1861.] Professcrr H, E, Roscoe on Spectrum Observations. 323 



WEEKLY EVENING MEETING, 



Friday, March I, 1861. 



Sir Henry Holland, Bart. M.D, F.R.S. in the Chair. 



Henry Enfield Roscoe, Esq. 



PaOFBSSOR OTt 0HEMI8TBY IN OWEN'S COLLEGB, MANCHKSTEE. 



On Bunsen and Kirchhoff^s Spectrum Observations. 



The speaker commenced by stating that the researches of Bunsen and 

 KirchhofF, which he had the honour of bringing before his audience, 

 marked a new era in the science of Analytical Chemistry ; that by 

 means of these discoveries the composition of terrestrial matter becomes 

 revealed to us with a degree of accuracy and delicacy as yet unheard of, 

 so that chemical elements supposed to be of rare and singular occur- 

 rence, are shown to be most commonly and widely distributed, and on 

 the first practical application of this new method of analysis two new 

 and hitherto undetected alkaline metals have been discovered. 



The importance of these researches becomes still more strikingly 

 apparent, when we hear that the conclusions derived from them outstep 

 the bounds of our planet, enabling us to determine with all the certainty 

 of definite experiment the actual presence of a number of elementary 

 bodies in the sun. 



The colours which certain bodies impart to flame, have long been 

 used by chemists as a test for the presence of such bodies. Thus 

 soda brought into a colourless flame produces a bright yellow light, 

 and substances containing soda in any form give this yellow colour. 

 Potash gives a violet flame, lithia and strontia impart to flame a crimson 

 colour, whilst salts of barium tinge it green. These colours are pro- 

 duced by the incandescence or luminosity of the heated vapour of the 

 various bodies placed in the flame. It is only because these sub- 

 stances are volatile, or become gases at the temperature of the flame, 

 that we observe the .peculiar colour. If any substance, such as pla- 

 tinum, which is not volatile at the temperature of the flame, be placed 

 in it, no coloration is observed. The higher the temperature of the 

 flame into which the same substance is placed, the greater will be the 

 luminosity ; and the more volatile the salt of the same metal, the more 

 intense is the light produced. 



