1 824. J Fulminate of Silver. 4 1 7 



with that which forms the bath, and the volume of air in the gra- 

 duated receiver is noted, as well as its temperature. When the 

 mixture is decomposed, the gases which are evolved depress the 

 mercury in the graduated tube ; but by properly shifting the 

 wooden arm along its support, the mercury is maintained at 

 nearly its original level, it being continually added to fill the 

 space which the receiver leaves by rising out of the bath. When 

 the decomposition is finished, the fire is removed, and when the 

 apparatus is cooled, the mercury is brought to the same level in 

 the receiver and in the bath, and the temperature is noted. It is 

 evident that the volume of air contained in the graduated 

 receiver, after the operation, less than that which existed 

 there before it, indicates exactly the volume of the gases which 

 result from the decomposition, the corrections for temperature 

 and barometric pressure being made ; but as the whole of the 

 operation continues at most but half an hour, it is seldom requi- 

 site to make any corrections. 



The water which is formed during the decomposition of an 

 hydrogenous substance by the oxide of copper, is usually col- 

 lected by causing it to pass over chloride of calcium contained 

 in a tube placed between the conducting tube and that which 

 contains the mixture ; but the following arrangement, which 

 consists in introducing the chloride of calcium into the same tube 

 as that in which the decomposition is effected, has appeared to 

 us to be preferable. 



We take a very small tube, w, fig. 4, the external diameter of 

 which is nearly equal to the internal diameter of the tube, m, 

 containing the mixture ; to this a small tube, o, is attached by 

 melting them together, and it is made to pass tightly through 

 the tube, m, and after having filled it with chloride of calcium, 

 it is drawn to a point at the other end, p, leaving only a small 

 aperture. Having noted the weight, it is to be placed in the 

 tube, m, as shown by fig. 2 ; the gases have then no other pas- 

 sage for escape but over the chloride of calcium, and they then 

 deposit their moisture. When the mixture is introduced into the 

 tube, m, care must be taken to leave an empty space, m s, below 

 the upper side of the tube, that it may not be projected forward 

 by the gases at the moment of their expulsion. Lastly, it has 

 been often recommended to use a spirit-lamp to effect the 

 decomposition of the mixture; but we find it to be much more 

 convenient to place the naked tube upon a grating of iron wire, 

 supported by a furnace, the door and ash-hole of which are kept 

 shut, and to surround it with red-hot charcoal occasionally added. 

 This method also possesses the advantage of enabling us to heat 

 the whole of the tube in every part at the same time, and with a 

 little practice, it is easily rendered of a dull red heat, without any 

 risk of softening it. 



The process of analysis by oxide of copper being very well 

 New Series, vol. vu. 2 e 



