414 PRINCIPLES OF AGRICULTURAL CHEMISTRY 



This quantity of carbon, subtracted from 672.5 grams, leaves 

 649.7 grams carbon, which is contained in 849.3 grams of fat, 

 since beef fat contains 76.5 per cent, carbon. Hence this animal 

 gained 43.4 grams of flesh and 849.3 grams of fat per day : 



Apparatus to Determine the Carbon Balance. The respiration 

 apparatus 1 consists essentially of an air-tight chamber to hold the 

 animal, provided with a window and door and suitable openings 

 for the introduction of food and water. A current of air is 

 sucked through the apparatus by a ventilating fan connected with 

 a gas meter for measuring the volume of the air drawn through. 

 A portion of the air entering the chamber is sucked out by a 

 mercury pump and measured by a sma 1 ! gas meter. It then 

 passes through a series of tubes containing a solution of barium 

 hydroxide, of known strength, to absorb the carbon dioxide. 

 Barium carbonate is precipitated, and the excess of barium 

 hydroxide can be determined by titration with an acid of known 

 strength. The carbon dioxide may also be absorbed by soda lime 

 and weighed. This gives the amount of carbon dioxide in the 

 air subjected to analysis, and the total quantity contained in the 

 known quantity of air which passes through the respiration 

 chamber can be easily calculated. Another measured portion of 

 the air passes through a tube containing copper oxide, heated red 

 hot by means of a combustion furnace, and then through a sec- 

 ond series of barium hydroxide tubes. The marsh gas or other 

 organic carbon compounds are oxidized in the tube to carbon 

 dioxide, which is absorbed by the barium hydroxide as before. 

 We thus know the total quantity of carbon as carbon dioxide and 

 as organic carbon, which goes into the respiration chamber with 

 the air taken in. 



Measured portions of the air which goes out of the chamber 

 are withdrawn, and passed through an apparatus exactly similar 

 to that described above. The exact quantity of carbon in carbon 

 dioxide and in organic forms given off by the animal, is the 

 difference between that in the air which leaves and that which 

 enters the respiration chamber. 

 1 Exp. Station Record 10, p. 813. 



