60 ABSORPTION SPECTRA OF SOLUTIONS. 



FERRIC CHLORIDE WITH CALCIUM CHLORIDE. (See Plates 49 and 51 A.) 



The concentration of ferric chloride in the solutions used in making 

 the negative for A, Plate 49, was constant and equal to 0.182 normal. 

 The concentrations of calcium chloride, beginning with the solution whose 

 spectrum is adjacent to the scale, were 3.97, 3.40, 2.85, 2.30, 1.75, 1.20, 

 0.64, and 0.00. For B the concentration of ferric chloride was 0.035, and 

 for A, Plate 51, it was 0.007; the concentrations of the calcium salt were the 

 same as for A, Plate 49. The common depth of absorbing layer was 1.5 cm. 



The dilute solutions without calcium chloride were yellow, or very faint 

 yellow, depending upon concentration. With increasing amount of the 

 calcium salt the color deepened very markedly, becoming orange to reddish- 

 orange, according to the concentration of the colored salt. 



The spectrograms show the marked increase in width of the absorp- 

 tion band with addition of the dehydrating agent. In A the solution 

 containing no calcium chloride transmits as far as A 4600, while the one 

 containing the greatest amount of the calcium salt ceases to transmit at 

 A 5250. For B the corresponding wave-lengths are A 4150 and A 4950, and 

 for A, Plate 51, they are A 3860 and A 4620, respectively. 



In each case the line formed by the limits of transmission is curved, 

 with its concave side towards the region of short wave-lengths, showing 

 that the absorption decreases most rapidly at first with addition of the 

 calcium salt. The increments in the concentration of the dehydrating 

 agent from solution to solution were sensibly the same, namely 0.55 normal. 



FERRIC CHLORIDE WITH ALUMINIUM CHLORIDE. (See Plates 50 and 51 B.) 



The concentration of the iron salt in the solutions used in making the 

 negative for A, Plate 50, was constant and equal to 0.182 normal. The 

 concentrations of aluminium chloride, beginning with the solution whose 

 spectrum is adjacent to the numbered scale, were 2.61, 2.25, 1.88, 1.52, 

 1.16, 0.79, 0.43, and 0.00; the successive increments in concentration 

 were all 0.366, except the last, which is 0.43. For B the concentration^ 

 ferric chloride was 0.035, and for B, Plate 51, it was 0.007, the concentra- 

 tions of the aluminium chloride being the same as for A, Plate 50. 



The common depth of absorbing layer was 1.5 cm., and the exposure 

 which was made to the light of the Nernst lamp lasted only 1 minute, 

 the slit having the usual width of 0.01 cm. 



The spectrograms are very similar to those made with the solutions 

 containing calcium chloride as dehydrating agent, the only difference 

 being the somewhat greater widening of the absorption band in the pres- 

 ent case. Since the concentrations of the iron salt were the same, set for 

 set, with calcium chloride, as in the present case, the spectrograms are 

 directly comparable. 



The limits of transmission for the solutions containing no dehydrating 

 agent are of course the same in the two cases, as we need only compare 

 the limits for the solutions containing the greatest amount of the calcium 

 or aluminium salt. We find that in the series containing the greatest 

 amount of the iron salt, the limit of transmission is 50 A.U. nearer the red 

 end of the spectrum for the solution containing the aluminium salt than for 



