322 



Dr. T. Ewan on the Absorption- Spectra of 



The following table contains the numbers obtained for copper 

 chloride. Under X x are the wave-lengths of the two positions 

 read for concentrated solutions; under X 2 the same read- 

 ings for dilute solutions. The dilute solutions were about 

 -j 1 ^ the concentration of the strong solutions. The numbers 

 are all the means of two or three readings, and the concen- 

 trations are given in gram-equivalents of salt in 1 litre of 

 solution. The differences are taken so that a positive dif- 

 ference means an increase in the length of the visible spectrum, 

 and vice versa. 





Table I 



. — Copper Chloride. 





Con- 

 centration 

 of strong 

 solutions. 



Violet end. 



Red end. 



K 



X 2 . 



\~\' ' 



K 



X 2 . 



X 2 — X r 



4-261 



478-7 

 486-8 



429-6 

 443-0 



+49-1 

 +43-8 



528-4 

 543-2 



531-2 

 540-8 



+2-8 

 -2-4 



2-1305 



451-0 

 4630 



439-0 

 451-0 



+12-0 

 + 12-0 



537-2 

 551-6 



539-6 

 552-4 



+2-4 

 +0-8 



1-7044 



431-0 



444-6 



427-6 

 437-2 



-1- 3-4 

 + 7-4 



572-0 

 576-4 



567-8 

 579-4 



-4-2 

 +3-0 



1-3612 



426-2 

 435-8 



421-0 



428-0 



+ 5-2 



+ 7-8 



575-2 

 579-8 



575-0 



577-4 



-0-2 

 -2-4 



1-227 



424-0 

 430-6 



415-4 

 427-0 



+ 8-6 

 + 3-6 



580-6 

 584-0 



580-6 

 584-0 



+0 

 TO 



1-018 



414-8 



420-8 



412-4 



417-8 



+ 2-4 

 + 3-0 



596-6 

 6020 



5966 

 602-0 



+0 



+o 



The temperature varied from 15° to 17°*2 on different days. 

 The wave-length of the extreme violet end of the spectrum 

 when the trough was filled with distilled water was found (on 

 different days) 416;0, 417«2, and 411'2. This shows that the 

 more dilute solutions transmitted the whole of the violet 

 light. The average difference of a single reading from the 

 mean was about +1'5 units in the wave-length. 



The above numbers show that the position of the absorption 

 at the red end of the spectrum does not vary with dilution. 

 The differences vary irregularly in sign, and are of about the 

 magnitude of the experimental error. The absorption in the 

 violet (which extends into the green in the case of the strongest 

 solution) disappears on dilution, so that a layer of 102 milfim. 

 of a solution containing about 1 gram-equivalent of salt in a 

 litre shows no noticeable absorption. No change can, of 

 course, be seen on further dilution : 



it would, however, be 



