Blood-Spectrum

Abstract

IN the account of the Progress of Science in Italy in NATURE for October 12, Mr. W. Mattieu Williams says that Prof. C. Campani has shown that the spectrum of an ammoniacal solution of carmine is undistinguishable from that of blood, and that perhaps I should be able to tell whether any difference can be distinguished by more minute examination. In my first paper on this subject, so long ago as 1865*, I alluded to this similarity, and in subsequent paper† I have shown how the colouring matter of blood can be distinguished from that of cochineal, and even a small quantity recognised when mixed with a relatively considerable quantity of that dye. I have always argued that in such inquiries we must not rely on the spectrum, but compare the action of various reagents. On adding a little boric acid to an aqueous solution of blood, no change takes place in its spectrum, whereas that of cochineal is completely altered. This effect is not produced in the case of carmine suspended in water, but the absorption-bands of blood are at once removed by deoxidising the solution with a ferrous salt, which, on the contrary, has no effect in the case of carmine or cochineal. Weak acids decompose hæmoglobin into hæmatin, which gives entirely different spectra, but they do not cause any permanent change in the colouring matter of cochineal or carmine. In my opinion there is no more probability of an experienced observer mistaking these substances for blood, because the ammoniacal solutions give nearly the same spectrum, than of a chemist confounding aluminium bronze with gold, because they are of nearly the same colour.