150 



CALORIFIC POWER OF FUELS. 



GAS-COMPOSIMETER. 



The gas-composimeter of Uehling is an apparatus for 

 automatically and continuously determining the quantity of 

 carbonic acid contained in waste gases. 



It is based on the laws governing the flow of gas through 

 small apertures. 



FIG. 38. 



If two such apertures, A and B (Fig. 38), form respectively 

 the inlet and outlet openings of chamber C, and a uniform 

 suction is maintained in the chamber C' by the aspirator D, 

 the action will be as follows : 



Gas will be drawn through the aperture B into the cham- 

 ber C' , creating suction in chamber C, which in turn causes 

 gas to flow through the aperture A. The velocity with 

 which the gas enters through A depends on the suction in the 

 chamber C, and the velocity at which' it flows out through B 

 depends upon the excess of the suction in chamber C f over 

 that existing in chamber C, that is, the effective suction in C' . 

 As the suction in C increases, the effective suction must 

 decrease, and hence the velocity of the gas entering at A 

 increases, while the velocity of the gas passing out through B 

 decreases, until the same quantity of gas enters at A as passes 



