some Copper Salts in Aqueous Solution. 



323 



rash to conclude that the change has reached a limit at a 

 dilution of 1 gram-equivalent in a litre, as with an Argand 

 burner the visible spectrum only extends to about halfway 

 between G and H ; it probably goes on till much greater 

 dilutions are reached, only in the ultra-violet. 



Table II. 



CuS0 4 . 



Con- 

 centration 

 of strong 

 solution. 



Violet end. 



Red end. 



K 



X 2 . 



Xx-Aa, 



K 



X 2 . 



X 2 -A r 



1-89 



419-2 



428-0 



419-2 

 427-4 



+0-0 

 +0-6 



557-0 



568-4 



557-3 



568-4 



+0-3 



±0-0 



Cu(N0 3 ) 2 . 



4-4323 



429-0 

 440-2 



429-7 

 438-3 



-0-7 

 + 1-9 



525-7 

 527-8 



525-7 



527-8 



o-o 

 o-o 



The concentration appears to have no influence on the 

 spectra of copper sulphate and nitrate. This agrees with the 

 results of Knoblauch ; but, as will be seen later, this is not 

 quite accurate, the concentration really exerting a small 

 influence on the spectra. 



Comparisons of the absorptions of CuCl 2 and Cu(N0 3 ) 3 in 

 tolerably dilute solutions showed that no appreciable difference 

 exists between them. The numbers obtained are given in 

 Table III. (p. 324). 



This method of merely comparing the limits of the spectra 

 of two solutions does not appear to be sufficiently accurate. 

 It is quite possible that general absorptions may exist in 

 a spectrum which, not being sufficiently large to altogether 

 extinguish the light at any place, may pass unnoticed. For 

 example, the photometric measurements made on a strong 

 solution of copper nitrate showed that it exerts a small general 

 absorption over the violet part of the spectrum. This entirely 

 escaped detection by the method described. 



According to B. Walter *, the width of the penumbra round 

 an absorption-band is connected closely with, the presence oi' 



* B. Walter, Wied. Ann. xxxvi. p. 523 (1889). Compare Bohlendorft; 

 Wied. Ann. xliii. p. 784 (1891). 



