ANALYTICAL EDITION
JANUARY 15, 1938
sufficient time is permitted for complete conversion of the iron to the ferrous o-phenanthroline complex. ‘One
Of
the
found in traces in
15
M.,“Determination of Hydrogen Ions,” 3rd ed., Baltimore, Williams & Wilkins Co., 1928. (4) Hill, R., Proc. Roil. SOC.(London), B107, 205 (1930). ( 5 ) Sanford, A. H., Sheard, C., and Osterberg, A, E,, Am, J . Clin. (3) Clark, W.
except copper in amounts over 0.2 mg. and tin in amounts over-0.6 mg. interferes I+-iththe determination of iron by this method.
Path.. 3. 405 11933). (6) Saywell, L. G., and Cunningham, B. B., IND.ENG.CHEW,Anal. Ed., 9, 67 (1937).
Literature Cited
(7) Walden, G. H., Hammett, L. P., and Edmonds, S. M., J. Am Chem. SOC., 56, 350 (1934)
(1) Bernstein, S.S., Jones, R. L., Erickson, B. N., Wlliams, H. H . , Amin, I., and Macy, I. G. (in press). (2) Blau, Monatsh., 19, 647 (1898).
~I
RECEIVEDOctober 2 7 , 1937. Presented before the Division of Biological Chemistry a t the 94th Meeting of the American Chemical Society, Rochester, pi. T., September 6 to 10, 1937.
Determination of Air and Carbon Dioxide in Beer PHILIP P. GRAY
I
AND
IRWIN 51. STOKE, Wallerstein Laboratories, 180 RIadison Ave., New York, IV. Y
S YIEW of the relation of air content to beer stability, the determination of the amount of air present in packaged beer has, in recent years, assumed an importance a t least equal to that of the determination of carbon dioxide. Such methods for determining air as those of Murray ( 5 ) , Helm and Richardt (4),and Siegfried ( 6 ) ,while no doubt giving accurate results, are cumbersome and unwieldy. The chief attribute of the pressure method for determining carbon dioxide, which has been in use for many years in the carbonated beverage industry, is its convenience. I n view of the importance attached to air determination, any modification of the pressure method which results in the determination of both air and carbon dioxide a t the same time upon the same package in a satisfactorily accurate manner deserves consideration. I n a previous paper (Z), the authors worked out a precise chemical method for determining carbon dioxide in bottled beer and carbonated beverages, based on the use of the whole bottle as a sample, a foam suppressant, and an evolution regulating material. Complete liberation of gas was obtained by boiling, the liberated gas being absorbed in alkali and the alkali then being differentially titrated. This method was adopted as tentative by the Association of Official Agricultural Chemists ( 1 ) . I n the same paper, advantage was taken of the availability of this precise chemical method to study and evaluate the errors inherent in the customary pressure methods for determining carbon dioxide. The authors were able to establish that, if the influence of the variable amounts of air present during the pressure reading is taken into account, accurate carbon dioxide results may be obtained by the pressure method, and t h a t solubility of carbon dioxide in beer, under varying temperature and pressure conditions, can be satisfactorily predicted on the basis of publishedHenry’s law constants for carbon dioxide, assuming that the small amount of alcohol does not affect the total solvent properties of the combined alcohol and water in beer, and that extract has no other effect on solubility than as an inert diluent. Thus, there was made available an accurate, simple, and convenient pressure procedure once the equipment is a t hand. Results presented in the previous paper, as well as experience with the test in the authors’ laboratories since that time, amply justify the conclusion that, for most purposes the pressure method, correcting for air and using solubility of carbon dioxide in beer as a basis, yields satisfactory, accurate, and reproducible data for carbon dioxide. The paper ( 2 ) outlined
the pressure method and supplied the principles for carrying out the calculations, but did not give in detail the actual method for making the air determination. Experience with this method has indicated that more accurate results are obtained when all pressure determinations are carried out a t 25” C. rather than a t much lower temperatures. At this temperature, which is generally easy to maintain, the pressure reading is high, minimizing any gage errors; the air is readily evolved from the beer; and the selection of a single temperature reduces any errors due to differing solubility-temperature coefficients or deviations from gas laws which might enter into the results when determinations are carried out, sometimes a t one temperature and sometimes a t another. For example, with the much lower pressures prevailing a t temperatures close t o cellar temperatures in the brewery, a given amount of air will naturally exert, proportionately, a greater effect on the total pressure; in fact, evidence has accumulated that, for the same samples, slightly higher carbon dioxide results are to be expected if the pressures are measured a t these lower temperatures. The authors have also adopted, based on considerable experience with a large number of samples, a revised value for a (per cent of carbon dioxide per pound pressure) a t 25” C.namely, 0.00965 instead of 0.0095 (3)-embodying an adjustment for such errors as are always involved in assuming an “average beer,” and correcting for experimental errors on routine samples. The value has been found to give results which are quite as satisfactory as the precise chemical methods. I n the present paper, details are given for determining both “air” and carbon dioxide by the pressure method. The results of special experiments are also presented, carried out to determine the extent to which the procedure is capable of recovering all the air present in the package. While there is no need, either from the standpoint of controlling air content or as regards the accuracy of the carbon dioxide results, to ensure 100 per cent recovery of the free and dissolved air present, these experiments indicate substantially complete recovery beyond amounts Tv’hich might be anticipated on the basis of solubility. Another important factor having a bearing on the accuracy of carbon dioxide results by the pressure method, which has heretofore not been touched upon, is the mechanical difficulties and errors inherent in the usual type of pressure gage. The usual gage, based on mechanical spring action, is frequently found to lag and stick and give erratic results after some use. In view of the frequency with which this occurs,
16
INDUSTRIAL AND ENGINEERING CHEMISTRY
VOL. 10, NO. 1
a method was developed for regular calibration of the gages used, based on comparison with a specially constructed mercury manometer. The details of this calibration procedure are also presented.
Method PIERCING APPARATUS FOR BOTTLES. This consists of a gastight packing box and fastening for adjustment over the crown and a hollow spike connected to an accurate pressure gage and outlet valve. A suitable apparatus ma be obtained from the C. J. Tagliabue Manufacturing Co., the Liquid Carbonic Corp., the Bishop I% Babcock Manufacturing Co., etc. PIERCING APPARATUSFOR CANS. This consists of a metal frame in which the can is placed. The top, which is pressed or screwed down and locked over the can top, contains a hollow spike surrounded by a compressible rubber sealing plug. The hollow spike leads to an accurate pressure gage and an outlet valve. One apparatus, adjustable for use for bottles and cans, may be
FIQURE 1. ABSORPTIONBURET
PER c m CARBON DIOXIDE BY BY
Volume
Weight
- 100
60
.- & 55/
45 50
2.40
i
:I 35
--
60
..
40
.- 20
i.
-
20 2.00
PRESSURE Pounds Per Square Inoh
GAGE
W G M l w T CBART
for E i t l m t l o n or Carbon D l o x l d a i n Beer
rrm
PreaBure and Alr Content at 25%.
1.60
FIGURE2l Chart copyrighted.
into the bulb. Open stopcocks B and A and repeat the above operation, tapping the bottle or can to accelerate evolution of carbon dioxide. Close upper stopcocks A and B and shake thoroughly to absorb last traces of carbon dioxide. Bring leveling bulb to a position so that the levels of the solution in the !eveling bulb and buret are the same and read unabsorbed gas, w h i c h i s reported as ‘6air.’’ The operation is repeated until consecutive readings as to “air” are the same.
JANUARY 15, 1938
ANALYTICAL EDITION
will give volume of beer in milliliters. Fill empty can with water and weigh. Weight of water in grams is also volume in milliliters, so that the difference between volume of water and volume of beer represents head space in milliliters. Calculate carbon dioxide by weight by the following formula:
x 14.7)] x 0.00965 ml. of head space P = absolute pressure in pounds per square inch’ a t 25‘ C. = (ordinary gage pressure 14.7)*
+
A few typical results are given in Table I. TABLE I. CARBON DIOXIDE RESULTS ON CONSECUTIVE BOTTLES FROM SAMEBOTTLING Sample
Absolute Pressure a t
1
2
3
4
25’ C. Lb./sq. in. 49.5 50.5 51.5 52.0 52.5 53.5 53 54 54 54 46 45 45 45 45.5 48 49 50 50
Air
Air, ’% of Head Space
.W. 0.7
3 4 9 16 17.5 24.5 43 48 50 48 32 24 25 20 35 51 66 71 69
0.8 1.9 3.8 4.2 6.2 7.3 8.1 9.0 8.2 5.5 3.6 4.0 3.6 2.1 5.1 4.6 6.4 6.2
Pressure Correction
COX
Lb./sq. in. - 0.4 - 0.6 - 1.3 - 2.4 - 2.6 - 3.6 - 6.3 - 7.1 - 7.4 - 7.1 - 4.7 - 3.5 - 3.7 2.9 - 5.2 - 7.5 - 9.7 -10.4 -10.1
0.474 0.482 0.484 0.479 0.482 0.482 0.451 0,453 0,450 0.453 0.398 0.401 0.398 0.406 0.389 0.391 0.379 0.382 0.385
-
% ’
Carbon dioxide results for beer need not be reported beyond the second decimal. In carrying out the pressure-air procedure at Z f i O C . , a n alignment chart has been prepared for calculating the corrected carbon dioxide percentage from the gage reading and air result (Figure 2). To use this chart, merely place a straight edge on the determined value of “per cent air in head space” on the right-hand vertical line. Adjust the straight edge so that it also intersects the determined “gage pressure” on the center vertical line. The corrected carbon dioxide value is then read off a t the point where the straight edge intersects the left vertical line.
Calibration of Gages The following procedure was
17
sional marks about 1 cm. apart. Fill the capillary tube with mercury from mnrk A to the open end, and place in a vertical position. Adjust the mercury level exactly to mark 9. The weight of the portions of mercury between each centimeter divisional mark is determined (as in calibrating a buret, except that the weight of the mercury between the last divisional mark and stopcock 1 is also determined). Dividing the weights of mercury by the specific gravity of the mercury at the temperature employed gives the volumes of t’he capillary bore under the divisions of length V . Adding together the divisional volumes gives the total volume from the inside of stopcock 1 to line A . Boyle’s law states that: at constant temperature, the volume of a gas is inversely proportional to the pressure. For the range of pressures in the simple case a t hand, this law may be expressed as follows:
VIPl = VzP2= constant where VI = the total volume of tube V above PI = absolute atmospheric pressure P , = absolute known pressure applied during testing of gage V Z = compressed volume of gas when pressure Pz is applied The absolute pressure is the ordinary gage pressure plus atmospheric pressure. Using Boyle’s law and the capillary volume as determined above, the manometer tube is calibrated in pressure readings as follows: Place the manometer tube in the horizontal position shown in Figure 3. With stopcock 1 open, bring the mercury to line A and close stopcock 1. The air now contained in the space b e tween the mercury and the stopcock has the volume V Lunder atmospheric pressure PI. For the sake of simplicity and illustration, we will assume that VI = 1 ml. and PI = 14.7 pounds per square inch. In order to determine how far the mercury will progress in the tube if a pressure of 5 pounds is applied, we calculate the volume of the enclosed air in V under this pressure ( 5 pounds per square inch on gage = 14.7 5 = 19.7 pounds per square inch absolute).
+
VIP1 = V2Pz
1.0 X 14.7 = V: X 19.7 V I .= 0.746 ml.
From the divisional volume calibration of the capillary bore the point representing a volume of 0.746 ml. from the stopcock may be accurately picked off on the tube. It is to this point that the mercury will progress under an applied pressure of 5 pounds. Similar calculations are made for 10, 15, or any other desired gage readings. After the tube is calibrated in gage readings, a scale may be scratched or etched on a sheet of aluminum which can be
n
devised for the purpose of calibrating gages, and is used daily in connection with routine tests: The apparatus consists of a calibrated, isobaric, capillary mercury manometer having a three-way stopcock and means for connecting a tank of carbon dioxide and the gage under test. Figure 3 illustrates the apparatus. The capillary is about 1 mm. in diameter and contains a bulb (of about 50-cc. capacity) which acts as a mercury reservoir and is filled with mercury to the level of the capillary tube as shown. The capillary, V, is about 45 to 50 cm. (18 to 20 inches) long and the exact volume of the interior is determined as follows: The ca illary f r o m l i n e A t o stopcocf: 1 is graduated by divi1
Pounds per sq. inch X 0.070307
kg. per s q . om.
-
a For routine work 15 may conveniently be substituted for 14.7.
FIGURE 3.
hfANOMETER FOR
CALIBR.4TIXG GAGES
VOL. 10, NO. 1
INDUSTRIAL AND ENGINEERING CHEMISTRY
18
TABLE11. RECOVERY OF AIR IN AIR DETERMINATION 7
T
Expt.
Total Air
M1. 1
2
3 4 5 6 7 8 9 10 11
2.2 3.1 3.5 4.2 7.7 8.6 10.2 12 9 13.4 17.2 19.2
First 100 ml.
Air Contained in Evolved Gas A t 2 5 O C. 100 t o 200 t o 300 t o 400 t o 200 ml. 300 ml. 400 ml. 500 mi.
.
7 7
300 ml.
%
%
M1.
XL.
M1.
xi.
1.6 2.4 2.4 3.0 5.7 6.0 7.0 10.0 12.4 13.6 15.0
0.1 0.2 0.2 0.3 0.3 0 6 1 0 0.7 1 0 1 1 1 4
0.1 0 1 0.3 0.2
0.1 0 1 0.2 0 2 0 5 0.8 0.6 0.5 0.8 0 6 1.3
0.1 0.1 0.1 0.1 0.2 0.4
0.2 0.2 0.3 0.4
73 77 69 72 74
0.4 0.4 0.6 1.1 0 6 0.6
70
2.5
0.9 0.9
0.2 0.4 0.6 0.4
...
conveniently mounted behind the tube. For precise work, several scales may be prepared to cover the range of the varying initial atmospheric pressures as shown in the illustration. For the average gage, however, the multiple scale is not necessary. The gage is standardized as follows: Place the apparatus, with the horizontal manometer tube perfectly level, in a position protected from drafts and sudden changes of temperature. Connect the gage t o an empty bottle or can, connect also a tank of carbon dioxide equipped with a fine adjustment needle valve as shown in Figure 3. With stopcock 2 in position a and stopcock 1 open, apply a slight amount of pressure from the tank to bring the mercury to line il. When the mercury reaches this line, close stopcock 1 and release the pressure by bringing stopcock 2 t o position b. Make a barometric reading of atmospheric pressure and bring the appropriate scale into position behind the tube. Change stopcock 2 to position a, and apply pressure from the carbon dioxide tank. When the mercury reaches the 5-pound line make a reading of the gage. Apply more pressure, check the gage against the mercury reading for several pressures, and note any corrections. After the determination is finished, shut off the pressure. Bring stopcock 2 into position c to release pressure in the apparatus, and then carefully bring it to position b to release pressure slowly in the mercury manometer. The apparatus is so designed that the correction for varying hydrostatic pressures of mercury is eliminated, which greatly simplifies its use. Satisfactory results have been obtained in the authors’ laboratories over a period of about 3 years, during which time 0
FIGURE4.
To
200 rnl.
%
M1.
0.5
Recovery of Air At 250 C.
First 100 ml.
MZ.
0.4 1.0 0.7
To
25’ t o 102’ C.
0.5
69
78 67 79
78 xv. 73 3
77 84 74 79 78 77 79 83
73 86 86 79 5
To
400 rnl.
%
82
86
87 83 83 84 81
90 89
~~
88 89 86 91 90 85 9
88 9 1 .~
91 94 92 91 94 97 91.3
To
500 ml.
% 91 94 92 90 94 .~ 95 96 95 94 97 97 94 2
25‘to 102” C.
% 9 6 8 10 6
5
4 5 6 3 3 5 9
hundreds of samples of packaged beer have been examined by the above pressure-air method and carefully checking the gages. E x t e n t of Air R e c o v e r y Since the influence of air on packaged beer and the importance of its determination have come t o be realized, some attempts a t distinguishing between “head space,” or “free” air, and “dissolved” air have been made from time to time. Actually, of course, this is of only academic interest, since there is a constant absorption of air by the beer from the head space and diffusion into the head space from the beer, depending upon physical conditions. Actual damage to the beer can result only from dissolved oxygen, but the supply of dissolved oxygen is, in turn, replenished from the head space air rcservoir of oxygen. While generally the ideal, in analytical methods, is to accomplish 100 per cent recovery, this is by no means necessary where a constant proportion of the total amount present is always yielded by the procedure. Thus, there would be no point in boiling the beer to recover 100 per cent of air, an inconvenient method, if i t could be shown that a fairly constant, large proportion of the total air would always be recovered by shaking a t 25” C. As far as its use in correcting the pressure reading for determining carbon dioxide is concerned, complete recovery of the air is not needed, as i t is only the head space air that introduces the error, and this is readily recovered in the first few shake-outs. Even though this question of completeness of recovery of air has no practical significance in the carbon dioxide determination, i t is of importance in so far as the question of air control in connection with beer stability i s c o n c e r n e d . Therefore, in order to ascertain the extent to which the total air is recovered by the present procedure, the following experiments were carried out:
DIAGR.4M O F .APPARATUS
The apparatus c o n s i s t s of a setup similar to that used for the usual air determination, except that a large gas buret is inserted in the line and the gage is removed, as shown in Figure 4. T h e u s e of t h e g a s b u r e t , C, permits the removal of measured portions
AN.4LYTICAL EDITION
JANUARY 15, 1938
of the air-carbon dioxide mixture from the beer, and these are
then analyzed in the alkali buret, B. The absorption buret, B, is filled with 15 per cent alkali; gas buret C is filled with 20 per cent sodium sulfate solution acidified with sulfuric acid, and contains a few drops of hexyl alcohol. All tubes and connections are rendered air-free by filling with water. The cap is punctured with the spike in the usual manner, and 100 cc. of gas are permitted to flow into buret C. Stopcock D is then turned and the 100 cc. of gas are diverted into buret B , where the carbon dioxide is absorbed by the alkali and the "air" is measured. Another 100 cc. are permitted to flow into buret C, and the process is repeated as long as carbon dioxide is evolved from the beer at 25" C. When all the gas has been evolved at 25" C., the beer bottle is placed in a boiling dilute aqueous-glycerol bath (102' t o 103" C.). Leveling bulb E is lowered to produce a partial vacuum in C and help draw over any gas from the boiling beer. When all the gas has evolved, the gas mixture is moved into B , the carbon dioxide is absorbed, and increase in air is not,ed. Table I1 gives the results of these experiments on a number of beers. It will be seen that the bulk of the air (70 to 80 per cent) comes over in the first 100 cc. of the gas evolved from the beer, and that by using ordinary care to evolve as much gas as possible a t 25" C., an average recovery of 94 per cent of the total air is possible. It is therefore apparent that this pressure method is not only suitable as an accurate carbon dioxide method, but also gives sufficiently accurate air r e x l t s for most purposes. I n carrying out the air determination in the usual manner the results may be slightly reduced by reason of the absorption of some of the oxygen in the evolved air by the small amount
19
of alkaline beer contained in the absorption buret,. This error is small and except for the most precise work generally needs no correction.
Summary 1. A simple, rapid, and precise pressure method for determining carbon dioxide in packaged beer or other carbonated beverages, which corrects for the air error is further described in detail. 2. The method is suitable for the determination of air in packaged beers and carbonated beverages, and is especially valuable for routine control work. 3. The extent of recovery of the air in bottled beers by this method has been determined, and i t is shown that a n average recovery of 94 per cent may be obtained a t 25" C. 4. A simple primary pressure standard for checking the pressure gages is described. 5. An alignment chart for simply calculating the analytical data is presented.
Literature Cited (1) Assoc. Official Agr. Chem., Official and Tentative Methods of Analysis, 4th ed., p. 151 (1935). (2) Gray and Stone, S.Assoc. Oficial Ap-. Chem., 19, 162 (1936). (3) Ibid., p. 171. (4) Helm and Richardt, S. Inst. Brewing, 42, 171 (1936). (5) Murray, Ibid., 31, 137 (1925). (6) Siegfried, Schtceit. Brau.-Rundschau, 48, 1 (1937). RECEIVED October 7 , 1937.
Determination of Rotenone in Derris and Cube 11. Extraction from the Root HOWARD A. JONES, Bureau of Entomology and Plant Quarantine, Beltsville, Md., AND J. J. T. GRAHARI, Food and Drug Administration, U. S. Department of Agriculture, Washington, D. C.
S
ISCE the publication of the earlier methods for the ana-
lytical extraction of rotenone from derris and cube roots using Soxhlet extraction with ether (9) and with carbon tetrachloride ( 6 ) as solvents, various other procedures have been proposed. Danckwortt and Budde (4) have used roomtemperature extraction with a given weight of chloroform followed by filtration and removal of an aliquot of the filtrate by weight. Cahn and Boam ( 3 ) have suggested Soxhlet extraction with trichloroethylene. I n a method proposed by Rowaan (10) the sample is extracted a t room temperature with successive lots of chloroform. The method of Beach (1) is similar to that of Danckwortt and Budde except that an aliquot of the filtrate is taken by volume. Worsley (12) has used percolation with hot ethyl acetate, and Begtrup ( 2 ) proposes percolation with toluene a t room temperature. Recently Seaber (11) has presented results by various extraction procedures and has stated Beach's method to be preferable. The object of the present work was to qtudy some of these methods of extraction and others already in use in the writers' laboratories with a view to deciding on the best procedure to be used in conjunction with the crystallization method already published ( 7 ) .
Extraction AIethods It has been known for some time that Soxhlet extraction with carbon tetrachloride for as much as 24 hours does not always completely recover the rotenone. It is also generally
supposed that some of the rotenone may decompose during the long boiling necessary in such an extraction. Accordingly some test's were made of a method partially overcoming t,his objection in which most of the extract was removed and not subjected to continued boiling. The flask containing the extract was changed after 3 hours and the extraction continued for the usual length of time. I n addition to Soxhlet extraction, four other general methods of extraction were tested : 1. BOILIXG-MULTIPLE EXTRACTION METHOD.The sample was refluxed with the solvent under a condenser on the steam bath for 1 to 2 hours and filtered by suction. The marc was washed on the filter with hot solvent and then refluxed again with fresh solvent, followed again by filtration and washing. This was followed by a third refluxing, filtering, and washing. 2. BOILIKG-ALIQUOT METHOD. The sample was treated with a weighed amount of solvent and refluxed under a condenser on the steam bath for 2 to 3 hours. After the solution had cooled to room temperature, solvent was added to replace that lost, until the mixture was brought' to its original weight,. The extraction mixture was chilled in the refrigerator, filtered through folded filter paper, precautions being taken to prevent loss by evaporation, and an aliquot of the filtrate was t,aken by volume. 3. R O O M TEMPER.4TURE-MULTIPLE EXTRACTION hIETHOD. This method was similar to method 1 but was carried out at room temperature. 4. ROOMTEMPERATURE-ALIQUOT METHOD. This was substantially the method proposed by Beach. The sample mas shaken with an accurately measured volume of solvent, the time of shaking ranging from 4 hours to overnight. The remaining procedure was the same as in method 2.
