GAS SAMPLER. 



133 



is usually sufficient to cause a thorough mixing of the gases. 

 In case there are several dampers, the first one may be dis- 

 pensed with for the time being. 



When the gases are taken quite near the fire, they must be 

 drawn very slowly in order to gradually cool them down and 



FIG. 32. 



avoid dissociation. In this case a stoneware tube may be 

 used for suction. If this precaution is neglected the gases 

 collected may be entirely different from those passing off at 

 the chimney. Metal tubes are inadmissible, since they 

 abstract oxygen, and hence cause a change in composition. 



ANALYSIS OF THE GASES. 



The collected gases contain nitrogen, oxygen, carbonic 

 acid, carbonic oxide, hydrocarbons, and occasionally free 

 hydrogen. To determine all these a eudiometric method 



