upon the Composition of Coal. 123 



with oxide of copper, washings* of the same, a further quan- 

 tity of oxide of copper, and lastly slips of metallic copper. 

 The shaded part of the tube b was filled with hydrate of 

 potash. 



The whole apparatus being arranged, the receiver d was 

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

 apparatus was considered air-tight. The air in the receiver d 

 was now measured, the temperature and barometer being noted 

 at the same. The combustion was conducted in the usual 

 way, the water and carbonic acid were absorbed by the pot- 

 ash, while the azote forced the receiver to rise. When the 

 combustion was finished, the hydrate of lime was heated slowly 

 to redness, and the aqueous vapour thus formed drove out all 

 carbonic acid into the tube of absorption. The apparatus was 

 now allowed to cool, while the aqueous vapour condensed, 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 the following : — 

 The mixture of the substance with the oxide of copper must 

 be most intimately made, and the combustion proceeded with 

 as slowly as possible; the pressure of the gas in the receiver 

 must also be quite equable, otherwise the tube of combustion 

 will be either increased or diminished in size, and consequently 

 an incorrect result obtained ; the heating of the hydrate of lime 

 must be gradually performed ; and care must be taken on the 

 cooling of the apparatus that the condensed vapour which 

 flows back be retained in the first ball of the tube of absorp- 

 tion, which is blown for this purpose. 



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. 



^G'O cc ... Air in the receiver before commencement. 

 120*0 cc ... Mixture of gas and air after cooling. 



76*0 cc ... Azote. 



76 cc azote reduced to 0° thermometer, and 28° barometer, 

 give 70*4 cc which is equal to 32'24 per cent. From the ana- 

 lysis of Liebig, this acid contains 33*36 per cent., so that there 

 is a loss of 1*12 per cent. 



The analysis was repeated, but the loss was nearly the 

 same. 



* By washings I mean the oxide of copper employed in cleaning out the 

 mortar wherein the mixture of the substance has been made. 



