AND RATIO OF THEIR ATOMIC WEIGHTS. 107 



hydio^eu. I made five experiineiits, which show that a tube contaiiiiiig palhuliuiii 

 and filled witli hydrogen as in all my use of it, gives ott" no watei'. Tlie tube con- 

 taining six hundred grammes of palladium was chai'ged in the usual way, and then 

 connected with a U tube containing phosphorus pentoxide, Avhicli had been care- 

 fully weighed against a tube similar in shape and etpial in volume. The hydrogen 

 was expelled through the drying tube at the rate of not more than six litres an 

 hour, it being collected ovei' water to control the rate. This was repeated five 

 times. The drying tube showed the usual slight variations of weight from day to 

 day, but the weight did not increase. When two hundred litres had been passed 

 through it, the weight was the same as at first, and the algebraic sum of all the 

 slight variations during the course of the experiment was zero. It is obvious there- 

 fore that if palladiuiu is charged with hydrogen as in my experiments, it will give 

 off no watei'. 



15. SYNTHESIS OF WATER. IS OXYGEN ABSORBED BY THE PHOSPHORUS 



PENTOXIDE USED ? 



A source of error in the present series of experiments would exist, if the drying 

 tubes used were capable of absorbing oxygen in their ordinary use. If this were 

 the case, the drying tubes h, h. Fig. 36, would absorb oxygen, which would seem to 

 have been combined with hydrogen. But all the pentoxide used in these experi- 

 ments had been examined to determine whether it were suitable for the purpose. 



A drying tube filled with the [)eutoxide, a f>, Fig. 39, was fused to the short 

 arm of a syphon barometer lying on its side as seen. Pure diy oxygen was passed 

 into c, escaping at d, and these two tubes were 

 closed by fusion while the current was pass- 

 ing. The barometer was then set upright, and 

 securely fixed to a wall, so as to remain undis- 

 turbed for months. A tank of water was put 



so as to cover the drying tube, giving the Fig. 3g.— Apparatus for detecting absorption of 

 „ , • , 1 , , e ii oxygen by phosphorus pentoxide ; tilling; 



means ot knowing the temperature ot the gas. '^ "^ ^r^^ oxygen. 



A thermometer divided into fiftieths of a 



degree was placed in the water, and two other thermometers gave the temperature 

 of the column of mercury. The apparatus was set up in a basement room of tol- 

 erably constant tempei'ature. As soon as it was set up, I'eadiugs wei'e taken till 

 equilibrium was attained, when a split tube was fixed with its lower edge tangent 

 to the upper meniscus of the mercuiy, at e, Fig. 40. The reading having been vei'i- 

 fied several times, by warming or cooling the water till the mercuiy was again 

 tangent to the mark, the pressure of the enclosed oxygen was known. 



