182 Prof. Mitscherlich on the Spectra of Compounds 



If the spectra are compared with one another, it is found that 

 the metallic spectra consist of individual sharp lines, and that those 

 of their compounds with the metalloids (excepting the haloid salts 

 of calcium, strontium, and barium, whose spectra consist of indi- 

 vidual lines) are composed of broad luminosities with narrow 

 dark lines which recur at definite intervals. 



By means of that property, the spectra of the haloid com- 

 pounds of calcium, strontium, and barium are readily compared 

 with each other; and it is at once observed that individual 

 characteristic lines recur in the spectra of one and the same 

 metal, which, according to the halogens, are more or less distant 

 from one another, by which means the metal is easily recognized 

 in the spectra of its compounds. The fluorides form an excep- 

 tion to this. 



If this phenomenon is investigated in the case of the barium 

 compounds by the spectra depicted, it is found that the distances 

 of the two prominent lines in the various spectra are to each 

 other as the atomic weights of these compounds. This relation 

 gives rise to further interesting conclusions. Thus from an ob- 

 served distance of such lines, the distance of the corresponding 

 lines in the spectra of other barium compounds may be calcu- 

 lated ; further, from the distance and one known atomic weight 

 that of the other compounds may be determined. 



If we start from the chloride-of-barium lines, which are most 

 easily procured, and if we form from the atomic weights of the 

 compounds and the distance of the chief lines of the chloride-of- 

 barium spectrum, which is expressed by 3' 9 degrees of the scale, 

 the equation for the distance of these lines in the iodide-of- 

 barium spectrum, we obtain, taking the atomic weight of iodide 



3*9 104 

 of barium at 195*5, that of chloride of barium at 104, — = .,^ K _ , 



x 19o*5 



from which #=7*3 : the drawing gives 7*3. 



Just as these equations may be stated for the lines of iodide 



of barium from those of chloride of barium, so in like manner 



we get for bromide of barium, whose atomic weight is 148*5, 



the equation — = ———-, from which # = 5*5 : according to 

 ^ x 148*5 



the drawing it is 5*2. 



Of course the atomic weights of the barium compounds men- 

 tioned may be calculated from the spectra, as well as the spectra 

 from the atomic weights. Other equations may also be obtained 

 which express the relations of bromide of barium to iodide of 

 barium. 



The feebler lines of the chloride- and bromide-of-barium 

 spectra may also be compared like the strong lines ; but in the 

 case of iodide of barium they could not be drawn, and in bro- 



