1863.] 637 



containing 67*01 per cent, of that element, while munjistine contains 

 only 64. The spectra afforded by solutions of the two substances, as 

 may be seen from the following extract from a letter received from 

 Professor Stokes, are decidedly different. 



" The two substances are perfectly distinguished by the very differ- 

 ent colour of their solution in carbonate of soda, when a small quantity 

 only of substance is used. The solution of munjistine is red inclining 

 to pinkish orange, that of rubiacine a claret-red. The tints are 

 totally different, and indicate a different mode of absorption. Both 

 present a single minimum in the spectrum ; but while that of rubia- 

 cine extends from about D to F, that of munjistine extends from 

 a good way beyond D to some way beyond F. The beginning 

 and end of the band in each case is not very definite, and varies of 

 course with the strength of the solution ; but by comparing the sub- 

 stances with different strengths of solution, there can be no doubt 

 of the radical difference in the position of the band of absorption. 

 In this way it is easy to convince oneself that the difference of colour 

 is not to be explained by the possible admixture of some small im- 

 purity present in one or other specimen. With caustic potash mun- 

 jistine gives as nearly as possible the same colour as rubiacine, 

 agreeing with the colour of rubiacine in carbonate of soda, There 

 appears to be a slight difference in the spectrum of the munjistine 

 and rubiacine solutions, but not enough to rely on ; so that the 

 substances are not to be distinguished by their solutions in caustic 

 alkalies. 



" A second perfectly valid distinction is, however, afforded by the 

 different colour of the fluorescent light of the ethereal solutions. 

 The solid substances themselves and their ethereal solutions are fluo- 

 rescent to a considerable degree ; but the tint of the fluorescent light 

 of the ethereal solution of rubiacine is orange-yellow, while that of 

 the ethereal solution of munjistine is yellow inclining to green. The 

 examination in a pure spectrum shows that the difference is not 

 due to the admixture of a small impurity, itself yielding a fluorescent 

 solution; but the tints may be readily contrasted by daylight, 

 almost without apparatus, by the method I have described in a paper 

 ' On the existence of a second crystallizable fluorescent substance in 

 the bark of the horse-chestnut' (Quart. Journal Chem. Soc. 

 vol. ii. p. 20). I consider either of the two points of difference I 



