1879.] on Spectroscopic Investigation. 211 



tiroly ; but if any hydrogen or traces of moisture bo present it comes 

 out when the pressure is much reduced. In such cases the liydrogen 

 lines C and F are always visible as well. Sometimes several fine lines 

 appear on the more refrangible side of this line, between it and the b 

 grouj), which give it the appearance of being a narrow band, shaded on 

 that side. Various samples of magnesium used as electrodes, and hydro- 

 gens 2)re})ared and purified in dilferent ways, gave the same results. 



In addition to the above-mentioned line, there is also produced a 

 series of fine lines, commencing close to the most refrangible lino 

 of the h group, and extending with gradually diminishing intensity 

 towards the blue. These lines are so close to one another, that in a 

 small spectroscope they appear like a broad shaded band. We have 

 little doubt that the dark absorption line, with wave-length about 

 5,140, shading towards the blue, observed in our iron tubes, was a 

 reversal of part of these lines, though the latter extend much further 

 towards the blue than the observed absorption extends. 



Charred cream of tartar in iron tubes, arranged as before, gave a 

 broad absorption band extending over the space from about wave- 

 length 5,700 to 5,775, and in some cases still wider, with edges ill- 

 defined, especially the more refrangible edge. By placing the charred 

 cream of tartar in the tube before it was introduced into the furnace, 

 and watching the increase of light as the tube got hot, this band was 

 at first seen bright on a less bright background, it gradually faded, 

 and then came out again reversed, and remained so. No very high 

 temperature was required for this, but a rise of tem23erature had the 

 effect of widening the band. Besides this absorption, there appeared 

 a very indefinite faint absorption in the red, with the centre at a wave- 

 length of about 6,100, and a dark band, with a tolerably well-defined 

 edge on the less refrangible side, at about a wave-length of 4,850, 

 shading away towards the violet. A fainter dark band was sometimes 

 seen beyond, with a wave-length of about 4,645 ; but sometimes the 

 light seemed abruptly terminated at about wave-length 4,850. It will 

 be noticed that these absorptions are not the same as those seen when 

 potassium is heated in hydrogen, nor do they correspond with known 

 emission lines of potassium, although the first, which is also the most 

 conspicuous and regularly visible of these absorjDtions, is very near a 

 group of three bright lines of potassium. It seemed probable that 

 they might be due to a combination of potassium with carbonic oxide. 

 Potassium heated in carbonic oxide in glass tubes, united readily with 

 the gas, but the compound did not appear to volatilize at a dull red 

 heat, and no absorption, not even that which potassium gives when 

 heated in nitrogen under similar circumstances, could be seen. Induc- 

 tion sjDarks between an electrode of potassium and one of j^latinum 

 in an atmosphere of carbonic oxide, gave the usual bright lines of 

 potassium, and also a bright band, identical in position with the above- 



♦ With greater dispersion this liuc is seen as the sharp edge of a series of very 

 fiue Hues shading off towards the blue like the ordinary hydrcjcarbon spectrum. 



