564 



NATURE 



{Oct. 14, 1880 



and in a short time becomes nearly full of hydrogen. The 

 spectrum of the capillary then shows the hydrogen lines 

 intensely bright. After sometime the gas comes off far 

 less freely, and an approach to a vacuum is again ob- 

 tained. Another phenomenon now begins to show itself: 

 on passing the current a yellow glow is seen, which 

 gradually fills the whole space between the pole in the 

 retort and the metal ; its spectrum consists of the lines of 

 hydrogen and the yellow line of sodium, the red and 

 green line being both absent until the experiment has gone 

 on for some time. 



As the distillation goes on, the yellow glow increases in 

 brilliancy, and extends to a greater distance above the 

 pole, and the red and green lines presently make their 

 appearance as very faint lines. 



The upper boundary of the yellow is quite sharp, the 

 lines and fluted spectrum of hydrogen appearing above it. 



After the yellow glow-giving vapour (which does not 

 attack the glass) has been visible for some time, the pump 

 is stopped and the metal lu-atcd more strongly. On 

 passing the current a little while afterwards, a very 



brilliant leaf-green vapour is seen underlying the yellow 

 one, and connected with it by a sap-green vapour. The 

 spectra then visible in the tube at the same time are — 



Leaf-green ... Green and red lines of sodium and C of 

 hydrogen ; D absent. 



Sap-green Green, red, and yellow sodium lines of 



equal brilliancy and C of hydrogen. 



Yellow D alone and C. 



Bluish-green ... C and F and hydrogen structure. 



To observe the green sodium hne alone it is necessary 

 to point the direct-vision spectroscope just above the 

 surface of the metal where the green is strongest. It is 

 also necessary to guard against internal reflections from 

 the glass, as this may sometimes cause the D line to be 

 seen by reflection from the surface. 



This method of inquiry has been tried also with potas- 

 sium, calcium, and some other metals, and with metallic 

 salts. 



With potassium and calcium we get the same inversion 

 of phenomena, the yellow-green lines of potassium being 



Fig. 2.— DislUl.ition .\ppaiaUis. 



seen without the red ; while in the case of calcium the 

 blue line alone was seen. 



The fact that in these experiments we get, as before 

 mentioned, vapours which at one and the same time 

 exhibit different colours and different spectra at different 

 levels in the tube, at once suggests the phenomena of 

 fractional distillation. 



It is also suggested, as a result of the application of 

 this new method, that in the case of a considerable 

 number of chemical substances not only the line spectrum 

 is compound in its origin, as I suggested many years ago, 

 but that a large number of the lines is due to molecular 

 groupings of considerable complexity, which can be 

 kept out of the reaction by careful low temperature 

 distillation. 



So much then for one method. Now for the other. 



In this I have attempted to gain new evidence in the 

 required direction by adopting a method of work with a 

 tpark and a Bunsen flame, which Col. Donnelly suggested 

 1 should use with a spark and an electric arc. This con- 



sists in volatilising those substances which give us flame 

 spectra in a Bunsen flame and passing a strong spark 

 through the flame, first during the process of volatilisa- 

 tion, and then after the temperature of the flame has 

 produced all the sim; lification it is capable of producing. 



The results have been very striking ; the puzzles which a 

 comparison of flame spectra and the Fraunhofer lines has 

 set us find, 1 think, a solution ; while the genesis of spectra 

 is made much more clear.' 



To take an instance, the flame spectrum of sodium 

 gives us, as its brightest, a yellow line, which is also of 

 marked importance in the solar spectrum. The flame 

 spectra of lithium and potassium give us, as their brightest, 

 lines in the red which have not any representatives among 

 the Fraunhofer lines, altbough other lines seen with higher 

 temperatures arc present. 



Whence arises this marked difierence of behaviour? 



' I allude more especially to the production of triplets, their change into 

 quartets, and in all probability into flutings, and to the vanishing of flutmgs 

 into lines, by increasing the rate of dissociation. 



