478 



NA TURE 



[September 17, 1903 



It is a general rule that substances which agree closely 

 in structure exhibit similar series of absorption spectra, 

 while those which differ essentially jn structure show 

 absorption curves which are different ; and to this rule 

 neither aromatic compounds, alkaloids, nor dyes and 

 coloured substances form any exceptions. That this is so 

 is easily understood from the theory of absorption spectra. 

 It must, however, be distinctly understood that the essential 

 feature of importance in all such investigations is the 

 quantitative relation of the substance to its spectra, whether 

 these relations are based upon equal weights of material 

 or equimolecular proportions in solutions of given volume 

 and thickness. 



The relationship of morphine, C,jH,,NO(OH)j, and 

 codeine, or methylmorphine, C,,H„NO.(OH)(OCH3), was 

 shown by their spectra, the latter being a homologue of the 

 former. A similar instance has been investigated recently 

 by Dobbie and Lauder. The resemblance between the 

 spectra of laudanine, CjoH^^O^N, and laudanosine, 

 CjjHjjOjN, confirms the view that they are homologous 

 bases. The close agreement of their absorption curves 

 with those of corydaline and tetrahydropapaverine clearly 

 indicates a similarity in structure to that of these alkaloids, 

 but the relationship of laudanosine to corydaline is probably 

 closer than to tetrahydropapaverine, and may be best ex- 

 plained by the formulae 



C,,H„0,N-CH,+ H, 



Corydaline 



C„H„0,N 



Laudanosine 



The removal of a methyl group from such a compound 

 would scarcely cause any appreciable change in the curve 

 of molecular vibrations, and very many cases are known 

 where, when two atoms of hydrogen are introduced into a 

 compound without altering the close linking of the carbon 

 atoms of the ring formation in the compound, the alteration 

 in the spectrum is insignificant. 



A particularly interesting example of tautomerism already 

 mentioned has been observed by Dobbie and Lauder in 

 studying the constitution of cotarnine, a substance prepared 

 from narcotine. Three formulee have been proposed for it : 

 one represents it as an aromatic aldehyde in which one 

 hydrogen is replaced by an open change containing 

 nitrogen ; a second gives it the character of a carbinol base ; 

 while a third" that of an ammonium base. It has been 

 supposed that in solution it is a mixture of two or all three 

 such substances in a state of equilibrium, but as to what 

 is the formula to be assigned to solid cotarnine the data are 

 insufficient to determine. There are, however, two different 

 solutions of the substance obtainable ; that in ether or 

 chloroform is quite colourless, like the solid ; but a solution 

 in water or alcohol is yellow. From the molecular absorp- 

 tion spectra of these solutions and of certain derivatives 

 with which they are compared there is very distinct 

 evidence that a solution in alcohol or water contains the 

 ammonium^ base, while under the influence of sodium 

 hydroxide it assumes the condition of the carbinol form. 

 Moreover, the rate of transformation and the conditions 

 which influence this isomeric change have been studied. 

 It suffices here to state that a solution containing entirely 

 the one form may be converted wholly into the other. 



The two formulse referred to are given below : — 



/CH(0H).N.CH3 



^CH^ CH2 



Carbinol Form 



GsHeOa^^^ \^^^ " :JC3He03 



yCH = N(CH3).0H 



^CHj.CHs 

 Ammonium Base 



Emission Spectra. 



Spark Spectra and their Constitution. 



As it became necessary to make accurate measui-ements 

 of absorption spectra in the ultra-violet, the work of obtain- 

 ing the wave-lengths of lines in twenty metallic spectra 

 was undertaken. They were for the most part in a region 

 which, except in the case of two or three elements, had 

 not been previously explored. A small Rutherford grating 

 was employed, combined with quartz lenses with a focal 

 length of three feet. Experience has shown that it was 

 advisable in describing these spectra to give measurements 

 in hundredths of an inch of the positions of the lines on the 



NO. 1768, VOL. 68] 



published photographs of the prismatic spectra in the 

 Journal of the Chemical Society (March, 1882), and to 

 follow Lecocq de Boisbaudran by giving a description of 

 the character of each of the lines. In this way they are 

 easily identified, and the value of the measurements for 

 practical purposes is greatly enhanced. Prior to the 

 publication of the work (1882), in the prosecution of which 

 Dr. Adeney was associated with me, Liveing and Dewar, 

 who had been engaged on a similar investigation, but 

 operating in a different manner, published an account of 

 the spectra of the metals of the alkalies and alkaline earths, 

 and subsequently the lines of iron, nickel, and cobalt.' .They 

 showed a rhythmic grouping of the lines to be characteristic 

 of the spectra of the alkali metals. 



In connection with the prismatic spectra which were 

 photographed some remarkable facts were noticed ; for 

 instance, the character of the lines belonging to different 

 groups of elements was a noticeable feature, as well also 

 their disposition or arrangement, more particularly in the 

 ultra-violet. Similarities in the visible spectra of zinc and 

 cadmium, of calcium, strontium, and barium, and in those 

 of the alkali metals had been observed by Mitscherlich, by 

 Lecocq de Boisbaudran, and also by Ciamician. As to the 

 grouping of the lines as observed on the photographs, it 

 appeared that the spectra of well-defined groups of elements 

 had characteristics in common which were different from 

 those of other groups. For instance, the alkali metals 

 differed from the alkali earth metals which appeared to 

 form a group by themselves. Then in marked contrast to 

 these simple spectra were those of iron, nickel, and cobalt, 

 which though very complicated were seen to be much alike. 

 Nearest to these but differing from them in certain respects 

 were the palfadium, gold, and platinum spectra. 



It was observed how these elements with certain chemical 

 and physical properties in common could be recognised as 

 being relations owing to their family likeness when their 

 spectra were photographed. Then it was remarked that 

 the spectra of magnesium, zinc, and cadmium, had dis- 

 tinctive characters in common ; for instance, the individual 

 lines in these spectra were marked by similar character- 

 istics, such as a great extension of the strong lines above 

 and below the points of the electrodes. This extension was 

 increased with the atomic mass of the metal, and with the 

 greater atomic mass in this group the volatility of the 

 metal is also greater. An arrangement of _ the lines in 

 pairs and triplets was noticed, the triplets being repeated, 

 but less distinctly than in the first instance, and again 

 repeated sharply but less strongly, so that there were three 

 different sets of triplets in each spectrum. The point of 

 greatest interest and importance was the connection ,traced 

 between the atomic mass and the numerical differences 

 observed in the intervals between the lines of different 

 gioups when measured by their oscillation frequencies. 



These differences were not in the spectrum of one element, 

 but were in the lines of each metal of the group, and were 

 clearly associated with the atomic mass and chemical 

 pioperties in each case. 



The arrangement of the lines, which was common to all 

 the metals in the magnesium, zinc, cadmium group, may 

 shortly be described as follows :— Three isolated lines and 

 one pair of lines in magnesium, with four sets of triplets,; 

 one isolated line and one pair of lines in zinc, with three 

 sets of triplets ; one isolated line and one pair of lines in 

 cadmium, with three sets of triplets. 



Besides the arrangement of these lines there were in the 

 spectrum of each element two groups of the most refrangible 

 lines, consisting one of a quadruple group and the other 

 of a quintuple group, the groups and the lines composing 

 them being similarly disposed in each spectrum. It was, 

 however, not distinctly proved that these particular groups 

 were strictly homologous, the most refrangible lines in the 

 zinc spectrum being very difficult to photograph even on 

 specially prepared plates, though the lines are strong. It 

 was furthermore observed that with an increase in the 

 atomic mass the distances between the lines both in pairs 

 and triplets were greater. The same was the case with the 

 quadruple and quintuple groups. In the magnesium spec- 

 trum, if we compare the first with the second group of 

 triplets, we find the intervals extending from the first line 

 in the first group to the first line in the second group, and 

 from the second line in the first group to the second line 



