508 Professors Kirchhoff and Bunscn on Chemical 



these several readings we called A, B, C, &c. An interpolation 

 scale was then calculated and drawn, in which each division 

 corresponded to a division on the scale of the instrument, and 

 in which the points corresponding to the observations A, B, C, 

 &c. were placed at the same distances apart as the same lines on 

 our first drawings of the spectrum. By help of this scale, curves 

 of the new spectra were drawn, in which the ordinates express 

 the degrees of luminosity at the various points on the scale, 

 as judged of by the eye. The lithographer then made the 

 designs represented in fig. 4>, Plate V. from these curves*. 



As in our first memoir, so here we have represented only 

 those lines which, in respect to position, definition, and intensity, 

 serve as the best means of recognition. We feel it necessary to 

 repeat this statement, because it has not unfrequently happened 

 that the presence of lines which are not represented in our draw- 

 ings has been considered as indicative of the existence of new 

 bodies. 



We have likewise added a representation of the potassium 

 spectrum to those of the new metals for the sake of comparison, 

 so that the close analogy which the spectra of the new alkaline 

 metals bear to the potassium-spectrum may be at once seen. 

 All three possess spectra which are continuous in the centre, and 

 decreasing at each end in luminosity. In the case of potassium 

 this continuous portion is most intense, in that of rubidium less 

 intense, and in the csesium-spectrum the luminosity is least. 

 In all three we observe, the most intense and characteristic lines 

 towards both the red and blue ends of the spectrum. 



Amongst the rubidium lines, those splendid ones named lib a 

 and Bb/3 are extremely brilliant, and hence are most suited for 

 the recognition of the metal. Less brilliant, but still very cha- 

 racteristic, are the lines RbS and Rhy. From their position 

 they are in a high degree remarkable, as they both fall beyond 

 Fraunhofer's line A; and the outer one of them lies in an nltra- 

 red portion of the solar spectrum, which can only be rendered 

 visible by some special arrangement. The other lines, which 

 are found on the continuous part of the spectrum, cannot so well 

 be used as a means of detection, because they only appear when 

 the substance is very pure, and when the luminosity is very 

 great. Nitrate of rubidium, and the chloride, chlorate, and per- 

 chlorate of rubidium, on account of their easy volatility, show 



* The coincidence of this chromolithograph plate with that published 

 in the former memoir is by no means complete, but this does not seriously 

 interfere with the utility of either of the representations ; for if the posi- 

 tion of an observed hne be found, by help of the scale above described, to 

 be near to that of the line of any known substance, it is easy, by placing 

 some of this substance in one of the flames, and in the other some of the 

 body under examination, to see whether the lines are coincident or not. 



