Chemical Instruments and Operations. 271 



Fig. 2. — subsidiary eudiometer. 



4. OP THE USE OF THE SUBSIDIARY EUDIOMETER. 



It may sometimes happen that the quantity of gas to be 

 examined may be too small to be measured into the bell glass 

 by a volumeter, as above described. In that case, a subsi- 

 diary eudiometer is employed. Excepting that it is shorter, 

 the rod, in this instrument, has precisely the same dimen- 

 sions 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, may be 

 learned from my memoirs, vol. x, page 67, of this Journal."^ 



5. 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 

 principal eudiometer, the manipulation being the same as 

 above described in the case of the mixture. In the next 

 place, the subsidiary eudiometer must be supplied with one 

 hundred measures of cyanogen, by introducing the apex into 



* To prepare the instiument and prove it to be in order, depress the glass 

 receiver below the surface of the mercury in the pneumatic cistern, the cap- 

 illary orifice being uppermost, and open ; draw the rod out of its tube, and re- 

 turn it alternately, so that at each stroke, a portion of mercury may pass in, 

 and a portion of air may pass out. During this operation, the instrument 

 should be occasionally held in such a posture, as, that all the air may rise into 

 the glass recipient, without which its expulsion, by the action of the rod, is 

 impracticable. Now close the orifice, (at the apex A,) and draw out a few 

 inches of the rod, in order to see whether any air can enter at the junctures, 

 or pass between the collar of leathers and the sliding rod. If the apex be held 

 uppermost, any air which may enter will occupy a greater or less space near 

 the orifice, so as to prevent the mercury from entering that space, when the 

 rod is returned to its previous position. 



