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VOL. 85, NOS. 7–8 243

PURNIMA SINHA AND HER DOCTORAL WORK UNDERPROFESSOR S.N. BOSE

RAJINDER SINGH*, SUPRAKASH C. ROY**

Purnima Sinha (nee Sen-Gupta) was the first woman who received D.Phil. degree in Physics fromthe University of Calcutta. She was also one of the few students who did Ph.D. under the guidanceof Professor Satyendranath Bose of Bose-Einstein statistics fame. Since very little is known abouther research work done at Calcutta University under Prof. S.N. Bose, the present article has beenwritten with the intention of filling up this gap.

ARTICLE

* Research Group: Physics Education and History of Science, Physics Institute, University of Oldenburg, Germany. E-mail: [email protected].

** Editor-in-Chief, Science and Culture, Indian Science News Association, Kolkata 700 009.# Calcutta University offers D.Sc. degree to candidates who do their research independently and D.Phil. (equivalent to Ph.D) degree to

candidates who perform their research work under the guidance of a supervisor. We have used D.Phil and Ph.D. interchangeably in thisarticle.

Introduction

In India not much has been written on the achievementof female scientists. Not long ago, the Indian Academyof Sciences, Bangalore brought out “Lilavati’s

Daughters: The Women Scientists of India”.1 The booktalks about 100 women scientists from Victorian era topresent-day. There is a brief mention of Purnima Sinha (PS)in an article “ Like Mother like Daughter” in the abovebook. To the best of our knowledge, nothing is knownabout her scientific work, which she did in the Departmentof Physics of the Calcutta University, under the guidanceof the renowned Indian physicist S.N. Bose, who is famousfor Bose-Einstein statistics. She received her D.Phil#. degreein 1956 from Calcutta University. She was a ResearchAssociate in the Biophysics Laboratory of StanfordUniversity, USA and was a scientist in the Central Glassand Ceramic Research Institute in Kolkata. The presentarticle deals with her scientific work done at the Universityof Calcutta.

Purnima Sinha Credit : Prof. Sukanya Sinha

244 SCIENCE AND CULTURE, JULY-AUGUST, 2019

Importance of Clay – A HistoricalBackground

Twentieth century was dominated by atomic andparticle physics research. Surprisingly, while at the end of1940s and beginning of the 1950s, M.N. Saha and H.J.Bhabha started establishing institutions for the study ofnuclear physics, S.N. Bose was interested in studying“clays”. To a general reader the situation seems a bitstrange because, when we talk about clay, what comes toour mind is its relation with agriculture and pottery. Whatmade the scientist like S.N. Bose study clay is that verylittle work has been done on Indian clays and therefore,scientific classification of Indian clays using modernscientific techniques is important to understand the differentenvironmental conditions under which the particular claywas formed. In order to understand the significance ofSinha’s work, it is pertinent to start with a short history ofthe subject as given in the following paragraphs.

Scientifically, the term clay is used for shales,soilclays, and glacial clays.2 The major constituent of claymineral is illite.3 Clay minerals are a diverse group ofhydrous layer aluminosilicates that constitute the greaterpart of the phyllosilicate family of minerals. Geologistsdefine them as hydrous layer aluminosilicates with a particlesize less than 2μm, while engineers and soil scientistsdefine clay as mineral particle less than 4μm. Clay mineralsare commonly greater than 2μm, or even 4μm in at leastone dimension.4

Clay minerals are inexpensive because they areavailable in abundance in nature.5 From a historical pointof view, the praxis of washing of woollen cloth with claygoes back to about 5000 BC in Cyprus.6 In these daysclays and clay minerals have applications in various fields,such as, paper filling and coating, catalysts, ceramics, civilengineering, environmental technology, foundry sandsbinders, well drilling, bleaching and refining of oil, waterand sewage treatment, soaps and detergents, soilstabilization, cosmetics and pharmaceuticals, and fracking.7

Purnima Sinha’s Initial Scientific Work andPublication in “Nature”

In 1954, the first scientific publication of PS jointlywith A.K. Bose, Department of Physical Chemistry,University of Calcutta, was published in “Nature”. Thepaper dealt with the study of Indian montmorillonitessamples from Kashmir, Nimlinadi and Barme, and blackcotton soils from Satara, and Indore. The study was doneby x-ray diffraction and differential thermal methods (detaillater). They observed that the x-ray pattern of the clay

fraction, when treated with glycerol had the basal spacingof 17.7Å, which agreed with that of standard glycerol-montmorillonite. In the case of Nimlinadi sample, apartfrom usual montmorillonite lines, two new lines at 7.1Åand 3.5Å were observed. They were attributed to kaolinite.8

The base exchange capacities of Kashmir, Nimlinadiand Barme samples were 100, 50 and 90 milliequivalentper 100 gm. respectively. The authors were of the opinionthat the lower value in the case of Nimlinadi compared tomontmorillonite was due to the existence of kaolinite.9

In case of Kashmir montmorillonite samples, theyobserved endothermic peaks at 200°C, 680°C and 880°Cby differential thermal method. These values were inagreement with the standard curve of montmorillonite. Theexothermic peak was at 1000°C, which was 50°C morethan expected. They justified that this might be due to thehigh magnesium substitution in the octahedral layer.

From the chemical analysis they found that clay wasmade up of water: 8.4%. SiO2: 63.18%. Al2O3: 25.26%.MgO: 4.15%. Fe2O3%: trace. In the case of other foursamples the differential thermal curves differed from thestandard curve for montmorillonite.

They concluded that the studied samples: “belong tothe montmorillonite group on the basis of x-ray data; butdifferential thermal analysis reveals significant deviations,and indicates that montmorillonites from Nimlinadi andBarme, and black cotton soils from Satara, and Indoreconstitute a subgroup intermediate between montmorilloniteand nontronite. This probably means a smaller amount ofiron in the lattice than in nontronite.”10

They also studied two nontronite samples: Garfield(Washington), and Sandy Ridge (North Carolina). Theyconcluded that the information obtained from samplesmontmorillonites from Nimlinadi and Barme, and blackcotton soils from Satara and Indore, nontronite fromGarfield “form a more or less continuous link in themontmorillonite – nontronite series.”11

The article was based on her doctoral research work,which she did at the University of Calcutta.

Purnima Sinha’s Doctoral Thesis

P. Sinha’s thesis titled: “X-ray & differential thermalanalysis of Indian clays” was submitted in 1955 (Figure 1)and the degree was awarded in 1956. In “Introduction”she wrote that chemical analysis of clays shows that theyare composed essentially of silicon (Si), aluminium (Al),and water, occasionally mixed with magnesium (Mg),

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sodium (Na), calcium (Ca), potassium (K), iron (Fe) etc.Clay materials are described as amorphous gels of SiO2and Al2O3.

12 Clays have layer lattice structure. The forcesholding the layers are comparatively weak. Theclassification of clays is difficult, because in themineralogical investigation of clays, a particular samplecannot be subjected to a single, rigid system havingminerals of a particular chemical composition. R.E. Grim,U.S.A., had suggested the classification of claysasamorphous, crystalline and mixed-layer mineral.13

PS theoretically discussedcontemporary methods for studying claysand clay minerals, such as: “X-raydiffraction method”, “Differential thermalmethod”, “Dehydration”, “Base exchangecapacity”, and “Electron micrographs”. Inher investigations she mainly used the firsttwo techniques, but whenever necessary,base exchange capacity measurement andchemical analysis were also done.

In the late 1940s and the beginningof the 1950s clay minerals were being

studied in the U.S.A., U.K., Russia and other countries.About the objective of her investigations, PS wrote:

“Very little work has been done in India in x-rayand differential thermal analysis with the claysavailable in this country. As clays are formed underwidely varying environmental conditions, the studyof minerals from regions still unexplored isimportant both for the purpose of verification ofconclusions based on data so far obtained, and fornew information.”14

She studied 50 samples of clays, soils and shales fromdifferent parts of India and classified them by the followingmethods.15

X-ray Diffraction (XRD)

X-rays were discovered by W.C. Röntgen in 1895.Within about six months after the discovery, x-ray machinewas imported at the Indian Association for the Cultivationof Science (IACS), Calcutta and experiments wereperformed immediately using x-rays16. For this discoveryRöentgen was awarded the first Physics Nobel Prize in1901.17 In 1912, German physicists Max von Laue, W.Friedrich and P. Knipping established the fact that a crystaldiffracts x-rays.18,19 The British physicists W.H. Bragg andW.L. Bragg showed that reflected x-ray pattern obtainedin a Laue-photograph is characteristic of the crystal andnot of the incident x-rays.20 They gave the followingequation, which shows the relation between wavelength ofthe incident x-rays and space between the two planes ofreflection: 2d sin θ = n λ, where, d is the space betweendiffracting planes, θ is the incident angle, n is any integer,and λ is the wavelength of the incident beam. Study ofcrystals by x-rays was well known to scientists. However,Assar Hadding of Sweden studied clays by the x-raydiffraction method for the first time in 1923.21

C.V. Raman seems to be the first Indian who startedresearch work on crystals using x-rays at IACS. In order

Figure 1: Title page of P. Sen-Gupta’s doctoral thesis. Credit: Prof.Sukanya Sinha.

Figure 2: Cross-section of x-ray tube.25


to establish this field of research his student B.B. Ray wentto Europe and worked in the laboratories of M. Siegbahn,Sweden, and N. Bohr, Denmark. On his return to India in1926, he struggled hard to establish a x-ray laboratory atthe University of Calcutta. He died in July, 1944, at theage of 50. S.N. Bose left Dhaka and took charge of thelaboratory. Obviously, he had a well-equipped laboratory.In the end of 1940s, PS started working on clays in thislaboratory with x-ray diffraction technique (details below).

Experimental Set-up

Unfortunately, the photographs of the experimental setup of PS is not available. As was the tradition at that time,students built their own instruments in the laboratory.According to her own words: “Around the middle of 1951I started working on my Ph.D. with Prof. S.N. Bose at theKhaira Laboratory in Kolkata. He advised me to carry outan investigation on the structure of clay from various partsof India. He suggested that I could use techniques ofthermal and chemical analysis along with X-ray scatteringand also suggested that I fabricate my own X-ray tube ofthe Coolidge kind so that the parts could be dismantledand put together at will. At that time about ten of us wereinvolved in experimental research at the Khaira laboratory.Each of us used to fabricate his or her own instrumentaccording to individual need. This was an unwritten rulein our laboratory. The more experienced research studentsused to initiate newer students in this mode of doingresearch and Prof. Bose would routinely keep track of theproblems we faced in the lab as well as our progress. Therewas constructive cooperation between fellow students andpeople working in related departments. We all enjoyed theexcitement of doing science in this manner.” She continued“The high voltage transformer used for our X-rayequipment was fabricated in the applied physics departmentof our university. We had put together our X-ray equipmentfrom the World War II surplus gathered in the lane behindDr. Bidhan Roy’s house. The rest of the parts were puttogether at the workshop in our department.”23.

The x-ray tube she used in studying clay mineralscontained a Cu-target which was supplied with a peakvoltage of 75 kilovolt. The target was cooled with water.“A hair-pin shaped platinum filament, coated with doublecarbonate of Ca and Sr was used. A three stage mercurydiffusion pump backed by a fore pump constitutes thevacuum system. The tube operates at 30 RV and 20 mA.”24

Figure 2 is the schematic diagram of her set up, with onlydifference that she used platinum as filament.

PS also wrote that some of the photographs weretaken with a sealed Machlette unit (Figure 3).

Figure 3: Machlette tube without cover.26

In her later life, PS was proud of her self-madecamera. As mentioned in her thesis, she preferred to useadjustable plate cameras instead of commonly used circularcameras for the following reasons.

(i) “By using plate camera, specimen-to-film distancecan be decreased with the resulting gain in exposuretime.”(ii) “The adjustability of the camera helps to bringthe specimens closer to the film for minerals havingcomparatively larger spacings, and the resolution of lowerangle lines can also be increased for a particular mineral,if necessary.” (iii) “The plate camera has the additionaladvantage of permitting easier centering of the specimen,and film mounting.”27

As clays do not have structure like a crystal, the x-ray diffraction (XRD)28 alone is not enough to findinformation in a sample. This was pointed out by PS inher thesis as well.

Differential Thermal Analysis (DTA)

In 1887, H. Le Chatelier, France, studied clay mineralsby thermal dehydration method. He found that dehydrationof the fine clay materials take place within definitetemperature regions. He opined that clay must becrystalline.29 In 1905, Albert M. Atterberg, a Swedish soilscientist, investigated the flocculation of different soilfractions and developed a technique to separate clay andclay minerals by sedimentation method.30 Though credit isgiven to H. Le Chatelier for discovering the differentialthermal analysis (DTA) method, the importance of thetechnique was not realised, until 1935, before the work ofJ. Orcel, who extensively studied thermal curves of differentclays and clay minerals.31 Three years later, that is, in 1938,

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F.H. Norton started systematic studies.32 Tostudy clays the DTA was improved byseveral investigators, such as R. Wohlen33,J. Orcel34, S. Cailliere35, F. Norton36, andS.B. Hendricks37 et al.38

In differential thermal analysis, asample under investigation, and a standardsample are made to undergo identicalthermal cycles, to record thermal reactionstaking place at different temperatures. Anytemperature difference in reactions betweensample and reference is noted. Thisdifferential temperature is plotted againsttime, or against temperature. The endo- orexothermic changes in a sample can bedetected relative to the standard reference.From the known peak temperature of thestandard sample, the mineralogicalcomposition of an unknown sample couldbe determined. A differential thermal plotgives information on the transformationsthat had occurred during heating, such ascrystallization and melting.

PS wrote that she applied the experimental set up asdesigned by the American L.H. Berkelhamer. However, thedocument “United States – Department of the Interior,Bureau of Mines, Report of investigations 3764, July 1944”shows that the article was not written by Berkelhamer, butby S. Speil. Figure 4 shows the experimental set up fromthe year 1950, which appears similar to PS’s experiment,as in her thesis we read the mention of “an electric furnaceand sample holder”, “ sample block”, “temperaturecontroller”, and “photographic recorder”.

The above two methods are not enough to know thestructure of clays and clay minerals. As stated above, PSalso used the following techniques.

Base-Exchange Capacity Measurement

The exchange of cations and anions in chemicalcompounds is a common process in chemical reactions. In1852, J.T. Way, U.K., investigated the base-exchangecapacity of soils. His aim was to find out methods to cleansewerage water or convert sea’s salty water into drinkablewater. He performed 96 experiments to investigate theabsorption of different materials, urine, and ammonia bydifferent types of soils and clays.40 One of his conclusionswas:

“ordinary soils possess the power of separating fromsolution, and of retaining for the purposes ofvegetation, the bases of the different alkaline saltsand certain animal and vegetable substances, andthat this power extends to all those substances towhich we attach the chief value as manure.”41

In Holland, in 1888, J.M. Van Bemmelen, carried outinvestigations on the composition of infertile soil inGroeningen province. He proved that the gel-like silicatesprovide the adsorption sites in the soils. His aim was toimprove the infertile soil.42

The base-exchange can be represented by theequation: AX+B+ BX+A+, where AX and, BX representthe exchange material saturated with A+ and B+ cations ofequal charge. When the exchange material has only onekind of exchangeable cation, the material is said to besaturated with that ion. The total capacity of soil or claymineral to hold exchangeable cations is named as baseexchange capacity, which is expressed as milli equivalentsper 100 grams.43

Some clay minerals can absorb cations and retain themin an exchangeable state. The cations become a part of thelattice. Clay minerals of different groups have characteristicexchange capacities. “Measurement of cation exchange

Figure 4: Differential thermal analysis test equipment from the year 1950. A: Furnace, B:Specimen holder, C: Transformer to heat the furnace, D: A motor driven variable transformerto control the voltageinput to the furnace, E: Potentiometer pyrometer to record furnacetemperature and regulatethe heatingrate., and F: Autographic recording instrument to measuresthetemperature of the clay sample and the difference intemperature between the clay sampleand the thermalstandard.39 Right: Differential thermal analysis recording equipment. A:Differential thermal curve, B: Thermal curve of test material, and C: thermal curve of thermalstandard


capacity when combined with other methods, helpsidentification of clays”, wrote PS.44

PS applied I. Barshad’s method to study base-exchange. She took a small amount of material in a smallbeaker, which contained neutral normal solution of thedesired cation. The solution was heated to 70°C for severalhours. Following Barshad, “The material was thentransferred to a sintered glass bottom crucible under suction.After the solution had passed through the filter completely,the material was transferred back to the beaker with freshsalt solution and the process was repeated two or threetimes daily for about 10 days.”45 Solutions thus preparedwere analysed by standard methods to determine the basesreplaced from the sample and the bases adsorbed by thematerial from the solution.

Chemical Analysis

The XRD, DTA and base-exchange are not enoughto get complete information. PS wrote: “chemical analysisstill gives useful information for providing support to resultsof x-ray and other analysis. In the matter of determiningthe nature of isomorphous replacement in the lattice, it isstill the only exact method available.”46

The above stated method was used to study varioussamples. The results of PS’s experimental work are givenbelow.

Investigation of Montmorillonite Group

Montmorillonite is a very soft phyllosilicate group ofminerals. Today we know that it has two tetrahedral sheetsof silica sandwiching a central octahedral sheet of alumina.PS’s thesis shows that in the 1950s there was a considerabledifference of opinion regarding the structure. She wrote:“The structure is supposed to be like pyrophyllite but unlikethe latter, it has a variable c-axis depending on watercontent, and a charged lattice, due to isomorphoussubstitution of Mg2+, Fe2+ for Al3+ in the octahedral layer,or Al3+ for Si4+ in the tetrahedral layer.”47PS investigated22 montmorillonite: 14 samples of bentonites and eightsoils. Apart from them Sandy Ridge and Garfield nontronitewere taken as standard probes.

Study of Bentonites

Bentonite is an absorbent aluminium phyllosilicateclay consisting mostly of montmorillonite.They are namedafter the respective dominant element, such as potassium,sodium, calcium, and aluminium. Bentonites studied by PSare shown in Table 1.

TABLE 1: Names and locations of bentonites studiedby P. Sen-Gupta.

S. No. Name Place

1 Wyoming -

2 Kashmir (pink) Punjab

3 Kashmir (grey) Punjab

4 Arizona -

5 Bihar Bihar

6 Tinpahar Tinpahar, Behar

7 SanthalPargana SanthalPargana

8 Taljhari Taljhari, SanthalPargana

9 Bisala Jodhpur

10 Maober Jodhpur

11 Akli Jodhpur

12 Bhadres Jodhpur

13 Barme Jodhpur

14 Nimlinadi -

For all samples she measured the inter-planar spacing(d) in [ú] units, and relative intensity (I). A part of hermeasurements is shown in Table 2.

Figures 5 and 6 show the diffraction patterns andthermal differential curves of some of the samples.

Figure 5: X-ray diffraction pattern of Kashmir, Behar, Taljhari andBarme bentonites.

Soils

Eight soils studied by PS are shown in Table 3.

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Results and interpretation: She presented detailedstudy of the observations of each probe. For instance,sample 1 - Myoming bentonite treated with glycerol, by x-ray diffraction and differential thermal analysis, showed thesame results as observed by other researchers. In samples2 and 3, that is, Kashmir bentonite (pink) and Kashmirbentonite (grey), results were similar to probe 1, but withone exception, that is, the appearance of an exothermicpeak from 950°C to 1000°C. This she attributed to highercontent of magnesium. Sample 4, Arizona bentonites hadtwo extra lines at 7 Å and 3.4Å, which were attributed tokaolinite. This sample also had high amount of magnesiumcontent as was evident from the exothermic peak towards1000°C. Rest of the results in other samples were similarto probes 2 and 3.48

All soil probes showed characteristic x-ray pattern ofthe montmorillonite group. X-ray lines were broader ascompared to that of bentonites. Differential thermal curveswere similar to items 9-14 (see Table 1). With the exceptionof sample 11, in all other samples a very weak 7Å linewas observed, which was supposed to be due to a minoramount of kaolinite; as founded by the base-exchangecapacities method.49

Effect of temperature: Kashmir, Akli, Barme andNimlinadi bentonites were heated for four hours to 550°C.In all the cases, a contraction of the basal spacing to about9.8Å was noted.50

From the observed shift toward lower temperature PSconcluded that these samples contain more iron in theoctahedral layer than in the case with montmorillonite withshifts toward higher temperature.51

With X-ray diffraction method shefound that out of 20 studied bentoniteand soil samples “only two givedifferential thermal curves similar to thatof standard montmorillonite asrepresented by Wyoming and Arizonabentonites, which were studied forcomparison.”52 The specific endothermfor most of the samples was in the rangeof 500-600°C. It was intermediatebetween pure montmorillonite and purenontronite. The final exothermic peakfor the samples corresponded to that ofpure montmorillonite.

Based on the differential thermalanalysis she divided them to Group I(which have characteristics of the

TABLE 2 : Values of inter-planar spacing (d), order of relative intensities(I) of different samples.

Nyoming Kashemir Kashmir Arizona Sentihal Taljhari(grey) (pink) Pargana

d I d I d I d I d I d I

17.71 VS 17.80 VS 17.71 VS 17.70 VS 17.74 VS 17.80 VS

6.90 m 9.12 m 9.02 m 8.90 s 8.96 m 8.81 m

7.20 m

5.56 w 5.99 w 6.01 w 5.91 w 5.91 w

4.52 s 4.51 s 4.47 s 4.50 s 4.49 s 4.50 s

3.55 vs 3.55 vs 3.59 s 3.56 m 3.51 m 3.57 m

2.97 w 2.97 wvs, s, m, w, vw, bd denote very strong, strong, moderate, weak, very weak, and broad diffuserespectively.

Figure 6: From above to below : Differential thermal curves of samplesfrom 9-19. X-axis : temperature in degree centigrade.


standard montmorillonite) and Group II (showing thecharacteristic endotherm at a lower temperature ascompared to Group I). She suggested that Group II couldbe considered as a subgroup, intermediate betweenmontmorillonite and nontronite. This subgroup has smalleramount of iron substitution in the lattice than nontronite.However, the chemical analysis by her proved that ingeneral montmorillonite group II contains more iron thangroup I. This she attributed to the existence of free ironoxide in the samples.53

She concluded: “Montmorillonite (Group II) and theSandy Ridge nontronite are thus representatives of acontinuous series, and are themselves the connecting linkbetween pure montmorillonite and pure nontronite.”54

She saturated a bentonite of group I with potassiumion. The basal spacing of the glycerol treatedprobes indicated a loss of swelling properties. Thespacing corresponded to that of illite. However,the thermal curves did not alter. From that sheconcluded: “It seems not unlikely therefore, thatif montmorillonite (Group II) were treated in asimilar way it would become indistinguishablefrom illite, as the differential thermal curves ofmontmorillonite (Group II) is similar to that ofillite.”55

Study of Vermiculite, Chlorite andMica

Chlorite: Chlorite is a dark green mineral.It consists of a basic hydrated aluminosilicate ofmagnesium and iron. From structure point of view,it resembles mica, which is a shiny silicatemineral with a layered structure. It is found ingranite and rocks.

It was known that vermiculites had flaky structure likemica. Their structure consist of layers, which are separatedby a coating of water of a definite thickness. When ionsare replaced by cations, the basal spacing and the natureof the water-loss peaks alter, as different cations take upwater in different ways. PS studied some Indianvermiculites (Table 4) in their natural form as well as aftersaturating them with K+, H+, Mg2+ etc. She wanted to know,whether all probes exhibit similar properties through similarcation saturation.

She noted that except samples 7 and 9, all othersamples exfoliated on heating. PS gave detail of observationin each sample. For instance, (i) in “Hazaibagh mica” the“x-ray pattern and differential thermal curve correspond tothose of mica.” (ii) In “Finland vermiculite” “x-ray patterncorresponds to that of vermiculite or chloride.”56 She found:

“In the powder pattern of all vermiculite samples,the basal reflection circle is broken into arcs ofirregular intensity, so displaced as to appear inplaces to be split into two, three or even four linesand merging again elsewhere into a single broadline (Figure 7). This pattern is in most casessymmetrical about the centre. In all the powderphotographs of vermiculite, chlorite and micasample, similar peculiarities in the structure of thebasal line were observed.”57

“The split basal lines in the power photographs ofvermiculites seem to be somewhat different fromthe usual αβ lines.”58

TABLE 3: Soils and their location.No. Name Place

15 Indore black soil, surface soil Central India

16 Satara black soil Satara, Bombay

17 Coimbator red soil, Surface soil (size 0-9"), Madrasunirrigated

18 Himayatsagar soil (size 6-12") Himayatsagar

19 Himayatsagar soil (size 0-9") Himayatsagar

20 Padegaon black soil, D-type surface soil Bombay

21 Coimbator black soil, surface soil Madras(size 0-9")

22 Akola black soil, surface soil (0-9"), Madhya PradeshAkola Farm, cultivated

TABLE 4: Samples of vermiculite, chloride and mica and theirlocation.

No. Vermiculite Place

1 Bagespura (light brown laminated soft mass with Bagespura, Mysorea small number of silver green crystals)

2 Malavanghatta (dark brown laminated mass. Malavanghatta,Harder than sample 1) Mysore

3 Hazaribagh (soft, light brown laminated mass) Hazaribagh, Bihar

4 Montana (brown laminated mass) -

5 Ranchi (light brown laminated mass) Ranchi, Bihar

6 Salem (dark brown flakes, softer than mica) Salem, Madras

7 Hazaribagh white mica Hazaribagh, Bihar

8 Finland (light yellow, light brown and light red - flakes in the mass)

9 Chlorite green flakes (Indian chlorite) Supplied byGeographical Surveyof India

VOL. 85, NOS. 7–8 251

Figure 7: Diffraction pattern of Bagespura vermiculite.

In most of the photographs the split basal lines ofvermiculite had comparable intensity, and in someportions of the circumference there were more thantwo lines. The cause of splitting was found notdue to any defect of collimator system but was inthe sample considered to be inherited in thesample.59

“It appears that in the powder samples sufficientlylarge oriented crystallites (which give strong á âlines) are present, in different direction.”60

Though all the samples were saturated with thesame cation and in the same manner, the x-rayspacing remained constant for a particular cation,while the differential thermal characteristicschanged unpredictably.61 “The exothermic peak ofvermiculite appears to depend on the interlayercation. But since all vermiculites having the sameinterlayer cation do not show this peak, theinterlayer cation does not seem to be the onlyfactor which determines the nature of theexothermic peak.”62

She noted that from her observations no conclusioncan be drawn as to whether the exothermic peak is anessential feature of vermiculites or not, as either “theexothermic peak may occur due to any extraneous mineral(like chlorite) in the sample, hence the absence of the peakmay be a characteristic feature of pure vermiculite”, or “thepeak may occur due to a rearrangement of the lattice afterOH loss in complete (as in montmorillonite), and is maskedin some samples due to an opposing reaction in any othermineral which may be present in the sample”, or “the two

types may represent two polymorphic variation of thevermiculite group. Depending on the nature of substitutionin the lattice, the exothermic reaction may be retarded.”63

The overall conclusion was:

(i) From the appearance of exothermic peak, nodefinite conclusion can be drawn regarding thestructure of vermiculite.

(ii) Mg2+ saturation in vermiculites plays importantrole in identifying vermiculite.

(iii) “If all these vermiculite samples have to beaccommodated within the same group, the basalspacing of the group would be in the range from10 Å to 14 Å, and it would be impossible to fixany family characteristics for the differentialthermal curve.”64

Experiments by differential thermal method showedthat out of the five vermiculate probes only three showedthe standard results. They did not show exothermic peakas reported by others. She also observed that in two probesthe peak almost disappeared when saturated with certaincations. She posed the question: Whether the exothermicpeak could be considered as a determining characteristicof vermiculites, which is masked by the presence ofimpurities?

Study of illite

The name illite was proposed by R.E. Grim “for clayminerals related to mica but more hydrous and lower inK2O content.”65 Illite is a clay mineral of group resemblingmicas. It has lattice structure, which does not expand onabsorption of water.

Apart from a standard illite, PS studied Fithian, asample taken from Paddle mixer site, Burma (named byher as Shale No. 1), Yenangyet-, Manatken-, Yenangyanung-and Eocene shale. All of them were from Burma (nowMyanmar). Also, the following eight soils were taken forthe investigations: Aligarh, Cawnpore, Dokri (2 of differentsizes), Sakrand, Belgaum, Dacca (now Dhaka, Bangladesh)and Jorhat. PS found that her samples belong to the illitegroup. Their high temperature endo- and exothermic peakswere flatter than that of standard illites. In her opinion thiswas due to poor crystalline structure of illites.

Kaolinite investigated

Kaolinite is a layered silicate clay mineral formedfrom the chemical weathering of feldspar or otheraluminium silicate minerals. Kaolinite belongs to the group


of industrial minerals. Its chemical composition is:Al2Si2O5(OH)4. PS studied three samples of Indiankaolinites (i) Rajmahal, Bihar. (ii) Singbhum, Bihar. (iii)Gum Corporation, Jabhalpur, Madhya Pradesh. Her datafor kaolinite probes agreed with the standard values. Inthe case of Gum Corporation kaolin an additional line at9.25Å was observed. The differential thermal curve showeda small exothermic dip near 200°C. She concluded: “itseems that, in addition to kaolinite, particularly hydratedhalloysite is present in sample iii.”66

What we see from the foregoing is that PS studied50 samples of clays, soils and shales from different partsof India and classified them into montmorillonite;vermiculite, chlorite, and micas; Illite; and kaolinite.

As we shall see below, based on her D.Phil. (Science)thesis she sent an article to “Nature.”

Second Article in “Nature”

Purnima Sinha’s second article in Nature waspublished in 1962. PS was in the U.S.A. from 1961 to1964, but the paper showed her affiliation with the KhairaLaboratory of Physics, Calcutta University and thankedProf. S.N. Bose for advice which suggests that her articlewas sent while she was in India. Therein she reported onthe studies of three Indian vermiculite samples (1)Bagespura, (2) Malavanghatta, and (3) Hazariabagh (Figure8).

Figure 8: Differential thermal curves of Bagespura, Hazariabagh, andMalavanghatta vermiculites. Credit: “Nature”.

Based on the study by x-ray diffraction and differentialthermal analysis she concluded: “It appears difficult todraw, on the basis of the data obtained so far, a validconclusion regarding the true characteristic of thevermiculites in so far as the appearance of the exothermicpeak is concerned.”67

It will be explored elsewhere that later she took jobat the Glass and Ceramic Research Institute, and continuedcooperation with the University of Calcutta.

Conclusions

Purnima Sinha, the first female scientist from WestBengal who did her doctorate in physics, investigated 50samples of clay for her D.Phil. thesis. With differentmethods she classified them to four different classes. Herscientific work was of international standard as a part of itwas published in the renowned journal “Nature”. Her workalso suggests that in the 1950s scientists at the Universityof Calcutta designed their own instruments. Thus thetradition set up by J.C. Bose, C.V. Raman, S.N. Bose wascontinued after India’s independence.

Acknowledgements

We are thankful to Professor Sukanya Sinha, IndianStatistical Institute, Bangalore, and Prof. Supurna Sinha,Raman Research Institute, Bangalore, for sending us a copyof P. Sinha’s thesis. Without their support this article wouldnot have been possible. One of us (R. Singh) thanks Prof.Dr. Michael Komorek, Head of Physics Institute, Universityof Oldenburg, for providing research facilities.

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