LIGHT. 115 



Each end being bent up at right angles, the glass 

 may be bound to it by clamps, as in the other tank. 



" A solution of alizarin in carbonate of potassium 

 or sodium, or in ammonia, exhibits a spectrum having 

 a band of absorption in the yellow, another narrower 

 one between the red and the orange, and a third very 

 inconspicuous band coinciding with the line E. Pur- 

 purine dissolved in carbonate of potassium or sodium 

 exhibits two dark bands of absorption about the green 

 part of the spectrum. A solution of the same sub- 

 stance in aqueous alum exhibits the same peculiar mode 

 of absorption, but likewise a yellow fluorescence. A 

 solution of purpurine in sulphide of carbon exhibits 

 four bands of absorption, of which the first, situated 

 in the yellow just beyond D, reckoning from the red 

 extremity, is narrower than the rest. The second is 

 situated in the green, nearly coinciding with the line 

 E. The third in the blue, near F, and the fourth, 

 which is very inconspicuous, in the indigo. Lastly, the 

 solution of purpurine in ether gives a spectrum giving 

 two bands of absorption, one narrow and very dark in 

 the green, nearly coinciding with E. The second in 

 the blue, broader and less strongly marked, and having 

 its centre at the line F ; the solution is also slightly 

 fluorescent." (Stokes.) 



The following series of experiments upon Absorption 

 is taken from an article by A. H. Allen in Nature, vol. 

 4, p 346. A lime light may be used if it is desirable 

 to project these when sunlight is not available : 



" A beam of light from the lantern is passed through 

 a slit, focussed by a lens, refracted by a bisulphide of 

 carbon prism, and the spectrum exhibited in the usual 

 way. A flat cell containing a solution of permanga- 

 nate of potash is next placed in front of the slit. With 



