120 Dr. Hare on the Construction arid Applications of the 



By moving the lever D, a communication must also be opened 

 between the receiver E and the reservoir, and the apex of 

 the subsidiary eudiometer must be introduced into a tunnel- 

 shaped cavity, with which the cock C is furnished. The rod 

 of the subsidiary instrument being, under these circumstances, 

 pushed home, the gas must pass from it into the funnel-shaped 

 cavity, and thence rise into the receiver above it. When this 

 object has been effected, close the communication with the re- 

 servoir, and open that with the iron tube 1 1 ; also open the cock 

 H. Then appealing to the gauge, adjust the rod so that the 

 pressure of the included gas may be m equilibrio with that of 

 the atmosphere. An explosion is now to be effected ; after which 

 on opening the gauge, if the cyanogen be pure, there will be 

 no condensation*. The residual gas, by transfier to the re- 

 ceptacle, may be deprived of carbonic acid ; and the deficit 

 thus arising may be measui'ed by transferring what remains to 

 the receiver, and ascertaining how many measures the rod 

 must enter, in order to eject it into the air, or to return it into 

 the receptacle. 



Modifications of the Eudiometer, described in the preceding Article. 



The opposite figure represents another form of the sliding- 

 rod eudiometer, in which the apparatus for the removal of 

 carbonic acid is omitted. The gauge in this eudiometer is at- 

 tached to the cock of the receiver, instead of surmounting the 

 bell-glass. It answers equally well in either situation. 



If, instead of the bell and jar, a self-regulating reservoir of 

 hydrogen were attached to the flexible pipe, a convenient ar- 

 rangement would be obtained for ascertaining the proportion 

 of oxygen in the atmosphere. In that case the mode of ope- 

 rating would be as follows. The pipe and tubes of the gauge 

 being filled with hydrogen, and the receiver with mercury, 

 also the cocks H and O being open, draw out the sliding- 

 rod 50 degrees. A quantity of hydrogen, in bulk equivalent to 

 the part of the rod withdrawn, will pass from the reservoir 

 through the flexible pipe into the cavity of the receiver. The 

 cock O being shut, on appealing to the gauge it will be found 

 that the hydrogen, in consequence of the hydrostatic pressure of 

 the reservoir, will be a little denser than liin cqulUhrio with the 

 atmosphere. By relaxing the pressure of the screw G upon the 

 spring, as much hydrogen will escape as may be necessary to 



* Before the explosion, two volumes of oxygen and one of cyanogen 

 are present ; the latter comprising two volumes of carbon, and one of nitro- 

 gen. During the inflanunation, the carbon is transferred to the oxygen 

 without altering it in bulk, while the nitrogen is set at liberty, uncondensed, 

 so as to occupy as much space as the cyaniigcn did previously. 



produce 



