Prof. 11. Bunsen's Spectral- Analytical Researches. 533 



The sulphates of the barium group are not sufficiently vola- 

 tile to afford flame-spectra. In order to convert these salts into 

 chlorides, the portion under examination is wrapped in several 

 folds of paper, supported on a fine platinum wire and heated in 

 the oxidation-flame until the paper is reduced to ash; the flame 

 is then made luminous, whereby the sulphate is reduced to sul- 

 phide ; and this salt is converted into chloride by a drop of 

 hydrochloric acid applied by means of a capillary tube. 



In these reactions the substance under examination should 

 be repeatedly heated in the oxidation-flame and moistened with 

 hydrochloric acid in order to remove the sodium compounds, 

 the continuous spectra of which often greatly obscure the lines 

 in the spectra of the chlorides. 



3. Spectra of the Elements of the Earth Group. 



The chlorides of aluminium and beryllium do not exhibit 

 lines, either in the flame- or spark-spectra, whereby they may 

 be recognized. 



The spectra of the chlorides obtained from the so-called cerite 

 and ytterite earths are mapped in Plate V., nos. 11 to 14. 



As the separation of these earths presents very considerable 

 difficulties, and as the methods hitherto employed do not yield 

 altogether satisfactory results, it appears to me to be necessary 

 that I should say something concerning the preparation of the 

 perfectly pure material with which the spectra hereafter de- 

 scribed were obtained. 



Cerite from Utoe was pulverized and mixed in a Hessian basin 

 with concentrated sulphuric acid in quantity sufficient to fill the 

 basin to one third ; the excess of acid was removed by strongly 

 heating the dish ; the powdered residue was mixed with water at 

 0° C, care being taken that no rise of temperature should 

 ensue ; the solution was separated by filtration from the solid 

 matter, which was again treated with sulphuric acid, &c. From 

 the solution saturated with sulphuretted hydrogen (in order to 

 remove arsenic,molybdenum, bismuth, copper, and lead), strongly 

 acidified with hydrochloric acid and oxidized by chlorine, the 

 oxalates of cerium, lanthanum, and didymium were precipitated 

 by means of oxalic acid. The oxides, obtained by strongly 

 heating the precipitated oxalates, were dissolved in nitric acid, 

 and the solution was evaporated to the consistence of a syrup 

 over the water-bath. By dissolving the mass after cooling in 

 cold water, and boiling the liquid for some time with water con- 

 taining 2 cub. centims. of concentrated sulphuric acid per litre, 

 the greater part of the cerium was precipitated as basic sulphate 

 (three litres of the acidified water were required for 250 

 grammes of cerite). 



