Prof. J. P. Cooke on a new form of Eudiometer . 59 



is nitrogen. Hence it follows, since chlorine always combines 

 with its own volume of hydrogen, that ammonia contains only 

 one volume of nitrogen to every three volumes of hydrogen, 

 the point to be proved. To complete this series of illustrations, 

 it only remains to show that in ammonia-gas the four volumes 

 are condensed to two. For this pupose some dry ammonia-gas 

 is passed up into the eudiometer-tube as in fig. 9. The side 

 tube is then replaced as in fig. 7, the mercury-level adjusted, and 

 the position marked with a rubber ring. A stream of electric 

 sparks from a Ruhmkorff coil is now passed through the gas, so , 

 arranging the connexions that the sparks may traverse the whole 

 length of the gas-column ; and the amount of gas should be 

 small enough to render this possible. The decomposition pro- 

 ceeds somewhat slowly; but, after sufficient time, on readjusting 

 the level it will be found that the volume of the gas has doubled. 

 Besides the experiments described above, there are many others 

 to which these same forms of apparatus are applicable ; but these 

 •will suggest themselves to every teacher, and therefore it is not 

 necessary to enter into further details. 



Eudiometer. — The eudiometer described above, although ori- 

 ginally contrived for the lecture-table, has proved to be of still 

 greater value in the laboratory in all processes of gas-analysis 

 for which such an instrument is required. It is not only very 

 cheap, simple, and easily repaired, but also equally as accurate 

 as the most complicated apparatus. It can be used in a room 

 of the most variable temperature; for, by passing a current of 

 water or of steam, as the case may require, through the outer 

 tube, the temperature of the eudiometer-tube may be easily 

 maintained absolutely constant. The various gases are passed in 

 as shown in fig. 9, and through the same opening the reagents 

 used in the processes of analysis are readily introduced. By re- 

 placing the open tube, as in fig. 7, and bringing the two mer- 

 cury columns to the same level, the residual volumes may always 

 be read off under the atmospheric pressure and at a constant 

 temperature, indicated by a thermometer placed in the annular 

 space between the tubes. Or, on the other hand, by varying 

 the height of the mercury-column in the outer tube, we may reduce 

 the gas to the same volume and measure the difference of tension 

 according to the method of Reguault. This form of eudiometer 

 is especially adapted for the admirable methods of gas-analysis 

 devised by Bunsen. The absorbent balls used by him are most 

 readily introduced when the apparatus is arranged as shown in 

 fig. 9 ; and the volume of aqueous vapour formed after combus- 

 tion may easily be measured by replacing the current of cold 

 water through the outer tube by a current of free steam. In 

 this case it will be best to measure the gas under as great a dif- 



