Chemical Constitution of Saline Solutions. 289 
Banp V. (Blue). 
ANNs BO 0 ; : . 488 to 486, extending to 481 
At 100°, . . . . 488 to 486, 99 481 
There is a praseodymium line at 4823, and Thalén gives an erbium line at 
487°7 to 486°5. 
Banp VI. (Blue). 
IMB WN : : . 478 to 477 
ANG OO", j : . 477 to 474 
Probably praseodymium, 4828 to 4759. 
Banp VII. (Blue). 
MS WO 5 0 oo o COC to CH 
MUO, 6 o o o &® to GH 
There is a praseodymium band hereabouts, 4692. 
Banp VIII. (Indigo). 
ING XO 6 . 5 . 403 to 449 (Neodymium). 
AMG OO, : : . Allabsorbed. Nothing visible. 
As already mentioned in the Introduction, Bunsen,* in 1886, examined the 
absorption spectra of salts of didymium both im the state of crystals and in 
solution, and found that they presented several differences. ‘The width of the 
absorption bands varies with the thickness of the layer of solution and the quantity 
of the salt contained in it. Solutions of the chloride sulphate and acetate, each 
containing the same quantity of didymium, yielded different spectra, the bands 
being shifted towards the red with increase in the molecular weight of the salt. 
It may be mentioned that H. Becquerelf more recently has observed such 
variations both in the crystallized salts and in their solutions. In any one salt 
the positions of the bands differ from those of the same salt in solution, and 
both in the solid and the state of solution the different salts slightly vary. In 
the measurements which he made he distinguishes the praseodymium from the 
neodymium, though the two were not separated. 
But Becquerel’s measurements were made with too small a dispersion to show 
any marked differences in the spectra of the solutions; and such differences as 
occur in the solids were shown by Bunsen to be due to double refraction, the 
ordinary and extraordinary rays exhibiting spectra with the same bands, but in 
different positions. 
* Ueber die Erscheinungen beim Absorptions-Spectrum des Didyms. Pogg. Ann., vol. 128, p. 100. 
+ ‘Sur les variations des spectres d’absorption du didyme.”” Comptes Rendus, vol. 144, pp. 777-780 and 
1691-1698. 
