150 



Report on the Progress of Cuemistry. 



atmosphere, the spectrum consists of many shaded bands, 

 but that at the ordinary pressure of the atmosphere the 

 spectrum is entirely different, consisting of clearly cut 

 bright Hues. This discovery we owe to Pliicker, and, to 

 quote Dr. Watts, "Among all the additions made to our 

 knowledge of spectrum analysis within ten years none is 

 so startling as the discovery that a substance may give two 

 totally different spectra which have no line or band in 

 common." 



Another principle early announced by Bunsen and Kirch- 

 off, was that the spectrum of a metal would be the same 

 whatever compound might be used. Thus, for example 

 sodium gave the same double yellow line whether burned 

 as the element or in combination as a chloride, an iodide 

 a sulphate or a carbonate. But this is now known to be 

 true only in certain cases ; indeed it seems to be so only when 

 the temperature of the flame is high enough to decompose 

 the compound. From compounds which are not broken 

 up at the high temperature employed, spectra very dif- 

 ferent from those of its elements are obtained. A charac- 

 teristic difference seems to be this: the spectrum of a metal 

 usually consists of sharply defined lines, while that of its 

 compounds contains broad bands instead. And just here 

 should be noticed the very suggestive fact that the. high 

 pressure spectrum of nitrogen differs from its low pressure 

 spectrum just as the spectrum of an element usually differs 

 from that of its compound; and Dr. Watts remarks that, 

 " It remains for future experiments to confirm or modify 

 the indications thus given of the compound nature of 

 nitrogen." To the Quarterly Journal of Science and the 

 Journal of the Franklin Institute, attention is especially di- 

 rected for full accounts of recent investigations in this 

 department. 



With these examples to illustrate the activity of chemists 

 in examining and rebuilding the very ground-work of their 



