84 THE ABSORPTION SPECTRA OF SOLUTIONS. 



uranous chloride dissolved in concentrated nitric acid will stand for hours 

 before it is oxidized to the uranyl condition. Most of the neutral uranous 

 salts are precipitated when heated to 80 or 90 C; but if some free acid, or 

 if in the case of uranous chloride other chlorides are present, the uranous salts 

 are stable at these higher temperatures. 



It might be expected that if the effect of rise in temperature is to break 

 up aggregates, then in the case of concentrated acid solutions of the uranyl 

 salts the shift towards the red should be very great for a concentrated nitric 

 acid solution of uranyl nitrate; while in the case of a hydrochloric acid solu- 

 tion of uranyl chloride, or of a sulphuric acid solution of uranyl sulphate, the 

 shift should be in the opposite direction. On the other hand, if the shift caused 

 by change in temperature is due to some other cause and the aggregates are 

 not broken up, no effect of this kind would be expected. 



In a solution of uranous sulphate in sulphuric acid the uranyl bands are 

 slightly shifted to the red as the temperature is raised from 10 to 90, while 

 the uranous bands are slightly shifted to the violet. The shift of the neutral 

 uranyl sulphate bands to the red is greater than that of the acid sulphate 

 bands. The shift of the uranyl nitrate bands in nitric acid is about 15 Ang- 

 strom units. All bands are shifted about the same amount. 



Neodymium Salts in Acid Solutions. 

 Plate 59, A. This spectrogram shows the effect of hydrochloric acid, 

 sodium chlorate, and temperature on the neodymium chloride bands. Strip 

 1 is the absorption of neodymium chloride in water at about 10, strip 2 

 the same at about 90. Strip 3 represents the absorption of the same amount 

 of neodymium chloride in concentrated hydrochloric acid at 10, strip 4 the 

 same at 90. Strip 5 represents the absorption at 10 of neodymium chloride 

 in methyl alcohol, and strip 6 the same containing sodium chlorate. 



Plate 59, B. This spectrogram shows the absorption of a 0.02 normal 

 solution of neodymium acetate at 10 in strip 1 and at about 90 in strip 2. 

 Strip 3 represents the absorption of a small amount of neodymium chloride 

 added to acetic acid so as to fill the quartz cell at 10, and strip 4 the same at 

 90. Strip 5 represents the absorption of neodymium acetate in acetic acid 

 at 10, and strip 6 the same at about 90. Strip 7 represents the absorp- 

 tion of a solution in methyl acetate and acetic acid at 10, and strip 8 the 

 same at 90. 



The first two strips in A show that the effect of rise in temperature on 

 an aqueous solution of the chloride is to cause a very slight shift of the bands 

 towards the red, and to give them a much more diffuse and washed-out appear- 

 ance. The hydrochloric acid solution of neodymium chloride shown in strips 

 3 and 4 is but very slightly changed by rise in temperature, and there is no indi- 

 cation that the spectrum becomes more closely like that of the neutral aqueous 

 solution. The shift to the red is very small. It can easily be noticed for the 

 bands of the e group. At 10 the long wave-length bands of the 8 group are 

 very much like the two bands of the neutral aqueous solution. At 90 these 

 bands have both become very diffuse, blending into a single band, and the 

 whole center of the band is greatly shifted towards the red. This is the great- 

 est temperature change in the whole spectrum. The presence of sodium 



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