254 



NOTES. 



Spectroscopic Examination of the Diatomacece. 



The vegetable nature of the Diatomacese is now generally admitted ; but if 

 any farther proof is needed, we have it iu 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 diato'-nin, or the olive- 

 brown endochrome of the Diatomacese. The spectrum-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 

 specimen 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 chlorophylls identical with that of diatomin. A very black, narrow 

 band in the extreme red, reading at the lower edge, which appears to be constant, 

 about I 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 

 constant in the position of its lower edge. In making comparisons of spectra, 

 it is of the utmost importance that the slit of the spectroscope should be abso- 

 lutely in the focus of the achromatic eye-lens. If this be not attended to, there 

 will be a slight parallax ; and bands really identical in position, e.g., those of 

 blood (scarlet cruorine) will not absolutely correspond where two spectra are 

 formed ; — one from blood on the stage of the microscope, and the other from the 

 same on the stage of the eyepiece. The dark band of the chlorophyl-spectrum 

 is slightly variable in width ; and the action of acids and alltalies sometimes 

 causes a slight displacement, the former raising (mo\'ing towards 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 in the dark reddish mass of the dead 

 diatomacefB, almost identical in colour with the ferrous carbonate so often 

 found in bays where the large diatoms are abundant ,' and what is more remark- 

 able is, that the carbonate gives no absorption bands at all. As a general rule, 

 alcoholic solutions ofchlorophyl and diatomin have the band slightly depressed, 

 reading 1 to 1^ on the interference scale. — Paper by H. L. Smith in Sillimcm's 

 American Journal, July, 1869. 



END OF VOL. I. 



