36 



J. G. MACGEEC40R ON THE 



544"8 aud 516'8 we have one of the absorption bands characteristic of dilute solutions of 

 this salt. It is impossible to determine from these observations the exact w ave length 

 of the centre of the band, i.e., of the minimiim of intensitj- of light, in the case of either 

 solution. But it is easy to see that in the case of the strong solution it has a greater wave 

 length than in that of the weak solution. From the approximate equality of the intensi- 

 ties of light in the second and third regions, in the case of the weaker solution, it is 

 obvious that the centre of its band is near the common boundary of these regions, 

 while the relatively much greater difference between the intensities in the same regions, 

 in the case of the stronger solution, shews that the centre of its band is well within 

 the second region. If curves be drawn as above, it will be found that the wave length 

 of the centre of the band in the case of the weaker solution is about 528, while in the case 

 of the stronger solution it is about 530. The general form of the curves is the same. But 

 the curve for the weak solution is higher than the other throughout, the difference being 

 greatest at the red- ward side of the band. In other words, the absorption of the strong 

 solution is greater than that of the weak throughout aud the amount by which its absorp- 

 tion is the greater is greater on the red side than on the A'iolet side of the centre of the 

 band. 



In all the solutions examined, therefore, of this salt, increase of concentration seems 

 to extend the absorption at the red-ward end of a band more than it does at the violet- 

 ward end. 



Gr. and H. Kriiss' have examined the effect of elevation of temperature on the position 

 of all five of the absorption bands of a dilute solution of the same salt. Their results are 

 as follows : 



In all cases, therefore, elevation of temperature causes the bands to move towards the 

 red end of the spectrum — the same effect as is shown above to follow upon increase of 

 concentration. 



Vierordt- has made observations on solutions of different strengths of Potassium 

 monochromate, similar in all respects to those of G. Kriiss referred to above. I have 

 treated them in the same way, and the results are given in the following two tables. 

 Potassium monochromate has a one-sided absorption spectrum, light of the shorter wave 



' ' Kolorimetrie,' p. 273. 

 ■' Ibid., p. 165. 



