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An improved nitrometer for Dumas nitrogen determination
MICROCHEMICAL
7, 277-282 (1963)
JOURNAL
An Improved
Nitrometer for Dumas Nitrogen Determination TETSUO
Department
MITSUI
of Agricultural Kyoto
Chemistry, College of Agriculture, University, Kyoto, Japan
Received July 16, 1963 INTRODUCTION
A nitrometer operated without a leveling bulb was reported in a previous paper (2). Although it has been conveniently used hitherto in the author’s laboratory, the number of nitrogen analyses carried out with an apparatus is increasing due to the contribution of a rapid combustion with an increased flow-rate of carbon dioxide, so that it appears to be necessary to have a much larger capacity of the potash solution in the nitrometer. A nitrometer described here is assembled with several parts which are connected with ground glass joints. MATERIALS
Description
AND
METHODS
of the Nitrometer
Figure 1 shows the assembled apparatus. It consists of a barrel (A) with a gas inlet tube (B), a zigzag tube (C), an inverted funnel (D), a ground glass dome (E) with an air inlet tube (F), a stem (G), a roll of nickel gauze (H), a bulb (I), a plunger of Daiflone (J), and a knurled brass disk (K). The combustion gases introduced into the nitrometer rise from the beak end of the gas inlet tube through the mercury; all of the gas bubbles pass up through the zigzag tube, which has been hung from the funnel with a stainless steel wire. The speed of the bubbles rising in the potash solution is retarded by the tube, so that the reaction of carbon dioxide with potash is assured to be complete. The funnel is conjugated to the stem with a piece of polyethylene tubing. Two kinds of graduations are marked on the stem, as has been reported in a previous paper (2). The graduation starts from about 1.5mm below 277
TETSUO
278
MITSUI
J K i
-0.OOml.
1
--r
26cm.
-l.OOml.
H
-1.50ml.
20cm.
I
~.
FIG. 1.
Assembled nitrometer.
NITROMETER
279
the upper orifice up to 1.00 ml, in 0.01 ml graduations. A line of 1.50 ml is marked about 30 mm below the 1.00 ml line without any interval divisions. A roll of nickel gauze (about 100 mesh, 10 mm in length) is inserted into the stem until the lower end of the roll coincides with the zero line of the graduation. This arrangement serves to stop the gas bubbles rising in the potash solution at the zero line, so that the top meniscus of the nitrogen column can be situated exactly at the zero line without further adjustments. The walls of the tube are drained slowly so that the volume of nitrogen can be read immediately after the combustion, without the usual waiting period. The plunger is made of Daiflone (or Teflon) and is clamped with three screws (L in Fig. 1) in the knurled disk; a male plug (M) has been fixed into the top opening of the nitrometer with Kroenig’s cement as a sealing agent. Filling
of the Nitrometer
Pure mercury is poured into the barrel of the nitrometer until its level is about 2 mm higher than the beak end of the gas inlet tube; the potash solution is then added up to the neck of the barrel. Since the barrel has a capacity of approximately 450 ml, at least 150 determinations can be carried out without renewing the potash solution. The dome, to which the stem, funnel, and zigzag tube have been connected, is attached to the barrel with a small amount of grease as a lubricating agent. The ground surface of the dome must not be contaminated by potash solution since the surface will be attacked and the ground joint may be apt to stick. The gas inlet tube is then connected to the combustion train in the usual way. A small air pump (or a hand-bellows) is connected to the air inlet tube by means of a vinyl tubing. The barrel is opened to the atmosphere through the air pump when the pump is not being operated. The plunger is raised by rotating the knurled disk, and the air pump is operated to force the solution upwards. When the barrel, stem, and lower part of the upper bulb are filled with the solution, the upper orifice is closed with the plunger. The pressure of nitrogen (p) collected in the stem is lower than the atmospheric pressure, as illustrated by the following equation: p=p-H
(1)
where P is the atmospheric pressure and H is the height of the potash meniscus from the level of the potash solution in the barrel. The actual
280
TETSUO MITSUI
volume of the nitrogen (V) under the atmospheric pressure is therefore calculated by the following equation:
I/xv-((H-h)vp/P=v-c where v is the nitrogen volume read under the pressure p, h is the height of the column of the potash solution rising up in the stem by capillary attraction, and p is the density of the potash solution. In the previous paper, tolerable deviation of the values of P, H, and p were calculated and it was shown that each of P and p could be estimated practically as a constant value. Table 1 shows the correction values c, calculated from equation (2).
2oc
1.00
0
-1.60
: 0.020
0.5
ml
1.0
NITROMETER
READINB
(ml.1 FIG. 2.
Correction
curve plotted
from correction
values c.
For practical use, such a corrective curve as shown in Fig. 2 is prepared, with which the volume of nitrogen in the nitrometer can be reduced to the volume under the atmospheric pressure. The nitrogen content is therefore calculated as: N% = 100 X F X f X (v--)/S,
281
NITROMETER
where F (mg) is the weight of 1 ml nitrogen at the barometric pressure and the temperature in the laboratory, f is the summarized correction factor at room temperature obtained from the table of Hozumi (I), c (ml) is the correction value obtained from Fig. 2, and S (mg) is the weight of the sample. If the volume of nitrogen collected in the nitrometer exceeds 1.00 ml, the plunger is raised slightly by rotating the knurled disk so that the nitrogen column is lowered with the potash solution until the bottom meniscus coincides with the scale line of 1.50 ml, and then the upper meniscus (21’) is read. The nitrogen volume ZJis calculated from: 21= 1.500 - U’ After the reading of the nitrogen volume is complete, the plunger is raised and the air pump is operated so that the nitrogen in the stem TABLE CALCULATED
v (ml)a 1so 1.oo 0.90 0.80 0.70 0.60 0.50 0.40 0.30 0.20
0.10
H--h
1
CORRECTION VALUES
(cm)
v(H-h)
(c)
CT (H-h)
v p/P (ml)
9.3
13.95
0.00195
12.6
12.60
0.00176
14.2
12.78
15.8
12.64
0.00179 0.00177
17.5 19.1 20.7 22.4 23.9 25.6 27.2
12.25 11.46 10.35 8.92 7.17 5.12 2.72
5 H, length measured with 1033.6 cm H,O.
the nitrometer;
0.00171 0.00160 0.00145 0.00125
0.00100 0.00072 0.00038
h, 0.9 cm; p, 1.445; P, 760 mmHg =
is expelled through the pad of the roll of nickel gauze with the potash solution and the nitrometer is now ready for the next combustion. SUMMARY A nitrometer having a large capacity for potash solution is described. With the nitrometer, 150 or more microdeterminations can be carried out without renewing of the potash solution. It is operated without a leveling bulb, but the volume of nitrogen read in the nitrometer is reduced to its equivalent under atmospheric pressure with a correction curve. Other modifications are made in which a small pad of nickel gauze is inserted in the stem to stop the nitrogen bubbles at the zero
282
TETSUO
MITSUI
position, and a zigzag tube is placed in the barrel to ensure the absorption dioxide in the potash solution.
of carbon
REFERENCES 1. 2.
K., AND AMAKO, S., Modified Dumas nitrogen determination: The correct temperature for the reduced copper. Mikrochim. Acta 1969, 230-242. MITSUI, T., A new simple nitrometer for Dumas nitrogen determination. Mikrochim. Acta 1960, 150-156. HOZUMI,
7, 277-282 (1963)
JOURNAL
An Improved
Nitrometer for Dumas Nitrogen Determination TETSUO
Department
MITSUI
of Agricultural Kyoto
Chemistry, College of Agriculture, University, Kyoto, Japan
Received July 16, 1963 INTRODUCTION
A nitrometer operated without a leveling bulb was reported in a previous paper (2). Although it has been conveniently used hitherto in the author’s laboratory, the number of nitrogen analyses carried out with an apparatus is increasing due to the contribution of a rapid combustion with an increased flow-rate of carbon dioxide, so that it appears to be necessary to have a much larger capacity of the potash solution in the nitrometer. A nitrometer described here is assembled with several parts which are connected with ground glass joints. MATERIALS
Description
AND
METHODS
of the Nitrometer
Figure 1 shows the assembled apparatus. It consists of a barrel (A) with a gas inlet tube (B), a zigzag tube (C), an inverted funnel (D), a ground glass dome (E) with an air inlet tube (F), a stem (G), a roll of nickel gauze (H), a bulb (I), a plunger of Daiflone (J), and a knurled brass disk (K). The combustion gases introduced into the nitrometer rise from the beak end of the gas inlet tube through the mercury; all of the gas bubbles pass up through the zigzag tube, which has been hung from the funnel with a stainless steel wire. The speed of the bubbles rising in the potash solution is retarded by the tube, so that the reaction of carbon dioxide with potash is assured to be complete. The funnel is conjugated to the stem with a piece of polyethylene tubing. Two kinds of graduations are marked on the stem, as has been reported in a previous paper (2). The graduation starts from about 1.5mm below 277
TETSUO
278
MITSUI
J K i
-0.OOml.
1
--r
26cm.
-l.OOml.
H
-1.50ml.
20cm.
I
~.
FIG. 1.
Assembled nitrometer.
NITROMETER
279
the upper orifice up to 1.00 ml, in 0.01 ml graduations. A line of 1.50 ml is marked about 30 mm below the 1.00 ml line without any interval divisions. A roll of nickel gauze (about 100 mesh, 10 mm in length) is inserted into the stem until the lower end of the roll coincides with the zero line of the graduation. This arrangement serves to stop the gas bubbles rising in the potash solution at the zero line, so that the top meniscus of the nitrogen column can be situated exactly at the zero line without further adjustments. The walls of the tube are drained slowly so that the volume of nitrogen can be read immediately after the combustion, without the usual waiting period. The plunger is made of Daiflone (or Teflon) and is clamped with three screws (L in Fig. 1) in the knurled disk; a male plug (M) has been fixed into the top opening of the nitrometer with Kroenig’s cement as a sealing agent. Filling
of the Nitrometer
Pure mercury is poured into the barrel of the nitrometer until its level is about 2 mm higher than the beak end of the gas inlet tube; the potash solution is then added up to the neck of the barrel. Since the barrel has a capacity of approximately 450 ml, at least 150 determinations can be carried out without renewing the potash solution. The dome, to which the stem, funnel, and zigzag tube have been connected, is attached to the barrel with a small amount of grease as a lubricating agent. The ground surface of the dome must not be contaminated by potash solution since the surface will be attacked and the ground joint may be apt to stick. The gas inlet tube is then connected to the combustion train in the usual way. A small air pump (or a hand-bellows) is connected to the air inlet tube by means of a vinyl tubing. The barrel is opened to the atmosphere through the air pump when the pump is not being operated. The plunger is raised by rotating the knurled disk, and the air pump is operated to force the solution upwards. When the barrel, stem, and lower part of the upper bulb are filled with the solution, the upper orifice is closed with the plunger. The pressure of nitrogen (p) collected in the stem is lower than the atmospheric pressure, as illustrated by the following equation: p=p-H
(1)
where P is the atmospheric pressure and H is the height of the potash meniscus from the level of the potash solution in the barrel. The actual
280
TETSUO MITSUI
volume of the nitrogen (V) under the atmospheric pressure is therefore calculated by the following equation:
I/xv-((H-h)vp/P=v-c where v is the nitrogen volume read under the pressure p, h is the height of the column of the potash solution rising up in the stem by capillary attraction, and p is the density of the potash solution. In the previous paper, tolerable deviation of the values of P, H, and p were calculated and it was shown that each of P and p could be estimated practically as a constant value. Table 1 shows the correction values c, calculated from equation (2).
2oc
1.00
0
-1.60
: 0.020
0.5
ml
1.0
NITROMETER
READINB
(ml.1 FIG. 2.
Correction
curve plotted
from correction
values c.
For practical use, such a corrective curve as shown in Fig. 2 is prepared, with which the volume of nitrogen in the nitrometer can be reduced to the volume under the atmospheric pressure. The nitrogen content is therefore calculated as: N% = 100 X F X f X (v--)/S,
281
NITROMETER
where F (mg) is the weight of 1 ml nitrogen at the barometric pressure and the temperature in the laboratory, f is the summarized correction factor at room temperature obtained from the table of Hozumi (I), c (ml) is the correction value obtained from Fig. 2, and S (mg) is the weight of the sample. If the volume of nitrogen collected in the nitrometer exceeds 1.00 ml, the plunger is raised slightly by rotating the knurled disk so that the nitrogen column is lowered with the potash solution until the bottom meniscus coincides with the scale line of 1.50 ml, and then the upper meniscus (21’) is read. The nitrogen volume ZJis calculated from: 21= 1.500 - U’ After the reading of the nitrogen volume is complete, the plunger is raised and the air pump is operated so that the nitrogen in the stem TABLE CALCULATED
v (ml)a 1so 1.oo 0.90 0.80 0.70 0.60 0.50 0.40 0.30 0.20
0.10
H--h
1
CORRECTION VALUES
(cm)
v(H-h)
(c)
CT (H-h)
v p/P (ml)
9.3
13.95
0.00195
12.6
12.60
0.00176
14.2
12.78
15.8
12.64
0.00179 0.00177
17.5 19.1 20.7 22.4 23.9 25.6 27.2
12.25 11.46 10.35 8.92 7.17 5.12 2.72
5 H, length measured with 1033.6 cm H,O.
the nitrometer;
0.00171 0.00160 0.00145 0.00125
0.00100 0.00072 0.00038
h, 0.9 cm; p, 1.445; P, 760 mmHg =
is expelled through the pad of the roll of nickel gauze with the potash solution and the nitrometer is now ready for the next combustion. SUMMARY A nitrometer having a large capacity for potash solution is described. With the nitrometer, 150 or more microdeterminations can be carried out without renewing of the potash solution. It is operated without a leveling bulb, but the volume of nitrogen read in the nitrometer is reduced to its equivalent under atmospheric pressure with a correction curve. Other modifications are made in which a small pad of nickel gauze is inserted in the stem to stop the nitrogen bubbles at the zero
282
TETSUO
MITSUI
position, and a zigzag tube is placed in the barrel to ensure the absorption dioxide in the potash solution.
of carbon
REFERENCES 1. 2.
K., AND AMAKO, S., Modified Dumas nitrogen determination: The correct temperature for the reduced copper. Mikrochim. Acta 1969, 230-242. MITSUI, T., A new simple nitrometer for Dumas nitrogen determination. Mikrochim. Acta 1960, 150-156. HOZUMI,