THE CALORIMETER SYSTEM AND MEASUREMENT OP HEAT. 133 



Check measurements of the accuracy of the meter. From time to time 

 the accuracy of the meter is checked by direct weighing. By means 

 of the pot and funnel mentioned above, this check is very readily and 

 rapidly carried out. Usually, one weighing of the water delivered from 

 each can is all that is required. With the weighing, the reading of the 

 pointer is taken and the weight actually observed, then directly com- 

 pared with the weight as indicated by the curve. The meter has been in 

 use for two years and has given excellent satisfaction. 



THERMOMETERS FOR MEASURING TEMPERATURE o* WATER. 



The temperature of the water for absorbing heat is measured as it 

 enters and as it leaves the chamber. The thermometers used for these 

 measurements are seen in the small closet on the front wall of the cal- 

 orimeter, at the left of the observer's table, in figure 37. The method of 

 installing them in the water-pipes may be seen in figure 32. 



These thermometers are of special form. They are L-shaped, with 

 one arm 52 cm. long and the other 36 cm. long. The arm with the 

 mercury bulb is inserted in the water-pipe, extending through the 

 wooden plug (N, N, in fig. 32), the length of the arm being such that 

 the bulb comes directly under the upright pipe that conducts the water 

 to or from the heat-absorber. By this provision the temperature that 

 affects the mercury in the bulb is that of the water just as it enters or 

 just as it leaves the chamber. 



The graduations on the other arm of the thermometer begin just above 

 the betid and extend to near the end of the arm. The thermometer 

 used to determine the temperature of the ingoing water is graduated 

 from zero to 12 in fiftieths of a degree. The 12 degrees of the grad- 

 uation cover a section of the stem 420 mm. long, thus allowing 0.70 mm. 

 for each one-fiftieth degree, or 0.35 mm. for each one-hundredth degree. 

 Readings can be taken accurately without the use of a lens to one- 

 hundredth of a degree. The thermometer for the temperature of the 

 outgoing water is graduated from 8 to 21. As the temperature of 

 the calorimeter chamber, especially in the summer time, frequently goes 

 above 21, an enlargement of the capillary is made at the top of the 

 thermometer to permit of the expansion of the mercury without danger 

 of breaking the instrument. 



The thermometers have been very carefully calibrated twice each year, 

 and although the zero points changed slightly at first, they have appar- 

 ently now become fixed. The readings of the two thermometers were 

 compared with those on a metastatic thermometer of the Beckmann type, 

 manufactured by Fuess and calibrated by the Physikalisch-technische 

 Reichsanstalt, of Charlottenburg, Germany. 



