398 



NATURE 



\_August 25, 1881 



step of the highest interest has already been taken by my col- 

 leao-iie, Capt. Abney. 1 will read what it is, and the lantjiiage 

 of "Prof. Roscoe, the President of the Chemical Society, is so 

 clear and so admirably put, that it is impossible for any one 

 to improve upon it.' Referring to the work which Capt. Abney 

 and Col. Festing have done together, he says : This work " is 

 no less than a distinct physical test of the existence in organic 

 compounds, of the organic radicals, and a means of recognising 

 the chemical structure of an organic compound by means of the 

 spectroscope." This result "is accomplished by photographing the 

 absorption spectra of organic compounds in the infra-red part of 

 the spectnuu. In these invisible portions characteristic and distinct 

 absorption lines and bands occur for each organic radical. The 

 ethyl compounds all show one special ethyl band ; the methyl 

 compounds a special methyl band ; and thus, just as a glance at 

 the luminous portion of the spectrum satisfies us of the presence 

 of calcium, lithium, and rhubidium, so a simple inspection of 

 these infra-red photographs enables us to ascertain the presence 

 of the various organic radicals. This invention is still in its 

 infancy, but one of greater importance to chemists has seldom if 

 ever been communicated to the .Society." I have been the more 

 anxious to give these results in Prof. Roscoe's own words, 

 because it will be seen that, mutatis niutandis, these remarks 

 touching the spectra of organic radicals are precisely the state- 

 ment I have been endeavouring to make with regard to inorganic 

 radicals. It cannot therefore be said that the nature of the 

 principle I bring forward is one with which chemists are not 



familiar. In this beautiful work, then, we have an analogy 

 between the behaviour of known compounds and assumed 

 elementary bodies. 



A new method of laboratory work which I have recently 

 started may, I think, in the course of time furnish us with 

 another analogy, and in connection w ith it there is an experi- 



C KXETENE 

 " '' 270-C 



Fig. 47. — Hypnthetical spectra obtained on distilling at successively in- 

 creasing temperatures a mucture of light and heavy hydrocarbons. 



ment to which reference may advantageously be made, because 

 it will show what kind of results we expect to get. It is simply 

 referred to as an indication of the probable fruit which will 

 come fi-om many new kinds of experimentation which might be 

 adopted, provided always we bear in view the idea which it has 

 been my duty to bring forward. This experiment is founded on 



Fig. 48.— Fractional distillation of potassium. A, hard gla>s tube containing the potassium and connected »-!t'i a Sprengel pump c by a tube B, having two 

 bulbs with platinum electrodes sealed into them, between which an induced current may be made to pa's: F, spirit lamp ; H, battery ; D, spectro- 

 scope ; E, lens to focus image of spark on slit of spectroscope. 



the behaviour of compound bodies when they are distilled at 

 different temperatures. If we take, for instance, a mixture of 

 hydrocarbons, some of them very complex in their nature, and 

 others more simple ; when a low temperature is employed it 

 is found that the simpler hydrocarbon comes over in the shape 

 of vapour. If therefore we were fortunate enough to be able 

 to observe the spectra of these different vapours, assume that 

 that series of hydrocarbons, for instance, shown in the ac- 

 companying diagram (Fig. 47), had each of them a distinct 

 spectrum, we should be able to follow spectroscopically the effect 

 of each change of temperature, and we could in that way associate 

 the known fact of the greatest density of the vapour which comes 

 over at a higher temperature with a spectrum of a certain kind. 

 ' yon-nml of the Chemical Society, May, 18S1. 



Now in our experiment we deal not with a compound body 

 in the ordinaiy sense, but with the so-called elementary body, 

 potassium, which we have in a hard glass tube of the form 

 shown in Fig. 48. By means of a Sprengel pump the tube 

 is very perfectly exhausted, and then ^'gently warmed with a 

 spirit lamp, the exhaustion going on during the whole pro- 

 cess. On passing a current between the platinum electrodes we 

 see a beautiful green glow in the tube, and obtain a certain 

 spectrum. On replacing the spirit-lamp by a Bunsen burner 

 we find as the result of this increased temperature that the 

 colour in the tube is blood-red, and the resulting spectrum is 

 entirely different. The spectrum of potassium is one which 

 requires a very great deal of study, for the reason that it varies 

 very much under different experimental conditions. If the 



