198 



Journal of Agricultural Research 



Vol. Ill, No. 3 



Table V. — Composition of detached bananas during ripening in tlie humidity chamber- 

 Continued 



COMPOSITION EXPRESSED IN TERMS OF PERCENTAGE OF THE WHOLE GREEN BANANAS — COntillued 



In order to determine correctly the respiration rate at interv'als on 

 ripening, it was necessar}' to collect the carbon dioxid evolved during 

 relatively short periods. 



The bananas were placed in a tubulated desiccator, kept in the dark 

 at 20° C, and a rapid current of air passed through. The air was first 

 freed from carbon dioxid by passing it through a long wide glass tube 

 filled with soda lime. The carbon dioxid evolved by the bananas was 

 collected by drawing the air from the desiccator through a Reiset scrub- 

 bing tube containing soda solution. The Winkler method of titration of 

 the absorbed carbon dioxid was employed. 



In operating the flask of the Reiset apparatus was charged with a 

 mixture of 500 c. c. of distilled water and 100 c. c. of an approximately 

 normal solution of sodium hydroxid. The distilled water had pre\dously 

 been well aerated to remove carbon dioxid, and the titer of the soda 

 solution (after addition of barium chlorid to precipitate carbonates) was 

 known. After mixing, the Reiset tube was inserted, comiection made 

 with the desiccator containing the bananas, and suction applied. After 

 absorption, the contents of the Reiset apparatus were washed into a large 

 precipitating jar with aerated distilled water, excess of barium chlorid 

 added, and the solution titrated with normal hydrochloric acid, using 

 phenolphthalein as indicator. Each cubic centimeter of normal alkali con- 

 sumed equals 0.022 gm. of carbon dioxid. In titrating it was necessary 

 to admit the acid under the surface of the solution and stir well to avoid 

 escape of carbon dioxid freed by local momentary excess of acid. As the 

 amounts of carbon dioxid expected were approximately known it was 

 found convenient to use a slight excess of solution of barium chlorid of 

 such strength that each cubic centimeter decomposes i c. c. of normal 

 sodium carbonate.' 



Lead tubes were used in leading the air to and from the desiccator. 

 The air entered it near the top and was withdrawn from near the bottom. 



' For a criticism of volumetric methods of estimation of carbon dioxid, see Kuster (15). 



