184 Prof. Mitscherlich on the Spectra of Compounds 



These relations cannot be established in the case of fluoride 

 of barium. 



Comparing the spectra of the haloid compounds of calcium, 

 which mostly consist of three lines, two very near each other, 

 the third somewhat distant, with the atomic weights of these 

 compounds, it is found that the distances from each other of corre- 

 sponding lines are inversely proportional to the atomic weights. 



Taking for the atomic weight of iodide of calcium 147, of 

 bromide of calcium 100, and of iodide of calcium 55*5, we obtain 

 the following equation for calculating the distance of the most 

 divergent lines of bromide of calcium (which I denote by sc), from 

 the distance of the chloride of calcium lines, which, according to 

 calculation is 6*5 for the latter compound :— - 



^ = §?' fromwhich * =3 ' 6 ' 



From the drawing of the bromide-of-calcium spectrum the same 

 result is obtained, # = 3*6. 



From the observed position of the lines of both compounds, 

 the equation for the starting-point of the spectra of the calcium 

 compounds is the following, in which y is the distance of the 

 least refracted lines of the chloride-of-calcium spectrum from the 

 starting-point, which in this case is opposite to the starting- 

 point found in the spectra of the barium compounds : — 



Distance of the first chloride-of-calcium line y 



Distance of the second chloride-of-calcium line y + 6'5 

 Distance of the first bromide-of-calcium line y — 1*2 

 Distance of the second bromide-of-calcium line ?/ + 2 , 2' 

 from which y = 2'6. 



The starting-point lies near 129*8 of the division. 



In iodide of calcium I have not succeeded in observing a spec- 

 trum ; I shall calculate this from the distance of the chief lines 

 of chloride of calcium and from the atomic weights, taking the 

 starting-point found as a basis. In accordance with this, the 

 equation for the two lines of iodide of calcium which have the 

 greatest difference is 



-rz = -^-r=i from which x=2'5. 

 6*5 147 



The equation for the position of the lines of iodide of calcium is 

 as follows, if the distance of the line nearest the starting-point 

 from the starting-point is 9 = y: — 



