NEODYMIUM SALTS. 79 



both bands coexist when the neodymium salt is dissolved in a mixture of 

 the solvents. But the X 4288 band apparently shifts gradually into the 

 X 4274 "water " band. No sign of the two bands coexisting is to be seen. 



Neodymium Nitrate in Nitric Acid. 



Plate 42, B, gives the absorption spectra of neodymium nitrate in 

 nitric acid. The effect of free nitric acid is very pronounced. All the bands 

 are wide and diffuse and differ very much from the absorption when there 

 is no free acid. The first band to appear is X 5830 and it appears as a very 

 faint diffuse band. Then come the bands U. 3470, 3520, 3550, 5130, 5250, 

 5730, 5970, and for a greater depth of cell XX 4280, 4310, 4340, 4360, 4390 to 

 4460, 4480, 4600, 4650 (weak), 4705 (strong), 4745 (strong), 4840, 5385 

 (strong), 6245, 6275, and 6770. 



In general, it has been shown that the presence of nitric acid is to shift 

 the uranyl and uranous bands to the violet. This does not seem to be the 

 effect of adding a large amount of acid to neodymium nitrate in aqueous 

 solution. Many of the above bands do not seem to be bodily shifted to the 

 red, but, like the band marked X 4280, they are widened on the red side. 

 The narrow band X 4274 of the neutral nitrate lies within the broad and 

 diffuse band X 4280. As will be remembered, the action of free nitric acid 

 on the uranyl nitrate bands was to cause them to become sharper. At the 

 same time the bands were shifted to the violet. 



Some of the bands that Stahl considered as absent in the presence of 

 nitric acid appear on our plates, the band X 4705 above apparently being his 

 bands XX 4690 and 4710. 



SPECTROPHOTOGRAPHY OF CHEMICAL REACTIONS. 



During the progress of the work quite a number of photographs were 

 made of a salt in mixtures of two solvents. It seemed of interest to 

 photograph the absorption spectra of a salt when different amounts of 

 an acid were added to the given salt in solution. In the case of uranyl 

 salts several were found to have different absorption spectra. In the case of 

 neodymium, however, it was found that the various salts had practically 

 the same absorption spectra. The absorption of the acetate was, however, 

 found to differ from that of the other salts, so that the chemical changes 

 produced by adding various acids were photographed with the aid of the 

 spectroscope. 



Plate 41, B, represents the absorption spectra of an aqueous solution 

 of neodymium acetate, the concentration being kept constant and only 

 the depth of cell being changed. 



It will be seen from a mere glance that the absorption spectra of the 

 acetate is quite different from that of the other neodymium salts. All the 

 bands are much wider and less intense. Many of the broad bands that 

 appear as several finer bands in the spectra of the other salts, appear here 

 as single and very weak when the depth of cell is small. 



The following are the wave-lengths of a few of the bands: XX 3485, 

 3520, 3820, 4040, 4200, 4295, 4333, 4360, 4460, 4630, 4720, 4770, 4850, 5140 

 (very wide and weak), 5260, 5360, 5660, 5800 to 5860, 6820, and 6950. 



