Composition of O'd of Cassia. 309 



This has been accomplished by Mr Herschel in a very inte- 

 resting experiment, of which he has given the following ac- 

 count: — 



" The following experiment would seem to point out the %- 

 drogen of the latter oil (oil of cassia) as the principle to 

 which its extraordinary dispersion is due, and is otherwise in- 

 structive, as exemplifying strongly the independence of the two 

 powers inter se. A stream of chlorine was passed through oil 

 of cassia till it refused to act any farther. The oil was at 

 first greatly deepened in colour; but as the action proceeded, 

 it changed to a much lighter ruddy yellow, which it retained 

 till the action was complete, (and which in a few days changed 

 to a fine rose red.) Copious fumes of muriatic acid gas were 

 given off during the whole process, indicating the abstraction 

 of abundance of hydrogen, and at length the oil was converted 

 into a viscous mass, drawing out into long threads, having 

 entirely lost its peculiar perfume, and acquired a pungent pe- 

 netrating scent, an acrid astringent taste, totally unlike its for- 

 mer aromatic flavour. It was inflammable, though less than 

 before, burning with a flame green at the edges, indicating the 

 presence of chlorine. Its refractive power was very little di- 

 minished. A drop being placed in the angle of two glass 

 plates, and close to it a drop of unaltered oil of cassia, the 

 spectrum of a line of light was viewed at once with the same 

 eye through both the media. They still formed a conrtinuous 

 line, the spectrum of the unaltered oil being more refracted by 

 only about one-fourth the breadth of that of the altered speci- 

 men. But the dispersive power of the latter was most remark- 

 ably diminished, being brought below not only that of the un- 

 altered oil, but even below that of flint glass. When the disper- 

 sion of the unaltered oil was corrected by flint-glass, that of the 

 altered was found to be much more than corrected ; and when 

 the angle of the glass plates was such that the dispersion of 

 the latter was just corrected by a prism of Dollond's ^ heavy' 

 "flint, whose refracting angle = about 25°, the uncorrected 

 spectrum of the former was about equal to that of the flint 

 prism. The dispersion, then, had been diminished to half its 

 former amount, while the refraction had sufl'ered hardly any 

 appreciable change. — (October 7, 1827.^ 



