218 



Miscellaneoits, 



Sjjeetroscojnc Examination of the Biatomacece. By H. L. Smith. 



The vegetable nature of the Diatomacege is now generally admit- 

 ted; but if any further proof is needed, we have it in marked results 

 from the application of the spectroscope. I have been enabled to 

 prove the absolute identity of cliloropliyl or the green endochrome of 

 plants with diatomin or the olive-yellow endochrome of the Diato- 

 maceae. The sijectrum-microscope is now too well known to need 

 any description here. The one I have used was made by Browning 

 of London. It is not at all difficult to obtain a characteristic sjjec- 

 trum from a living diatom, and to compare it directly with that of a 

 desmid, or other plant. 



I need not here give the results in detail. Suffice it that, from 

 about fifty comparisons of spectra, I can unhesitatingly assert that 

 the spectrum of chlorophyl is identical with that of diatomin. 



The spectrum in question is a characteristic one, and is figured 

 below. 



A very black narrow band in the extreme red, reading at the lower 

 edge, which appears to be constant, about | of Mr. Sorby's scale, is 

 too characteristic to be mistaken. There are two other very faint 

 bands, not easily seen, and somewhat more variable in position. 

 The black band in the red is always present, and is remarkably con- 

 stant in the position of its lower edge. In making comparisons of 

 spectra it is of the utmost importance that the slit of the spectro- 

 scope should be absolutely in the focus of the achromatic eye-lens. 

 If this be not attended to, there wiU be a slight parallax ; and bands 

 really identical in position, e. g. those of blood (scarlet cruorine), 

 will not absolutely correspond when two spectra are formed, one 

 from blood on the stage of the microscope, and the other from the 

 same on the stage of the eye-piece. 



The dark band of the chlorophyl- spectrum is slightly variable in 

 width ; and the action of acids and alkalies sometimes causes a slight 

 displacement, the former raising (moving toward the blue end) and 

 the latter depressing. The endochrome of a diatom after treatment 

 with acid is green, and the acid, in this case, produces scarcely any 

 displacement of the band, which may be observed even in the dark 

 reddish mass of the dead Diatomacese, almost identical in colour 

 with the ferrous carbonate so often found in bogs where the larger 

 diatoms are abundant; and what is more remarkable is, that the 

 carbonate gives no absorption-bands at all. As a general rule, 

 alcoholic solutions of chlorophyl and diatomin have the band slightly 

 depressed, reading 1 to 1| on the interference scale. — SillimavCs 

 American Journal, July 18G9. 



