221 



enabling the operator to raise or depress the eudiometer at pleasure, 

 so as always to bring the gas which it contains to the same pressure 

 as the air in the pressure-tube. Both the eudiometer and the 

 pressure-tube are held in a perpendicular position by means of 

 clamps which slide on upright rods. Each clamp is provided with 

 a simple kind of slow movement, by which the tube can be raised or 

 lowered by the operator whilst he is looking through a horizontal 

 telescope, at a suitable distance. We place the pressure-tube in front 

 of the eudiometer, and by means of the fine adjustment bring the 

 column of mercury in the small tube exactly to the normal mark. 

 The eudiometer is then adjusted, also by means of the slow move- 

 ment, so that the top of its meniscus (as seen through the horizontal 

 telescope) exactly coincides with the top of the meniscus in the 

 pressure-tube. This is easily done ; for the diameter of the pressure- 

 tube is considerably smaller than that of the eudiometer, and the 

 meniscus in the latter can be clearly seen on both sides of the me- 

 niscus in the pressure-tube. 



By this method we are able to obtain very accurate results with 

 considerably less trouble than by Bunsen's method, and also without 

 having any calculations to perform. The following analyses made 

 during very stormy weather, of air deprived of its carbonic acid by 

 potash, gave results amongst which the greatest difference was only 

 four hundredths of a per cent. (*04). 



I. 



Volume of air taken . . . . 144*81 

 After addition of hydrogen . . 234-50 



After explosion 144-00 



Nitrogen . . . 79-168 

 Oxygen. . . . 20'832 



100-000 

 II. 



Volume of air taken .... 139'55 

 After addition of hydrogen . . 229'07 



After explosion 141*89 



Nitrogen . . . 79-176 



Oxygen. . . . 20-824 



100-000 



