Mr. Richardson on the Composition of Coal. 



403 



raised a little, and if the mercury retained its new level, the apparatus was 



considered tight. 



Cn.0 



CaO+*p 



si 



Mi x Turt 



WasAinfs 



i 



^VS 



The air was now measured, the temperature and barometer being noted 

 at the same time. The combustion was conducted in the usual way, the 

 water and carbonic acid were absorbed by the potash, while the azote forced 

 the receiver to rise. When the combustion was finished, the hydrate of 

 lime was heated slowly to redness, and the tube thus filled with aqueous 

 vapour, all azote and carbonic acid were completely driven out. The ap- 

 paratus was now allowed to cool, and the increase of volume in the receiver 

 denoted the quantity of azote in the substance submitted to analysis. The 

 precautions necessary to be taken are, viz. — that the mixture of the sub- 

 stance with oxide of copper must be most intimately made, and the com- 

 bustion proceeded with as slowly as possible ; also the pressure of the gas in 

 the receiver must be quite equable, otherwise, the tube will be either in- 

 creased or diminished in size, and consequently an incorrect result obtained. 

 The first ball in the tube containing the potash is to retain the condensed 

 vapour, which flowing back on the tube, would cause it to crack. 



By this method, the following results were obtained : — 



•2768 grm. Uric acid were submitted to analysis. 

 27°5 Barometer at the time of the experiment. 

 12° Thermometer at the time of the experiment. 



46-0 c c Air in the receiver before commencement. 

 120-0 c c Mixture of gas and air after cooling. 



76 c c Azote. 



