution, I the thickness of layer and A a constant if Beer's 

 law holds. Strictly speaking the above equation holds for mono- 



