VEGETABLE AND FRUIT DEHYDRATION 157 



point is obtained if it is too high. The acetone complex is unstable, and the 

 titration must be conducted in the range of pH 1.8 to 2.6, where, in these 

 cabbage tests, the complex shows greatest stability. Therefore both the 5 N 

 NaOH and the 5 N HG1 should be added by pipettes rather than from graduated 

 cylinders. 



Analysis of Atmosphere in Cans of Dehydrated Vegetables 



In plants where dehydrated vegetables are gas-packed in accordance 

 with purchasing specifications, a method of analyzing the atmosphere 

 of the packed cans is useful. Figure 68 shows a gas-sampling assem- 

 bly, a can-puncturing device, and an Orsat gas-analysis apparatus. 



The base of the gas-sampling assembly is a steel plate 12 x 12 x % 

 inches. Two metal rods of %-inch diameter (B) are screwed into 

 the base. A wooden base of hardwood can be substituted, with lock 

 nuts on the rods to fasten them firmly to the base. The metal rod (C) , 

 which carries the puncturing device, is held in position by the clamp 

 holders (D) and can be raised or lowered to any suitable height. 



The can-puncturing device consists of a threaded tee (E), which 

 supplies the force required to puncture the can, and the puncturing 

 device proper, (F) . These are also shown in detail. Glass capillary 

 tubing (2-mm. bore) connects the can-puncturing device to a gas- 

 sampling tube (G) of approximately 300-cc. capacity. This tube is 

 connected by rubber tubing to a leveling bulb (H) containing mercury. 

 All necessary stopcocks are shown in the diagram. As a substitute 

 for mercury, a solution made up in the ratio of 10 gm. of anhydrous 

 sodium sulfate, 40 gm. of water, and 2 cc. of sulfuric acid, with the 

 addition of some methyl orange indicator can be used. 



Figure 68 also shows (upper left) a portable Orsat gas- analysis 

 apparatus, consisting of a gas burette (A) enclosed in a water jacket 

 (B), absorption pipettes (0 and D) for carbon dioxide and oxygen, 

 respectively, and a leveling bottle (E) filled with a confining liquid 

 of the same composition described above as a substitute for mercury. 

 All necessary stopcocks are shown, and the apparatus is enclosed in 

 a wooden case (F). Other types of gas-analysis apparatus are also 

 suitable. 



A commonly used stock solution for the preparation of absorbents 

 for carbon dioxide and oxygen consists of 800 gm. of potassium hydrox- 

 ide per 1,000 cc. of solution. For carbon dioxide, the stock solution is 

 diluted with water in the ratio of 100 cc. of stock to 60 cc. of water. 

 Ordinarily the absorption pipettes have a capacity of 160 to 180 cc. 

 of solution. To make up the alkaline pyrogallol solution for oxygen 

 determinations, ascertain how much solution will be required to fill 

 one leg of the pipette and about a quarter of the other leg. In the 

 oxygen absorption pipette (D), allow for the use of a half -inch layer 

 of mineral oil (U. S. P.) to be used on the surface of the open side of 

 the pipette. Now add the calculated amount of caustic potash solu- 

 tion from stock to the open side of the pipette. On top of that solution 

 add a half-inch layer of the oil. The pyrogallol required is in the 

 ratio of 15 gm. of pyrogallol to 100 cc. of stock caustic solution. Dis- 

 solve the pyrogallol in two-thirds of its weight of hot water, place 

 a long-stemmed funnel in the pipette with the tip below the layer 

 of oil, and run the pyrogallol solution into the caustic. The oil pre- 

 vents rapid oxidation of the alkaline pyrogallol solution, by contact 



