710 Journal of Agricultural Research vol. vi, No. 18 



DETERMINATION OF THE QUANTITY OF HEAT PRODUCED 



The amount of heat resulting from the activity of the material in the 

 respiration chamber is ascertained from determinations of (i) the quan- 

 tity of latent heat in the water vapor of the outgoing water; (2) the quan- 

 tity of sensible heat absorbed and carried away by water flowing in a coil 

 of pipe in the chamber; and (3) the quantity of heat involved in changes 

 in the temperature of the active material and of other objects in the 

 chamber and also of the walls of the chamber. The gain or loss of sensible 

 heat through the walls or in the ventilating current of air is prevented. 



LATENT HEAT 



The quantity of water vapor carried from the chamber is determined 

 from the gain in weight of the first sulphuric-acid bottle in the absorber 

 train, as explained on page 706. If this quantity is multiplied by the 

 factor 0.586, the product will be the number of Calories of latent heat at 

 20 C. carried from the chamber in the water vapor of the outgoing air. 1 



SENSIBLE HEAT 



Sensible heat emanating from the active material is removed from the 

 chamber by a current of water flowing in a heat absorber, and the amount 

 of heat thus removed in a given period is determined from the weight of 

 water that flows through the absorber during the period and its tempera- 

 ture increase, with due allowance for the specific heat of the water at the 

 mean temperature of the flow as compared with that at the temperature 

 taken as standard. By controlling the rate at which water flows through 

 the heat absorber, or the temperature at which it enters the absorber, the 

 removal of heat is made to accord with its production, so that the tem- 

 perature of the air of the chamber is kept as closely as possible to that 

 which it is desired to maintain. 



The heat absorber consists of 15 m. of copper tubing of 3-mm. bore in a 

 double coil soldered to the upper and under surfaces of a piece of sheet 

 metal 38 cm. square, with a double loop of pipe about 80 cm. long extend- 

 ing downward from each edge of the sheet. The absorber is removable 

 and is slipped into position after the material under observation has been 

 packed in the chamber. When in position, it is suspended with the sheet 

 metal parallel to the ceiling of the chamber and about 25 mm. below it, 

 with the double loops extending down the sides of the chamber and about 

 25 mm. from them. 



REGULATING THE RATE OF THE WATER FLOW 



The water for the heat absorber flows from a constant level reservoir 

 on a shelf above the calorimeter chamber, which is supplied from a tank 

 on the lower shelf of the absorber table. The water that leaves the 

 absorber is returned to the tank, from which it is raised again to the 



1 Langworthy, C .F., and Milner, R. D. Op. cit., p. 315. 



