SALTS OF COPPER. 55 



were 0, 4, 6 ; 8, 10, 12, 14, 16, 18, 20, 22, 24, 26, 30, 35, and 40. The depth 

 of the absorbing layer was in this case only 0.4 cm., owing to the practical 

 opacity of the solutions containing the least amount of water in layers of 

 2.0 cm. or more. 



The first six solutions changed from a deep-brown to a greenish-brown. 

 From the seventh to the sixteenth the color changed from a clear bluish- 

 green to a light greenish-blue. The exposures to the light of the Nernst 

 lamp and spark were, respectively, 1 and 3 minutes in length; the width 

 of the slit was 0.01 cm. 



Leaving out the first two solutions, where the general absorption was 

 so great that very little light was transmitted, we find for the limit of 

 transmission towards the ultra-violet for the third solution A 4750. From 

 this the limit moves gradually to the shorter wave-lengths, reaching X 3450 

 in the solution containing the greatest amount of water. The absorption 

 band here narrows much more rapidly with addition of water than was the 

 case with the solutions in methyl alcohol. A part of this effect is no doubt 

 due to the shallower layer of the solutions here used, but that will hardly 

 account for all of it, since the edge of the band is comparatively sharp, 

 showing that it does not widen very rapidly with increase in the depth of 

 the solution. It can not be accounted for by a difference in concentration, 

 as could be done in the case of the chloride solutions, for here the actual 

 concentration of the ethyl alcohol solutions was greater than that of the 

 solutions in methyl alcohol. The effect is, hence, very probably due to 

 some action of the non-aqueous solvent, or possibly to some mutual action 

 of the water and the non-aqueous solvent, which would be different for 

 the two alcohols. 



In the red the band narrows gradually with addition of water, its limit 

 in the solution containing no water being at A 7100, and reaching the limit of 

 the sensibility of the photographic plates used in the solution containing 18 

 per cent of water. The smaller amount of absorption here as compared with 

 the methyl-alcohol solutions is to be ascribed to the shallower layer used. 



COPPER NITRATE IN WATER BEER'S LAW. (See Plate 44.) 



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 4.04, 3.00, 2.00, 1.33, 0.92, 0.67, and 0.50; the corresponding 

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

 concentrations were 0.67, 0.51, 0.34, 0.22, 0.15, 0.11, and 0.084; the depths 

 of cell were the same as in A. 



The most concentrated solutions were blue, and on dilution the color 

 changed to a light greenish-blue. The exposures to the light of the Nernst 

 lamp and spark were of 1 and 3 minutes duration, respectively; the width 

 of the slit being as usual 0.01 cm. 



There is an absorption band in the ultra-violet distinct from the NO, 

 band which we have seen before. The limit of transmission for the most 

 concentrated solution in A is at A 3600, from which it moves gradually 

 towards the region of shorter wave-lengths until the fifth solution is 

 reached, where transmission ceases at A 3390. This is perhaps the limit of 



