48 A RESPIRATION CALORIMETER. 



peratureof 17.89 and then through a weighed U tube containing pumice 

 stone and sulphuric acid. 



Air saturated with water vapor at 760 mm. and 17.89 contains 

 0.01513' gram of water per liter. 



In this test the air when passed through the meter contained o. 3055 

 gram of water vapor in 20.103 liters apparent volume or 20.42 liters 

 corrected volume. This corresponds to 0.3055 -^ 20.42 = 0.01496 gram 

 of water vapor per liter an agreement inside of the error of experi- 

 mentation. It is assumed, therefore, that the air passing through the 

 meter is saturated with water vapor. 



APPARATUS FOR DRAWING SAMPLE. 



Obviously, with the closed circuit, it would be undesirable to remove 

 from the system so large a sample as 10 liters of air at the end of every 

 two hours. By means of the apparatus shown in figure 19, it is possi- 

 ble to draw as large a sample of air as is desired through the U tubes, 

 remove from it carbon dioxide and water vapor, and return it to the 

 system dry, free from carbon dioxide, and diminished in volume only 

 by the volume of the carbon dioxide and water vapor removed by the 

 absorbents. 



The apparatus consists of a glass suction-pump A, a separating cham- 

 ber B, in which the air and the water used for aspiration are separated, 

 and the drying chamber D, in which the water vapor taken up by the 

 dry air from the water-pump is removed before the air is returned again 

 to the system. The sample of air after leaving the U tubes passes 

 through the Elster meter (see fig. 18) and then enters the suction- 

 pump at the tube a. As the air and water issue from the glass exten- 

 sion tube they strike against the side of the separating chamber B. 

 The water flows through the overflow c into the drain d. The air 

 passes out through the enlarged tube c, bubbles through concentrated 

 sulphuric acid in the drying chamber D, and finally passes through 

 the small tube/ back into the air system. It has been found by repeated 

 experiment that i o liters of air saturated with water vapor at the tempera- 

 ture of the laboratory, i, c. , 20, passing through the drying chamber 

 in three or four minutes, will be completely freed from water vapor. 

 The acid in the chamber is replenished from time to time by removing 

 the central stopper and withdrawing the acid by suction. 



Two valves, ze> 3 and w^ are used to admit water to the suction-pump. 

 The valve w^ is permanently adjusted so that the supply of water pass- 

 ing through the pump will be that best fitted for drawing the sample 



1 Smithsonian Meteorological Tables (1897), p. 133. 



