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
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.)
Recovery
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.
%
Copper Added None
44.4
481
ANALYTICAL EDITION
..
95
Summary
ether. After removal of the ether the sample should be a dry powdery solid which may. be ground in a mortar to give a uniform 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 Metals in Beer, 1941. (2) Clifcorn, L. E., Proc. .4m. SOC. Brewing Chemists, 4 t h A n n u a l Meeting, 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 , Mm. 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 ...
482
INDUSTRIAL AND ENGINEERING CHEMISTRY
d
d
?.'
Y
"w m Nm
Y Y "? N L , N mN 10
Vol. 14, No. 6
0
-0.5
FIGURE1. EFFECT
483
ANALYTICAL EDITION
June 15, 1942
0.5
1.0
T E M P E R A ~ ON R E CALCIUM CARBONATE
LOG
OF
above 520' C. to change it to the carbonate and Ziemens (15) found that the dissociation of barium carbonate is complete a t 1360' C. Table I gives the previously determined dissociation pressures of barium carbonate. The apparatus and method used in this work were those previously described (IS, Figure 1) except for the following minor modifications: The micro combustion tube, E, was Vycor glass; for temperatures below 953" C. a micro absorption tube was used in the absorption train, G, and one was also used in the by-pass, H,to determine the carbon dioxide liberated during the flushing period; the cold junction of the thermocouple was kept a t 0" C. Before starting the work on barium carbonate, the apparatus was checked by several determinations with calcium carbonate. The purified calcium carbonate was ignited at 500" C. and spectrographic analysis showed the absence of strontium and the presence of only very small traces of other elements. Using 0.5 gram of calcium carbonate and a gas rate of 13 ml. per minute a t 705" C., a value was obtained which when plotted with the previously obtained results ( I S ) shows fairly good agreement (Figure 1). Kahlbaum's "purest crystal" barium nitrate was recrystallized three times from distilled water. After the third recrystallization the crystals were filtered on a sintered-glass funnel and dried overnight at 110" C. One hundred and twenty grams of the recrystallized barium nitrate were dissolved in 1.5 liters of distilled water. This and a solution of ammonium carbonate (90 grams in 800 ml. of water) were added, s l o ~ l yand simultaneously, to 1.5 liters of hot water. The solution in the reaction vessel was stirred constantly during the addition of the reacting solutions and the barium nitrate was always kept in slight excess. After the solutions were mixed, a slight excess of carbonate was added. The barium carbonate was digested overnight on a steam bath, filtered on a sintered-glass funnel, washed free from ammonia, and ignited a t 600" C. for 12 hours. Spectroscopic analysis showed that the barium carbonate contained no significant amount of impurity and quantitative analysis by transformation to barium sulfate gave results of 99.94 and 99.95 per cent purity. The results for the determination of the dissociation pressures at various temperatures and gas rates are tabulated in Table I1 and are shown in Figure 2 b y plotting the logarithm of the pressure against the reciprocal of t h e absolute
P
FIQURE 2. EFFECT OF TEMPERATURE temperature. From this it can be easily seen that the rate
at which the inert gas is passed over the sample has a profound effect on the pressure of the carbon dioxide. If the ignition of barium carbonate is carried out in a muffle furnace, the carbon dioxide is in equilibrium with the barium carbonate and oxide; if the ignition is carried out over a blast burner in a covered crucible, the pressure of the carbon dioxide also should be very close t o the equilibrium value. Therefore, i t is desirable t o determine as closely as possible the equilibrium values for the system carbon dioxidebarium carbonate-barium oxide at various temperatures. In Figure 3 the values for the logarithm of the pressure are plotted against the rate. Because of the sharp rise in these
0
IO
RAT E
20 ML./M IN.
3(
FIQURE 3. I ~ ~ F Z C OFTRATEOF Gas FLOW
484
INDUSTRIAL AND ENGINEERING CHEMISTRY
Carbon dioxide is normally present in the atmosphere in a concentration of 0.03 per cent b y volume (8). Assuming the average barometric pressure in this vicinity is 740 mm., then the partial pressure of carbon dioxide in the atmosphere is 0.222 mm. Decomposition of the barium carbonate on heating should therefore begin when the pressure of the carbon dioxide in equilibrium with barium carbonate and oxide exceeds 0.222. According to Figure 2 the equilibrium pressure of carbon dioxide is equal to 0.222 mm. at about 860" C. It can be predicted therefore that barium carbonate if heated above 860" C. will start to lose weight.
0.5
:
953OC.
O
-0.5
-I 0
FIGURE 4
curves, the extrapolation to a rate of 0 ml. per minute cannot be made with any degree of accuracy. However, if the cube root of the rate is plotted against the logarithm of the pressure, as shown in Figure 4, a straight line results which can be extrapolated to a rate of 0 ml. per minute. The extrapolated values for the logarithm of the pressure are shown against the reciprocal of the absolute temperature in Figure 2. This line should represent approximately the equilibrium values for the pressure of carbon dioxide in the system carbon dioxidebarium carbonate-barium oxide. If White's data (IS) from heating calcium carbonate at various rates at 636" C. are plotted b y the same method, the extrapolated value for the logarithm of the pressure at zero rate is close to 0.67, which is Johnston's (IO)equilibrium value for this temperature. In order t o make sure that the decomposition of barium carbonate was proceeding according to the reaction BaC08 -+ BaO
Vol. 14, No. 6
+ CO?
several of the experiments (34, 37, 39, and 42) were checked by weighing the boat and sample before and after and comparing this loss t o the total gain in weight of the absorption tube in the train and of the one in the by-pass. The results are given in Table 111. The largest difference is 0.5 mg. and in all cases the loss in the sample was less than or equal t o the gain in the absorption tubes, which indicates that the above equation correctly represents t h e reaction occurring at this temperature.
To verify this conclusion, loss-in-weight experiments were conducted with a platinum-wound muffle furnace of about 700-ml. capacity ( l a ) . The same temperature regulator was used as in the determination of the dissociation pressures and the temperature was measured with a Bureau of Standards calibrated platinum-platinum rhodium thermocouple. The temperatures are believed to be accurate to within +5" C. Two samples of barium carbonate were wei hed into 10-ml. platinum crucibles and placed in the muffle. 8 n e crucible was covered and the other uncovered. After heating the desired length of time at a given temperature, they mere removed, allowed to cool for 20 minutes in a desiccator, and weighed. Using the same samples this procedure was repeated, varying the time of heating and the temperature. Although the barium carbonate had previously been ignited at 600" C. and was dried overnight at 110" C., a loss in weight of about 0.2 per cent occurred during the first 2 hours' heating at 845" C. This loss was thought to be due to loss of water and was confirmed in another experiment bv first heating the barium carbonate at 300" C. for 20 hours. In this case approximately the same loss occurred at 300" C., at which temperature the barium carbonate xould certainly not dissociate. The results, omitting the first 2-hour loss a t 845" C., are given in Table IV. At 865" C. a small but constant loss in weight occurred with both the covered and uncovered crucibles. This loss would not be appreciable in an ordinary analytical determination but it confirms the prediction of the dissociation curve that decomposition should start at this temperature. At 885" C. the loss, although noticeable, is not large enough to cause an appreciable error in an analytical determination if the ignition is made under
TABLE111. COMPARISOX OF Loss .kBSORPTION
BY
SAMPLETO GAIN IN
TUBES AT 999"
Run No. Weight lost by sample, mg. Cot gain in microtube in by-pass, mg. CO, ain in macrotube, mg. Totaf COz gain, mg. Total loss, mg. Difference, mg.
c.
34
37
39
42
7.5
9.1
9.0
8.9
2.670 5.3 7.97 7.5 +0.47
2.533 7.0 9.533 9.1 4-0.433
2.480 6.7 9.18 9.0 f0.18
2.520 6.4 8.92 8.9 4-0.02
CARBONATE TABLE IV. Loss IN WEIGHTOF BARIUM Sample 2 (Covered), Original Sample 1. (Uncovered), Original
Temp.
C. 845
865
885
905
Time Total at each Each temperaignition ture Hours Hours 2 16
2 14 10 12 2.5 7 12 10.5 12
38 2.5 9.5 21.5 32 44
2 2 3 12
2 4 7 19
5 lo 12
24 34 46
26
2
2
4 2
6 8
Weight 1.412a Grams ,-Loss in WeightWeight Loss Total after in at Loss each each each per hour igniiqni- temperation tion ture (av.) Grams Me. Mg. %-
Weight 1.2979 Grams ,---Loss in WeightLoss Total Weight after in at Loss !ach each each per igniigni- temperahour tion ture (av.) tion Grams Me. Mg. %
1.4122 1.4122 1.4122 1.4122 1.4121 1.4118 1.4115
1.2978 1.2976 1.2976 1.2976
0.1 0.2 0.0 0.0
0.1 0.3 0.3 0.3
0.3 0.0
0.7 0 .7
1.4113 1.4113 1.4112 1.4111 1,4109 1.4107 1.4102 1.4098 1.4090 1,4078 1.4072
0.2 0.0 0.1 0.1 0.2 0.2 0.5 0.4 0.8 1.2 0.6
0.9
1.2976 1.2974 1.2972 1.2971 1.2970
0.0 0.2 0.2 0.1 0.1
0.0 0.2 0.4 0.5 0.6
1,2970 1,2970 1.2969 1.2968 1.2967 1.2964 1.2959 1.2953 1.2943 1.2938
0.0 0.0 0.1 0.1 0.1 0.3 0.5
0.0 0.0 0.1 0.2 0.3
0.3 0.0 0.0 0.0 0.1 0.3
0.3 0.3 0.3 0.3 0.1 0.4
0,0006
0.0014
0.0
0.1 0.2 0.4 0.6 1.1 1.5 0.8 2.0 2.6
0,0023
0.023
0.6 1.0 0.5
0.0006
0.0010
0.0018
0.6
1.1 0.6 1.6 2.1
0.020
485
ANALYTICAL EDITION
June 15, 1942
conditions similar to these. At 905’ C. the loss in weight is appreciable in the course of an hour and an analytical determination would not be satisfactory if the heating were continued at this temperature for more than a few minutes. To be certain that the loss in weight was not due to the volatilization of the platinum, the empty crucibles were heated for 113 hours at 905’ C. The total loss in weight of the two crucibles was 0.2 and 0.1 mg.
Summary The dissociation of barium carbonate has been studied b y the gas saturation method of determining vapor pressures. The extrapolation of the curve of the cube root of the rate of gas flow against the logarithm of the pressure gives values for zero rate of flow or equilibrium pressures which can be used to predict the temperature at which barium carbonate will start to decompose. A prediction of the temperature at which a noticeable loss in weight mill occur when barium carbonate is ignited has been made and experiments to determine the loss in weight have borne out this prediction. Under the conditions described barium carbonate may be ignited for a short time
Glass Valve Pressure Regulator MARION J. CALDWELL
AND
H. N. BARHAM
Kansas Agricultural Experiment Station, >Ianhattan, Kans.
I
N THE course of investigations involving the evolution of highly corrosive vapors, i t became desirable to conduct experimentation at, carefully controlled pressures, both above and below atmospheric pressure. A search of the literature failed to reveal any simple device deemed capable of continued operation under the conditions to be encountered. The glass regulator here described has been found by laboratory trial to meet satisfactorily the conditions imposed. The apparatus, the construction of which is shown in the diagram, involves the sealed-chamber principle found in the vacuum regulator of McConnell ( 1 ) . It consists of two glass chambers, communicating across the ExnAu5r bottom through a mercury pool and across the top through a stopcock. Floating on the mercury in one-arm is a leadweighted float, carrying a glass rod having at its free end a ground-glass tip which serves as a needle to close the ground opening in the exhaust line. The valve parts are held in alignment by a closefitting sleeve surrounding the float stem. The vertical motion of the valve assembly is limited to about 1 mm. by the valve seat above and the glass stop beloxv. The dimensions of the regulator may be varied WEIGH within xide limits: hoxFLOAT% ever, it is essential that the H weight of the float be sufficient to ensure the opening of the valve against the
as high as 885’ C. without affecting the accuracy of the usual analytical determination, but above this temperature the loss in weight becomes appreciable.
Literature Cited Abich, Pogo. Ann., 23, 314 (1831). Brill, 2. anorg. Chem., 45,275 (1905). Dutoit, J . chim. phys., 24, 110 (1927). (4) Finkelstein, Ber., 39, 1585 (1906). (5) Hackspill and Wolf, Compt. rend., 204, 1820 (1937). (6) Hedvall, 2. anorg. Chem., 98, 47 (1916). (7) Herzfeld and Stiepel, 2. Ver. deut. Zucker-Ind.. (Z), 35, (1) (2) (3)
830
(1898). (8) (9) (10) (11) (12)
Intern. Critical Tables, Vol. I, 393 (1926). Isambert, Compt. rend., 86, 332 (1878). Johnston, J.Am. Chem. SOC.,32,938 (1910). Nakayama, J . Chem. SOC.J a p a n 47, 197 (1926). Nichols and Schempf, IND.ENQ.CHEM.,ANAL.ED., 11, 278
(13) (14)
Nichols and White, Ibid., 13,251 (1941). Pott, from Mellor, “Comprehensive Treatise on Inorganio and Theoretical Chemistry”, Vol. 111, p. 655, London, Longmans, Green and Co., 1923.
(1939),
(15) Ziemeris, 2. physik. Chem., B37, 231, 241 (1937).
pressure differential at the valve seat. Rough calculations show that slightly over 10 grams are required to open a 1 sq. mm. openingagainstapressure differentialof one atmosphere. As this weight should be displaced by the mercury column in as small a pressure range as possible, it is necessary that the cross section of the float be relatively large. A float made from a 25-mm. Pyrex ignition tube has been found to give satisfactory results. In this case, the lead-loaded float weighs approximately 100 grams, giving a sizable safety factor. In operation, the pressure in the system is allowed to build up to the desired level with the regulator stopcock open. The stopcock is then closed, thereby sealing in the large chamber a body of gas at the selected pressure. As the pressure in the system further increases, the mercury in the float chamber is depressed, allowing the valve to open and exhaust the accumulated gases until the mercury in rising again closes the needle valve. If, in operation, the system does not evolve sufficient gas to maintain the desired pressure, an inert gas may be supplemented, as indicated in the diagram. The pressure fluctuations necessary to actuate the valve mechanism may be largely eliminated a t the reaction flask by interposing a bottle of a few liters’ capacity to act as a cushion. This apparatus has been used in the authors’ laboratories for the regulation of both positive and reduced pressures. Positive pressures thus far have not exceeded 1500 mm. of mercury, although there appears no reason why higher pressures could not be controlled equally well, provided the weight relationships are kept in balance. As a reduced pressure regulator, the “exhaust” line is connected to the vacuum system and a controlled air leak is attached to the “inert gas” entrance. It is not expected that the valve should operate a t very low pressures, since several millimeters variation in pressure is required to actuate the mechanism. As the control is based upon the equalization of pressure between the system and the sealed chamber, temperature variations within the chamber directly affect the regulator precision. Under proper operating conditions, the apparatus has been found capable of controlling pressure either above or below atmospheric pressure, to about 1 mm. of mercury.
Literature Cited (1)
McConnell. C . W., IXD.ENG.CHEM.,ASAL. ED.,7,4 (1935).
CONTRIBETION No. 272, Department of Chemistry, Kansas State College Manhattan, Kans.
