BY MEANS OF THE RADIOMICROMETER. 



17 



the neighborhood of the 0.77/j. water-band. This is a very faint band, 

 and even for the above depth of water the actual absorption is only 

 between 3 and 4 per cent. It will thus be seen that for the first band 

 whose center is represented by head-reading 489, the concentrated and 

 dilute solutions absorb with equal intensity. 



Wave-length of light represented by head-reading 503 is the point 

 which indicates the center of the first neodymium band in the infra- 

 red. With slit-width of 0.2 mm., the water contained in 2 mm. of the 

 more concentrated solution has an absorption of 1 per cent for this 

 particular wave-length, while the water contained in 16 mm. of the 

 more dilute solution has an absorption of 2 per cent. Here, as in the 

 case of the other bands, the intensity of the bands for the dilute and 

 concentrated solutions is the same. 



TABLE 4. Testing Beer's Law. 



Head-reading 518 marks the position for the last neodymium band 

 we could study. The wave-length of light corresponding to this band 

 would be approximately 0.87^i, which is sufficiently close to the IM 

 water-band for the dilute solution to cause considerable absorption on 

 account of the water present. For this wave-length 16 mm. of the 

 more dilute solution has about 7 per cent absorption due to water; 

 whereas the 2 mm. of the more concentrated solution has 2 per cent 

 absorption at this wave-length. It will thus be seen that only in the 

 case of this one band is there an increase in intensity with dilution. 

 The more dilute solution has a band which is nearly 3 per cent more 

 intense than that for the more concentrated solution. 



It should also be noted that the absorption bands of the more dilute 

 solution are broader than those of the more concentrated. This is 

 shown by the fact that the percentage transmission of the more dilute 

 solutions are always lower than those of the more concentrated. There 

 is no evidence of a shift in the bands for the dilute solution. 



