improved Sliding-Rod and of the Volumescope. 119 



carbonic acid. In order to insure a competent supply of oxy- 

 gen, four volumes of it may be mixed with one of the olefiant 

 o-as in the bell-glass, and the same manipulation resorted to 

 as in the case of carbonic oxide, excepting that before the ex- 

 plosion, the rod V must be drawn out to the greatest extent; 

 and that as soon as the explosion has taken place, the rod must 

 be returned into the tube, so as nearly to compensate the con- 

 densation before resorting to the gauge. 



Fig. 2. — Subsidiari] Eudiometer. 



Of the Use of the Stidsidiary Eudiometer. 



It may sometimes happen that the quantity of gas to be ex- 

 amined may be too small to be measured into the bell-glass by 

 a volumeter, as above described. In that case, a subsidiary 

 eudiometer is employed. Excepting that it is shorter, the rod 

 in this instrument has precisely the same dimensions as in that 

 described in the preceding article ; and the graduation in both 

 is exactly the same. The use of the spring and lever, also 

 the method of manipulation, has been described in Phil. Mag. 

 vol. bcvii. page 21. 



Analysis of Cyanogen. 



Let us suppose it were an object to ascertain the products 

 which result from the combustion of a volume of cyanogen. 



A quantity of oxygen gas amply sufficient for the intended 

 experiments must be introduced into the bell-glass N, (fig. 1.) 

 and two hundred measures drawn into the receiver of the prin- 

 cipal eudiometer, the manipulation being the same as above 

 dccribed in tiie case of the mixture. In the next place the 

 subsidiary eudiometer must be supplied with 100 measures of 

 cyanogen, by introducing the apex into a bell-glass contain- 

 ing the gas over mercury, and duly drawing out the rod, the 

 orifice of the receiver being kept open by pressing on the 

 lever, only while above the surface of the mercury, and inside 

 of the bell. The gas thus taken into the subsidiary instru- 

 ment is next to be transferred to the jirincipal one, xcliicli viuxt 

 in this case be placed over the mcrctiriid reservoir, anil be filled 

 with mercury, tiic rod V being half witlidrawn from lis tube. 



By 



