PRESSURE EFFECT UPON ABSORPTION. 565 



about 8 Angstroms, to shift the violet edge about 2 units toward the 

 longer wave-lengths, and to reduce the width of the whole band to 

 about 5 units. 



Bands 5088 and 5122 are somewhat narrowed by pressure and the 

 separation between them is made more distinct. 4690, 461 1 and 4329, 

 are slightly narrowed and intensified by pressure but the effect is very 

 small. The group of red bands, 6730, 9 6790, and 6890, appearing only 

 in the more concentrated solutions, is made more distinct by pressure. 



In the neodymium ammonium nitrate solutions, band 4754, shown 

 in Figure 3, did not appear. Two broad, hazy bands not shown in 

 this figure, at wave-lengths 4410 to 4465 and at 4813, were observed 

 which were evidently due to an impurity of praseodymium. No 

 decided effect upon either of these bands could be noticed when the 

 pressure was raised. 



Neodymium Nitrate. 



Solutions of neodymium nitrate, prepared from pure neodymium 

 oxalate obtained from James, show a pressure effect which is simi- 

 lar to that observed in the ammonium nitrate. An excess of free acid 

 seems to increase the effect. The band at 5800 which, at normal pres- 

 sure shows itself to be made up of several poorly defined compo- 

 nents, is resolved and intensified by a pressure of 2500 atmospheres. 

 It is made narrower on the red side and the components of the group 

 which are of longest wave-length disappear at this high pressure. The 

 band at 5200 is sharpened and intensified and the band at 4272 which 

 is not so sharp as in the ammonium nitrate, is made narrower and 

 slightly shifted toward the red. 



Neodymium Chloride. 



The effect of pressure upon neodymium chloride is similar to that 

 observed in the nitrate but much smaller. The components of the 

 groups at 5800 and 5200 were more distinct at normal pressures than 

 in the nitrate but the effect of pressures from 1500 to 1800 atmospheres 

 was exceedingly small. Concentrations were used which were greater 

 than those of the other salts and bands appeared between 6222 and 

 6366 which did not show in the nitrate solutions. These were slightly 

 intensified by pressure and the red bands, 6730, 6790, and 6890 were 

 also intensified and slightly shifted toward the violet. 



9 Wave-lengths taken from Little, — Text-book of Inorganic Chemistry, 

 Vol. IV, p. 288. 



