18 TIIK AKSUEITIOX AND KMISSION <>K All!. 



iind closed without trouble by simply turuiug the tube about its capillary axis. 

 Tbe absorbents used were phosphorus peiitoxide, sulphuiic acid, aud platiuuin black. 



There is a pheiioraeiioti which readily comes into play in the Paalzow-Vogcl 

 tubes which 1 regard as affording a moie certain proof that oxygen and hydrogen 

 combine under the electric spark 'even at a pressure of but a few millimeters: 

 niiniely, if such a tube be filled witli a mixture of the two gases, its initial bright- 

 ness rapidly falls off, and after a short time the tube fluoresces in the highest 

 degree. But the capillary shines forth more or less brightly. The only possible 

 explanation of this phenomenon is that, after oxygen and hydrogen have combined 

 to form water, this is promptly absorbed by the sulphuric acid, which affords a 

 relatively huge sui'face, and that there is consequently a great diminution of pres- 

 sure, giving rise to the fluorescence. The gases were not mixed by me in equivalent 

 proportions, so that, after the formation of the water, one or other must have re- 

 mained in excess, and this excess, enjoined with the ineradicable carbon monoxide 

 from the inq)urities of the tube, would occasion the light in the capillaries. But 

 although I followed these i)henomena spectrograph ically, I have never obtained the 

 lines which, in the other spectra of aqueous vapor, can be regaided as water-lines. 

 Still, a reason foi- the Paalzow-Vogel tubes not giving these lines may be found in 

 the circumstance that the vapor was too quickly absorbed by the sulphuiic acid to 

 give a si)ectrum for a sufficient time to make an image capable of being photogi-aphi- 

 cally developed. 



Ilydrofjen. — Armand Gautier found that this gas in the free state occurs in the 

 air ill no negligible [jroportion. I should, therefore, in any case, have had reason 

 to include it in the list of ingredients of the air here investigated. Besides that, it 

 affords me an admirable com[)arison spectrum. For none of the si^ectra with which 

 I have become acquainted beyond 185 fin has its energy so uniformly distributed 

 and such a wealth of lines as this. Nor is there any that extends so far as that of 

 hydrogen. 



The gas was produced fi-om the purest chemicals, sometimes chemically, some- 

 times electrolytically ; and moi-eover, whei-e it seemed necessary, it was most cai'e- 

 fully purified by sodium hydrate, silver sulphate, and potassium hj-drate. Particular 

 pains were taken in drying it; for the gas for the final experiments flowed through 

 three successive vessels, filled with phosphorus j)entoxide, with stopcocks in their 

 connections, in such a way as to remain for some time enclosed in each before it 

 was allowed to escape into the next. 



The transparency of hydrogen had appeared by my former expei'iments to be 

 uncommonly great. But my new experience has shown that it is a matter of great 

 difliculty to attain perfect definiteness on this point, since the production of thick 

 strata of pure hydrogen is well-nigh impossible. The walls of the place of absorp- 

 tion will, even with the most scru[)ulous cleansing, always at last secrete small 

 amounts of gaseous im[»urities; and these will affect the transparency of hydrogen 

 more propoitionately than they would that of other gases, precisely because its 

 transparency is so extraordin;ii'ily great. At any rate, it is in that way that I explain 

 the repeated contradictions in the results which 1 have obtained for the absorption 



