46 ABSORPTION SPECTRA OF SOLUTIONS. 



In the red the first strip of A shows complete absorption from X 5900 

 to the end of the spectrum. The seventh strip shows transmission as far 

 as X 6150. The corresponding readings for the first and seventh strips of 

 B are X 6450 and X 6675. The edge is, however, very indefinitely defined 

 in B, the shading being considerable. * 



It appears, therefore, that the red band also narrows with dilution, 

 although much less than the ultra-violet one. It also narrows more rapidly 

 at first, giving the edge of the band a curved form, concave towards shorter 

 wave-lengths. At great dilutions and correspondingly deep layers of solu- 

 tion, the edge of the band would in all probability be straight, and per- 

 pendicular to the length of the strips. 



COPPER CHLORIDE IN WATER MOLECULES CONSTANT. (See Plate 31.) 



The concentrations of the solutions used in making the negative for A, 

 beginning with the one whose spectrum is adjacent to the numbered scale, 

 were 4.53, 3.59, 2.63, 1.97, 1.50, 1.19, and 0.97; the corresponding depths of 

 absorbing layer were 3, 4, 6, 9, 13, 18, and 24 mm. For B the concentrations 

 were 1.50, 1.22, 0.91, 0.68, 0.52, 0.415, and 0.335; the depths of cell were the 

 same as for A. The exposures to the light of the Nernst lamp and spark 

 lasted, respectively, 1 and 3 minutes, the width of the slit being 0.01 cm. 



In this spectrogram we find that the absorption band in the ultra- 

 violet still narrows rapidly, while that in the red shows a tendency to 

 widen with dilution. The limits of transmission shown by the first and 

 seventh strips of A are X 4750 and X 4100, with the edge showing a com- 

 pound curve similar to the one in Plate 30 A, but with less curvature. 

 For the first and seventh strips of B the limits are X 3990 and X 3500, the 

 edge forming a curved line convex towards the region of short wave- 

 lengths. In the red, the first strip of A gives the limit of transmission as 

 X 6050. In the second and third strips the limit is a little farther up in the 

 red, being near X 6075. In the fourth strip it is again at X 6050, from which 

 it moves gradually towards shorter wave-lengths until the seventh strip is 

 reached, where it is at X 5975. The edge of the band is hence curved, with 

 the convex side towards the longer wave-lengths. 



In B the band widens continuously with decreasing concentration, 

 the limit of transmission for the solution pertaining to the first strip being 

 X 6500, while the seventh strip shows complete absorption at X 6400. The 

 edge is not sharply defined, the shading extending as far as X 5000 with 

 considerable intensity. From X 6000 to X 5950 the blackening of the nega- 

 tive increases very rapidly, and this position of most rapid increase in 

 transmission seems to be sensibly the same for all the solutions of the one 

 series. This is also nearly the position of the limit of transmission for the 

 concentrated solutions used in A, and also in Plate 30 A. Hence, it seems 

 likely that this is the real limit of the absorption band. 



COPPER CHLORIDE IN METHYL ALCOHOL BEER'S LAW. (See Plate 32.) 



The concentrations of the solutions used in making the negative for 

 A, beginning with the one whose spectrum is adjacent to the numbered 

 scale, were 0.744, 0.595, 0.469, 0.372, 0.297, 0.233, and 0.186; the corre- 



