ON OUR KNOWLEDGE OF SrECTRCM ANALYSIS. 131 



witli other elements such as oxygen and nitrogen, is due to hydrogen, 

 there can be no manner of doubt.' 



' The next point that required solution was the effect of the presence 

 of oxygen on the body under examination, and here we had ample material 

 on which to make our observations. It apjaears that in every case where 

 oxygen is present, otherwise than as a part of the radical, it is attached to 

 some hydrogen atom in such a way that it obliterates the radiation between 

 two of the lines which are due to that hydrogen.' . . . ' If more than 

 one hydroxyl group be present, we doubt if any direct effect is produced 

 beyond that produced by one hydroxyl group, except a possibly greater 

 general absorption ; a good example of this will be found in cinnamic 

 alcohol and phenyl-propyl alcohol, which give the same spectra as far as 

 the special absorptions are concerned. . . . 



' Hitherto we have only taken into account oxygen which is not con- 

 tained in the radical ; when it is so contained it appears to act differently, 

 always supposing hydrogen to be present as well. We need only refer to 

 the spectrum of aldehyde, which is inclined to be linear rather than 

 banded, or rather the bands are bounded by absolute lines, and are more 

 defined than when oxygen is more loosely bonded.' 



Perhaps the most interesting passage is that which refers to the 

 detection o! the radical, and we therefore quote it in full. 



' An inspection of our maps will show that the radical of a body is 

 represented by certain well-marked bands, some differing in position 

 according as it is bonded with hydrogen, or a halogen, or with carbon, 

 oxj-gen, or nitrogen. There seem to be characteristic bands, however, of 

 any one series of radicals between 1000 and about 1100, which would 

 indicate what may bo called the central hydrocarbon group, to which 

 other radicals may be bonded. 



* The clue to the composition of a body, however, would seem to lie 

 between A. 700 and \ 1000. Certain radicals have a distinctive absoi'ption 

 aboat X 700 together with others about \ 900, and if the first be visible 

 it almost follows that the distinctive mark of the radical with which it is 

 connected will be found. Thus in the ethyl series we find an absorption 

 at 740, and a characteristic band, one edge of which is at 892, and the 

 other at 920. If we find a body containing the 740 absorption and a 

 band with the most refrangible edge commencing at 892, or with the 

 least refrangible edge tei'minating at 920, we may be pretty sure that 

 we have an ethyl radical present. So with any of the aromatic group ; 

 the crucial line is at 867. If that line be connected with a band we 

 may feel certain that some derivative of benzine is present. The benzyl 

 group show this remarkably well, since we see that phenyl is present, as 

 is also methyl. It will be advantageous if the spectra of ammonia, 

 benzine, aniline, and dimethyl aniline be compared, when the remarkable 

 coincidences will at once become apparent, as also the different weighting 

 of the molecule. The spectrum of nitro-benzine is also worth comparing 

 with benzine and nitric acid. We should have liked to have said more 

 regarding the detection of the different radicals, but it might seem pre- 

 sumptuous on our part to lay down any general law on the results of the 

 comparatively few compounds whichwe have examined. In our own minds 

 there lingers no doubt as to the easy detection of any radical which we 

 have examined, but it will require more energy and ability than we possess 

 to thoroughly classify all the different modifications which, may arise. 



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