330 Professors Kirchhoff and Bunsen on Chemical 



If a drop of the mother-liquor of the Diirkheim water be 

 brought into the flame of the spectrum-apparatus, the charac- 

 teristic lines of sodium, potassium, lithium, calcium, and stron- 

 tium are at once seen. If the lime, strontia, and magnesia be 

 separated according to well-known processes, and if the residual 

 alkaline bases in the form of nitrates be washed out with alcohol 

 and the lithium removed as completely as possible by precipita- 

 tion with carbonate of ammonium, a mother-liquor is obtained 

 which in the spectrum-apparatus shows the lines of sodium, 

 potassium, and lithium, but besides these, two splendid blue lines 

 situated close together, and almost coinciding with the blue 

 strontium line Sr o\ 



As no known elementary body produces two blue lines in this 

 portion of the spectrum, we may consider the existence of this 

 hitherto unknown alkaline element as thus placed beyond a doubt. 



The facility with which a few thousandths of a milligramme 

 of this body may be recognized by the bright blue light of its 

 incandescent vapour, even when mixed with large quantities of 

 the more common alkalies, has induced us to propose for it the 

 name Caesium (and the symbol Cs), derived from the Latin 

 " caesius," used to designate the blue of the clear sky*. 



If Saxony lepidolite be treated by any of the known plans 

 for separating the alkalies from the other constituents, and if 

 the solution of the alkalies thus obtained be precipitated with 

 bichloride of platinum, an abundant precipitate is formed, which, 

 when -examined in the spectrum-apparatus, shows only the bright 

 potassium lines. If this precipitate be repeatedly washed with 

 boiling water, and the residual salt occasionally examined in the 

 apparatus, two splendid violet lines, lying between the strontium 

 line Sr $ and the blue potassium line K/3, will be noticed on the 

 gradually fading continuous background of the potassium spec- 

 trum. These new lines increase in brilliancy as the washing is 

 continued, and a number more appear in the red, yellow, and 

 green portions of the spectrum. 



None of these lines belong to any previously known body. 

 Amongst them are two which are especially remarkable, as lying 

 beyond Fraunhofer's line A and the potassium line Ka coinci- 

 dent with it, and therefore situated in the outermost portion of 

 the red solar rays. Hence we propose for this new metal the 

 name Rubidium (and the symbol lib), from the Latin "rubidus," 

 which was used to express the darkest red colour f. 



Before describing the special spectra of caesium and rubidium, 



* Aulus Gellius, in the Nodes Atticce, ii. 26, quotes Nigidius Figulus as 

 folloivs : — Nostris autem veteribus cassia dicta est, quae a Graecis y\avKa,7n>, 

 ut Nigidius ait, de colore cceli quasi ccelia. 



t Aulus Gellius, Nodes Atticce, ii. 26. Rubidus autein est rufus atrior 

 et nigrore multo inustus. 



