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Indian Journal of Chemical Technology

 

 

 

ISSN: 0971-457X

 

CODEN:ICHTEU 10(5) 441-578

Volume 10

Number 5

September 2003

                   

CONTENTS

Research Articles

 

A sensitive extractive spectrophotometric method for the determination of palladium(II)

with 1, 3-bis(hydroxymethyl) benzimidazole-2-thione in catalysts                           447

S H Gaikwad & M A  Anuse    

 

Determination of felodipine in bulk drug and in tablets by high performance liquid chromatography                                                                                                  454

K Basavaiah, U Chandrashekar & H C Prameela

 

Determination of trace amounts of silver in natural waters after  flotation using

mercury(II) sulphide as a coprecipitant and oleic acid as a surfactant                      457

S E Ghazy & G A H Mostafa

 

Chemical and biocidal investigations on rhizome volatile oil of Curcuma

zedoaria Rosc.-Part 32                                                                                       462

Gurdip Singh, Om Prakash Singh, Y R Prasad, M P Lampasona & C Catalan

 

Spectrophotometric determination of yttrium in Y-Al alloys with

5,7-diiodoquinoline-8-ol and Rhodamine 6G                                                            466

B Vijayalekshmy, V M Biju & T Prasada Rao

 

Improvement in the yield and quality of soybean oil through an integrated biotech

approach                                                                                                            470

R P Patil, V V Gite, V L Maheshwari & R M Kothari

 

Development of a model for drying of solids in a continuous fluidized bed dryer        477

Y  Pydi Setty & J V Ramana Murthy

 

Pair interaction potential energy function for some practically important refrigerants

from the viscosity in  the limit of zero density                                                         483

Behzad Haghighi

 

Microwave-assisted synthesis of a new resin functionalized with adenine moiety

and its application for the separation of zinc and cadmium in microwave-digested

industrial sludge samples                                                                                    489

Bhim Chandra Mondal & Arabinda K Das

 

Treated fly ash: A potential catalyst for alkylation of phenol with

tert-butyl alcohol                                                                                                495

Keka Ojha, Narayan C Pradhan & Amar Nath Samanta

 

High pressure epoxidation of soyabean oil                                                            501

D  Ratna,  S K  Srivastava &  Ajit K Banthia

 

Epoxidation of olefin using Mn(III) tetraphenylporphyrin complex as catalyst         505

N Sengottuvelan, D Saravanakumar, G Thirumal, T Prabu, V Narayanan and M Kandaswamy

 

Sulphonation of arylamines: Part 13-Kinetics and mechanistic aspects of

solid state sulphonation of dichloroanilines                                                            510

Gurdip Singh, Jaya Srivastava & Jaspreet Kaur

 

Fluorescence and lasing characteristics of fluorescein calix[4]aryl hydroxamic acid   519

M S Gidwani, S K Menon &  Y K Agrawal

 

Behaviour of organic polymers on the rheological properties of Indian

bentonite-water based drilling fluid system and its effect on formation damage         525

A  Senthil Kumar, Vikas Mahto & V P  Sharma

 

Membrane based U(VI) transport across supported liquid membrane from

aqueous acidic media                                                                                           531

S R Sawant, J V Sonawane, A K Venugopalan, P K  Dey, Anil Kumar

& J N Mathur 

 

Heat   release  estimator  based  globally  linearizing  control of a chemical 

reactor                                                                                                                539

P Anand, J  Sridhar and  Ch  Venkateswarlu

 

Process  optimization for extraction and purification of Bixin from Annatto              545

V K Koul, Suman Koul & C L Tikoo

 

Studies on the copolymerization of cyclic ketene acetals with styrene                       548

Dhiraj Bhatia, D Braun & Veena Choudhary

 

Notes

Osmotic pressure measurement of polymer solutions by dynamic methods: A

discussion                                                                                                              558

M A Islam, M M R Khan & M A Sawpan

 

Density measurements of plastics – A simple standard test method                           561

Dibyendu S Bag, Bhanu Nandan, Sarfaraz Alam, L D Kandpal & G N  Mathur

 

Educator

Heike Kamerlingh-The Virial Equation of State                                                       564

Jaime Wisniak

 

 

 

Indian Journal of Chemical Technology

Vol. 10, September 2003, pp. 447-453

 

 

A sensitive extractive spectrophotometric method
for the determination of palladium(II)
with 1, 3-bis(hydroxymethyl) benzimidazole-2-thione in catalysts

S H Gaikwad & M A Anuse *

 

A simple, rapid and highly sensitive extraction method has been developed for the spectrophotometric determination of palladium(II) with 1,3-bis(hydroxymethyl)benzimidazole-2-thione[BHMBT] in methyl isobutylketone. The optimum perchloric acid range for the complexation is 0.7-3.5M. The yellow complex has an absorption maximum at 370 nm. Beer's law is obeyed up to 6.0 ppm of palladium(II). The optimum concentration range evaluated by Ringbom's method was found to be 1.32-5.01 ppm. The method of continuous variations, molar ratio method, and slope-ratio method confirmed a palladium(II) to BHMBT ratio of 1:1 in the complex. The molar absorptivity and Sandell's sensitivity were 1.543´104 L mole-1 cm-1 and 0.0068 mg cm-2, respectively. The optimum conditions have been investigated by studying parameters like effect of medium, effect of acidity, reagent concentration, time period, solvent and effect of diverse ions. The method has been applied successfully to the determination of palladium(II) in synthetic mixtures, corresponding to alloys and hydrogenation catalysts.

 

 

 

Indian Journal of Chemical Technology

Vol. 10, September 2003, pp. 454-456

 

 

Determination of felodipine in bulk drug and in tablets by high performance liquid chromatography

K Basavaiah*, U Chandrashekar & H C Prameela

 

A rapid assay procedure based on high-performance liquid chromatography (HPLC) has been developed for the specific determination of antihypertensive drug felodipine in pharmaceutical formulations (tablets). The HPLC determination was carried out on a reversed-phase C18 (250´4.6 mm i.d) column using a mobile phase consisting of acetonitrile- 20 mM aqueous ammonium acetate buffer of pH 4.5 (80+20) at a flow rate of 1.0 mL min-1 with UV defection at 236 nm. Calibration graph was linear from 2.49 to 99.60 mg mL-1. The method has been validated according to current guidelines including the assay of pharmacopoeial standard tablets. Recoveries ranged from 97.80 to 102.10%. The excipient present in the tablets did not interfere in the method. The described HPLC method is comparable in terms of accuracy and precision with that of a reported method.

 

 

 

Indian Journal of Chemical Technology

Vol. 10, September 2003, pp. 457-461

 

 

Determination of trace amounts of silver in natural waters after flotation using mercury(II) sulphide as a coprecipitant and oleic acid as a surfactant

S E Ghazy* & G A H Mostafa

 

A method for the separation and determination of trace amounts of silver in different aqueous media is based on coprecipitation of silver with Hg(II) sulphide, flotation of the precipitate with oleic acid (HOL) surfactant and redissolution with (1:1) concentrated nitric and sulphuric acids. Ag is determined by flame atomic absorption spectrometry (AAS). The different parameters influencing the processes of flotation and determination of silver viz. concentrations of coprecipitant, surfactant and major elements possibly present in some brines, acidity of the medium, agitation time, temperature and the effect of some selected foreign ions are investigated. At the optimal acidity value of the medium (0.2 M HNO3), silver is separated quantitatively (~ 100%). The procedure is extended to recover and determine silver in natural water samples (3000 mL, successful flotation 3×1000 mL); the mean concentration of Ag being 2.5 μg/L.

 

 

 

Indian Journal of Chemical Technology

Vol. 10, September 2003, pp. 462-465

 

 

Chemical and biocidal investigations on rhizome volatile oil of Curcuma zedoaria Rosc—Part 32

Gurdip Singh*, Om Prakash Singh, Y R Prasad, M P Lampasona & C Catalan

 

 Chemical investigations on Curcuma zedoaria rhizome volatile oil, using HPLC, GC and GC-MS techniques, showed the presence of 1,8-cineole (18.5%), o- and p-cymene (18.42%) and α-phellandrene (14.93%) as major constituents followed by terpinolene (4.11%), α-pinene (3.28%), β-turmerome (3.1%), β-pinene (2.93%), β-phellandrene (2.0%), etc. This oil was found to be highly insecticidal against Odontotermes obesus Rhamb. (white termite) and the minimum dose for 100% mortality was recorded as 2μL per petriplate for 24 h exposure duration. It also showed complete mycelial inhibition of Colletorichum falcatum at 4 μL per petriplate of the oil and was ineffective in controlling the mycelial growth of Aspergillus terreus, Fusarium graminearum, F. solani and Curvularia pallescens.

 

 

 

Indian Journal of Chemical Technology

Vol. 10, September 2003, pp. 466-469

 

Spectrophotometric determination of yttrium in
Y-Al alloys with 5,7-diiodoquinoline-8-ol and
Rhodamine 6G

B Vijayalekshmy, V M Biju & T Prasada Rao*

 

A simple and sensitive spectrophotometric method for the determination of yttrium in Y-Al alloys has been developed. The method is based on the extraction of ternary ion-association complex yttrium-5,7-diiodoquinoline-8-ol-Rhodamine 6G into toluene that has an absorption maximum at 540 nm. Beer’s law is obeyed over the range 0-20 mg of yttrium and the molar absorptivity coefficient is 5.3×105 L mol-1cm-1. The ternary ion-association complex in toluene is stable for about 2 h.

 

 

 

Indian Journal of Chemical Technology

Vol. 10, September 2003, pp. 470-476

 

Improvement in the yield and quality of soybean oil through an integrated biotech approach

R P Patil, V V Gite, V L Maheshwari* & R M Kothari

 

Cultivation of soybean on vast scale, deserves consideration primarily by virtue of its nutritional contents and yield improvement to be a viable oilseed on global benchmark. Using IPNM approach, comprising of soil conditioner, 3 bio-fertilizers and plant growth regulators, factorial randomized block design was conceived for experimental purpose to determine the combination of inputs that afforded maximum output. The performance of experimental design was monitored by estimating the yield of soybean seeds, its oil and protein content, as also fodder and their value addition for nutrition. By each parameter, it has been demonstrated that IPNM approach has inherent strength to improve the yield of soybean, fodder as well as quality of oil.

 

 

 

Indian Journal of Chemical Technology

Vol. 10, September 2003, pp. 477-482

 

Development of a model for drying of solids in a continuous fluidized bed dryer

Y Pydi Setty* & J V Ramana Murthy

 

A mathematical model to describe the drying characteristics of solids in a continuous fluidized bed dryer has been developed. The RTD model proposed by Pydi Setty et al.1 is used to obtain the required drying model. Experimental data in a continuous fluidized bed dryer are satisfactorily matched with the model developed. Using the model, one can predict the average moisture content relative to the initial moisture content in a continuous fluidized bed dryer for the given operating conditions.

 

 

 

Indian Journal of Chemical Technology

Vol. 10, September 2003, pp. 483-488

 

Pair interaction potential energy function for some practically important refrigerants from the viscosity in the limit of zero density

 Behzad Haghighi

 

An iterative inversion procedure is used to obtain the effective isotropic part of the pair-interaction potential for some pure refrigerants from the proposed correlation function for the zero density collision integrals of viscosity. The Lennard-Jones (LJ12-6) potential energy function is used as the initial model potential required by the method. Over a range of reduced temperature extending from 1 to 100, this measured potential can be used in the calculation of the orientation-averaged viscosity collision integrals and the dimensionless ratios which are essential to calculate other transport properties.

 

 

 

Indian Journal of Chemical Technology

Vol. 10, September 2003, pp. 489-494

 

Microwave-assisted synthesis of a new resin functionalized with adenine moiety and its application for the
separation of zinc and cadmium in microwave-digested
industrial sludge samples

Bhim Chandra Mondal & Arabinda K Das*

 

A procedure for simultaneous preconcentration and separation of traces of Zn(II) and Cd(II) has been described. It is based on the sorption on a chelating resin containing adenine moiety which has been synthesized by using microwave irradiation. The resulting resin was characterized by elemental analyses, infrared spectra and thermogravimetric analyses. The exchange capacity of the resulting resin for Zn(II) and Cd(II) was found to be 0.25 and 0.30 mmol g-1 respectively at pH 1.0. In the column operation, the recoveries of Zn(II) and Cd(II) were 98.7±3.5 and 97.5±2.1% respectively at 97.5% confidence level for both. The detection limits were found to be 4.4 ng mL–1 for Zn(II) and 9.0 ng mL–1 for Cd(II). The loading half life (t1/2) periods were 14 and 12 min for Zn(II) and Cd(II) respectively. The mutual separation of Zn(II) and Cd(II) was carried out as a function of eluting agents. The reliability of the method has been tested by analysing NIES certified pond sediment sample. The developed method has been successfully applied in analysing industrial sludge samples.

 

 

 

Indian Journal of Chemical Technology

Vol. 10, September 2003, pp. 495-500

 

Treated fly ash: A potential catalyst for alkylation of phenolwith tert-butyl alcohol

 Keka Ojha, Narayan C Pradhan & Amar Nath Samanta*

 

Alkylation of phenol was carried out with tert-butyl alcohol (TBA) over a variety of non-conventional catalysts, namely fly ash, zeolite prepared from fly ash, and commercial 13X zeolite. Zeolite prepared from fly ash by hydrothermal treatment showed the highest activity for the reaction under otherwise identical conditions. The effects of various parameters such as reaction temperature, reactant ratio (molar ratio of phenol to tert-butyl alcohol) and catalyst loading on the rate of reaction of phenol were studied with the catalyst prepared from fly ash. The alkylation reaction was found to be surface reaction controlled with negligible inter-particle mass transfer resistance.

 

 

 

Indian Journal of Chemical Technology

Vol. 10, September 2003, pp. 501-504

 

High pressure epoxidation of soyabean oil

D Ratna, S K Srivastava & Ajit K Banthia*

 

The effects of various process parameters for the high pressure epoxidation of soyabean oil have been studied. It was observed that high epoxy yield up to 80% can be obtained by optimizing the process parameters like temperature, pressure etc. Pressure was found to have significant effect on epoxy yield. Epoxy yield increases linearly with pressure and becomes constant at about 20 MPa. Optimum temperature was found to be 100°C above which the epoxy yield decreases. FTIR spectroscopic analysis indicates ring opening side reaction at higher temperature. It was also found that the epoxy yield decreases when oil to CHP ratio reduced beyond 10.

 

 

 

Indian Journal of Chemical Technology

 Vol. 10, September 2003, pp. 505-509

 

Epoxidation of olefin using Mn(III) tetraphenylporphyrin complex as catalyst

N Sengottuvelan, D Saravanakumar, G Thirumal, T Prabu, V Narayanan & M Kandaswamy*

 

Manganese(III) tetraphenylporphyrin acetate (Mn(III)(TPP)OAc) has been synthesized and characterised by C, H, N analysis, IR and electronic spectra. The electrochemical studies of the complex show a single quasireversible electron transfer process at Epc = 0.620 V. Polyisoprene and polychloroprene were epoxidized using Mn(TPP)OAc complex as catalyst and NaOCl or PhIO as oxygen donor. Both polyisoprene and polychloroprene were epoxidized completely within 7 h using NaOCl as oxygen donors and in 12 h using PhIO as the oxygen donor. The reaction was monitored by IR spectroscopy. The peak at 1020 cm-1 due to –CH=CH- disappears completely and a peak has been observed at 970 cm-1, characteristic of oxiranes, indicating the complete conversion of the polyene to polyepoxide. Cyclohexene and styrene were epoxidised using Mn(TPP)OAc complex as catalyst and NaOCl and PhIO as oxygen donors. Epoxidation of styrene is complete in 30 min with 100% yield of styrene epoxide using PhIO, whereas it takes 1 h for the completion of the reaction using NaOCl and gives mixed products with 59.71% styrene epoxide, 21.89% benzaldehyde and 18.40% phenylacetaldehyde. Epoxidation of cyclohexene is complete in 1 h using NaOCl with 33.57% cyclohexeneoxide, 13.01% of cyclohex-2-ene-1-ol and 53.42% of cyclohex-2-ene-1-one, whereas the reaction was only 31.22% completed in 1 h using PhIO with 22.06% yield of 2-cyclohexeneoxide, 4.23% of cyclohex-2-ene-1-ol and 4.93% of cyclohex-2-ene-1-one. The reaction was monitored by using gas chromatography.

 

 

Indian Journal of Chemical Technology

Vol. 10, September 2003, pp. 510-518

 

Sulphonation of arylamines: Part 13¾Kinetics and mechanistic aspects of solid state sulphonation of dichloroanilines

Gurdip Singh*, Jaya Srivastava & Jaspreet Kaur

 

Four dichloroanilinium sulphate (DCAS) and one dichloroanilinium hydrogen sulphate (DCAHS) salts have been prepared and characterized by elemental analysis and spectral data. Thermolysis of these salts has been evaluated by TG (static air), simultaneous TG-DTG (inert atmosphere) and isothermal analyses. Dynamic and isothermal TG data were used to obtain the kinetic parameters using mechanism based kinetic equations. The thermal decomposition pathways have also been suggested for both types of salts via solid-state sulphonation involving proton transfer as primary step.

 

 

Indian Journal of Chemical Technology

Vol. 10, September 2003, pp. 519-524

 

Fluorescence and lasing characteristics of fluorescein
calix[4]aryl hydroxamic acid

 M S Gidwani, S K Menon* & Y K Agrawal

 

A new fluorogenic calix[4]arene has been synthesized by reacting acid chloride of fluorescein and partially reduced nitrocalix[4]arene. The synthesized compound is characterised by UV, NMR and mass spectra. Fluorescence characteristics of N,N¢-(fluorescein)-7,19-dinitro-25,26,27,28-tetrahydroxy-1,13 calix[4]aryl hydroxamic acid have been investigated in methanol, chloroform, toluene and dioxane and tested for lasing performance. Relative output, lasing wavelength and laser yield of the compound are reported. The dependence of solvent polarity on its lasing properties are discussed.

 

 

 

Indian Journal of Chemical Technology

Vol. 10, September 2003, pp. 525-530

 

Behaviour of organic polymers on the rheological properties of Indian bentonite-water based drilling fluid system and its effect on formation damage

A Senthil Kumar, Vikas Mahto & V P Sharma*

 

The usefulness of medium grade Indian bentonite clay for oil well drilling has been studied. The rheological properties of water bentonite system needed improvement to meet the desired results expected from a oil well drilling fluid. The effects of certain polymers like partially hydrolyzed polyacrylamide (PHPA), low viscosity sodium carboxy methyl cellulose (CMC) and polyanionic cellulose (PAC) on the rheological properties of bentonite water suspension are studied. The impact of the favourable drilling fluid developed on the formation damage is also studied by using Ruska liquid permeameter.

 

 

Indian Journal of Chemical Technology 

Vol. 10, September 2003, pp. 531-538

 

Membrane based U(VI) transport across supported liquid membrane from aqueous acidic media

S R Sawant, J V Sonawane, A K Venugopalan, P K Dey, Anil Kumar* & J N Mathur

 

Carrier-facilitated transport of U(VI) from dilute acidic nitrate solutions has been examined across a flat sheet supported liquid membrane (FSSLM) and hollow fiber supported liquid membrane (HFSLM) deploying Cyanex 272 (Cy 272) as the novel carrier. Using FSSLM system, the apparent rate constant (Kobs) increased with increasing carrier concentration and became nearly constant above 0.2 M Cy 272, thereafter decreased slightly at 0.4 M Cy 272. Accurel polypropylene thin film support coded as 2E-PP and dodecane as the membrane solvent were invariably used. Among the several reagents tested, oxalic acid (0.9 M) served as the most efficient strippant for U(VI) across Cy 272-FSSLM as well as HFSLM systems. Application of this simple method has been extended for the removal of uranium from phosphate waste, which is generated in analytical laboratory of fuel reprocessing plant. In addition, transport of uranium was accomplished in presence of plutonium, americium and fission product contaminants from aqueous acidic media.

 

 

 

Indian Journal of Chemical Technology

Vol. 10, September 2003, pp. 539-544

 

Heat release estimator based globally linearizing control of a chemical reactor

 P Anand, J Sridhar & Ch Venkateswarlu*

 

An energy model based, globally linearizing controller (EMBGLC), supported by a deterministic filter, is presented for temperature control of an exothermic batch reactor. The deterministic filter is used to estimate the rate of heat release required for the controller. The results of the EMBGLC supported by the deterministic filter are compared with the EMBGLC based on other deterministic heat release estimators including a direct energy balance and a kinetic rate expression. The results show that the EMBGLC based on deterministic filter provides better performance for the temperature control of the exothermic batch chemical reactor.

 

 

 

Indian Journal of Chemical Technology

Vol. 10, September 2003, pp. 545-547

 

Process optimization for extraction and purification of Bixin from Annatto

 V K Koul*, Suman Koul & C L Tikoo

 

Annatto seed of the tropical bush Bixa orellana, and its products bixin and norbixin are excellent source of natural edible colours. Process optimization of extraction of crude bixin from annatto seeds by water and mechanical agitation followed by its purification to obtain bixin by solvent extraction has been achieved. The various process parameters optimized during this study are: temperature, water/seed ratio, solvent/crude ratio, number of extractions and time of each extraction. The optimization was carried out by performing different sets of experiments and varying only one parameter, at a time, in each set of experiments. For extraction step, four extractions of one hour each at room temperature with 1:3 seed/water ratio was optimized, as this combination gave maximum yield. Similarly in case of purification, ten extractions of one hour each and refluxing in 1:20 crude bixin/solvent ratio, yielded maximum percentage of pure bixin with carotenoid percentage of 18.6%.

 

 

 

Indian Journal of Chemical Technology

Vol. 10, September 2003, pp. 548-557

 

Studies on the copolymerization of cyclic ketene acetals with styrene

Dhiraj Bhatia, D Braun & Veena Choudhary*

 

The paper describes the synthesis, characterization and copolymerisation behaviour of 2-ethylidene-4-methyl-1, 3-dioxolane (A)/2-ethylidene-4 ethyl-1,3-dioxolane (B)/2-ethylidene-1,3-dioxepane (C)/2-ethylidene-1,3-dioxane (D) monomers with styrene. Homopolymerization and copolymerization of these monomers with styrene was carried out in bulk using free radical initiator. Structural characterization was done using FTIR and 1H-NMR spectroscopy. 1H-NMR and FTIR spectroscopy was also used for the calculation of percentage ring opening and copolymer composition. The ring opening in case of ethylidene monomers having seven membered ring was maximum and minimum in case of ethylidene monomers having five membered ring.

 

Thermal characterization was done using differential scanning calorimetry and thermogravimetry in nitrogen atmosphere. Homopolymers of monomers A, C and D had Tg values of 50, -60 and -62ºC respectively. Tg of the copolymers decreased with increasing amounts of cyclic ketene acetal monomers in the copolymers. All the homopolymers and copolymers were stable upto 350°C. Biodegradability of the polymers was also evaluated using the enzyme lipase. Incorporation of 0.2 mole fraction of these cyclic ketene acetals in polystyrene backbone improves its biodegradability.

 

 

 

Indian Journal of Chemical Technology

Vol. 10, September 2003, pp. 558-560

 

Osmotic pressure measurement of polymer solutions by dynamic methods: A discussion

M A Islam*, M M R Khan & M A Sawpan

 

The data treatment procedure of osmotic pressure measurement by dynamic methods is discussed in the light of the theory of pressure relaxation. Some drawbacks of the procedures are noted and finally an improved method is proposed for the purpose.

 

 

 

Indian Journal of Chemical Technology

Vol. 10, September 2003, pp. 561-563

 

Density measurements of plastics — A simple standard test method

Dibyendu S Bag*, Bhanu Nandan, Sarfaraz Alam, L D Kandpal & G N Mathur

 

The standard test methods1 for specific gravity and density measurements of plastic materials are well-known in ASTM D792-98. The ASTM method uses the double pan beam balance. However, the beam balance is, now-a-days, being replaced by the more easily available and more sophisticated single pan electronic balance which is much easier to handle and is less time-consuming for mass measurements. The procedure and formulae for specific gravity and density measurements using a single pan electronic balance are described here. The formulae are justified with some experimental results.

 

 

 

Indian Journal of Chemical Technology

Vol. 10, September 2003, pp. 564-572

 

Heike Kamerlingh¾The Virial Equation of State

 Jaime Wisniak*

 

The main scientific contributions of Heike Kamerlingh Onnes (1853-1926) were on thermodynamics, the equation of state, and optical, magnetic, and electrical phenomena. Kamerlingh Onnes proposed the virial equation of state (a significant improvement over the one of van der Waals), extended the concept of corresponding states, performed brilliant work on the achievement of very low temperatures, studied the behaviour of materials at these low temperatures, and discovered the phenomenon of superconductivity. He was awarded the 1913 Nobel Prize for Physics for his investigations on the properties of matter at low temperature, which eventually led him to liquify helium in 1908.