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Study on the cementation of the regenerated activity (from spent resin using ferric as regenerant) containing ferric in cement matrix showed that compressive strength and leaching behaviour are better when the ferric strength was < 5 N. The diffusion coefficient of Cs from the cement matrix was found to be in the range 2.4 × 10−5 cm2/day and 5.9 × 10−5 cm2/day with ferric solutions of strength in the range 0.5–3 N. When bentonite and vermiculite were included in the cement matrix, the diffusion coefficient of Cs was found to be in the range 6.2 × 10−7 cm2/day to 1.26 × 10−5 cm2/day with ferric strength in the same range.

Volume reduction studies were carried out on low level radioactive plastic wastes containing polyethylene, PVC and neoprene by melt densification. The optimized temperature for melting of plastics was between 170 and 180 °C. Based on laboratory scale studies. Plant scale studies were planned and conducted. The volume reduction factors obtained were around 30, which was 6-10 times higher than that of the conventional compaction process. Thermogravimetry and infrared spectroscopy were used to investigate the thermal and structural properties of the given materials. The effect of the presence of salts like potassium permanganate and hydrazine sulphate on the thermal properties of the materials was also evaluated. Leaching studies were also performed on melt-densified specimens in the laboratory. The average leach index was observed to be around 9, which was higher than the minimum stipulated value.

The presence of EDTA in decontamination wastes can cause complexation of the radioactive cations resulting in interferences in their removal by various treatment processes such as chemical precipitation, ion exchange etc. Further, it might also impart elevated leachability and higher mobility to cationic contaminants from the conditioned wastes i.e. waste immobilized in cement or other matrices and can adversely influence the quality of the final form of waste. Advanced Oxidation Processes (AOP) using ozone, H 2 O 2 , ultrasound (US), ultraviolet radiation (UV), Fenton’s reagent (FeII + H 2 O 2 ) alone or in combination is considered as possible methods of clean and ecologically safe remedial treatment for the degradation of organics. In the present study, kinetics of sonochemical degradation of EDTA (20,000 mg/l) utilizing combination of processes viz., ultrasound + Fenton’s reagent and ultrasound + H 2 O 2 at lower and higher frequencies of 40 and 130 KHz.was investigated. This was compared with the chemical degradation using H 2 O 2 and Fenton’s reagent. Both chemical and sonochemical oxidation yielded complete degradation of EDTA at different rates. The sonochemical reaction was found to follow first order kinetics, the reaction being faster at high frequencies. From the observed pH changes during the oxidation processes, it could be concluded that there was loss of chelating ability of EDTA. Formation of amides in the sonochemical degradation using Fenton’s reagent and formation of acidic intermediates during the sonochemical degradation using H 2 O 2 and chemical oxidation using Fenton’s reagent alone was confirmed.

Polyvinyl acetate based strippable polymer has been developed for surface decontamination. Stainless steel, mild steel, polyvinyl chloride and rubber have been selected as candidate materials for the radioactive decontamination studies. The ease of strippability and homogeneity of the polymer coating has been studied using infrared spectrophotometer. Decontamination of used radioactive respirator has been carried out and the peels obtained have been subjected to leaching and incineration studies. The infrared spectrophotometric studies also have been counducted to study the interaction between polyvinyl acetate and ions, like cesium, strontium and cobalt.

An attempt has been made to synthesize ceramic titania and zirconia membranes by sol-gel process by filtering respective viscous colloidal sol through microporous alumina support and gelling followed by sintering at 400°C and 470°C respectively. The static charge on the pores of the so formed membranes and the pore size distribution determine the applicability in filtering colloidal solution. The mean pore size from SEM were found to be 0.65 μm and 0.54 μm for titania and zirconia membranes respectively with 1.47 × 107/cm2 as pore density for both. The filtration characteristics during membrane layer formation showed that the membrane layer formation started after 35 minutes in the case of titania membrane and 40 minutes in the case of zirconia membrane. From the gravimetric estimation of water content of the membranes the thickness of the membrane was found out to be 3 μm and the porosity was found out to be 0.30 for both the cases. The particle charge density was estimated from the zeta potential and the particle size. The pore charge density was estimated from the particle charge density, pore density, pore diameter and the thickness of the membrane layer. The membrane pore charge density was found to vary between 3 to −1 μ Coulombs/cm2 in the case of titania membrane and 7 to −0.5 μ Coulombs/cm2 in the case of zirconia membrane in the pH range 1–12.

Mesoporous silica molecular sieves MCM-41 containing zinc and aluminum ions (Zn-Al-MCM-41) with Si/(Zn + Al) ratio equal to 340 and 380 and only aluminum ions with Si/Al ratio equal to 93 and 104, respectively, were synthesized under hydrothermal conditions using cetyltrimethylammonium (CTMA + ) surfactants as template in the absence of auxiliary organics. The mesoporous materials, viz. Zn-Al-MCM-41 and Al-MCM-41 were characterized using several techniques, e.g. powder X-ray diffraction (XRD), nitrogen adsorption measurements, Fourier transform-infra red spectroscopy (FT-IR) and thermogravimetric–differential thermal analyzer (TG–DTA). XRD studies indicated that the calcined materials had the standard MCM-41 structure. Nitrogen adsorption was used to determine specific surface area, pore volume, and pore size distribution in the Zn-Al-MCM-41(340), Zn-Al-MCM-41(380), Al-MCM-41(93) and Al-MCM-41(104) mesoporous molecular sieves. FT-IR studies showed that Zn and Al ions were incorporated into the hexagonal mesoporous structures of Zn-Al-MCM-41 and Al-MCM-41. The thermal stability of the as-synthesized materials was studied using TG–DTA. The effect of reaction temperature, WHSV and isopropanol:toluene ratios on the selectivity of p-cymene were studied. The Zn-Al-MCM-41(340) catalyst containing larger pore size and higher number of Bronsted acid sites was found to be more effective in the alkylation of alkyl aromatics, for example, in the production of p-cymene from toluene, using 2-propanol as the alkylating reagent. The selectivity of p-cymene under varying experimental condition, viz. effect of reaction temperature, WHSV and ratio of isopropanol:toluene for the various catalysts follows the sequence Zn-Al-MCM-41(340 )> Al-MCM-41(93 )> Zn-Al-MCM-41(380 )> Al-MCM-41(104). © 2002 Elsevier Science B.V. All rights reserved.

The potential use of copper ferrocyanide - polyurethene foam (CFC-PU foam) developed in our laboratory was investigated in the treatment of radioactive liquid waste for the removal of cesium. The pilot plant scale studies were carried out so that these studies can be further extended to the plant scale operations. Decontamination factors obtained were found to be function of total dissolved solids. A correlation studies on results obtained from pilot plant and laboratory scale were made and observed that they are in good agreement with each other.

Mesoporous aluminosilicate Al-MCM-41 with Si/Al=93 and 104 were synthesized using cetyltrimethylammonium bromide as the structuring agent and the materials were characterized using several techniques. The mesoporous structure was confirmed by X-ray diffraction (XRD) technique. The surface area, pore size and wall thickness was calculated by BET equation and BJH method using nitrogen sorption technique. Fourier transform-infrared (FT-IR) spectroscopy was used in order to obtain information on incorporated aluminum atoms in the mesoporous structure of Al-MCM-41. Thermogravimetric–differential thermal analyzer (TG–DTA) was used to determine the thermal stability of the materials. The effect of reaction temperature, WHSV and isopropanol:toluene ratios on the selectivity of p-cymene were studied. The Al-MCM-41 (93) catalyst exhibited excellent selectivity in the production of p-cymene by the isopropylation of toluene using isopropanol as the propylating agent.

The growth of Sb-based crystals (InSb, GaSb etc) was undertaken using resistive heater furnace by vertical directional solidification (VDS) technique. Crystal—melt interface shape during the growth was shown to convert from concave to convex along the crystal axis of the ingots. Many antimonide (Sb) crystals of 8 mm to 18 mm diameter were grown by optimized growth parameters. The forced convection and absence of conducting support to ampoule showed improvement in crystal quality of as grown ingots. Crystals showed preferred orientation and self-seeding. Results on interface shape and crystallinity of ingots were found to be in good agreement with the experiments.

Chemical treatment assumes an important role in the management of radioactive wastes as it is a simple technique and offers advantage in terms of handling of wastes thereby reducing the risk of mansievert exposure. Low level wastes (LLW) and intermediate level wastes (ILW) are generated in various facets of nuclear fuel cycle and have various chemical composition. A systematic study was carried out by using copper ferrocyanide and calcium phosphate precipitation methods for the removal of cesium and strontium, respectively. The supernatants were subjected to ultra filtration (UF) using a membrane having a pore size of 0.2 μm. The decontamination factors (DF) at 2 and 24-hour intervals with and without UF were estimated. The DF obtained was in the range of 200–300 for cesium and 200 for strontium with LLW solution which has chemical characteristics similar to ground water. Two hours of settling is adequate for strontium before UF. In case of cesium there is no much change in the DF values by UF. However, the UF has helped in the solid — liquid separation as the flocks of copper ferrocyanide precipitate are feathery in nature. The effect of ionic strength and the presence of TBP on the removal efficiency of cesium and strontium have also been studied. DF are observed to be a function of ionic strength and are low in deionized water, in salt solutions containing 1 to 4M sodium nitrate and also in solutions of ILW. However, increasing the chemical dosing to two times of normal plant dosing has yielded a DF of about 200 for sodium nitrate solutions with respect to cesium removal. When the concentration of ammonium nitrate in the waste exceeds 0.1M, the DF reduces. Entrained TBP as well as soluble TBP reduces the removal efficiency of cesium. This paper deals with the experimental data and mechanism of the processes involved in the removal of cesium and strontium.

A method has been developed for the removal of cesium from the aqueous radioactive waste using a composite ion-exchanger consisting of Copper-Ferrocyanide Powder (CFC) and Polyurethane (PU) Foam. Polyvinyl acetate has been used as a binder in the preparation of CFC-PU foam. The physical properties of CFC such as density, surface area, IR stretching frequency and lattice parameters have been evaluated and also its potassium and copper(II) content have been estimated. Optimization of loading of CFC on PU foam has been studied. The CFC-PU was viewed under microscope to find out the homogeneity of distribution. Exchange capacities of the CFC-PU foam in different media have been determined and column studies have been carried out. Studies have been undertaken on extraction of cesium from CFC foam and also on digestion of spent CFC-PU foam and immobilization of digested solution in cement matrix. The cement matrices have been characterized with respect to density, bio-resistance and leaching resistance.

Hexacyanoferrates (HCFs) are known to be efficient sorbents for the removal of Cs from aqueous solutions. But the powdery precipitate of HCF is unsuitable for use in columns. To make it amenable to column application, it has been coated on polyacrylic fibres by in situ precipitation. In batch and column experiments, the fibres coated with Cupric ferric hexacyanoferrate provided good removal of137Cs from radioactive effluents. Leaching of Cs from the fibres was found to be only 14% in demineralised water medium. The Cs-loaded fibres could easily be incinerated to a smaller volume for further conditioning.

We have successfully grown high mobility undoped and Te doped InSb crystals of size 10–12 mm dia. and 60 mm length under inert argon atmosphere in closed quartz ampoules, by vertical directional solidification (VDS) technique. The crystals showed predominantly (220) orientation along the growth axis. The surface defects, such as voids were reduced drastically by selecting proper lowering rate, rotational speed and cone angle of the ampoule. The high mobility and quality crystals were obtained with the ampoule conical angle less than 20°, lowering rate 5mm/h, and rotational speed 10 rpm.

Sorption data analysis was carried out using the Freundlich, Langmuir, and Modified Freundlich isotherms for the uptake of sodium and potassium in an initial concentration range of 10–100 mg/L on backfill materials, viz., bentonite, vermiculite, and soil samples. The soil samples were collected from a shallow land disposal facility at Kalpakkam. The Freundlich isotherm equation is validated as a preferred general mathematical tool for representing the sorption of K+ by all the selected backfill materials. The Modified Freundlich isotherm equation is validated as a preferred mathematical tool for representing the sorption of Na+ by the soil samples. Since a negative sorption was observed for the uptake of Na+ by commercial clay minerals (vermiculite and bentonite clay in the laboratory experiments), sorption analysis could not be carried out using the above-mentioned isotherm equations. Hill plots of the sorption data suggest that in the region of low saturation (10–40 mg/L), sorption of K+ by ver...

Studies have been carried out on the removal of radioactive cobalt (60Co) from synthetic intermediate level waste (ILW) and decontamination waste using neat polyurethane (PU) foam as well as n-tributyl phosphate–polyurethane (TBP–PU) foam. The radioactive cobalt has been extracted on the PU foam as cobalt thiocyanate from the ILW. Maximum removal of cobalt has been observed when the concentration of thiocyanate in the solution is about 0.4 M. Cobalt can be separated from decontamination waste containing ethylenediaminetetraacetic acid (EDTA) and iron(II). The extent of extraction of cobalt is slow and the separation of iron and cobalt is better with the neat PU foam compared to the TBP–PU foam. The presence of iron in the decontamination waste facilitates the extraction of cobalt thiocyanate on the PU foam. Column studies have been carried out in order to extend these studies to the plant scale. The capacities of the PU foams for cobalt have been determined. The effect of density and the surface ...

Experiments on the growth of high-mobility Te-doped n-type InSb and undoped p-type InSb crystals by vertical directional solidification are reported. Hall mobility of the Te-doped crystals is 26 000 cm2/V·s and of the undoped crystals 42 000 cm2/V·s at 300 K. The Hall coefficient of Te-doped samples is negative over the entire temperature range, but the Hall coefficient of the undoped samples is positive at low temperature, and changes sign at higher temperatures.

Various methods have been evaluated for the removal of 131I from actual liquid waste received from a reactor and from simulated effluents containing the isotope. The options included both precipitation (along with silver iodide and bismuth hydroxide) and ion-exchange/adsorption (using anionic exchangers and activated carbon) processes. Of all the schemes, passing through anion exchange resin columns was found to be the most effective, indicating that iodine was present mostly as anions.

Experiments were carried out on the removal of n-tributyl phosphate (TBP) from the synthetic effluents of intermediate level waste (ILW). The candidate materials selected for this study were XAD-4 resin, Tulsion-A-72 MP resin, activated charcoal, and polyurethane foam. These materials were characterized for their distribution coefficients of TBP in a TBP-ethanol-water medium. XAD resin and PU foam showed better removal of TBP. To understand the mechanism of removal of TBP by the candidate materials, such physical properties as specific surface area, pore size distribution, and zeta potentials were determined. The zeta potential of the TBP in an ethanol-water medium was measured. The pore size distribution compared to the specific surface area and surface charges of the samples played an important role in the removal of TBP. XAD-4 resin was used in column studies for the removal of TBP from synthetic ILW. About 13,500 bed volumes of ILW could be passed before a 0.1% breakthrough capacity was attained.

Fixation of Copper Ferrocyanide Cake (CFC), which is generated from the chemical treatment plant of low-level radioactive liquid effluent in a urea-formaldehyde (UF) matrix, was carried out. Boric acid was used as a catalyst for the UF polymerization. The physical properties such as compressive strength and diffusion coefficient were evaluated for UF waste forms and were compared with those of Ordinary Portland Cement (OPC) waste forms. While the compressive strengths of UF and OPC waste forms were comparable, the former showed diffusion coefficients about two to three orders lower. Almost all the cesium was released from the OPC waste form that contained less than 18% of CFC by weight in the final waste form. The release of cesium from the OPC waste forms was high due to the presence of high alkalinity and calcium ions in the cement. To find out the temperature rise in the preparation of UF waste form, blocks having a size of about 5 1 were prepared; it was observed that there was no increase in peak center temperatures during the curing process.

Studies have been carried out on the immobilization of spent ion-exchange resins produced in nuclear power plants in urea-formaldehyde matrix. The matrices were prepared by incorporating different types of ion-exchange resins in the pH range of 4.5 to 5.0, using boric acid as a catalyst. Characterization of the matrices was carried out with respect to dimensional changes, compressive strength, and leach resistance. The cumulative percentage weight loss and volume change were observed to decrease with the increase in boric acid concentration before attaining a plateau. The diffusion coefficients were in the order of 10−16 M/s, and the compressive strengths were in the range of 0.83 to 12 MPa. Infrared spectral studies on the urea-formaldehyde matrices revealed that the rate and the extent of cure depended on the type of resin. © 1994 John Wiley & Sons, Inc.

Fluoride in wastewater is normally introduced through industrial processes and manufacturing. The toxicity of fluoride is well understood and considerable work has been done on the defluoridation of well waters and wastewaters. The present paper describes a two-stage method that utilizes lime in the first stage for the removal of the bulk of fluoride and zirconium in the second stage as an agent for polishing. This method brings down the fluoride to a level less than 0.2 mg/L from an initial concentration in excess of 100 mg/L. The fluoride from zirconium hydroxide precipitate generated in the second stage could be quantitatively removed by a dilute solution of sodium hydroxide, thus affording recycling of zirconium, which makes this method cost effective.

Ion exchange process is one of the treatment methods for radioactive waste. The resin becomes no longer useful after number of cycles of usage. At the same time the regenerated resin cannot be considered as non active waste for disposal. Hence it is felt necessary that the regenerated resin is treated in a fashion so as to result in a form which can be considered as inactive material. It is possible to convert this spent resin into multivalent ionic form which are generally non leachable, thus providing the necessary properties for meeting the disposal criteria. Studies were carried out for the exchange of radioactive ions on these resins with ions like Al3+, Sn4+, Pb2+ and Fe3+ etc. The studies included leachability aspects, exchange with other active ions, thermal characteristics, compressive strength of the cement blocks loaded with the resin etc. Our studies indicated that the order of the stability of the resin with respect to properties like leachability, exchange properties etc. follow the trend as follows: Sn4+Pb2+Al3+Fe3+.

The Calutron‐Bernas ion source has been modified for high‐dose ion implantation (>1016 ions/cm2). The modified ion source has stable arc, uniformly bright illumination, and dense plasma. It consists of a hairpin‐shaped tungsten (W) filament as a hot cathode at one end, and a disk‐type graphite anode at the other end about 8 cm away; both the electrodes are fitted in an arc discharge chamber made of graphite only. The anode potential of 150–200 V and filament current of about 60 A initiates a stable bright arc. A magnetic field (0.1–0.5 kG) along the cathode‐anode axis enhances the electron ionizing efficiency, helps in collimating the electrons, and contributes also in the plasma confinement near the aperture. The operational life of W filament (1.2 mm diam) in an ambient of oxygen or nitrogen at pressure 10−3–10−4 Torr varies from 25 to 35 h. Further, a needle valve or an in‐built minioven is used, respectively, when the feed material is a gas/liquid or a solid charge. The gas/vapors is/are admitted at a...

The paper describes work on the preparation of Ru/Al 2 O 3 catalyst containing different amounts of Ru and the effect of ruthenium loading on the removal of NO X vapours from air stream. The effect of residence time on the efficiency of removal is also discussed. The NO X analysis was carried out using spectrophotometer. The Phenol-di-sulphonic acid method was used for the estimation of nitrate. It was found that 1 wt% loading was the best for the removal of NO X in comparison to 0.2 wt% and 2 wt% loadings and a higher residence time of 0.6 sec gave much better removal compared to the residence time of 0.3 sec and 0.5 sec. In all the experiments the temperature of the bed was maintained at 200°C.

An exact solution of Einstein-Maxwell-Yukawa field equations has been obtained in a space-time with a static metric. A critical analysis reveals that the results previously obtained by Patel [9], Singh [10], and Taub [11] are particular cases of our solution. The singular behavior of the solutions has also been discussed in this paper. Further, extending the technique developed by Janis et al. [12], for static fields, to the case of nonstatic fields, an exact time-dependent axially symmetric solution of EMY fields has been obtained. Our solution in the nonstatic case is nonsingular in the sense of Bonnor [15] and presents a generalization of the results obtained by Misra [7] to the case when a zero-mass scalar field coexists with a source free electromagnetic field.

The production mechanism of deuterons in high-energy proton interactions with heavy nuclei has been investigated. The characteristics of deuterons and protons such as the frequencies of emission, the angular and momentum distributions have been given. The analysis of the experimental results suggests that at least two distinct processes are operating in the formation of deuterons of energies ∼ (40÷700) MeV.

Lichnerowicz (1960), by using a property of the Riemann tensor, has given the field equations, Rij=ϱwiwj, wiwi=0, ϱ being a scalar and has termed them as representing a state of « total radiation ». Recently Rao (1970) derived these field equations under a geometrical relation which as stated by him imposes on the Rieman tensor a severe restriction, and he obtained a class of exact solutions of the above field equations corresponding to the cylindrically symmetric space-time with two degrees of freedom. The present authors, in this paper, have obtained exact wave solutions of the field equations representing zero-rest-mass scalar field in the generalized Einstein-Rosen space-time, and it has been shown that by a suitable choice of the scalar field, the field equations considered by Lichnerowicz and Rao can be deduced without imposing any condition on the geometrical nature of the Riemann tensor. Finally a method is given by which most general solutions of these field equations, can be generated from those of the empty space field equations. It is further shown that the solutions of Rao (1960) are only a special case of those found in this paper.

Various attempts have been made to obtain wave solutions of nonsymmetric unified field equations of Einstein, Bonnor and Schrodinver in different space-times. Lal and Ali, Lal and Khare, Lal and Singh have obtained wave solutions of these field equations in different space-times under certain restrictions. In this paper plane wave solutions of both the weak and strong, nonsymmetric unified field equations of Einstein, Bonnor and Schrodinger have been investigated in a space which is more general than Pandey and Rao plane wave metric. It has been shown that the plane wave solutions of Einstein and Bonnor's equations exist but Schrodinger's field equations have no solution in this space-time.

The isomer shifts, quadrupole splittings, and magnetic hyperfine splittings of iron in α-Fe–Be: FeBe5, α-Fe–Nb, γ-Fe–Nb, α-Fe–Ru, γ-Fe–Ru, FeTe2, α-Fe–Ir, and γ-Fe–Ir alloys are measured using the Mossbauer effect. Some of these studies were carried out as a function of temperature in the temperature range 60 to 300 °K. All of the systems except FeBe5 and γ-Fe–Ir are studied for the first time. A possible new magnetic transition above 77 °K in the ϵ-phase of the Fe–Nb (30 at% Nb) alloy has been found. In FeTe2 a magnetic transition reported earlier from the susceptibility data is confirmed by these Mossbauer studies. The experimental results are explained in terms of the electronic configuration and the structure of these alloys. Isomere Verschiebung, Quadrupolaufspaltung und magnetische Hyperfeinaufspaltung von Eisen wurden in α-Fe–Be-: FeBe5; α-Fe–Nb-, ϵ-Fe–Nb-, α-Fe–Ru-, γ-Fe–Ru-, FeTe2-, α-Fe–Ir- und γ-Fe–Ir-Legierungen mit dem Mosbauereffekt gemessen. Einige dieser Untersuchungen wurden als Funktion der Temperatur im Bereich von 60 bis 300 °K durchgefuhrt. Alle Systeme bis auf FeBe5 und γ-Fe–Ir wurden zum ersten Male untersucht. Ein moglicher neuer magnetischer Ubergang oberhalb 77 °K in der ϵ-Phase der Fe–Nb (30 At% Nb)-Legierung wurde gefunden. In FeTe2 wird ein fruher aus Suszeptibilitatsdaten gefundener magnetischer Ubergang durch diese Mosbaueruntersuchungen bestatigt. Die experimentellen Ergebnisse werden mit der elektronischen Konfiguration und der Struktur dieser Legierungen erklart.

Recently Dunn(1974) has formulated a scalar-tensor theory of gavitation and proposed a set of field equations, by taking a modification of the Riemannian geometry and has obtained static spherically symmetric solutions of the vacuum field equations. In this paper we have investigated the cylindrical wave solutions of the above mentioned field equations in a space-time with a metric which is more general than that of Einstein-Rosen. It has been shown that these solutions can be deduced from the known solutions of the field equations representing empty space-time taken along with the Einstein-Rosen metric. Lastly some plane-wave solutions corresponding to the Bondi's general plane-wave metric, have come under inverstigation as a direct consequence of a certain assumption.

The commutation formulae in Finsler space have been studied by several authors. In this paper we have obtained various forms of commutation formulae for different geometric entities of the conformal Finsler space.

The nymphs that are here described belong to those species the biology of which has been discussed in a previous paper (Lal, 1934 b). The plan followed was the one originally adopted by Ferris (1923), in which descriptions and illustrations of all morphological features important in the identification of the species of the nymph, apart from the adult, were prepared from careful examination of specimens mounted for microscopic observation. The importance of such a study has been increasingly appreciated in the last decade, both from the economic and the systematic points of view. Harmful species of Psyllidæ are mainly injurious because of the feeding activities of their immature stages, and there are but two species known, Psyllia pyricola Först. and Paratrioza cockerelli Sulc., in which the adults have also been found to be capable of causing injury. On the other hand, the specific determination of immature stages has been rendered difficult owing to the fact (first) that the published descriptions of individual species of nymphs are often found to be applicable to species other than those to which the particular description refers; and (second) that sometimes the nymphs of two closely allied species are distinguished by such marked differences as to warrant the adults being assigned to different genera and even subfamilies. Such cases have been mentioned by Crawford (1919), Ferris (1928 a), Husain and Nath (1927), and have been summarised by Rahman (1932) in the introductory part of his paper. The present descriptions have, therefore, been prepared with the avowed objects of facilitating the determination of individual species, where comparison with allied species is impossible owing to lack of available material, and also of assessing the value of the various nymphal characters with a view to establishing a classification based on these as contrasted with one based upon the characters of the adults.

The insect parasites bred out of Psyllid hosts, in the course of studying their biology in Scotland, belong to four families of Hymenoptera and one of Diptera, the total number of species encountered being seven. Of these one and possibly two more of the hymenopterous species are hyperparasites. The hosts involved include four species, of which only one, Psyllia mali race peregrina, may be said to have been fairly heavily parasitised. As observed by Ferrière (1926), species of Psyllidae, in spite of their nymphs leading a comparatively sedentary life, are less susceptible to attack by parasites than are the other Homoptera. As a rule the hymenopterous parasites attack them in the nymphal stage, while the dipterous species parasites the adults as well.

Conclusions and Summary The conclusions based on these investigations may be summarised as follows: “P. peregrina” and P. mali of hawthorn are identical, and are only the seasonal forms of one and the same species. These insects are also morphologically indistinguishable from P. mali o. apple. The nymph of the forms occurring on hawthorn is different from the typical nymph of the apple sucker (P. mali), and has long been known as the nymph of “P. peregrina.” In it, however, there occurs a small percentage of variations, in which the characteristic brown longitudinal streak of the wing pads does not occur. Although morphologically similar, specimens of P. mali of hawthorn and apple do not mate with each other, nor do they oviposit interchangeably on each other's host plants. The nymph of either when transferred to the food plants of the other does not survive very long. 4. P. mali of the apple has a biological race on hawthorn, which has long been known as P. peregrina. This race should be distinguished as P. mali Schmidb. race peregrina, which is the name it is proposed to assipn to it. The two races, in view of their dissimilar nymphs, furnish an instance of poecilogony.