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Simultaneous microdetermination of carbon, hydrogen and chlorine or bromine in organic compounds by various rapid empty-tube combustion methods
7o1anroVol 21. pp. 1093to 1095 pergat~~onPressLtd 1980 Prmted m Great Britam
SIMULTANEOUS MICRODETERMINATION OF CARBON, HYDROGEN AND CHLORINE OR BROMINE IN ORGANIC COMPOUNDS BY VARIOUS RAPID EMPTY-TUBE COMBUSTION METHODS A. B. FARAG Chemistry
Department,
Faculty
of Science, Mansoura
University,
Mansoura,
Egypt
and
M. E. ATTIAand H. N. A. HASSAN National
Research
Centre,
Dokki,
Cairo,
Egypt
(Received 3 April 1980. Accepted 3 July 1980) standard Pregl absorption tube packed with polyurethane foam mixed with a cationexchanger in the silver form, backed with a layer of “Anhydrone”, and connected between the water and carbon dioxide absorption tubes and kept at room temperature, has been employed successfully for the simultaneous determinatioh of chlorine or bromine together with carbon and hydrogen. This foam tube is suitable for use with the Belcher-Ingram, rapid straight empty-tube and rapid flash-combustion methods. Summary-A
Various
methods’p5
have
been
used
for the retention
in microdetermination of carbon and hydrogen in organic compounds by combustion in oxygen,‘-’ and for the simultaneous determination of carbon, hydrogen and halogen. Metallic silver in various forms,6-‘0 at temperatures between 400 and 600”, is most commonly used for halogen retention. Copper,’ ‘*I2 antimony,13 bismuth,14 manganese dioxide,’ 5p’ ’ lead dioxide,” silica gel,’ 9 strontium silicate” and the products from thermal decomposition of potassium permanganate2’ have also been used. Recent work22 has demonstrated that open-cell polyurethane foam can be used for the quantitative retention of iodine produced during the combustion of iodine-containing compounds. In the present work, the possibility of using the foam for the retention of chlorine and bromine and for the simultaneous determination of carbon, hydrogen and either of these halogens, has been investigated. Three rapid empty-tube combustion procedures23-25 were used. of halogen-containing
combustion
products
EXPERIMENTAL
The unloaded polyurethane foam (in cubes of about 5 mm edge) was washed three times with acetone and then dried at 80”. Silver foam was prepared by shaking 5 g of heterogeneous cation-exchange foam with 50 ml of 0.5M silver nitrate in a stoppered flask for 1 hr on a mechanical shaker, decanting the solution, and repeating the shaking with fresh silver nitrate solution. The “silver-foam”, i.e., ion-exchange foam in the silver-form, was dried at room temperature in a vacuum desiccator for 6 hr. Preparation qf the silver-foam tube A standard Pregl absorption tube was two-thirds filled with I g of the dried silver-foam followed by a thin quartzwool plug, the rest being filled with “Anhydrone” (14-22 mesh). Procedures The procedures used with the Belcher-Ingram emptytube method, 23 the straight empty-tube methodz4 and the flash-combustion method2’ were essentially those in the literature cited, but with the modifications suggested by Gawargious and Farag’ for the quantitative decomposition of highly halogenated compounds. The halogen absorption tube was connected between the water and carbon-dioxide absorption tubes and kept at room temperature. After the combustion, the combustion train was flushed with oxygen for 15 min. The absorption tubes were detached and wiped as usual. The weights of the absorption tubes were recorded on the 3rd minute for water, the 6th for carbon dioxide and the 10th for halogen.
Reagents and materials All reagents were of microanalytical-reagent grade unless otherwise specified. Flexible polyurethane foam, a polyether of open-cell type, was supplied by Greiner K. G. Schaumstoffwerk-Kremsumunster, Austria. PolyurethaneVarion KS heterogeneous ion-exchange foam26 was kindly provided by Professor Dr. T. Braun, Institute of Inorganic and Analytical Chemistry, L. Eiitvijs University, Budapest, and contained 40% w/w of Varion KS sulphonated polystyrene cation-exchanger, 0.34.5 mm particle size (Nitrokemia, Fuzfogyartslep, Fuzfo, Hungary). TAL. 27:12-E
RESULTS AND DlSCUSSlON
Simultaneous determination of carbon, hydrogen and chlorine or bromine, has gained little popularity, because the halogen absorption vessel must generally be heated. Polyurethane foam, however, can retain relatively large quantities of iodine at room temperature.22 Unfortunately, it proves not to be successful for chlorine or bromine. 1093
1094 Table
SHORT COMMUNICATIONS
1. Simultaneous microdetermination pounds with silver-foam
of carbon, hydrogen and chlorine or bromine in halogenated as external absorbent for halogen (mean of 4 determinations)
Belcher-Ingram method
Straight emptytube method
organic
com-
Flash combustion method
Theoretical, No.
Compound
1.
;;Cdhlorobenzoic
2.
Arginine.
3.
Benzidine.
4.
Chloroisatin
5.
Phenylsemicarbazide. HCl
6.
p-Chloroaniline
HCI
HCI
C H Cl C H Cl C H Cl C H Cl C H
Cl
Chloranil Hexachloroethane p-Bromobenzoic acid
Found,
%
C H Cl C Cl C Cl C H Br c H Br C H Br C H Br C
53.70 3.22 22.64 34.21 7.18 16.83 56.04 5.49 27.57 52.91 2.22 19.53 44.80 5.37 18.90 56.49 4.74 27.79 29.23 57.77 10.15 89.95 41.82 2.51 39.75 30.55 1.71 67.75 41.65 2.91 46.19 65.39 3.53 31.08 17.01
10.
p-Dibromobenzene
11.
p-Bromophenol
12.
9-Bromophenanthrene
13.
Bromanil
14.
Bromoaniline
Br C H
75.44 41.89 3.52
15.
5,7-Dibromo-8hydroxyquinoline
Br C H Br
46.45 35.68 1.66 52.75
% Std. devn., % Found, % Std. devn., % Found, % Std. devn., %
53.74 3.34 22.67 34.23 7.23 16.92 56.15 5.56 27.40 52.92 2.31 19.58
0.38 0.28 0.41 0.37 0.32 0.26 0.24 0.19 0.13 0.22 0.34 0.29
29.11 57.61 10.12 89.92 41.75 2.51 39.67 30.42 1.70 67.59 41.52 2.87 46.13 65.47 3.62 31.01 17.21 75.29
0.26 0.23 0.09 0.10 0.13 0.13 0.22 0.18 0.27 0.28 0.27 0.20 0.25 0.34 0.11 0.22 0.27 0.06
Braun et a1.26,27 have prepared a heterogeneous ion-exchange foam in which a finely ground commercial ion-exchange resin (e.g., Varion KS) is built into a polyurethane foam matrix of the open-cell, polyether type. The mechanical properties of this ion-exchange foam were the same as those of the foam containing no ion-exchange resin, and the distribution of the ionexchange resin grains was uniform. We thought that this ion-exchange foam in the silver form might have a higher efficiency than polyurethane foam for the absorption of chlorine and bromine from the combustion products. The silver-foam was packed in a Pregl absorption tube and backed with anhydrone to retain any moisture removed from the foam layer by the fast flow of
53.89 3.03 22.77 34.43 6.99 16.97 56.29 5.10 27.68 52.78 2.12 19.71 44.74 5.10 18.62 56.65 4.41 27.73 29.34 57.47 10.36 89.95 42.07 2.65 39.68 30.66 1.78 67.85 41.87 3.04 46.39 65.48 3.75 31.22 17.01 75.14 41.80 3.46 46.56 35.67 1.64 52.50
0.20 0.11 0.32 0.22 0.06 0.17 0.13 0.09 0.31 0.19 0.05 0.25 0.17 0.06 0.25 0.26 0.11 0.30 0.24 0.16 0.24 0.39 0.05 0.03 0.22 0.13 0.11 0.13 0.10 0.15 0.03 0.15 0.06 0.06 0.21 0.11 0.24 0.12 0.29 0.31 0.20 0.28
53.77 3.25 22.80 34.27 7.15 16.85 56.02 5.53 27.45
0.20 0.20 0.20 0.24 0.28 0.34 0.30 0.20 0.22
29.16 55.55 10.09 86.49 41.79 2.59 39.66 30.56 1.87 67.53 41.64 2.95 46.09 65.49 3.51 31.07 17.11 73.28
0.14 0.33 0.22 1.24 0.18 0.13 0.19 0.24 0.15 0.05 0.26 0.24 0.25 0.29 0.07 0.26 0.23 0.82
oxygen, and used at room temperature between the water and the carbon dioxide absorption tubes. The results obtained by all three methods are summarized in Table 1. No problems were encountered in the analysis of halogenated organic compounds by the Belcher-Ingram and rapid straight empty-tube methods but with the flash combustion method low halogen figures were obtained for chloranil, bromanil and hexachloroethane, probably because of incomplete decomposition of these thermally stable organic compounds by this combustion method. Using the silver-foam material at room temperature is more convenient than using a silica absorption tube (packed with silver gauze) at 5oo”.9 The method was then examined for the analysis of
SHORT
COMMUNICATIONS
organic compounds carbon, hydrogen, suitable (cf. Table connected between
containing nitrogen together with halogen and oxygen, and found 1) if a manganese dioxide tube is the silver-foam tube and the carbon dioxide tube, for the removal of acidic nitrogen oxides from the combustion moducts. The method cannot be used for compounds containing sulphur, however. Although the results show no overall bias, the precision is moorer than that obtainable when the same combustion methods are used for the determination of only carbon and hydrogen, and the halogen is determined separately by methods such as oxygen-flask combustion and titration, but may be adequate for certain control-analysis
purposes.
9. Y. A. Gawargious and A. B. Farag, Microchem. J., 1969, 14, 363. 10. A. B. Sakla, M. Rashid, 0. Karim and B. N. Barsoum, Anal. Chim. Actu, 1978,98, 121. 11. A. S. Zabrodina and N. F. Egorova, Vesrn. Moskov. Univ., Ser. Khim., 1960, 66. 12. A. S. Zabrodina and S. Ya. Levina. Zh. Analit., Khim., 1962, II, 644. 13. A. A. Abramyan and S. M. Atashyan, Izv. Akad. Nauk Armyan SSR, Khim. Nauk. Ser. Rhim., 1961, 14,401.
14, Idem, ibid,, 1965,18, 216,
15. G. Ingram. Mikrochim Acta. 1953. 71. 16. R. Beicher and G. Ingram, &al. Chim. Acra, 1950, 4, 118. 17. 0. Hadiija, Mikrochim. Acta, 1968, 917. 18. Idem, ibid.. 1970, 970. 19 T. A. Mikhailova and N. V. Khromov-Borisov, Zh. Anal& Khim., 1970, 25, 1194; Anal. Absw., 1971, 21, 3441. 20. E. 1. Margolis and G. G. Lyamina, Vestn. Moskou. Univ., Ser. Khim., 1963, 66.
REFERENCES
21.
A. A. Abramyan and R. A. Mergoyan, irv. Akad. Nauk.
(ed.), 5th Ed., Churchill, London, 1951. A. Friedrich, Mikrochemie, 1931, 10, 342. S. J. Clark, Quantitative Methods of Organic Microanalysis, Butterworths, London, 1956. W. Potman, J. G. van Ommen and E. A. M. F. Dahmen, Mikrochim. Acta, 1975 1, 633. A. Campiglo, Farmaco, Ed. Sci., 1964, 19, 943. R. Belcher and C. E. Spooner, J. Chem. Sot., 1943, 313. N. E. Gel’man, V. I. Skorobogatova, Yu. M. Faershtein and I. M. Korotaeva, Zh. Analit. Khim., 1973, 28, 611. G. Gutbier and G. Rockstroh, Mikrochim. Acta, 1962,
22.
A. B. Farag, M. E. Attia and H. N. A. Hassan, Mikro-
686.
27.
1. F. Pregl, Quantitative Organic Microanalysis, J. 2. 3. 4. 5. 6. 7. 8.
1095
Grant
Armyan SSR, Ser. Khim., 1967, 2Q, 191. chim. Acra, in the press.
23. R. Belcher and G. Ingram, Anal. Chim. Acta, 1950, 4, 118. 24. Y. A. Gawargious and A. B. Farag, Mikrochim. Acta, 1969, 585. 25. V. A. Klimova and R. A. Dubinskii, IZU. Akad. Nauk SSSR, Ser. Khim., 1969, 191; Anal. Abstr., 1970, 18, 3146. 26. T. Braun, 0. Bekeffy, I. Haklits, K. Kadar and G. Majoros, Anal. Chim. Acta, 1973, 64, 45.
T. Braun and A. B. Farag, ibid., 1974, 68, I 19.
SIMULTANEOUS MICRODETERMINATION OF CARBON, HYDROGEN AND CHLORINE OR BROMINE IN ORGANIC COMPOUNDS BY VARIOUS RAPID EMPTY-TUBE COMBUSTION METHODS A. B. FARAG Chemistry
Department,
Faculty
of Science, Mansoura
University,
Mansoura,
Egypt
and
M. E. ATTIAand H. N. A. HASSAN National
Research
Centre,
Dokki,
Cairo,
Egypt
(Received 3 April 1980. Accepted 3 July 1980) standard Pregl absorption tube packed with polyurethane foam mixed with a cationexchanger in the silver form, backed with a layer of “Anhydrone”, and connected between the water and carbon dioxide absorption tubes and kept at room temperature, has been employed successfully for the simultaneous determinatioh of chlorine or bromine together with carbon and hydrogen. This foam tube is suitable for use with the Belcher-Ingram, rapid straight empty-tube and rapid flash-combustion methods. Summary-A
Various
methods’p5
have
been
used
for the retention
in microdetermination of carbon and hydrogen in organic compounds by combustion in oxygen,‘-’ and for the simultaneous determination of carbon, hydrogen and halogen. Metallic silver in various forms,6-‘0 at temperatures between 400 and 600”, is most commonly used for halogen retention. Copper,’ ‘*I2 antimony,13 bismuth,14 manganese dioxide,’ 5p’ ’ lead dioxide,” silica gel,’ 9 strontium silicate” and the products from thermal decomposition of potassium permanganate2’ have also been used. Recent work22 has demonstrated that open-cell polyurethane foam can be used for the quantitative retention of iodine produced during the combustion of iodine-containing compounds. In the present work, the possibility of using the foam for the retention of chlorine and bromine and for the simultaneous determination of carbon, hydrogen and either of these halogens, has been investigated. Three rapid empty-tube combustion procedures23-25 were used. of halogen-containing
combustion
products
EXPERIMENTAL
The unloaded polyurethane foam (in cubes of about 5 mm edge) was washed three times with acetone and then dried at 80”. Silver foam was prepared by shaking 5 g of heterogeneous cation-exchange foam with 50 ml of 0.5M silver nitrate in a stoppered flask for 1 hr on a mechanical shaker, decanting the solution, and repeating the shaking with fresh silver nitrate solution. The “silver-foam”, i.e., ion-exchange foam in the silver-form, was dried at room temperature in a vacuum desiccator for 6 hr. Preparation qf the silver-foam tube A standard Pregl absorption tube was two-thirds filled with I g of the dried silver-foam followed by a thin quartzwool plug, the rest being filled with “Anhydrone” (14-22 mesh). Procedures The procedures used with the Belcher-Ingram emptytube method, 23 the straight empty-tube methodz4 and the flash-combustion method2’ were essentially those in the literature cited, but with the modifications suggested by Gawargious and Farag’ for the quantitative decomposition of highly halogenated compounds. The halogen absorption tube was connected between the water and carbon-dioxide absorption tubes and kept at room temperature. After the combustion, the combustion train was flushed with oxygen for 15 min. The absorption tubes were detached and wiped as usual. The weights of the absorption tubes were recorded on the 3rd minute for water, the 6th for carbon dioxide and the 10th for halogen.
Reagents and materials All reagents were of microanalytical-reagent grade unless otherwise specified. Flexible polyurethane foam, a polyether of open-cell type, was supplied by Greiner K. G. Schaumstoffwerk-Kremsumunster, Austria. PolyurethaneVarion KS heterogeneous ion-exchange foam26 was kindly provided by Professor Dr. T. Braun, Institute of Inorganic and Analytical Chemistry, L. Eiitvijs University, Budapest, and contained 40% w/w of Varion KS sulphonated polystyrene cation-exchanger, 0.34.5 mm particle size (Nitrokemia, Fuzfogyartslep, Fuzfo, Hungary). TAL. 27:12-E
RESULTS AND DlSCUSSlON
Simultaneous determination of carbon, hydrogen and chlorine or bromine, has gained little popularity, because the halogen absorption vessel must generally be heated. Polyurethane foam, however, can retain relatively large quantities of iodine at room temperature.22 Unfortunately, it proves not to be successful for chlorine or bromine. 1093
1094 Table
SHORT COMMUNICATIONS
1. Simultaneous microdetermination pounds with silver-foam
of carbon, hydrogen and chlorine or bromine in halogenated as external absorbent for halogen (mean of 4 determinations)
Belcher-Ingram method
Straight emptytube method
organic
com-
Flash combustion method
Theoretical, No.
Compound
1.
;;Cdhlorobenzoic
2.
Arginine.
3.
Benzidine.
4.
Chloroisatin
5.
Phenylsemicarbazide. HCl
6.
p-Chloroaniline
HCI
HCI
C H Cl C H Cl C H Cl C H Cl C H
Cl
Chloranil Hexachloroethane p-Bromobenzoic acid
Found,
%
C H Cl C Cl C Cl C H Br c H Br C H Br C H Br C
53.70 3.22 22.64 34.21 7.18 16.83 56.04 5.49 27.57 52.91 2.22 19.53 44.80 5.37 18.90 56.49 4.74 27.79 29.23 57.77 10.15 89.95 41.82 2.51 39.75 30.55 1.71 67.75 41.65 2.91 46.19 65.39 3.53 31.08 17.01
10.
p-Dibromobenzene
11.
p-Bromophenol
12.
9-Bromophenanthrene
13.
Bromanil
14.
Bromoaniline
Br C H
75.44 41.89 3.52
15.
5,7-Dibromo-8hydroxyquinoline
Br C H Br
46.45 35.68 1.66 52.75
% Std. devn., % Found, % Std. devn., % Found, % Std. devn., %
53.74 3.34 22.67 34.23 7.23 16.92 56.15 5.56 27.40 52.92 2.31 19.58
0.38 0.28 0.41 0.37 0.32 0.26 0.24 0.19 0.13 0.22 0.34 0.29
29.11 57.61 10.12 89.92 41.75 2.51 39.67 30.42 1.70 67.59 41.52 2.87 46.13 65.47 3.62 31.01 17.21 75.29
0.26 0.23 0.09 0.10 0.13 0.13 0.22 0.18 0.27 0.28 0.27 0.20 0.25 0.34 0.11 0.22 0.27 0.06
Braun et a1.26,27 have prepared a heterogeneous ion-exchange foam in which a finely ground commercial ion-exchange resin (e.g., Varion KS) is built into a polyurethane foam matrix of the open-cell, polyether type. The mechanical properties of this ion-exchange foam were the same as those of the foam containing no ion-exchange resin, and the distribution of the ionexchange resin grains was uniform. We thought that this ion-exchange foam in the silver form might have a higher efficiency than polyurethane foam for the absorption of chlorine and bromine from the combustion products. The silver-foam was packed in a Pregl absorption tube and backed with anhydrone to retain any moisture removed from the foam layer by the fast flow of
53.89 3.03 22.77 34.43 6.99 16.97 56.29 5.10 27.68 52.78 2.12 19.71 44.74 5.10 18.62 56.65 4.41 27.73 29.34 57.47 10.36 89.95 42.07 2.65 39.68 30.66 1.78 67.85 41.87 3.04 46.39 65.48 3.75 31.22 17.01 75.14 41.80 3.46 46.56 35.67 1.64 52.50
0.20 0.11 0.32 0.22 0.06 0.17 0.13 0.09 0.31 0.19 0.05 0.25 0.17 0.06 0.25 0.26 0.11 0.30 0.24 0.16 0.24 0.39 0.05 0.03 0.22 0.13 0.11 0.13 0.10 0.15 0.03 0.15 0.06 0.06 0.21 0.11 0.24 0.12 0.29 0.31 0.20 0.28
53.77 3.25 22.80 34.27 7.15 16.85 56.02 5.53 27.45
0.20 0.20 0.20 0.24 0.28 0.34 0.30 0.20 0.22
29.16 55.55 10.09 86.49 41.79 2.59 39.66 30.56 1.87 67.53 41.64 2.95 46.09 65.49 3.51 31.07 17.11 73.28
0.14 0.33 0.22 1.24 0.18 0.13 0.19 0.24 0.15 0.05 0.26 0.24 0.25 0.29 0.07 0.26 0.23 0.82
oxygen, and used at room temperature between the water and the carbon dioxide absorption tubes. The results obtained by all three methods are summarized in Table 1. No problems were encountered in the analysis of halogenated organic compounds by the Belcher-Ingram and rapid straight empty-tube methods but with the flash combustion method low halogen figures were obtained for chloranil, bromanil and hexachloroethane, probably because of incomplete decomposition of these thermally stable organic compounds by this combustion method. Using the silver-foam material at room temperature is more convenient than using a silica absorption tube (packed with silver gauze) at 5oo”.9 The method was then examined for the analysis of
SHORT
COMMUNICATIONS
organic compounds carbon, hydrogen, suitable (cf. Table connected between
containing nitrogen together with halogen and oxygen, and found 1) if a manganese dioxide tube is the silver-foam tube and the carbon dioxide tube, for the removal of acidic nitrogen oxides from the combustion moducts. The method cannot be used for compounds containing sulphur, however. Although the results show no overall bias, the precision is moorer than that obtainable when the same combustion methods are used for the determination of only carbon and hydrogen, and the halogen is determined separately by methods such as oxygen-flask combustion and titration, but may be adequate for certain control-analysis
purposes.
9. Y. A. Gawargious and A. B. Farag, Microchem. J., 1969, 14, 363. 10. A. B. Sakla, M. Rashid, 0. Karim and B. N. Barsoum, Anal. Chim. Actu, 1978,98, 121. 11. A. S. Zabrodina and N. F. Egorova, Vesrn. Moskov. Univ., Ser. Khim., 1960, 66. 12. A. S. Zabrodina and S. Ya. Levina. Zh. Analit., Khim., 1962, II, 644. 13. A. A. Abramyan and S. M. Atashyan, Izv. Akad. Nauk Armyan SSR, Khim. Nauk. Ser. Rhim., 1961, 14,401.
14, Idem, ibid,, 1965,18, 216,
15. G. Ingram. Mikrochim Acta. 1953. 71. 16. R. Beicher and G. Ingram, &al. Chim. Acra, 1950, 4, 118. 17. 0. Hadiija, Mikrochim. Acta, 1968, 917. 18. Idem, ibid.. 1970, 970. 19 T. A. Mikhailova and N. V. Khromov-Borisov, Zh. Anal& Khim., 1970, 25, 1194; Anal. Absw., 1971, 21, 3441. 20. E. 1. Margolis and G. G. Lyamina, Vestn. Moskou. Univ., Ser. Khim., 1963, 66.
REFERENCES
21.
A. A. Abramyan and R. A. Mergoyan, irv. Akad. Nauk.
(ed.), 5th Ed., Churchill, London, 1951. A. Friedrich, Mikrochemie, 1931, 10, 342. S. J. Clark, Quantitative Methods of Organic Microanalysis, Butterworths, London, 1956. W. Potman, J. G. van Ommen and E. A. M. F. Dahmen, Mikrochim. Acta, 1975 1, 633. A. Campiglo, Farmaco, Ed. Sci., 1964, 19, 943. R. Belcher and C. E. Spooner, J. Chem. Sot., 1943, 313. N. E. Gel’man, V. I. Skorobogatova, Yu. M. Faershtein and I. M. Korotaeva, Zh. Analit. Khim., 1973, 28, 611. G. Gutbier and G. Rockstroh, Mikrochim. Acta, 1962,
22.
A. B. Farag, M. E. Attia and H. N. A. Hassan, Mikro-
686.
27.
1. F. Pregl, Quantitative Organic Microanalysis, J. 2. 3. 4. 5. 6. 7. 8.
1095
Grant
Armyan SSR, Ser. Khim., 1967, 2Q, 191. chim. Acra, in the press.
23. R. Belcher and G. Ingram, Anal. Chim. Acta, 1950, 4, 118. 24. Y. A. Gawargious and A. B. Farag, Mikrochim. Acta, 1969, 585. 25. V. A. Klimova and R. A. Dubinskii, IZU. Akad. Nauk SSSR, Ser. Khim., 1969, 191; Anal. Abstr., 1970, 18, 3146. 26. T. Braun, 0. Bekeffy, I. Haklits, K. Kadar and G. Majoros, Anal. Chim. Acta, 1973, 64, 45.
T. Braun and A. B. Farag, ibid., 1974, 68, I 19.