improved Sliding-Rod Eudiometer and of the Volumescope. 173 



so as to graduate aboutfour inches of the tube into eight equal 

 parts. These parts were measured by introducing into the 

 tube previously filled with water one hundred measures of air, 

 from a sliding-rod gas measure, eight times, and marking the' 

 height of the water after each addition*. As each degree 

 thus indicated by the strips will be equal to 100 of those of the 

 sliding-rod, the whole may be considered either as comprising 

 eight hundred measures of the latter, or as eight volumes, each 

 divisible into 100 parts by means of the gas measure. 



The apparatus being so far prepared and the tube exhausted 

 of air so as to become full of water, close the cock leading to 

 the air-pump, introduce two volumes of pure hydrogen, and 

 one volume of pure oxygen, which may be most conveniently 

 and accurately effected by the sliding-i-od gas measure. The 

 plates of the calorimotor being in the next place excited by 

 the acid, the ignition of the platina wire ensues, and causes the 

 hydrogen and oxygen to explode. When they are pure, the 

 subsequent condensation is so complete, that the water will pro- 

 duce a concussion as it rises forcibly against the leathern disk, 

 which, aided by the mahogany block, has been represented as 

 closing the upper orifice of the tube. 



If the preceding experiment be repeated with an excess of 

 either gas, it will be found that a quantity equal to the excess 

 will remain after the explosion. This is very evident when 

 the excess is just equal to one volume, because in that case 

 just one volume will remain uncondensed. By these means, a 

 satisfactory illustration is afforded of the simple and invariable 

 ratio in which the gaseous elements of water unite, when mixed 

 and inflamed ; which is a fact of great importance to the atomic 

 theory, and to the theory of volumes. 



Application of the Volumescope to the Illustration of the Ratio^ 



in "which Nitric Oxide, and the Oxygen in Atmospheric Air, 



are condensed by admixture. 



The tube being filled with water by exhausting it of air, as 

 in the preceding experiment, let five volumes of atmospheric 

 air be introduced into it. Afterwards by means of a volume- 

 ter or sliding-rod gas measure, add at once three volumes of 

 nitric oxide. In the next place fill the syphon S Y, (fig. 4.) and 

 the caoutchouc bag attaclicd to it, with water, and pass the leg 

 Y up through the bore of tlie eudiometer-tube ; then by al- 

 ternate pressure and relaxation, the water may be propelled 

 from the bag, through the syphon into the gaseous mixture, 

 so as to accelerate the absorption. 



If in five volumes of atmospheric air there be one of oxygen 



» Sec Phil. Mag. and Annals, vol. v. p. 129. 



gas, 



