336 



Absorption- Spectra of some Copper Salts. 



from the measurements on the strong solutions the part of 

 the light which would be left after passing through a layer of 

 1 centim. thickness of a solution containing 2 gram equivs. of 

 CuS0 4 in 1 litre, and from the dilute solutions, the fraction 

 which would remain after passing through 8 centim. of a 

 solution containing 025 equivs. The results of the calcula- 

 tion are contained in the following Table : — 



Table X. 



Region in 

 Spectrum (mean X). 



(1-iO 



Cone. Solution. 



a-p) 



Dil. Solution. 



Difference. 



612-6 



0-078 



0-077 



+0001 



586-1 



0-302 



0-259 



+0043 



563-6 



0-501 



0-509 



-0008 



5433 



0-701 



0-695 



+0-006 



526-1 



0-822 



0-811 



+0011 



509-7 



0904 



0-892 



+0-012 



493-5 



0-950 



0-946 



+ 0004 



4815 



0-975 



0-968 



+0-007 



Glan's numbers are given for comparison in the following 

 Table :— 



Table XL 



Mean X. 



(l—p) cone. 



(l-^)dil. 



Difference. 



] 

 Dilution. 



674 



0-077 



0073 



+0004 



1/7 



659 



0-155 



0-150 



+0-005 



V7 



626 



0-336 



0-330 



+0-006 



1/5 



J557 

 \557 



0-449 



0-441 



+0-008 



1/3 



0-510 



0-507 



+0-003 



1/7 



J525 

 \525 



0-822 



0-813 



+0-009 



1/3 



0-848 



0-854 



-0-006 



1/7 



With the exception of one number in each set of experi- 

 ments, the differences are all in the same direction. They are, 

 it is true, about the same magnitude as the experimental 

 error, but the circumstance that the two sets of numbers 

 were obtained by different methods and with different instru- 

 ments seems to point to the existence of a real difference 

 between the absorption of the strong and dilute solutions of 

 CuS0 4 . It is not, unfortunately, possible to compare the abso- 

 lute magnitudes of the absorption, as Glan has only given the 

 relative concentrations of his solutions (last column Table XL). 

 Glan's strongest solutions were, however, evidently saturated, 



