Chemical Instruments and Operations. 269 



\vhile the other is fastened to the insulated wire by means of 

 the gallows, z. To the rod which communicates with the 

 mercury, a piece of iron should be soldered so that the lead 

 need not be immersed, and consequently corroded. The 

 insulated wire, where it enters the cavity of the eudiometer, 

 is made air-tight by means of a small stuffing box. It is pro- 

 tected from the mercury within the receiver, by a covering 

 of twine, well soaked in, and coated with shell lac varnish. 



2. DETERMINATION OF THE QUANTITY OF CARBONIC OXIDE, IN 

 A GASEOUS MIXTURE, WHEN NO OTHER INFLAMMABLE GAS IS 

 PRESENT, BY THE IMPROVED MERCURIAL SLIDING ROD EU- 

 DIOMETER. 



In the first place the mixture must be well washed with 

 lime water, or a caustic alkaline solution, in order to remove 

 carbonic acid, if present. In the next place let us imagine 

 the bell glass, O N, after being adequately supplied over the 

 pneumatic cistern with equal measures of the purified mix- 

 ture and oxygen gas, has been transferred to the jar, I, con- 

 taining a sufficiency of water to displace the gaseous mixture 

 as required. 



In order to fill the receiver with gas, through the gage tube 

 and the pipe, Q,, by which it communicates with the gase- 

 ous mixture in the bell glass, the eudiometer must be filled 

 with mercury to the total exclusion of air, and the shding rod 

 wholly within its tube. Under these circumstances the spring 

 being pressed upon the apex of the receiver by the screw, G, 

 and the three cocks, H K O, being open ; on drawing out 

 the rod the receiver will be proportionally supplied from the 

 bell glass with the gaseous mixture. The receiver being 

 thus supplied, the cock, O, of the bell closed, and K, and H, 

 being open, on pushing the rod home, the gaseous mixture 

 driving the air before it through the interstices between the 

 gage tubes, will in part effect its escape, in part supply in the 

 tubes the place of the air which it has expelled. This pro- 

 cess may be repeated two or three times. After the atmos- 

 pheric air has, in this way, been removed from the apparatus, 

 the cocks between the bell and receiver being open, if the 

 rod be drawn out two hundred degrees, two hundred meas- 

 ures of the mixture, consisting of one hundred of each gas, 

 will enter the eudiometer. This being eflfected, the cock of 

 the bell must be closed. In consequence of the hydrostatic 

 pressure to which the gas will have been subjected in the 



