June 15, 1942
ANALYTICAL EDITION
viously at 110" C. to determine moisture and volatiles at that temperature. The weight need only be sufficient to give adequate accuracy with the balance used for the amount of oil present. The solvent used is petroleum naphtha (boiling point range approximately 110 to 167" C.), which costs about 25 cents per gallon and may be secured without difficulty. The wire basket is cylindrical with a flat bottom and is made to fit snugly to the sides of the beaker, so that the vapors in the second operation must pass through the turnings. If the holes in ordinary screening are too large for the material being extracted, a finer screen or perhaps a specially designed cloth bag is recommended. 2. With the cooling water flowing, the temperature is raised to the boiling point of the solvent and held there for about 1.5 minutes. This causes intimate contact of each piece of turnings with the solvent, which results in rapid heating of the turnings and maximum solution of the oil in the solvent. The bulk of oil in very oily turnings is thus removed. 3. As shown in Figure 2, the hot plate and beaker are then lowered, so that the level of the boiling solvent is 1.25 to 2.5 cm. (0.5 to 1 inch) below the bottom of the basket. The vapors from the solvent proceed to condense on the turnings and all the oil-bearing solvent finally finds its way into the beaker. The rate of boiling and distance from the bottom of the screen to the top of the solvent should be adjusted with the following points in mind: The boiling rate should be such that the vapors condense at a slow but noticeable rate on the bottom of the condenser and drip back through the turnings, so that all the turnings are brought in contact with solvent vapors. The solvent level should be far enough from the turnings so that violently boiling liquid does not come in contact with them.
479
This minimizes the possibility of a residue of oil-bearing solvent on the turnings. A further precaution concerns the possibility of bumping if some fine turnings pass through the screen in step 2. It may be necessary to remove the beaker from direct contact with the hot plate and insert an intervening layer of asbestos if bumping occurs. In the case of the petroleum naphtha used, the lower boiling fractions do the vapor-degreasing and they are subsequently easily removed from the clean turnings by heating on a hot plate under a hood. For example, from a batch of turnings containing 10 per cent of oil a sample of about 150 grams was taken. The extraction was performed as described above and the clean and dry turnings were weighed. The extraction was repeated in the same way using carbon tetrachloride, and the turnings were again dried and weighed. A difference of only 0.2 gram Kas observed between the weights obtained in the two extractions. This error is probably due to the crude balance used. For a determination of this sort this can be considered excellent. In other words, the petroleum naphtha was satisfactory. The errors in sampling far overshadow any errors in this determination. Xodifications in t h e details of the procedure can easily be made according t o the product being extracted and the solvent being used. Many mechanical improvements in the setup could be made, b u t i t is questionable whether the expenditure of time and money is warranted. Obviously this method can be used t o clean oil-covered solids on a laboratory scale.
Determination of Traces of Copper in Wort, Beer, and Yeast IRWIN STONE Wallerstein Laboratories, 180 Madison Ave., New York, N. Y.
I
NCREASED interest has been shown recently in the determination of copper in beer (2) and collaborative analytical work has been undertaken b y the Association of Official Agricultural Chemists (1). The methods studied in this collaborative work, which were considered the most practical and best of those available, were a direct xanthate method involving dry-ashing of t h e sample and a diethyldithiocarbamate method, including a wet-digestion as well as a hydrogen sulfide and dithizone separation t h a t could be omitted at the discretion of the collaborative analyst. This increased activity led the author t o prepare for publication t h e copper methods which this laboratory has been using in studies of wort, beer, and yeast. The results of these studies Till be published elsewhere. The details of the methods reported herein were worked out after considerable preliminary experimentation t o obtain optimum conditions for the various operations. Originally, a method was developed for determining the copper directly on the sample without preliminary ashing or wetdigestion. While good recovery of added copper was obtained, the results were not completely reliable for the copper originally present in many of the samples. The presence of stable copper complexes and t h e difficulty of counteracting interferences in the direct method indicated the need for destruction of organic matter present in the samples. In the present method a dry-ashing is employed rather than a wet-digestion because of its simplicity and the fact t h a t high blanks are obtained due t o traces of copper in the large volumes of concentrated acids usually employed in the
wet-digestion methods. The copper is determined photometrically as t h e diethyldithio complex after extraction with amyl acetate (3). Iron is the only common metal which is normally present in the wort, beer, or yeast in amounts sufficient t o interfere by forming a colored complex with the reagent. This interference is eliminated by the use of 2,2'-bipyridine (a,a-dipyridyl) as suggested by Parker and Griffin (4). The 2,2'-bipyridine combines with the iron and prevents i t from reacting with the copper reagent. This expedient greatly simplifies the procedure by avoiding the usual lengthy acid-hydrogen sulfide separation. The possible interfering effect of calcium ions is prevented b y avoiding alkaline reactions with consequent precipitation of calcium phosphate and by using a large excess of t h e copper reagent. A further advantage of this method is that most of the reactions are conducted in a single centrifuge tube and in the case of worts and beers no filtrations are involved. The spectrophotometric data relating t o the copperdiethyldithiocarbamate color have been worked out (3) and need not be repeated here. Calibration curves (Figure 1) have been made at two separated points on the spectrum (440 and 540 millimicrons), thus extending the range of copper concentrations covered without loss of accuracy. This permits the ready selection of the most suitable conditions (cell length, wave length of light, and optimum reading of instrument) for the amount of copper present in the particular sample used. The instrument employed throughout this work was the Aminco neutral wedge photometer, but the principles involved are readily adaptable to other visual or photoelectric photometers.
INDUSTRIAL AND ENGINEERING CHEMISTRY
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Vol. 14, No. 6
ethyldithiocarbamate, immediately cork the tube, and shake vigorously 60 times. Cool the tube in ice water and reshake twice again, giving 60 shakes each time and allowing the amyl acetate to separate between shakeouts. Centrifuge the cold tube and pour the separated colored amyl acetate into a suitable tube or cell and read in the photometer. If the amyl acetate is not perfectly transparent, the haze, which is due to a dispersion of water in the solvent, can be cleared by warming the cell slightly. Suitable blank determinations on the reagents should be conducted and correction of the results applied. With good grades of reagents, the blanks will generally run on worts and beers about 0.002 mg. of copper and on yeast about 0.004 mg. of copper. PREPARATION OF CALIBRATION CCRVES. Pipet into the centrifuge tubes quantities of the diluted copper standard sufficient to corer the range desired. This range will depend on the cell depth and wave length of light employed. The calibration plot for the neutral wedge photometer (Figure 1) viill indicate the range of concentrations possible on this instrument by this method. Add 1 ml. of sulfuric acid, dilute t o about 20 ml. with water, and then proceed as above, adding the various reagents and shaking out n-ith amyl acetate. Read the clear colored amyl acetate in the photometer, plot the results, and obtain the calibration curves. Beer's law appeared to be followed over the range of concentration employed on the author's photometer. The quantity of 2,2'-bipyridine used is sufficient to take care of about 0.2 mg. of iron in the sample. If the iron content of the sample is higher, the amount of 2,2'-bipyridine should be increased. The stronger bipyridine reagent listed under the determination of copper in yeast may be substituted.
FIGURB 1. CALIBRATION CURVES A . 2-inch cell B . 1-inch cell C. 0.5-inch cell
Determination of Copper in Wort and Beer REAGENTS.Concentrated c. P. nitric and hydrochloric acids. Dilute Sulfuric Acid (1 6). To 6 parts by volume of water add with stirring 1 part by volume of c. P. concentrated sulfuric acid. 2,2'-Bipyridine Solution. Add 1 ml. of glacial acetic acid to 0.2 gram of 2,2'-bipyridine (a,a-dipyridyl) contained in a beaker, dilute with water, and dissolve. Make up volume to 100 ml. Saturated p-Hydroxyphenyl lycine Solution. Prepare fresh before use by stirring thoroughfy 0.5 ram of p-hydroxyphenylglycine in 100 ml. of 0.1 N sulfuric acif, Allow to settle and use the clear supernatant solution. Sodium Acetate Solution. Dissolve 14 grams of sodium acetate trihydrate in water and dilute to 100 ml. Isoamyl Acetate. The g'rade with a boiling range 125" to 140' C. is satisfactory. Sodium Diethyldithiocarbamate. The 2,2'-bipyridine, p-hydroxyphenylglycine, isoamyl acetate, and sodium diethyldithiocarbamate are obtainable from the Eastman Kodak Co., Rochester, N. Y. Standard Copper Solution. Weigh out 3.93 grams of clean c. P. copper sulfate crystals (CuS04.5H20), dissolve in water, and dilute to 1 liter (1 ml. = 1 mg. of copper). For the calibration curve prepare a more dilute standard by pipetting 5.0 ml. into a 500-ml. volumetric flask and diluting to the mark with water (1 ml. = 0.01 mg. of copper). The use of copper sulfate crystals as a standard is sufficiently accurate for this purpose and avoids the usual lengthy method involving the dissolution of metallic copper. METHOD. Measure 100 ml. of beer into a clean silica dish and add 5 ml. of the dilute sulfuric acid. Evaporate, char, and ignite at about 500" to 550: C. in a muffle to obtain a fluffy, white, carbon-free ash, avoiding fusion of the ash. Cool, add 2 m!. of concentrated hydrochloric acid and 1 ml. of concentrated nitric acid, and evaporate to dryness on a steam bath. If any carbon is noted in the ash at this point, put it back in the muffle and reignite to give a completely carbon-free ash. Treat the reignited ash again with the nitric-hydrochloric acid and re-evaporate until the residue is thoroughly dry. Wet the residue with 1 ml. of the dilute sulfuric acid and transfer with hot Tvater to a 50-ml. centrifuge tube (Pyrex No. 2220), keeping the total volume below 20 ml. Add 2 ml. of the bipyridine solution, 1 ml. of the p-hydroxyphenylglycine solution, and 6 ml. of the sodium acetate solution. h4ake the volume up to 30 ml., mix, and warm to about 50' C. for 15 minutes. Cool and pipet into the tube exactly 15 ml. of amyl acetate. Add 0.2 gram of sodium dl-
+
RECOVERY OF ADDEDCOPPER. A suitable precise copper method of k n o m accuracy against which this method could be checked is lacking. As a recourse determinations were made to check additions of copper. Table I shows the excellent recovery obtained in the analysis of beers and worts containing added copper. The original iron content of the beers listed was about 0.2 p. p. m, and the wort contained about 0.5 p. p. m. of iron. The copper in yeast is determined as in wort and beer with a few changes in the ashing technique, necessitated b y the presence of quantities of readily fusible salts in the yeast samples. OF COPPER ADDEDTO BEER TABLE I. RECOVERY
Sample
Cop er hd&d
Iron Added
P . p . m . P . p , m .
Beer A Beer A Beer A Beer B Beer B Beer B Wort C Wort C
None 0.26 0.26 ljone 0.50 0.50
None
0.60
None None 2.0 None Xone 2.0
None Iione
Copper Determined Recovery Av. P . P . ~ . P . P . ~ . % 0.13,O.15 0.14 ... 0.38,O.38 0.38 96 96 0.38 0.38 0.13 0.12,O. 13 ... 0.61,0.61 0.61 96 0.61,0.64 0.63 100 ... 0.19,0.20 0.20 0.83,O. 77 0.80 100
Determination of Copper in Yeast REAGENTS.Ammonium Nitrate Solution. Dissolve 50 grams of c. P. ammonium nitrate in water and dilute to 100 ml. 2,2 '-Bipyridine Solution. Dissolve 1.0 gram of 2,2'-bipyridine in 2 ml. of glacial acetic acid and dilute to 100 ml. with water. Other reagents as in the wort and beer method. PREPARATION OF SAMPLE FOR ANALYSIS. Liquid yeast as obtained from the fermenter of a brewery consists of a viscous suspension of the yeast cells in a more or less fermented beer. If it is desired to determine the copper on the beer-free yeast, the yeast may be washed with ice water on a Buchner suction filter until free of beer and then drained and pressed dry. Since both liquid and pressed yeast contain high proportions of moisture, a determination of yeast solids should be included, so that results may be expressed on a dry basis. Liquid or pressed yeasts are perishable and undergo autolysis and decomposition on storage. Therefore, if some time is to elapse between collection and analysis, the sample should be dried by washing on a Buchner funnel consecutively with cold lvater, alcohol, and finally with
ANALYTICAL EDITION
June 15, 1942
per method, using 2 ml. of the stronger bipyridine solution in place of the weaker solution.
TABLE11. RECOVERYOF COPPER ADDED TO YEAST
46.8 89.7
92 95 99
96.5 Averagp of 2
RECOVERY OF ADDED COPPER. Table 11 summarizes and indicates the typical recoveries of copper added to a yeast sample. The iron content of this sample was 165 p. p. m. on the dry basis.
%
Recovery
44.4
4
(All results in p. p. m. on dry basis) Total Copper Copper Found Recovered 31.7a 73 9 4i:2 74.8 43.1 116.8 85.1 127.5 95.8 results (30.4 and 33.0 p. p. m.)
Copper Added None
481
..
95
Summary
ether. After removal of the ether the sample should be a dry powdery solid which may in a mortar to give a uniform . be ground stable sample. METHOD. Weigh about 0.5 gram of dried yeast or 2 to 3 grams of the messed veast into a flat silica dish. add 5 ml. of 50 aer cent ammo&um nitrate solution, and evaporate to dryness: Char and ignite in muffle a t a temperature not exceeding 500" C. Do not permit ash to fuse. When partly ashed, remove from muffle and allow to cool, add 5 ml. of water, and heat on a water bath to dissolve out soluble salts. Filter through a small KO. 40 Whatman paper and wash with small portions of hot water Reserve the filtrate. Ignite the filter containing the waterinsoluble material in the original silica dish. The temperature of this ignition may be higher than the first ignition, as all the easily fusible salts have been leached out. Cool the dish after a white ash is obtained and add the above filtrate. Evaporate to dryness and treat with 1 ml. of concentrated nitric acid and 2 ml. of concentrated hydrochloric acid in the usual manner. Evaporate to dryness and proceed from this point as in the previous cop-
Methods for the determination of small quantities of copper in wort, beer, and yeast involve dry-ashing the sample, reacting a solution of the ash with 2,2'-bipyridine to prevent interference of iron, and determining the copper photometrically with diethyldithiocarbamate after extraction with amyl acetate.
Acknowledgment The writer wishes to acknowledge the careful and precise work of Roy W. Seaholm who obtained many of the experimental data.
Literature Cited (1) Assoc. Official Agr. Chem.. R e p o r t of Referee on M e t a l s in Beer, 1941. (2) Clifcorn, L. E., Proc. .4m. SOC. Brewing C h e m i s t s , 4 t h A n n u a l M e e t i n g , p. 76, 1941. (3) Drabkin, D. L., J . Assoc. Oficial Agr. Chem., 2 2 , 3 2 0 (1939). (4) P a r k e r a n d Griffin, Can. J . Research, 17B,66 (1939).
~~
Decomposition Temperatures of Some Analytical Precipitates Barium Carbonate ,II. L. UICHOLS AND R. H. LAFFERTY,JR.], Cornell Universitj, Ithaca, N. Y.
T
HE decomposition temperature of barium carbonate is of interest because it is a weighing form for barium and
because of its similarity to calcium carbonate. Moreover, there are very few reliable data of value to analytical chemists, since most of the work has been done to determine when the decomposition of barium carbonate is complete and not when it starts. The earliest reported work on the decomposition of barium carbonate is by Abich ( I ) , who stated in 1831 that it is completely decomposed a t a white heat. I n 1878, Isambert (9) used the gas saturation method to determine the pressure of carbon dioxide in equilibrium with barium carbonate and oxide at 1083" C. By passing nitrogen over the sample at 12 ml. per minute he found the equilibrium ressure was 22 mm. In 1898 Herzfeld and Stiepel (7) reportef that complete decomposition occurred at about 1450" C., where the compound melted, but Brill (3) found that it melted without decomposition which occurred above 1450" C. Pott ( 1 4 ) , using the static method, determined the dissociation pressures and found the dissociation complete at 1200" C. However, his dissociation pressures for barium carbonate as well as those for calcium and strontium carbonates are higher than the usually accepted values and his work has been criticized by Johnston (IO). Finkelstein ( 4 ) , using the gas saturation method, made a very complete determination of the equilibrium pressures of carbon dioxide with barium carbonate and oxide. He used a gas rate of about 33 ml. per minute. I n the light of subsequent work, this rate as well as that used by Isambert is much too fast to obtain equilibrium values. Finkelstein also reported that a basic carbonate of the composition BaO.BaCO3 was formed, but Hackspill and Wolf (6) have recently proved by x-ray studies that no
basic carbonate is formed but that the fusion of a eutectic mixture of barium oxide and barium carbonate takes place between 1070" and 1150" C. Hedvall (6) reported the decomposition temperature to be 1361' C., and Hackspill and Wolf (5) using a similar method reported that the decomposition begins about 300' C. above the first decomposition of calcium carbonate. They also found that barium carbonate undergoes an allotropic transformation from rhombic to hexagonal a t 910' C. Dutoit ( S ) , using the gas saturation method with a slow gas rate, determined the dissociation pressures between 1102' and 1236' C. Kakayama (11) reported that barium oxalate should be heated
TABLE I. DISSOCIATION PRESSURE OF BARIUM CARBONATE Investigator Date Method Rate of gas flow, ml. per min.
t,
' C.
lull
1057 1083 1097 1102 1114 1132 1137 1140 1157 1197 1236
1300 I
Present addreen. Lehigh University, Bethlehem, Penna.
Isambert P o t t 1878 1905 Gas Static saturation 12 p , M m . Hg
..
..
22
.. .. .. .. .. .. .. .. ..
Finkelstein 1906 Gas saturation
Dutoit 1927 Gas saturation
...
33
P
P
P
...
...
... ...
...
5
45
... 120 ... ...
...
18 21.7
...
29
...
33.6
... ...
,..
240
340 675
... ...
206 381
0.7-0.8
... ... 26 29 27
...
31 ... ... 199 ...
