4il< Sir David Brewster on the Action of 



With great dilution the band between b and b 1 is beautifully 

 distinct. 



When the alcoholic solution of chica is mixed with water, its 

 colour and properties are unchanged. 



4. Cudbear, alcoholic solution, fine deep scarlet. It attacks 

 the spectrum at D and d almost simultaneously, and soon leaves 

 only bD, or a narrow red. When diluted, it becomes pink, 

 absorbs slightly about D g, and then the absorption extends 

 almost instantly from D to the violet. The line m is distinctly 

 marked. When diluted with water, it is still bluish pink. 



5. Sulphate of Indigo, diluted with water, attacks the spec- 

 trum at m and n, dividing the red into two by a darkish space 

 between m and n, and then absorbing rapidly the rest of the red 

 towards D, then the violet, and then on both sides up to E, on 

 one side and near F, and on the other side, at great thicknesses, 

 the space E F, of which E S is yellow, and 8 F blue. 



In this case the yellow is separated from the green by the 

 absorption of the latter, and exists at 8 and on the s blue space D F. 



At one time Be, cm, mn, and nD are all seen as distinct 

 bands. 



At a certain thickness this solution is greenish blue by daylight, 

 and bluish pink in candle-light. 



6. Soda, Sulphate of Chromium, bright green in daylight, and 

 pink in candle-light. Its action commences at D and D 2, absorb- 

 ing the space D, D 2, and then on both sides up to near E, and 

 also from the violet end to near F, the yellow remaining froml& to 

 8, and the blue from 8 to beyond F, almost exactly as in sulphate 

 of indigo. The remaining yellow has more green in it than in 

 sulphate of indigo. 



7. Nitrate of Cobalt, pale crimson-red by daylight, and ( ) 



in candle-light. It attacks the spectrum almost simultaneously 

 from b to near F, leaving a dark green, and then it attacks it 

 about halfway between F and G, rendering darker and bluer 

 the space from F 34 to F, and leave F 34 to G a ivhitish blue 

 band, the absorption having advanced from F 34 to F. The band 

 F 34 to G and the violet beyond G are left, and the absorption 

 is complete between F 34 and towards D, to which it gradually 

 approaches. 



8. Litmus, dissolved in water, a beautiful blue- in daylight, and 

 pink in candle-light. It attacks the spectrum at m, n, D, and 

 ]) 2, and at c, absorbing beautifully the band m D 2, so that at one 

 time, before that band vanishes, we see the luminous portions 

 between these lines about to disappear. At the thickness which 

 does this, all the other parts of the spectrum are unchanged. 

 At greater thicknesses it absorbs the rays towards b, then the 

 violet, leaving much green, yellow^ and blue. 



