davy's eudiometer.

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diuum diminished by gives us the bulk of the nitrogen gasof the air examined; which bulk subtracted from the originalmass of air, gives us the proportion of oxigen gas containedin it. The same allowance must be made in the eudiometer ofSeguin.

7 . DAWs EUDIOMETER.

Until very lately the preceding processes were the methodsof determining the relative proportions of the two gases whichcompose our atmosphere.

Some of these methods though very ingenious are so ex-tremely slow in their action, that it is difficult to ascertain theprecise time at which the operation ceases. Others have fre-quently involved inaccuracies, not easily removed.

The eudiometer we are now going to describe, is not only freefrom these objections, but the result it offers is always con-stant, it requires little address, and is very expeditious ; the ap-paratus is portable, simple and convenient.

Take a small glass tube graduated into one hundred equi-dis-tant parts; till this tube with the air to be examined, and plungeit into a bottle or any other convenient vessel, containing a con-centrated solution of green muriate or sulphate of iron, stronglyimpregnated with nitrous gas. All that is necessary to be doneis to move the tube in the solution a little backwards and for-wards ; under these circumstances the oxigen gas contained inthe air will be rapidly absorbed, and condensed by the nitrousgas in the solution, in the form of nitrous acid.

N. B. The state of the greatest absorption must be marked,as the mixture afterwards emits a little gas which would alterthe result.

This circumstance depends upon the slow decomposition ofthe nitrous acid (formed during the experiment), by the greenoxid of iron, and the consequent production of a small quantityof aeritorm fluid (chiefly nitrous gas) ; which having no affi-

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