416 MM. Liebig and Gay-Lussac on [June, 



which is itself adapted, by means of a flexible lead pipe, c, to a 

 small receiver placed upon the plate ]) of an air-pump. 



On making a vacuum in the apparatus, the air carries with it 

 the vapour of water, and re-enters the tube containing the mix- 

 ture only when dried by the chloride of calcium. But in order 

 still better to separate the hygrometric moisture of the mixture, 

 the tube containing it is placed in a tube, d e, of greater diame- 

 ter, fitted with a perforated cork, and filled with water which 

 may be boiled. The vapour escapes by the tube, /, and the 

 water which condenses in it falls into the vessel g placed below 

 it. By alternately filling and exhausting the apparatus, it will 

 be granted that the mixture must lose all its hygrometric moist- 

 ure. With respect to other substances, the decomposition of 

 which there is no reason to fear at a temperature above 212°, 

 the tube containing the mixture may be heated in an acid or 

 saline solution, or in a bath of oil. The apparatus which has 

 been described requires no copper pipe; the joinings are all 

 made with cork, and when this substance is of a good quality, 

 the apparatus sustains a vacuum perfectly without the use of any 

 cement, or, at most, a little isinglass or tallow may be introduced 

 into the pores of the cork when it appears to have any. 



The mixture of fulminate of silver and oxide of copper being 

 perfectly dried, it is decomposed by the action of heat, and the 

 gases resulting from this decomposition are to be received ; but 

 as by the usual processes, it is difficult to ascertain their real 

 volume, we employed the following apparatus which gives it 

 immediately. 



This consists of a footed receiver, a b, fig. 2, into which 

 are cemented, one in a, and the other in b, two rings or collars 

 of cork, for the purpose of directing the small graduated receiver, 

 c, in its motion. The tube, d, which conducts the gases into the 

 graduated receiver, has two vertical and parallel branches, the 

 ascending one of which nearly touches the top of the graduated 

 receiver when it is in its lowest place, and then passes on the 

 outside of the graduated receiver between the two openings of 

 the cork rings. The plan of these rings is represented by fig. .'•}. 

 The footed receiver being filled with mercury, and the as- 

 cending branch of the conducting tube being placed in the 

 Graduated receiver, the latter is plunged in mercury, and the air 

 escapes gradually by the conducting tube. The receiver is 

 fixed in its first position, by supporting it from its summit 

 with a cork fixed in a wooden arm, b, moving along a ver- 

 tical stand, i, upon which it may be stopped at any situation 

 by a screw, k. The tube, m, containing the mixture, is then 

 adapted to the conducting tube, and the latter is confined in the 

 wooden vice of the support, /, the parts of which are made to 

 approach by means of a screw, and separate by their own spring. 

 The mercury in the graduated receiver is put exactly on a level 



