June 25, 1874J 



NATURE 



155 



5. Now the continuous spectrum may be, and as a matter 

 of fact is, observed in the case of chemical compounds, whereas 

 all compounds known as such are resolved by the high tension 

 spark into their constituent elements. We have a right, therefore, 

 to assume that an element in the solid Etate is a more complex 

 mass than the element in a state of vapour, as its spectrum is 

 the same as that of a mass which is known to be more complex. 



6. The spectroscope supplies us with intermediate stages be- 

 tween these extremes. 



(a) The spectra vary as we pass from the induced current with 

 jar, to the spark without the jar, to the voltaic arc, or to the highest 

 temperature produced by combustion. The change is always in 

 the same direction ; and here again the spectrum we obtain from 

 elements in a state of vapour, a spectrum characterised by spaces 

 and bands, is similar to that we obtain from vapours of which the 

 compound nature is unquestioned. 



(6) At high temperatures the vapours of some elements (which 

 give us neither line nor channelled-space spectra at those tem- 

 peratures, although we undoubtedly get line spectra when elec- 

 tricity is employed, as stated in No. 4), give us a continuous 

 spectrum at the more refrangible end, the less refrangible end 

 being unaflectcd. 



(7) At ordinary temperatures, in some cases, as in selenium, the 

 moiL' refrangible end is absorbed ; in others the continuous spec- 

 trum in the blue is accompanied by a continuous spectrum in 

 the red. On the application of heat the spectrum in the red 

 disap])ears, that in the blue remains ; and further, as Faraday 

 has shown in his researches on gold-leaf, the masses which 

 absorb in the blue may be isolated from those which absorb 

 in the red. It is well known that many substances known to 

 be compounds in solutions, give us absorption in the blue or 

 blue and red, and also that the addition of a substance known to 

 be compound (such as water) to substances known to be com- 

 pound which absorb the blue, superadds an absorption in the red. 



7. In those cases which do not conform to what has been stated 

 the limited range of the visible spectrum must be borne in mind. 

 Thus I have little doubt that the simple gases at the ordinary 

 ccnditions of temperature and pressure have an absorption in the 

 ultra-violtt ; that highly compound vapours are often colour- 

 less because their absorption is beyond the red, with or with- 

 out an absorption in the ultra-violet. Glass is a good case in 

 point ; others will certainly suggest themselves as opposed to 

 the opacity of the metals. 



8. If we assume in accordance with what has been stated 

 that the various spectra to which I have referred are really due 

 to different molecular aggregations, we shall have the fol- 

 lowing series, going from the more simple to the more complex. 



First stage of com- 1 

 plexity of mole- \ Lire spectrum, 

 cule. ) 



Second stage Channelled-space spectrum. 



f Continuous absorption at the blue 



„. . , ) end, not reaching to the less re- 



S S frangibleend. (This absorption may 



( break up into channelled spaces.) 



I Continuous absorption at the red end, 



, ) not reaching to the more refran- 



fourth stage -j gible end. (This absorption may 



( break up into channelled spaces.) 



Fifth stage Unique continuous absorption. 



9. I shall content myself in the present note by giving one or 

 two instances of the passage of spectra from one stage to another, 

 beginning »t the fifth stage. 



From 5 to 4 

 I. The absorption of the vapours of K in the red-hot tube, de- 

 scribed in another note, is at lirst continuous. As the action of the 

 heat is continued, this continuous spectrum breaks in the middle, 

 one part of it retreats to the blue, the other to the red. 

 From 4 to 3 



1. P'araday's researches on gold leaf best illustrate this, but I 

 hold that my explanation of them by masses of two degrees of 

 complexity only, is sufficient without his conclusion ("Re- 

 searches in Chemistry," p. 417), that they exist "of inter- 

 mediate sizes or proportions." 



From 3 to 2] 

 ' I. Sulphur vapour first gives a continuous spectrum, at the blue 

 end, on healing this breaks up into a channelled-space spectrum. 



2. The new spectra of K and Na (more particularly relerred to 

 in the following note) make their appearance after the continuous 

 absorption in the blue, and red vanishes. 



From 2 to I 



1. In many metalloids the spectra without the jar are chan- 

 nelled ; on throwing the jar into the circuit the hne spectrum 

 is produced, while the cooler exterior vapour gives a channelled 

 absorption- spectrum. 



2. The new spectra of K and Na charge into the line- 

 spectrum (with thick lines which thin subsequently) as the heat 

 is continued. 



Spectrosco pic Notes.— On the Molecular Structure of Vapours 

 in connection with their Densities, by J. N. Lockyer, F.R.S. 



I. I have recently atienipted to bring the spectroscope to bear 

 upon the question v hether vapours of elements below the highest 

 temperatures aie truly hcnogereous, and whether the vapours 

 of different chemical elements at any one temperature aie all 

 in the same molecular condition. In the present note I beg to 

 lay before the Ro)al Scciety the preliminary results of my re- 

 searches. 



2. We start with the following facts : — 



I. All elements driven into vapour by the induced current 



give line-spectra. 



II. Most elements driven into vapour by the voltaic arc 

 give us the same. 



III. Many metalloids when greatly heated, some at ordi- 



nary temperatures, give us channelled-space spectra. 



IV. Elements in the solid state give us continuous spectra. 



3. If we giant that these spectra represent to us the vibra- 

 tions of difiercnt molecular aggregations, and this question is 



discussed'in another the previous (note) spectroscopic observations 

 should give us facts of some importance to the inquiry. 



4. To take the lowest ground. If, in the absence of all know- 

 ledge on the subject, it could be shown that all vapours at all 

 stages of temperature had spectra absolutely similar in charac- 

 ter, then it would be more likely that all vapours were truly 

 homogeneous and similar among themselves as regards molecular 

 condition than if the spectra varied in character, not only from 

 element to element, but fiom one temperaluie to another in the 

 vapour of the same element. 



5. At the temperature of the sun's reversing layer the spectra 

 of all the elements known to exist in that layer are apparently 

 similar in character, that is they are all line spectra ; hence it is 

 most probable that the vapours there are truly homogeneous and 

 that they all exist in the same molecular condition, than if the 

 spectium were a mixed one. 



6. The fact that the order of vapour densities in the sun's 

 atmosphere which we can in a measure determine by spectro- 

 scopic observations does r.ot agree with the order of the modem 

 atomic weights of the elements, but more closely agrees with the 

 older atomic weights, led me to take up the present research. 

 Thus I may mention that my early observations of the welling 

 up of Mg vapour all round the sun above the Na fapoiir, have 

 lately been frequently substantiated by the Italian observers. 

 So that it is beyond all question, I think, that at tlie sun the 

 vapour density of Mg is less than that of Na. 



7. The vapour densities of the following elements have been 

 experimentally determined : — 



Hi S 32 (at 1,000°) 



K 39 I 127 



As 150 Hg 100 



Br 80 N 14 



Cd 56 O 16 



CI 35-5 P 62 



S. To pursue this inquiry the following arrangements have 

 been adopted : — 



The first experiments were made last December upon Zn in 

 A glass tube closed at each end with glass plates ; and I have 

 to express my obligations to Dr. Russell for allowing them to be 

 conducted in his laboratory, and for much assistance and counsel 

 concerning them. 



A stream of dry H was allowed to pass. The tube was 

 heated in a Hofmann's gas furnace, pieces of the metal to be 

 studied having previously been introduced. It was found that 

 the glass tube mehed ; it was therefore replaced by an iron one. 

 The inconvenience of this plan, however, owing to the necessity 

 for introducing the mclal into the end of the hot lube when the 

 first charge had volatilised, and m.oreover the insufficiency of the 

 heat obtainable from the gas furnace, soon obhged me to replace 

 both tube and furnace by others, which have now been in use 

 for many weeks, and which still continue to work most satisfac- 

 torily 



