WASTE GASES BY THE ANEMOMETER. 143 



Prof. Jacobus recommends the use of the formula 



;N 

 Pounds of air per pound C = ,~^ . ~^ -r- 0.77 ; 



and in the case given above, where the actual quantity used 

 was 15.414 per cent, his calculated one is 15.434 per cent, 

 practically the same, and as near as errors of analysis would 

 allow a calculated result. 



VOLUME OF WASTE GASES BY THE ANEMOMETER. 



The fan-wheel anemometer is an instrument to measure 

 the force or rapidity of a current of gas. It consists of a 

 fan-wheel rotated by the moving gas, and which transmits 

 such motion to an index showing the number of revolutions. 

 Burnat used this apparatus to measure the quantity of air 

 passing in under the grate of steam-boilers. 



The coefficient to be used in calculating the flow is differ- 

 ent for each machine, and must be determined by actual 

 experiment. Burnat's formula, 



V = O. I2O -j- O. I3O7Z, 



means that the velocity is found by multiplying the number 

 of revolutions per second by 0.130 and adding 0.120 to the 

 product. 



To obtain satisfactory results with the anemometer, it 

 must be placed in the axis of a perfect cylinder at the depth 

 of a metre, as the indications vary with the position in the 

 flue. The formula needs correction for temperature, but the 

 correction of the apparatus much exceeds this. Burnat com- 

 pared his results with those obtained from a formula depend- 

 ing on the depression if under the grate (see page 147), and 

 found differences of not more than 5 per cent. 



