Heats of Solution,Transition, and Formation of Three Crystalline Forms of Metaboric Acid

The three crystalline forms of metaboric acid HBO₂ were prepared, purified, and analyzed. Heats of solution in water or of reaction with sodium hydroxide solution were compared with those of orthoboric acid H₃BO₃(c). The best values for the heats of transition at 25 °C are: (c,I) to (c,II), 2.33±0.23 kcal/mole; (c,II) to (c,III), 1.30±0.05 kcal/mole; (c,I) to (c,III), 3.63±0.24 kcal/mole. The following heats of formation at 25 °C were derived: −192.77 ± 0.35 kcal/mole for the cubic HBO₂(c,I), −190.43 ±0.34 kcal/mole for the monoclinic HBO₂ (c,II), and −189.13 ± 0.34 kcal/mole for the orthorhombic HBO₂(c,III).     

Phase Equilibrium Relations in the Sc2O3-Ga2O3 System

The phase equilibrium diagram was determined for the Sc₂O₃-Ga₂O₃ system. A quenching furnace, wound with 60 percent Pt—40 percent Rh wire, was employed for experiments conducted at temperatures up to 1,800 °C. An induction furnace, having an iridium crucible susceptor, was used to obtain higher temperatures. Temperatures in the quenching furnace were measured with both an optical pyrometer and a 95 percent Pt—5 percent Rh versus 80 percent Pt—20 percent Rh thermocouple. The melting point of Ga₂O₃ was determined as 1,795 ±15 °C. Experiments at temperatures as high as 2,405 °C failed to melt Sc₂O₃. Two intermediate binary phases, a compound believed to be 6Sc₂O₃·5Ga₂O₃ and a solid solution occur in the system. The solid solution phase appears as a single phase in the region roughly defined by the compositional limits of 55 to 73 mole percent Ga₂O₃ at the solidus. The 6:5 compound, stable only at high temperatures, melts incongruently at 1,770 ±15 °C and decomposes below 1,700 ±15 °C. The compound appears to have orthorhombic symmetry with a=13.85 A, b= 9.80 A, and c=9.58 A. The indicated uncertainties in the melting points are a conservative estimate of the overall inaccuracies.     

Thermodynamic Properties of Some Methylphosphonyl Dihalides From 15 to 335 °K

Measurements of the heat capacity of methylphosphonyl difluoride (CH₃POF₂), methyl phosphonyl dichloride (CH₃POCl₂), and methylphosphonyl chlorofluoride (CH₃POClF) were made from about 15 to 335 °K by means of an adiabatic calorimeter. These highly reactive and toxic substances were purified in a completely closed glass apparatus by combining slow crystallization and fractional melting procedures. The purities determined by the freezing-curve method are shown to be generally in agreement with those values obtained by the calorimetric method. From the results of the heat measurements, the triple-point temperature, heat of fusion, and their corresponding estimated uncertainties were found to be, respectively, 236.34±0.05 °K and 11,878±12 J/mole for CH₃POF₂, 306.14± 0.02 °K and 18,076±15 J/mole for CH₃POCl₂, and 250.70± 0.20 °K and 11,853±30 J/mole for CH₃POClF. Triple-point temperatures obtained by the freezing-curve method are in agreement with the above values. A table of smoothed values of heat capacity, enthalpy, enthalpy function, entropy, Gibbs free energy, and Gibbs free energy function from 0 to 335 °K was obtained from the data. The entropy and its corresponding estimated uncertainty for CH3POF2, CH3POCl2, and CH3POClF in their respective condensed phase at 298.15 °K and saturation pressure was found to be 208.3± 0.3, 164.8± 0.3, and 216.4± 0.4 J/deg mole, respectively. The entropies in the gaseous state at 298.15 °K and 1 atm pressure were found to be 312.7±3, 339.7±3, and 335.0±3 J/deg mole, respectively.     

Polymorphism of Bismuth Sesquioxide. I. Pure Bi2O3

Stability relationships of the four polymorphs of bismuth oxide have been determined by means of DTA and high-temperature x-ray studies. The stable low-temperature monoclinic form transforms to the stable cubic form at 730 ±5 °C, which then melts at 825 ± 5 °C. By controlled cooling, the metastable tetragonal phase and/or the metastable body-centered cubic (b.c.c.) phase appear at about 645 °C. Whereas b.c.c. can be preserved to room temperature, tetragonal will transform to monoclinic between 550 and 500 °C. Tetragonal Bi₂O₃, however, is easily prepared by decomposing bismutite (Bi₂O₃·CO₂) at 400 °C for several hours. The greatest transition expansion occurs at the monoclinic to cubic inversion, and cubic Bi₂O₃ shows the greatest coefficient of volume expansion. With exposure to air, Bi₂O₃ carbonates and partially transforms to bismutite and an unknown phase.     

Uranium-Platinum System

The phase diagram of the uranium-platinum system was constructed from data obtained by thermal analysis, metallographic examination, and X-ray diffraction. The system is characterized by four intermetallic compounds: UPt, formed peritectoidally at 961° C; UPt₂, formed peritectically at 1,370° C; UPt₃, melting congruently at 1,700° C; and UPt₅, formed peritectically at 1,460° C. One eutectic occurs at 1,005° C and 12 a/o platinum, and a second at 1,345° C and 87.5 a/o platinum. The maximum solubilities are 4.5 a/o uranium in platinum and 5 a/o platinum in gamma-uranium. Platinum lowers the gamma-beta uranium transformation to 705° C and the beta-alpha transformation to 589° C.     

Green synthesis of gold nanoparticles using Citrus maxima peel extract and their catalytic/antibacterial activities

The peel of Citrus maxima (C. maxima) is the primary byproducts during the process of fruit or juice in food industries, and it was always considered as biomass waste for further treatments. In this study, the authors reported a simple and eco‐friendly method to synthesise gold nanoparticles (AuNPs) using C. maxima peel extract as reducing and capping agents. The synthesised AuNPs were characterised by UV–visible spectrum, X‐ray diffraction (XRD), transmission electron microscope (TEM) and Fourier‐transform infrared spectroscopy (FTIR). The UV–visible spectrum of the AuNPs colloid showed a characteristic peak at 540 nm. The peaks of XRD analysis at (2θ) 38.30°, 44.28°, 64.62°, 77.57° and 81.75° were assigned to (111), (200), (220), (311) and (222) planes of the face‐centered cubic (fcc) lattice of gold. The TEM images showed that AuNPs were nearly spherical in shape with the size of 8–25 nm. The FTIR spectrum revealed that some bioactive compounds capped the surface of synthesised AuNPs. The biosynthesised AuNPs performed strong catalytic activity in degradation of 4‐nitrophenol to 4‐aminophenol and good antibacterial activity against both gram negative (Escherichia coli) and gram positive (Staphylococcus aureus) bacterium. The synthesis procedure was proved simple, cost effective and environment friendly.Inspec keywords: gold, nanoparticles, nanofabrication, X‐ray diffraction, ultraviolet spectra, visible spectra, transmission electron microscopy, Fourier transform infrared spectra, crystal structure, catalysis, antibacterial activity, nanobiotechnologyOther keywords: gold nanoparticles, Citrus maxima peel extract, UV–visible spectrum, X‐ray diffraction, transmission electron microscope, Fourier‐transform infrared spectroscopy, XRD analysis, faced centre cubic lattice, TEM images, catalytic activity, 4‐nitrophenol, 4‐aminophenol, antibacterial activity, gram negative bacterium, gram positive bacterium, Au     

Treasure of the Past VI: Standard Potential of the Silver-Silver-Chloride Electrode from 0° to 95° C and the Thermodynamic Properties of Dilute Hydrochloric Acid Solutions

From electromotive-force measurements of the cell without liquid junction: Pt;  H₂,  HCl (m),  AgCl;  Agthrough the range 0° to 95° C, calculations have been made of (1) the standard potential of the silver–silver-chloride electrode, (2) the activity coefficient of hydrochloric acid in aqueous solutions from m (molality) =0 to m=0.1 and from 0° to 90° C, (3) the relative partial molal heat content of hydrochloric acid, and (4) the relative partial molal heat capacity of hydrochloric acid.The extrapolations were made by the method of least squares with the aid of punch-card techniques. Data from at least 24 cells were analyzed at each temperature, and 81 cells were studied at 25° C. The value of the standard potential was found to be 0.22234 absolute volt at 25° C, and the standard deviation was 0.02 millivolt at 0° C, 0.01 millivolt at 25° C, and 0.09 millivolt at 95° C. The results from 0° to 60° C are compared with earlier determinations of the standard potential and other quantities derived from the electromotive force.     

Water Calorimetry: A Correction to the Heat Defect Calculations

In a recent publication, we used a reaction model (model III) to calculate the heat defect for the irradiation of aqueous solutions with ionizing radiation at 21 °C. Subsequent work has revealed that the literature value used for one of the rate constants in the model was incorrect. A revised model (model IIIR) incorporates the correct rate constant for 21 °C. Versions of models III and IIIR were created for irradiations at 4 °C. For our current water calorimetry protocol, the values of the heat defect for H₂/O₂-water (water saturated with a flow of 43 % H₂ and 57 % O₂, by volume) at 21 °C predicted by model III and model IIIR are similar but the value for 4 °C predicted by III is 30 % smaller than the value predicted by IIIR. Model IIIR predicts that the values of the heat defect at 21 °C and 4 °C lie within the range −0.023±0.002, in agreement with the values obtained from our water calorimetry measurements done using pure water and H₂-saturated water at 21 °C and 4 °C. The yields of hydrogen peroxide in H₂/O₂-water at 21 °C and 4 °C were measured and agree with the predictions of model IIIR. Our water calorimetry measurements made with pure water and H₂-saturated water are now of sufficient quality that they can be used to determine the heat defect for H₂/O₂-water better than can be done by simulations. However, consistency between the three systems continues to be an excellent check on water purity which is crucial, especially for the pure water system.     

Experimental study of the Ca–Mg–Zn system using diffusion couples and key alloys

Nine diffusion couples and 32 key samples were prepared to map the phase diagram of the Ca–Mg–Zn system. Phase relations and solubility limits were determined for binary and ternary compounds using scanning electron microscopy, electron probe microanalysis and x-ray diffraction (XRD). The crystal structure of the ternary compounds was studied by XRD and electron backscatter diffraction. Four ternary intermetallic (IM) compounds were identified in this system: Ca₃Mg_xZn_15−x (4.6 ⩽ x ⩽ 12 at 335 °C, IM1), Ca_14.5Mg_15.8Zn_69.7 (IM2), Ca₂Mg₅Zn₁₃ (IM3) and Ca_1.5Mg_55.3Zn_43.2 (IM4). Three binary compounds were found to have extended solid solubility into ternary systems: CaZn₁₁, CaZn₁₃ and Mg₂Ca form substitutional solid solutions where Mg substitutes for Zn atoms in the first two compounds, and Zn substitutes for both Ca and Mg atoms in Mg₂Ca. The isothermal section of the Ca–Mg–Zn phase diagram at 335 °C was constructed on the basis of the obtained experimental results. The morphologies of the diffusion couples in the Ca–Mg–Zn phase diagram at 335 °C were studied. Depending on the terminal compositions of the diffusion couples, the two-phase regions in the diffusion zone have either a tooth-like morphology or contain a matrix phase with isolated and/or dendritic precipitates.     

A Standard for the Measurement of the pH of Blood and Other Physiological Media

A buffer solution containing potassium dihydrogen phosphate (0.008695 molal) and disodium hydrogen phosphate (0.03043 molal) is proposed as a pH standard for the physiologically important range, pH 7 to 8. The proposed standard solution is prepared by dissolving 1.179 g (air weight) of potassium dihydrogen phosphate and 4.303 g (air weight) of disodium hydrogen phosphate in ammonia-free water and diluting to 1 liter at 25 °C. The ionic strength is 0.1.Standard pH values (pH_s) were assigned to this reference solution at temperatures from 0 to 50 °C by means of emf measurements of hydrogen-silver chloride cells without liquid junction. The activity coefficient of chloride ion, upon which the assignment of pH_s depends, was evaluated by means of a recently proposed convention. By this means, standard values precise to ± 0.001 unit could be derived from the emf data. At 25 °C pH_s is 7.414, and at 38 °C it is 7.382. The operational consistency of these standard values with those for the 0.025-m equimolal phosphate buffer (one of the NBS primary standards) was demonstrated.     

Systems Silver Iodide-Sodium Iodide and Silver Iodide-Potassium Iodide

The phase relations for the systems AgI-NaI and AgI-KI have been determined for the temperature range from room temperature to 685° C, using differential thermal analysis techniques. The AgI-NaI system has a eutectic at 50 mole percent NaI and 384° C. The AgI-KI system has eutectics at 20.8 and 28.5 mole percent KI and 254° C and 244° C, respectively. A compound of formula KAg₃I₄ is formed with a congruent melting point of 268° C.     

Characterization of Bi and Fe co-doped PZT capacitors for FeRAM

Ferroelectric random access memory (FeRAM) has been in mass production for over 15 years. Higher polarization ferroelectric materials are needed for future devices which can operate above about 100 °C. With this goal in mind, co-doping of thin Pb(Zr₄₀,Ti₆₀)O₃ (PZT) films with 1 at.% Bi and 1 at.% Fe was examined in order to enhance the ferroelectric properties as well as characterize the doped material. The XRD patterns of PZT-5% BiFeO₃ (BF) and PZT 140-nm thick films showed (111) orientation on (111) platinized Si wafers and a 30 °C increase in the tetragonal to cubic phase transition temperature, often called the Curie temperature, from 350 to 380 °C with co-doping, indicating that Bi and Fe are substituting into the PZT lattice. Raman spectra revealed decreased band intensity with Bi and Fe co-doping of PZT compared to PZT. Polarization hysteresis loops show similar values of remanent polarization, but square-shaped voltage pulse-measured net polarization values of PZT-BF were higher and showed higher endurance to repeated cycling up to 10¹⁰ cycles. It is proposed that Bi and Fe are both in the +3 oxidation state and substituting into the perovskite A and B sites, respectively. Substitution of Bi and Fe into the PZT lattice likely creates defect dipoles, which increase the net polarization when measured by the short voltage pulse positive-up-negative-down (PUND) method.     

Acid Dissociation Constant and Related Thermodynamic Quantities for Triethanolammonium Ion in Water From 0 to 50°C

Earlier studies of the dissociation constants of monoethanolammonium and diethanolammonium ions and the thermodynamic constants for the dissociation processes have been supplemented by a similar study of triethanolammonium ion from 0° to 50° C. The dissociation constant (K_bh) is given by the formula ?log K_bh = 1341.16/T + 4.6252 ? 0.0045666Twhere T is in degrees Kelvin. The order of acidic strengths of the ions is as follows: Triethanolammonium >diethanolammonium>monethanolammonium. Conversely, monoethanolamine is the strongest of the three bases. The thermodynamic constants for the dissociation of one mole of triethanolammonium ion in the standard state at 25° C are as follows: Heat content change (ΔH°) 33.450 joule mole⁻¹; entropy change (ΔS°), −36.4 joule deg⁻¹ mole⁻¹; heat-capacity change (ΔCp°), 52 joule deg⁻¹ mole⁻¹.     

Phase Equilibria in Systems Involving the Rare Earth Oxides. Part III. The Eu2O3?In2O3 System

The equilibrium phase diagram was determined for the Eu₂O₃−In₂O₃ system. An induction furnace, having an iridium crucible as the heating element (susceptor), was used to establish the solidus and liquidus curves. The 1:1 composition melts congruently at 1745 ± 10 °C. Melting point relations suggest that the 1:1 composition is a compound with solid solution extending both to 31 mole percent In₂O₃ and 71 mole percent In₂O₃. The compound is pseudohexagonal with a_H = 3.69 A and c_H = 12.38 A. Isostructural phases also occur in the 1:1 mixtures of both Gd₂O₃ and Dy₂O₃ with In₂O₃. The melting points of Eu₂O₃ and In₂O₃ were determined to be 2,240 ± 10 °C and 1910 ± 10 °C respectively. A eutectic occurs in the Eu₂O₃−In₂O₃ system at 1,730 °C and about 73 mole percent In₂O₃. The indicated uncertainties in the melting points are conservative estimates of the overall inaccuracies of temperature measurement.     

Magnetic soy protein isolate–bovine serum albumin nanoparticles preparation as a carrier for inulinase immobilisation

Magnetic nanoparticles (NPs) were functionalised with soy protein isolate (SPI) and bovine serum albumin (BSA) for inulinase immobilisation. The results revealed the nanomagnetite size of about 50 nm with a polydispersity index (PDI) of 0.242. The average size of the SPI NPs prepared by using acetone was 80–90 nm (PDI, 0.277), and SPI–BSA NPs was 80–90 nm (PDI, 0.233), and their zeta potential was around −34 mV. The mean diameter of fabricated Fe₃ O₄ @SPI–BSA NPs was <120 nm (PDI, 0.187). Inulinase was covalently immobilised successfully through glutaraldehyde on Fe₃ O₄ @SPI–BSA NPs with 80% enzyme loading. Fourier transform infrared spectra, field emission scanning electron microscopy, and transmission electron microscopy images provided sufficient proof for enzyme immobilisation on the NPs. The immobilised inulinase showed maximal activity at 45°C, which was 5°C higher than the optimum temperature of the free enzyme. Also, the optimum pH of the immobilised enzyme was shifted from 6 to 5.5. Thermal stability of the enzyme was considerably increased to about 43% at 75°C, and K _m value was reduced to 25.4% after immobilisation. The half‐life of the enzyme increased about 5.13‐fold at 75°C as compared with the free form. Immobilised inulinase retained over 80% of its activity after ten cycles.Inspec keywords: magnetic particles, nanoparticles, proteins, molecular biophysics, nanofabrication, enzymes, Fourier transform spectra, infrared spectra, scanning electron microscopy, field emission ion microscopy, transmission electron microscopy, pH, biochemistry, nanobiotechnology, biomagnetism, electrokinetic effects, iron compoundsOther keywords: magnetic nanoparticles, soy protein isolate, bovine serum albumin, inulinase immobilisation, nanomagnetite, polydispersity index, SPI‐BSA NP, zeta potential, inulinase, glutaraldehyde, enzyme loading, Fourier transform infrared spectra, field emission scanning electron microscopy, transmission electron microscopy images, enzyme immobilisation, pH, size 80 nm to 90 nm, temperature 45 degC, temperature 75 degC, Fe₃ O₄      

Facile microwave‐assisted synthesis of NiO nanoparticles and its effect on soybean (Glycine max)

NiO nanoparticles in high purity, 15 ± 0.5 nm in size, were prepared via solid‐state microwave irradiation. The [Ni(NH₃)₆](NO₃)₂ complex as a novel source was decomposed in the presence of microwave irradiation for a short time (10 min). The present method is facile, safe, and low‐cost. This method exhibits other advantages; there is no need of a solvent, fuel, surfactant, expensive material, or complex instrument. Synthesised NiO nanoparticles were determined by various analyses. Also, for the first time, NiO nanoparticle effects on biochemical factors in soybean were investigated. Seeds of soybean were grown in the Murashige and Skoog agar medium containing different concentrations of NiO nanoparticles (0, 200, and 400 mg/L) for 21 days under growth chamber conditions. Estimates of malondialdehyde, hydrogen peroxide contents, and antioxidant enzymes (catalase and ascorbate peroxidase) under treatment of NiO nanoparticles were assayed. The result showed that by significantly increasing the concentration of NiO nanoparticles, the activity of catalase and ascorbate peroxidase enzymes was enhanced. Malondialdehyde and hydrogen peroxide contents significantly increased in the presence of NiO nanoparticles. In this study, the increasing activity of catalase and ascorbate peroxidase was not enough for radical oxygen species detoxification.Inspec keywords: nickel compounds, molecular biophysics, biotechnology, microorganisms, nanoparticles, biochemistry, microwave materials processing, hydrogen compounds, enzymes, cellular biophysicsOther keywords: solid‐state microwave irradiation, synthesised NiO nanoparticles, soybean, facile microwave‐assisted synthesis, biochemical factors, Murashige, Skoog agar medium, malondialdehyde, hydrogen peroxide contents, antioxidant enzymes, ascorbate peroxidase enzymes, radical oxygen species detoxification, NiO, [Ni(NH₃)₆](NO₃)₂      

Acidic Potassium Dichromate Solutions as Ultraviolet Absorbance Standards

The absorbances of five concentrations of potassium dichromate in 0.001 M perchloric acid have been determined at eight wavelengths in the ultraviolet on the National Bureau of Standards Institute for Materials Research high-accuracy spectrophotometer. Four of the wavelengths—235, 257, 313, and 350 nm—correspond to absorbance maxima or minima in the HCrO₄^– spectrum and are useful wavelengths for checking the accuracy of the absorbance scale of narrow bandpass spectrophotometers. Although partial dimerization of HCrO₄^– to Cr₂O₇⁼ produces small positive deviations from Beer’s law at these wavelengths, the apparent absorptivities calculated for each concentration are reproducible to one part in a thousand. The estimated uncertainties in the absorptivity values are ± 0.7 percent at 0.1 absorbance (A) and ± 0.2 percent near A = 1. These uncertainties include all known sources of possible systematic error and the 95 percent confidence level for the mean. The remaining four wavelengths used for measurement are near two predicted isosbestic points in the HCr0₄^–/Cr₂O₇⁼ spectra. The absorptivities at 345 nm are sufficiently independent of concentration that this wavelength can be used for checking absorbance linearity to one part in a thousand over the range A = 0.2–1.     

Antifungal and antiovarian cancer properties of α Fe2 O3 and α Fe2 O3 /ZnO nanostructures synthesised by Spirulina platensis

Candida albicans (C. albicans) infection shows a growing burden on human health, and it has become challenging to search for treatment. Therefore, this work focused on the antifungal activity, and cytotoxic effect of biosynthesised nanostructures on human ovarian tetracarcinoma cells PA1 and their corresponding mechanism of cell death. Herein, the authors fabricated advanced biosynthesis of uncoated α‐Fe₂ O₃ and coated α‐Fe₂ O₃ nanostructures by using the carbohydrate of Spirulina platensis. The physicochemical features of nanostructures were characterised by UV–visible, high resolution transmission electron microscopy, Fourier transform infrared spectroscopy, and X‐ray diffraction. The antifungal activity of these nanostructures against C. albicans was studied by the broth dilution method, and examined by 2′, 7′‐dichlorofluorescein diacetate staining. However, their cytotoxic effects against PA1 cell lines were evaluated by MTT and comet assays. Results indicated characteristic rod‐shaped nanostructures, and increasing the average size of α‐Fe₂ O₃ @ZnO nanocomposite (105.2 nm × 29.1 nm) to five times as compared to α‐Fe₂ O₃ nanoparticles (20.73nm × 5.25 nm). The surface coating of α‐Fe₂ O₃ by ZnO has increased its antifungal efficiency against C. albicans. Moreover, the MTT results revealed that α‐Fe₂ O₃ @ZnO nanocomposite reduces PA1 cell proliferation due to DNA fragmentation (IC₅₀ 18.5 μg/ml). Continual advances of green nanotechnology and promising findings of this study are in favour of using the construction of rod‐shaped nanostructures for therapeutic applications.Inspec keywords: nanocomposites, toxicology, nanofabrication, cellular biophysics, X‐ray diffraction, iron compounds, biochemistry, cancer, antibacterial activity, transmission electron microscopy, biomedical materials, wide band gap semiconductors, DNA, II‐VI semiconductors, visible spectra, molecular biophysics, ultraviolet spectra, nanomedicine, zinc compounds, nanoparticles, microorganisms, Fourier transform infrared spectraOther keywords: Spirulina platensis, antifungal activity, α‐Fe₂ O₃ nanoparticles, antiovarian cancer properties, Candida albicans infection, cytotoxic effect, biosynthesised nanostructures, human ovarian tetracarcinoma cell PA1, cell death, uncoated α‐Fe₂ O₃ , coated α‐Fe₂ O₃ nanostructures, α‐Fe₂ O₃ ‐ZnO nanocomposite, carbohydrate, physicochemical features, UV‐visible spectroscopy, high resolution transmission electron microscopy, Fourier transform infrared spectroscopy, X‐ray diffraction, broth dilution method, 2′, 7′‐dichlorofluorescein diacetate staining, PA1 cell lines, comet assays, MTT assays, rod‐shaped nanostructures, surface coating, PA1 cell proliferation, DNA fragmentation, green nanotechnology, Fe₂ O₃ ‐ZnO, Fe₂ O₃      

Crystallization of Anhydrous Copper Sulfate From Sulfuric Acid—Ammonium Sulfate Mixtures

The growth of CuSO₄ crystals from a nonaqueous solvent, composed of (NH₄)₂SO₄ and H₂SO₄ is described. Solubility of CuSO₄ in solvents of varying (NH₄)₂SO₄ to H₂SO₄ ratio, at 200 °C, has been determined, as well as the temperature dependence of the solubility in 0.35(NH₄)₂SO₄ — 0.65H₂SO₄. Single crystal specimens, weighing up to 150 mg have been obtained.