16 



BOILEE TESTS. 



injector and heater are used, the temperature is taken at the 

 tank and at the entrance to the heater, as well as at the entrance 

 to the boiler. To avoid breakage, the thermometer is placed 

 in a cup filled with oil, which is set in the pipe. 



The temperature of the escaping gases is determined in a few 

 cases by means of a pyrometer, the stem of which is wholly 

 exposed to the gases in the centre of the flue. In general, the 

 temperature is obtained by means of a high grade thermometer 

 set in an oil pot filled with cylinder oil, which is lowered into 

 the centre of the flue. The pot is withdrawn when the ther- 

 mometer is read. When a pyrometer is used, it is verified by 

 comparisons with a thermometer. 



The draught suction is determined by means of a U-tube 

 gauge, of the form shown in the appended cut, connected to 

 the flue between the damper and the boiler. The tube, which 

 is made of glass, is provided with enlarged 

 chambers at the top, arranged so as to 

 give a magnified indication of the vacuum 

 produced by the draught. The instru- 

 ment is filled with two liquids of different 

 color, one liquid occupying the whole of 

 one side of the instrument, and that part 

 of the other side to near the top of the U- 

 tube ; and the other liquid occupying the 

 remaining space in the U-tube and the 

 opposite chamber. When connection is 

 made to the flue (the proper side being 

 connected) the line of division between 

 the two liquids, which, owing to the dif- 

 ferences of color and character, is clearly 

 defined, moves downward in the tube and 

 shows by the distance traversed the mag- 

 nified amount of vacuum which is acting. 

 The amount by which the true indication 

 is multiplied depends' upon the relation 

 which exists between the diameter of the two chambers and 

 that of the two legs of the tube. An instrument which multi- 



