VEGETABLE AND FRUIT DEHYDRATION 



159 



units. Before the sample is transferred to the Orsat apparatus, a 

 100-cc. sample of air is analyzed for oxygen. The result should be 

 close to 20.9 percent. The purpose here is to remove all oxygen and 

 carbon dioxide from the apparatus and to test for leaks. It is essen- 

 tial to have the gas burette buffered against temperature changes by 

 a water jacket, since otherwise changes in volume from one absorption 

 to the next will be affected by an unknown error. 



When gases low in carbon dioxide are to be analyzed, the residual 

 gas (nitrogen) in the burette is ejected to the zero mark; the sample 

 is then drawn in and analyzed. When the gas is high in carbon 

 dioxide, 50 cc. of the nitrogen is retained in the burette in order to 

 reduce the carbon dioxide concentration of the sample to be analyzed. 

 The gas sampling bulb G is connected with the intake of the Orsat, 

 a sample of gas (approximately 50 cc.) is taken into the burette A 

 and the reading is recorded. 



The carbon dioxide is absorbed by passage of the gas contents into 

 and out of the caustic potash pipette until constant volume is reached. 

 The burette reading is recorded. The volume of gas absorbed, multi- 

 plied by two, is the percentage of carbon dioxide present when a 

 sample of exactly 50 cc. is analyzed. Next the residual gases are 

 contacted similarly with the alkaline pyrogallol. This second loss in 

 volume, multiplied by two, is the percentage of oxygen. 



REHYDRATION TESTS 



Rehydration tests should be developed in each plant so that a daily 

 evaluation of the quality of the product can be made. The specific 



Figuee 69. — Equipment used in rehydration studies. Left to right 

 weighing, precise control of heating, and complete draining. 



Accurate 



procedure for these tests must be developed in each plant in order 

 that the equipment available, the amount of material to be tested, 

 and the complications of plant organization and management can be 



