1888.] A new Form of Eudiometer. 387 



A slow contraction now takes place as the heat produced by the 

 explosion is radiated from the instrument ; it is advisable to wait 

 about twenty minutes, until the contraction is complete, and the 

 volume of the gas is read off under atmospheric pressure. 



The instrument should be sheltered from any draught, or from the 

 direct radiation of a fire, and indeed be kept from any change of 

 temperature, and with that object I find it advisable to shelter it with 

 a cardboard tubular shield sliding up and down the mercury trough. 



If air taken directly from the atmosphere is to be analysed, in order 

 to ensure its being saturated it will be advisable to pass it through a 

 tube full of wet horse-hair, and obtain it directly from the tube into 

 the eudiometer. In the above account of the manipulation required, 

 the hydrogen is introduced before the air into the eudiometer. I 

 have tried to .let in the air first, but this plan was not successful 

 apparently because the mixture of air and hydrogen was incomplete 

 before the explosion. The hydrogen being collected first in the 

 eudiometer will rise from its comparative lightness as the air is 

 drawn in and mix with it perfectly, w r hile the stream is sufficiently 

 rapid to prevent any of the mixture from diffusing out of the tube. 

 It should be borne in mind that after a number of analyses the water 

 resulting from the explosions accumulates on the surface of the 

 mercury in the eudiometer, and the mercury meniscus is no longer 

 clearly seen. This can be easily avoided by drying the tube with 

 filtering paper after a certain number of analyses. The following are 

 a few determinations of oxygen in atmospheric air made with the 

 form of eudiometer described above. They are not selected, but 

 given in succession in the order in which they were made. And I 

 must here beg to record the valuable aid of my assistant, Mr. Charles 

 F. Townsend, F.C.S., in the present inquiry. 



Oxygen per cent, in Atmospheric Air. 

 First Series. Second Series.* 



21-01 20 

 20-98 20 

 21 -00 20 

 20 -97 20 

 20 -97 20 

 20 



Mean . . 20 "99 20 

 Greatest difference, "2 per cent. 



93 

 96 

 95 

 93 

 95 

 96 



Mean . . 20 "946 

 Greatest difference, "14 per cent. 



* One analysis omitted : obviously too high from insufficient rinsing. 



