112 



CHEMISTRY. 



red substance, which have no chemical action 

 on each other, are mixed together, the result- 

 ing color is orange. The explanation is un- 

 doubtedly to be found in the raising of the less 

 rapid red vibrations by the yellow, and the con- 

 sequent lowering of the yellow by the red, the 

 mean resulting vibration being that capable 

 of producing orange light." 



The Coloring-Matter in Foliage. Mr. II. C. 

 Sorby contributes an interesting paper on this 

 topic to Nature. He announces that, up to 

 the middle of 1871, he had been able to dis- 

 tinguish several dozen coloring-matters in the 

 leaves of different plants, and far more than 

 that number in the petals and fruits, and had 

 no doubt that further inquiry would readily 

 increase the list. The subject would be un- 

 manageable if he did not divide the varieties 

 of coloring-substance into well-marked groups 

 by means of their optical characters. The 

 colors are not only related to one another op- 

 tically and chemically, but also have a very 

 similar connection with the growth of the 

 plants. The very numerous tints of foliage 

 depend almost entirely on the relative and 

 absolute amount of the various colors of the 

 different groups. The groupings suggested by 

 Mr. Sorby are as follows : 



1. The Chlorophyll group is distinguished 

 by being insoluble in water, but soluble in 

 alcohol, and in bisulphide of carbon. There 

 are three or four species, giving well-marked 

 spectra, with several narrow, dark absorp- 

 tion-bands, one or more of which occur at the 

 red end. The mixed chlorophyll of ordinary 

 green leaves may be obtained in a tolerably 

 satisfactory state by heating in alcohol dark- 

 green holly-leaves, previously crushed so as to 

 insure rapid solution, and then, when cold, 

 agitating in a test-tube with bisulphide of car- 

 bon. This sinks to the bottom, holding nearly 

 the whole of the dark-green chlorophyll in 

 solution, while nearly all the xanthophyll re- 

 mains dissolved in the alcohol. 



2. The Xanthophyll group also contains sev- 

 eral distinct species, but only two are common 

 in leaves, one being more, and the other less, 

 orange. ^ They are characterized by being in- 

 soluble in water, but soluble in alcohol and in 

 bisulphide of carbon ; and when dissolved in 

 the latter their spectra show two not very 

 distinct absorption-bands at the blue end ; but 

 the red, yellow, and yellow-green rays are 

 freely transmitted. They may be obtained 

 from yellow leaves, by the use of alcohol and 

 bisulphide of carbon. 



3. The Erythrophyll group comprises a 

 number of colors soluble in water, in alcohol, 

 and in ether, but insoluble in bisulphide of 

 carbon. Those met with in leaves are more 

 or less purple, made bluer by alkalies, and red- 

 der by acids ; and thus sometimes plants con- 

 taining the same kind may vary more in tint, 

 owing to a variation in the amount of free 

 acid, than others colored by entirely different 

 kinds. The erythrophyll may be obtained, 



free from chlorophyll and xanthophyll, by 

 heating the leaves in alcohol, evaporating to 

 dryness, redissolving in water, filtering, and 

 evaporating at a gentle heat. 



4. The C'hrysotannin group contains a con- 

 siderable number of yellow colors, some so 

 pale as to be nearly colorless, and others of a 

 tine, dark, golden yellow. They are soluble 

 in water, in alcohol, and in ether, but not in 

 bisulphide of carbon. Their spectra show a 

 variable amount of absorption at the blue end, 

 usually with no bands when in their natural 

 state, but sometimes with one or more suffi- 

 ciently distinct when they are oxidized. They 

 may be obtained free from chlorophyll and 

 xanthophyll by processes similar to those 

 made nse of in the case of erythrophyll, and 

 leaves should always be selected which are as 

 free as possible from colors of that group. 



5. The Phaiophyll group comprises a num- 

 ber of more or less brown colors, insoluble in 

 bisulphide of carbon, and of variable solubility 

 in water or alcohol. The spectra show strong 

 absorption at the blue end extending over the 

 green ; often the red is very dull, and some- 

 times there are definite absorption-bands when 

 the solution is acid, neutral, or alkaline. 



Fluorescent Solutions. President Henry 

 Morton, of the Stevens Institute of Technol- 

 ogy, contributes to the American Journal of 

 /Science some interesting observations on the 

 color of fluorescent solutions. He examined 

 the tincture of turmeric, which is set down in 

 the standard works as fluorescing red. He 

 found that when concentrated it has a rich, 

 orange-red color, but, when the solution is 

 diluted until its color is reduced to yellow, 

 the fluorescence appears green. A marked in- 

 crease in the amount of fluorescence is visible 

 after the solution has been filtered through 

 bone-black, as the light-absorbing coloring- 

 matter is removed. By continuing the decol- 

 oration until the liquid is colorless, or of a 

 very light tint, the fluorescence is distinctly 

 blue. 



The results with the spectroscope, when it was op- 

 plied to this substance, were the same as with the 

 solution of asphalt. Such also is the case with tinc- 

 tures of chlorophyll, which, when fresh and green, 

 gives apparently a green light, and, when old and 

 brown, a gray color. 



Finally, I took up the nitrate of uranium, about 

 which such contradictory statements have been pub- 

 lished. This salt in its solid state gives a brilliant 

 green fluorescence, whose spectrum is figured hy 

 Becquerel, and abounds in green rays ; but in solu- 

 tion it gives a very feeble fluorescence, far inferior 

 to that of turmeric, and of no more green tint than 

 would be due to its yellow color. So in i'act says 

 also the spectroscope. 



From these results it would seem that the mole- 

 cules of fluorescent bodies in solution are not capable 

 of restricting their vibrations to limited ranges, but 

 move at rates corresponding with all refrangibilities, 

 having simply an excess of the higher ones, though 

 the same substances in the solid state may a-ct quite 

 differently, as in the case of nitrate of uranium, and 

 possibly the fluorescent material in the asphalt, which 

 may be related to the solid hydro-carbon fluorescing 

 green, which Becquerel mentions. 





