May, 1928
-_---.'THE JOURNAL OF INDUSTRIAL AND ENGINEERING CHEMISTRY
419
The Determination of Carbon Dioxide in Self-Rising Flour' By Benjamin R. Jacobs2 NATIONAL CEREAL
P R O D U C T S LABORATORIES, WASHINGTON,
The following method of determining carbon dioxide by absorpfion i n barium hydroxide has gioen wry satisfacfory results with self-rising flour. Contamination with atmospheric carbon dioxide is acoided by aspirating COp-free air through the apparatus, by working rapidly, and by keeping apparatus and reagents properly sfoopercd. The titration must be carried to a definite end-poinf.
N consideration of the enormous increase in the production of self-rising flours and of the large number of millers who are manufacturing them practically without chemical control, it seems desirable to present a rapid and accurate method of determining carbon dioxide in this product. Since the determination of carbon dioxide is made for a large variety of purposes, many methods and many forms of apparatus have been devised. Some require very elaborate apparatus and precautions, and the sources of error are many. Truog3 determined carbon dioxide in certain soil investigations by the alkali titrimetric method, using measured amounts of barium hydroxide, in which the carbon dioxide was precipitated as barium carbonate which is practically neutral to phenolphthalein. The excess of barium hydroxide was determined by titration and the amount of carbon dioxide by difference. The Truog method has been adapted by Gurgar4 t o the determination of carbon dioxide in plant respiration studies. The apparatus used by Gurgar is more elaborate than that of Truog, but it is also susceptible of greater accuracy, owing to the uFe of more dilute reagents, as well as to the precautions used against exposing the standard barium hydroxide solution to the atmosphere, I n determining carbon dioxide in self-rising flours the tcndency of the sample to lump when treated with water m w t be overcome: otherwise srnall lumps of dough containing dry flour in the center will cause errors in the determination. It has been found that this may be overcome by adding only enough water to form a thick paste, the amount required being about three times the weight of the sample. Vigorous shaking is necessary t o break up the lumps and form a homo-' geneous paste. APP24RATUS.
I
The apparatus shown in the accompanying figure consists of a tower, A, a flask, B, of 1000-cc. capacity, a 300-cc. round-bottomed flask, D, provided with a 100-cc. separatory funnel, C, and a glass bulb, E, connected with two 16-oz. bottles, F, filled with 50 per cent sodium hydroxide solution and perforated or solid glass beads, G. REAGENTS ACID-A 0.1 N Solution is used. HYDROXIDE-Seven g. of Ba(OH)2 are dissolved iii 1 liter of boiling water and filtered into a stock bottle which has been freed from carbon dioxide. A double filter paper is used and the funnel is never allowed to run dry until the solution has all gone through. Fifty cc. are used for each determination. About 19 cc. of 0.1 N HC1 are required to neutralize this amount of barium hydroxide. PHEKOLPHTHALEIN-One gram of phenolphthalein is disST.4KDARD HYDROCHLORIC BARIUM
Received January 18, 1922. Director, National Cereal Products Laboratones. a THISJOURNAL, 7 (19151, 1045. 4 Piant World, ao, 28s. 1
D.
C.
solved in 100 cc. of 95 per cent ethyl alcohol. Four drops are used for each determination, COZ-FREE WATER-This may be made either by passing C02-free air through water for 30 min. or by boilingfor 15min. DIASTASE soLuTIon'-This is made by dissolving 1 g. of diastase in a liter of COrfree water. 100 cc. are used for each determination. This solution should be made up fresh every day.
PROCEDURE Fifty cc. of the barium hydroxide solution are introduced into flask B through the tower A, the apparatus having previously been freed of GO2 by drawing (202-free air though it for 20 niin. Approximately 5 g. of the flour to be tested are weighed in a test tube and dumped into dried flask D, which is immediately corked for future use or connected Kith the rubber stopper provided with the separatory funnel C. Air is then passed through a t the rate of about four bubbles per second. One hundred cc. of the standard diastase solution are run into the separatory funnel. Approximately 15 cc. of this solution are introduced into the flask containing the sample and shaken gently until a homogeneous paste is obtained, whereupon the remaining portion of the diastase solution is introduced. Flask D is immersed in a dish containing water at 70" C. for about 10 min. in order to hasten the action of the diastase on the starch. The temperature of the water in the dish is then increased to boiling, the flask is shaken occasionally. and the determination continued for a total of 25 min. ,Just before the end of this time a flame is applied directly to the bottom of the flask and the contents are brdught to a boil for a few seconds. This should be done carefully to avoid charring. When the determination is completed the section is closed off with a stopcock connected to the tubing abovc the tower. The apparatus is disconnected at the side tube of the flask
