Chemical Instruments and Operations. 273 



a bell glass containing the gas over mercury, and duly draw- 

 ing out the rod, the orifice of the receiver being kept open 

 by pressing on the lever, only while above the surface of the 

 mercury, and inside of the bell. The gas thus taken into the 

 subsidiary instrument is next to be transferred to the princi- 

 pal one, which must in this case be placed over the mercurial 

 reservoir^ and be filled with mercury, the rod, V, being half 

 withdrawn from its tube. By moving the lever, D, a com- 

 munication must also be opened between the receiver, E, 

 and the reservoir, and the apex of the subsidiary eudiometer 

 must be introduced into a funnel-shaped cavity, with which 

 the cock, C, is furnished. The rod of the subsidiary instru- 

 ment 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 reser- 

 voir, and open that with the iron tube, t t ; also open the 

 cock, H. Then appealing to the gage, adjust the rod so 

 that the pressure of the included gas may be in equilibrio 

 with that of the atmosphere. An explosion is now to be ef- 

 fected ; after which, on opening the gage, if the cyanogen be 

 pure, there will be no condensation.* The residual gas, by 

 transfer to the receptacle, may be deprived of carbonic acid : 

 and the deficit, thus arising, may be measured by transfer- 

 ring what remains to the receiver, and ascertaining how ma- 

 ny measures the rod must enter, in order to eject it into the 

 air, or to return it into the receptacle. 



6. MODIFICATIONS OF THE EUDIOMETER, DESCRIBED IN THE 

 PRECEDING ARTICLE. 



The preceding figure represents another form of the shding 

 rod eudiometer, in which the apparatus for the removal of 

 carbonic acid is omitted. The gage in this eudiometer is 

 attached 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 



^ Before the explosion, two volumes of oxygen, and one of cyanogen, are 

 jsresent ; the latter comprising two volumes of carbon, and one of nitrogen. 

 During the inflammation, the carbon is transferred to the oxygen, without al- 

 tering it in bulk, while the nitrogen is set at liberty, uncondensed, so as to oc*- 

 cupy as much space as the cyanogen did previously. 



t See this Journal, Vol. xi. page 140. 



Vol. XV.— No. 5. 10 



