of the Absorption Spectra of Chlorophyll, $c. 391 



As I have been able to examine many more derivatives than the 

 former investigator, and as the results of my observations differ 

 from his, inasmuch that I find only some of the derivatives are 

 characterised by the single band, whilst in others two are apparent, 

 and in chlorophyll itself and chrysophyll three, and also that my 

 method of procedure differs from his, it will perhaps be of interest to 

 give the results of my experiments as compared with his. 



Method of Procedure. 



The spectroscope was a single prism one of Iceland spar, which 

 just divided the sodium lines. The lenses were of quartz, the foeal 

 length of the collimator lens being 12'5 inches, and that of the 

 camera lens 42 inches. The dark slide which held the plate was 

 movable at fixed intervals, so that seven exposures could be taken on 

 the one plate. The solutions were examined in a glass cell with 

 parallel quartz faces, placed in front of the slit, the whole apparatus 

 being set up for me by Mr. A. Hilger, of London. The source of 

 light used was a Welsbach incandescent mantle of sixty-candle 

 power, no chimney being used, placed 8 inches distant from the slit. 

 For reference lines a hydrogen vacuum tube was used, from which 

 the lines F, S', L, and H' were obtained, and the violet potassium line 

 K/s was at the same time thrown in by volatilising a little of the salt 

 in a Bunsen burner in front of the slit. The plate used was Messrs. 

 Cadett and Neal's " lightning," pyrosoda being adopted as the 

 developer. The exposure given in each case was half an hour, which 

 was found to be the most advantageous after various trials of different 

 times of exposure had been made. Under these conditions the photo- 

 graphs extended distinctly as far as the solar line Q. On each plate 

 a spectrum of the source of light used was thrown in for a compari- 

 son with the light absorbed by the solutions of the different deriva- 

 tives. In every case the solutions had to be excessively diluted 

 before the characteristic absorption became apparent on the photo- 

 graphic plate, so dilute that, with the exception of chrysophyll, caro- 

 tin, and chlorophyll, only a faint indication of colour was visible in 

 the solutions to the eye by transmitted light, and of the bands in the 

 visible region of the spectrum, only the first, the characteristic one 

 in the red, was visible, and that in the majority of cases only faint. 

 In the case of the hydrochloric acid compounds of phjlloporphyrin 

 and hsematoporphyrin one might say the solutions were colourless, 

 and yet these two derivatives give the single band more pronounced 

 and better defined than any of the others. As a very slight differ- 

 ence in the strength of the solutions gave an appreciable difference 

 in the resulting absorption spectra, three solutions of slightly varying 

 strengths were photographed of each derivative, and the most charac- 



2 G 2 



