344 Journal of Agricultural Research 



TESTS OF THE ACCURACY OF THE RESPIRATION CALORIMETER 



At frequent intervals the accuracy with which the respiration calorim- 

 eter will function is tested by burning ethyl alcohol in the chamber in 

 such manner as to insure complete combustion and measuring with the 

 apparatus the amounts of oxygen consumed and of carbon dioxid, water 

 vapor, and heat produced. Commercial alcohol, pure in quality and 

 containing about 90 per cent of ethyl hydroxid, is satisfactory for the 

 purpose. The actual percentage is ascertained from determination of 

 the specific gravity of the alcohol. The amount of oxygen that would 

 be required to bum i gm. of the commercial alcohol, and the amounts 

 of water vapor and carbon dioxid that would result from the combustion, 

 are computed from the chemical equation for the reactions occurring 

 in the combustion of ethyl hydroxid, with allowance for the water present 

 in the sample burned. The heat of combustion of ethyl hydroxid at 

 constant pressure is taken as 7.08 Calories per gram. 



The burner used in these experiments was made of two concentric 

 tubes of thin brass 5 cm. in length, the outer tube being 18 mm. in ex- 

 ternal diameter. At the lower end each tube is soldered to a brass ring, 

 which provides an annular space between them 3 mm. wide, in which is a 

 wick of asbestos; and as the inner tube is open at both ends, there is a 

 center draft for the flame. No products of incomplete combustion have 

 been found in the air of the chamber during a test in which alcohol was 

 burned with this burner. 



The burner is soldered to one end of a piece of 4-mm. copper tubing, 

 the other end of which passes through the wall of the chamber to the 

 alcohol supply outside, from which the burner is fed in such manner that 

 the rate of consumption is uniform. Attached to the outer end of the 

 copper tube is an elbow of 4-mm. glass tubing, with a side outlet in the 

 vertical arm to provide for an overflow. The height at which this outlet 

 is set with relation to the top of the burner governs the rate of consump- 

 tion of the alcohol. The level having been fixed, alcohol is fed into the 

 vertical tube so that some of it will drop regularly from the outlet. The 

 rate of combustion in the chamber is then very constant. The overflow 

 alcohol is caught in a small bottle, which is weighed with the supply flask 

 at the end of each period, the loss in weight of both containers showing 

 the quantity of alcohol tfnrned. The connection between the overflow 

 bottle and the outlet and also that between the supply flask and the feed 

 tube are such that the loss of alcohol by evaporation is negligible. 



The results of alcohol check tests of the respiration calorimeter indi- 

 cate that the determinations made with it are at least suflSciently 

 accurate for investigations of the character in which it is used. This 

 is shown by the data in Table II, which summarizes the results of two 

 tests selected from many equally good. 



In November, 191 3, in a 3-hour period, 56.3 gm. of commercial alcohol 

 containing 88.32 per cent of ethyl hydroxid were burned to test the 



