(From a German Correspondent)
M. VON JOLLY, in Munich, has recently constructed an apparatus for gas-determination by absorption. Its arrangement is, in general, similar to that of Frank-land's apparatus, but it is distinguished from this, as from all other apparatus hitherto used for gas analysis, by the principle of measurement that is peculiar to it. Measurement is made, not of the changes of volume, which, for example, the air undergoes through absorption of carbonic acid and of oxygen, but of changes of pressure, the volume remaining the same. All the air-quantities to be measured are brought to the same volume, through corresponding change of pressure, in a measuring vessel, the contents of which must not be known; while a temperature of o° is produced by surrounding the measuring vessel with snow or ice. Thus, each time the tension is measured under which the air-quantity to be considered assumes that constant volume, before and after absorption of a portion of the mixture. This process has various advantages over those hitherto in use. The calculation of the gas-volumes at normal pressure and temperature is rendered superfluous; the number of separate observations required is diminished.