DECOMPOSITION OF WATER BY HEAT. 313 



error could have been but very trifling. The hydrogen so 

 obtained contracted in volume -^th ; hydrogen prepared in 

 the same way, and exposed to phosphorus, gave dense white 

 fumes ; the phosphorus was luminous in the dark for more 

 than an hour, and the contraction (temperature and pressure 

 being carefully examined) was g^th ; the amount of contrac- 

 tion by the wire would'of course equal three times the volume 

 of oxygen mixed with the hydrogen, consequently the oxygen 

 would be y^th of the whole volume ; the platinum wire 

 induces therefore a greater absorption of oxygen than the 

 phosphorus, unless the volume of hydrogen is increased by 

 the phosphoric vapour ; the sequel of this paper will render 

 it probable that even the ignited wire does not, and cannot 

 induce combination of all the oxygen existing in the hy- 

 drogen. 



I have looked into the papers of MM. Berzelius and 

 Dulong, and of M. Dumas, on the equivalent weight of 

 hydrogen. The latter contains a most careful experimental 

 investigation, and is by far the best determination we have ; 

 although it is not there mentioned that hydrogen contains 

 oxygen, yet a correction is made for the air contained in the 

 sulphuric acid employed. M. Dumas does not state how the 

 quantity of that air is calculated. There can be no question 

 that nothing approaching in elaborate care to these experi- 

 ments has been yet performed on the subject ; but, with the 

 fullest consciousness of M. Dumas' skill, I have, in all my 

 experiments, perceived such an inveterate tendency of hy- 

 drogen to possess itself of oxygen, that I cannot help enter- 

 taining some doubts whether we have yet the real weight of 

 hydrogen within the assigned limits of error. 



It is difficult to see how hydrogen can be absolutely 

 deprived of oxygen which has once existed in it ; neither an 

 oxidable metal, as zinc, or an ignited inoxidable metal, as 

 platinum, getting rid of all the oxygen, and phosphorus, if it 

 does so, replaces it by its own vapour. The near approach, 

 however, of the equivalent of hydrogen, as determined by M. 

 Dumas, to the ratio of whole numbers, renders it probable 

 that it is a very close approximation to the truth. 



I have not been able to detect nitrogen in the hydrogen, 



