On the Action of various Coloured Bodies on the Spectrum. 443 



1. Alkanet root, an alcoholic solution, dark orange-red. At 

 great thicknesses it absorbs all the rays more refrangible than D, 

 that is, the part D H of the spectrum, eating out or absorbing m 

 and n, and leaving Cwa bright band. 



In a diluted state it begins by widening d or D 2, E, b, and F, 

 and also a line halfway between E and G. At a certain thick- 

 ness the absorbed bands E and b nearly join, leaving a sharp 

 luminous line between them. The space E F is then dark before 

 the space D 2, E, and the blue and violet spaces have disappeared. 

 The blue, however , has become nearly violet. At a greater thick- 

 ness D 2 E disappears, and about the same time the blue space 

 is almost gone, the violet remaining. At a greater thickness the 

 violet disappears, and there remains only the bright band C m, 

 the space D d gradually diminishing. 



"When some drops of the alcoholic solution are put into water 

 so as to produce a fine deep lilac, the fluid acts still more power- 

 fully upon the lines m and n, finally absorbing at an increased 

 thickness the space between them. The bands dE and E F, 

 which with B^sd make four bands pretty equal in size, vanish 

 almost simultaneously, the blue and violet still remaining, and 

 the red and violet appearing to be persistent. 



2. Cochineal, alcoholic solution, dark orange-red, but paler 

 than No. 1. At great thicknesses it absorbs all the rays more 

 refrangible than D, exhibiting m and C m slightly bright, and n 

 very faintly. 



When diluted, it first attacks 8 and the whole space between 

 D 5 and E, the space between 8 and D 5 being simultaneously 

 absorbed, leaving for an instant a brightish line on each side of 

 F. The blue then disappears after becoming slightly violet, then 

 the violet, the spectrum ending at D 4. In the red space m and n 

 are both seen. In a strong light the violet will continue longer. 



When the alcoholic solution is mixed with water so as to pro- 

 duce a fine lilac, it absorbs at great thicknesses all the rays more 

 refrangible than D. It begins at b and D 2, and absorbs D F 

 almost at the same time. The blue becomes violet, and then both 

 disappear. An aqueous solution of cochineal is of a nut-brown 

 colour, and acts pretty equally on all the rays of the spectrum. 



3. Chica, alcoholic solution, dark orange-red like cochineal. 

 At great thicknesses it absorbs all rays more refrangible than 

 D 2, the violet disappearing last. 



Diluted with alcohol it begins at F and D 5, absorbing rapidly 

 towards b, but leaving a narrow band b 2, and then the space 

 between D 5 and F vanishes, the blue becoming faint and slightly 

 violet. 



N.B. The blue space F G is most distinctly very violet before 

 evanescence. 



2G2 



