THE METABOLISM OF PLANTS. 155 



From the percentage composition of the crystals Gautier deduces the 

 formula Ci 9 H22N 2 O 3 , and draws attention to its resemblance to that of 

 Bilirubin (Ci 6 H 18 N 2 O 3 ). Hoppe-Seyler finds that when his chlorophyllan 

 is boiled with alcoholic solution of potash, cholin, glycerin-phosphoric 

 acid, an acid which he terms chlorophyllanic acid, and possibly also some 

 fatty acids are produced. He concludes that chlorophyllan contains 

 phosphorus in its molecule, and is either a lecithin or a lecithin-com- 

 pound. 



Now as to its physical properties. We have seen that it 

 is soluble in alcohol, and it is likewise soluble in ether, benzol, 

 carbon disulphide, and in various oils. A solution of chloro- 

 phyll possesses the property of 'fluorescence, so that when it is 

 viewed in reflected light it appears opaque and of a deep lake- 

 red colour; the light transmitted through a thin layer is green. 

 If the light which has passed through a layer of a moderately 

 strong solution be examined with the spectroscope, a charac- 

 teristic absorption-spectrum will be observed. Beginning at 

 the red end of the spectrum (see Plate, Fig. i,f) a well- 

 marked dark band will be seen between Frauenhofer's lines 

 B and C extending rather beyond C, a second dark band in 

 the orange between C and D, a third very faint band at the 

 junction of the yellow and greert, and a fourth more distinct 

 band in the green near the line E; the whole of the blue end 

 of the spectrum beyond the line F is absorbed. The absorp- 

 tion of the whole of the blue end of the spectrum is due to the 

 coalescence of three bands which can be seen separately when 

 very dilute chlorophyll solutions are used (Plate, Fig. I c), 

 two in the blue between the lines F and G, and one at the end 

 of the violet. The absorption-spectrum of chlorophyll pre- 

 sents then seven absorption-bands. 



The figure of the chlorophyll-spectrum in the Plate is due to Prings- 

 heim, who has devised an ingenious method for observing the spectrum. 

 Instead of using solutions of different degrees of concentration he employs 

 different thicknesses of a dilute solution. The numbers at the left-hand 

 side of the figure indicate the thickness in millimetres of the layer 

 examined: thus in a the thickness of the layer was 10 millimetres, and so on. 



It may be added, with regard to the fluorescence of chlorophyll, that 

 when the light reflected from a solution is examined with the spectro- 

 scope, it is found to be all red, the red being most intense in the positions 

 corresponding to the absorption-bands of the chlorophyll-spectrum. 



