274 Chemical Instruments and Operations. 



arrangement would be obtained for ascertaining the proper^ 

 tion of oxygen in the atmosphere. In that case, the mode 

 of operating would be as follows. The pipe and lubes of 

 the gage being filled with hydrogen, and the receiver with 

 mercury, also the cocks, H and O, being open, draw out the 

 sliding rod fifty 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 equivalent to the part of the rod withdrawn, will pass from 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 ihe 

 receiver. The cock, O, being shut, on appealing to the gage 

 it will be found that the hydrogen, in consequence of the 

 hydrostatic pressure of the reservoir, will be a little denser 

 than if in equilibrio with the atmosphere. By relaxing the 

 pressure of the screw, G, upon the spring, as much hydrogen 

 will escape as may be necessary to produce an equilibrium. 

 If while the cavity of the receiver is thus, in communication 

 with the atmosphere, the cock, H, being shut, the sliding rod 

 be drawn out 100 degrees further, so as to reach to 150 

 on the scale, 100 measures of air must enter. The pressure 

 ♦ of the screw, G, upon the spring, F, being restored, and an 

 explosion effected, agreeably to the directions already given, 

 by returning the rod into its tube, more or less, and appeal- 

 ing to the gage, the deficit may be ascertained. If no error 

 shall have taken place, expelling the residual gas will just 

 return the rod to the situation, which it occupied when the 

 experiment commenced. Of the deficit, of course, one-third 

 is due to oxygen. It may be proper to mention that some 

 delay is necessary, in order to permit the residual gas to part 

 with the heat, acquired from the combustion of the hydrogen 

 and oxygen. 



As for the analysis just described, the eudiometer may, as 

 represented in the preceding figure, be seated in a cup of 

 mercury, instead of being placed over a mercurial reservoir ; 

 and since the apparatus, when once put into operation, ena- 

 bles us to multiply experiments with great facility ; it will be 

 found peculiarly well calculated for a series of observations, 

 under circumstances in which access to a pneumatic cistern 

 cannot be had. 



7. Eudiometrical Apparatus analogous to the preceding^ ex- 

 cepting that it is constructed of Brass^ used with Water, 

 and that Explosions are caused in it by an Electric Sparh, 



In the analysis of atmospheric air, agreeably to the pro- 

 cess last described, no gaseous product being generated. 



