48 A STUDY OF THE ABSORPTION SPECTRA. 



76, and S7 for the concentrated solution, and 1, 15, 30, 45, 60, 75, 

 and 82 for the dilute solution. At 5 the concentrated solution shows 

 transmission from X 3600 to X 6500, at 87 from X 3800 to X 6000. For the 

 dilute solution there is practically no change of absorption due to heating 

 the solution from 1 to 82. The transmission extends from X 3550 to 

 X 6400. 



A spectrogram (Plate 25, B) was made of a copper nitrate solution in 

 water, 4.04 normal concentration and 3 mm. length of layer under the 

 same conditions as for the other copper nitrate solutions. At zero tem- 

 perature there was complete transmission from X 3550 to X 6000. At 82 

 the transmission extended from X 3800 to X 5900. The transmission spec- 

 trum was cut off quite sharply and completely in the violet, and the edge 

 of transmission receded towards the red as the temperature was raised. 

 The long wave-length edge of the transmission band was but slightly 

 affected by change in temperature. 



Hartley in his work on the effect of temperature on absorption spectra 

 reaches the conclusion that the salt solutions that show the greatest change 

 in their absorption spectra as the temperature is changed, are those that 

 crystallize with the greatest amounts of water of crystallization. The cop- 

 per salts show, however, that this is not the case; since of all these salts 

 the bromide shows a very great coefficient of temperature change, while 

 the nitrate shows a much smaller change. The copper salts are usually 

 given the following formulas at ordinary room temperatures: CuCl 2 .2H 2 0; 

 CuBr 2 .2H 2 0; CuS0 4 .5H 2 ; Cu(N0 3 ) 2 .3H 2 0. In many cases, however, 

 Hartley's rule seems to hold quite well, and there is certainly no doubt 

 that the water of combination plays a very important role in the absorp- 

 tion of light. 



