THE CALORIMETER SYSTEM. AND MEASUREMENT OF HEAT. 153 



to warm up this wall. Conversely, if there be a fall in temperature, 

 it is possible that the reverse may result. 



Inasmuch as with experienced observers the variations in tempera- 

 ture are very slight, and as the press of experimental work has pre- 

 vented our making further determinations of the hydrothermal equiva- 

 lent, we have used in all the investigations so far the results of an 

 experiment published 1 in 1899. In this test the calorimeter was held 

 at a constant temperature for several hours ; a small electrical current 

 was then passed through a resistance coil in it for two hours. During 

 this period of time especial pains were taken to keep the thermal junc- 

 tion circuits in the metal walls at equal temperatures, and as a result, 

 since no heat was allowed to pass through the walls, the temperature 

 of the calorimeter slowly rose. At the end of two hours the current 

 was stopped and the calorimeter allowed to assume a constant tempera- 

 ture. From the rise in temperature and the amount of heat generated 

 by the electric current, it was calculated that the apparatus required 

 about 60 large calories to raise its temperature i ; hence its hydro- 

 thermal equivalent is not far from 60. 



The true significance of this factor is becoming less and less each year 

 as the experimental skill of the manipulators increases. It is our pur- 

 pose, however, to repeat these tests, and consider a fall in temperature as 

 well as a rise in determining exactly the hydrothermal equivalent of the 

 apparatus. Suffice it to say that for the fluctuations ordinarily occur- 

 ring in experimental apparatus, it is known with sufficient accuracy. 



An attempt has been made to calculate the hydrothermal equivalent 

 from the weight of the different parts of the apparatus ; but, as these 

 weights were not taken at the time the apparatus was constructed and 

 the quantity 'of wood, solder, etc., involved in the framework is not 

 definitely known, these results are not at present available for use. 



CORRECTIONS FOR TEMPERATURE OF FOOD AND DISHES. 



In order to compute the total income and outgo of heat from the cal- 

 orimeter system, it is necessary to know the temperature of all articles 

 passed into or taken out of the calorimeter chamber. If the food, drink, 

 and dishes going into the chamber are below the calorimeter temper- 

 ature, there will be a certain amount of heat absorbed in warming the 

 material to the temperature of the chamber; and, conversely, if any of 

 the materials are warmer than the interior temperature, they will grad- 

 ually radiate heat until they assume the temperature of the calorimeter. 

 Similarly, if material is passed out of the chamber at a higher or lower 

 temperature, there is a loss or gain of heat. 



1 U. S. Dept. of Agr. , Office of Experiment Stations Bull. 63, p. 44. 



