THE RED GROUPS OF ALG2E. 



37 



sugar be heated for a short time to not above 80° C, only one of 

 the bands at the red end disappears, and the other remains until 

 the heat is raised to above 80° C. ; and then, when cold, only the 

 bands in the green remain. It will of course be apparent that 

 these changes do not depend on the temperature of the solution, 

 since it is examined after cooling, but on decompositions produced 

 by the heat. These facts will be better understood by means of 

 the following figure, which is to some extent diagrammatic, the re- 

 lative intensity of the bands being not exactly as seen in any one 

 thickness of the solutions. 



400 



I. 



II 



III. 



Fig. 2. Spectra of the colouring-matters from Porphyra vulgaris. I. In natural 

 state. II. Solution in syrup heated to 80° C. III. Solution in syrup heated 

 to above 80° C. 



Since on the present occasion it does not appear desirable to 

 enter into physics and chemistry, I will merely say that by these 

 and other means I have found that various red Algae contain at 

 least six different colouring-matters, which, however, have certain 

 characters in common. They all give spectra with one well- 

 marked absorption-band, and more or less distinct traces of a 

 second, lying nearer to the blue end. Five of them have a very 

 strong and splendid fluorescence ; and all are decomposed when 

 heated to a temperature below that of boiling water, which is not 

 the case with the red colouring-matters found so abundantly in 

 the leaves of the higher classes of plants, with which, in fact, 

 they have scarcely any thing in common. They are also decom- 

 posed by alcohol, which is not the case with the different kinds of 

 erythrophyl. 



I do not think that I could do better than indicate the more 

 important differences between the various kinds of phycocyan 

 and phycoery thrin than by means of the following Table, in which 

 the position of the centres of the principal bands of each substance 



