Hydrogen in the Oxyhydrogen Flanw. 375 



present, except in the part of the flame above the cone ; but 

 there is a gap in the cliannellings about Hp, so that line could 

 be seen easily if it were present. But I could not detect it. 



After such a series of negative results I can only come to 

 one conclusion, namely, that the temperature of the oxyhy- 

 drogen flame alone is not sufficient to cause hydrogen to emit 

 the rays we see produced by an electric discharge in that gas, 

 and that Pliicker must have mistaken some other rays for 

 those of hydrogen. What those rays probably were it is 

 almost impossible to say with the very scanty information he 

 has given. If the hydrogen he used were generated in the 

 gasometer, it may have had some fine spray of a zinc solu- 

 tion mixed with it. Such a spray in an oxyhydrogen flame 

 may, under favourable circumstances, give a spectrum of three 

 blue lines,of which the least refrangible is the strongest and has 

 a wave-length about 4810. A little zinc-ethyl in the hydrogen 

 gives them well. Pliicker does not say how he identified the 

 rays he saw with H a and Hp, but if he did not make a direct 

 comparison, and if his Babinet's goniometer had, as is probable, 

 only a single prism, it is possible that he might have mistaken 

 the zinc-line i'or Hp. An electric spark taken from a solu- 

 tion of zinc gives also a red line, but this line is not, so far as 

 I have observed, produced by zinc in any flame, so it will not 

 account for the line set down as H a . The only suggestion I 

 can offer for the red line is that it may have been the red line 

 of lithium. Lithium dust may easily have been present in 

 the laboratory, especially if a flame with lithium in it had 

 recently been employed ; and, as the dispersion of a single 

 prism in the red is but small, it is just possible that in a hasty 

 examination the lithium-line may have been mistaken for H a . 

 I am very unwilling to accuse such an observer as Pliicker of 

 the carelessness which is implied in the supposition that he 

 mistook the lithium-line for hydrogen, and should not think 

 of doing so if his whole account did not appear to be given 

 merely by the way in support of a theory which is not now 

 generally accepted. There remains the supposition that he 

 used, as Dibbits did, a jet of brass, or of some other metal, 

 which gave its own lines in the flame. 



Cambridge, Sept. 12, 1892. 



2D2 



