Form Of Prisms Research Articles

PREPARATION OF BADDELEVITE (MONOCLINIC ZrO2) USING PbF2 FLUX

To prepare large single crystals of monoclinic ZrO2 from PbF2 flux, it was found that the localized cooling method was the most suitable, followed by the combined method of localized and slow cooling, and further followed by the slow cooling method. Single crystals of high quality are in tabular form with {100}, {110}, {111} and [011] faces, whereas many of the twinned crystals are in prismatic form with developed {110} faces. Composition planes of the twinnings are (100) and (110). Polysynthetic (100) twinnings are also found in these crystals.

Crystallization and preliminary crystallographic data for the acid protease from Rhizopus chinensis

Acid protease from the fungus Rhizopus chinensis has been crystallized in the form of prisms. The space-group is P2 12 12 1 with a = 60.3 A ̊ ; b = 60.8 A ̊ ; c = 107.1 A ̊ . Considerations of cell volume and protein molecular weight indicate one molecule in the asymmetric unit.

FORMATION OF QUARTZ OVERGROWTHS IN THE PENRITH SANDSTONE (LOWER PERMIAN) OF NORTHWEST ENGLAND AS REVEALED BY SCANNING ELECTRON MICROSCOPY

SUMMARYThe development of optically continuous quartz overgrowths is governed by the atomic structure and crystallographic orientation of the detrital quartz grains. Initial growth commences with the appearance of numerous oriented projections, with rhombohedral and prismatic form, on grain surfaces. Merging and overlap of the projections results in the formation of large crystal faces whose form is dependent upon the initial location of the projections with respect to the internal crystallographic axes. Growth is particularly rapid along the direction of the c‐axis. For unicrystalline quartz grains the ultimate growth phase is the production of polyhedral quartz crystals having the appearance of hexagonal dipyramids. In polycrystalline grains each quartz unit within a single grain develops a separate overgrowth, the form of which is similarly controlled by the internal structure of the individual quartz units. Hence, the completed overgrowth shows an irregular distribution of diversely oriented prism and rhombohedral faces.

Excavation of Boreholes by the Gastropod,Urosalpinx: An Analysis by Light and Scanning Electron Microscopy

Penetration of shell by the muricid gastropod, Urosalpinx cinerea follyensis , is accomplished by successive alternating periods of (a) chemical activity by the accessory boring organ (ABO) , and (b) rasping by the radula. This paper reports on the functions of the radula and of the ABO in producing the characteristic geometry of the borehole, andon the effects of radular teeth and of the ABO secretion on the microscopic anatomy of the surface of the borehole during the process of shell-boring. Radulae of U. c. follyensis and the surfaces of incomplete boreholes in the shell of Crassoslrea virginica, Mytilus edulis , and Mya were examined by means of light and scanning electron microscopy. Hardness tests of radular teeth andshell of prey demonstrated that marginal teeth are harder than rachidian teeth, and that the range of hardness of rachidianteeth overlaps that of the three species of shell. Rasping is carried out by two, occasionally three, of the five rachidiancusps. Rasping patterns are shallow and asymmetric. Rachidian teeth are worn to the base with use; marginal teeth wear onlyslightly as they are employed mainly in feeding. The distance between the tips of rachidian cusps corresponds with the interval between the parallel cusp traces rasped by them in shell. During each rasping period, snails scrape off about 1/10 to 1/5 of the surface of the chemically treated area of the bottom of the borehole. Dissolution of shell is accomplished by secretion from the secretory disk of the ABO. With each application of the ABO,most or all of the radular marks of the previous rasping period are erased by solution of a thin layer of shell. The pattern of etching is specific for each of the species of shell studied. In oyster and mussel shell, initial solubilization occurs through the organic, non-mineralized, prism sheaths, exposing prismatic forms shown by other workers to be distinctive for these species, and then proceeds into the organic-calcareous structure of individual prisms. Etching of Mya shell revealed no fundamental prismatic form. Shell-penetration includes dissolution of both organic complexes and CaCO3 crystals. Shell-boring by this snail is principally a chemical process, and the geometry of the borehole is generally a reflection of the morphology of the ABO.

Study of the effect of test piece geometry on the propagation velocity and logarithmic decrement of longitudinal vibrations in fluoroplastics

The effect of the geometry of teflon test pieces on the speed of sound and the logarithmic decrement of longitudinal vibrations has been investigated. Conditions for the determination of the speed of sound in an infinite medium and in a rod have been obtained. A method is given for determining the dynamic moduli of longitudinal elasticity, the shear modulus, and the dynamic Poisson's ratio on test pieces in the form of rods and prisms, starting with a length of 30 mm.

Thermal resistance of shells of various configurations

A method is proposed for calculating the thermal resistances of shells of various configurations with allowance for the temperature dependence of the thermal conductivity of the material. Approximate formulas are presented for the thermal resistances of shells in the form of infinite prisms and parallelepipeds.

Preparation of single crystals of hexagonal silver iodide

Single crystals of AgI in the form of hexagonal prisms up to 20 mm in length and 2 mm in diameter can be grown by slow diffusive dilution of a solution of AgI in concentrated aqueous KI solution. The crystals are of good quality and have very small concentrations of potassium impurity.

Investigations of the domain structure of nickel single crystals

Investigations of the domain structure (DS) of nickel single crystals of cylindrical and prismatic form with [100] and [110] axes are reported. Using the Bitter technique we observe the colloid pattern on all faces around the crystal axis. The total DS is divided into the basic DS and the closure DS. The basic DS of the [110] crystals is a simple plate structure. The plates (approximate width 0.05 mm) are normal to the crystal axis and each consist of a single elementary domain. Neighboring plates are separated by 71° Bloch walls (for <tex xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">H_{e} = 0</tex> ). The basic DS of the [100] crystals also consists of plates (0.13 mm) normal to the axis, but now each plate contains several elementary domains; we call this a composed plate structure. In axial direction adjacent domains are separated by 109° Bloch walls. The basic DS is essentially the same in prismatic and cylindrical crystals. The closure DS of the [110] crystal forms a pattern of lines normal to the axis. The most remarkable result is, that the number of lines increases with increasing field; the closure DS varies not only quantitatively, but qualitatively with the field. We succeed in exploring many details of the secondary structure, so that we can draw quite a complete picture of the DS of these nickel crystals.

Twinning in iron-aluminium alloys

Both annealing and mechanical twins were studied in an iron alloy containing 23.5 at. % aluminium. Annealing twins were found after heat treatment at 1150°C, designed to induce considerable grain growth. The twins were bounded by three sets of coherent interfaces: (2̄1̄1), (112) and (1̄21). These planes are co-zonal, with zone axis [1̄1̄1]; the twins were therefore in the form of prisms. The crystallographic nature of these twins was confirmed by means of microbeam X-ray diffraction photographs. Mechanical twins were produced in the same alloy by impact while the samples were immersed in liquid nitrogen. Various states of long range order were induced by preliminary heat treatment and it was found, as predicted on geometrical grounds, that twins were formed only if the alloy was in a wholly or partially disordered condition. The critical value of the order parameter S was about 0.5. Some observations on the morphology of intersecting mechanical twins are also described.

33.北海道鴻ノ舞鉱山産コキンボ石

Coquimbite was found from an old adit of a Au-Ag vein of Konomai mine, Hokkaido associated with a few hydrous sulphate minerals. The colour varies from whitish purple, purple to reddish purple. The crystal displays hexagonal platy on prismatic form composed of c (0001) and m (10I0) with rare small faces a (1120) and r (10I1). It was identified with the lights of chemical analysis and X-ray study.

On the formation and properties of helical dislocations

Abstract The factors influencing the development of helical dislocations found in CaF2 by Bontinck and Amelinckx are discussed. At temperatures near and below 700°c the principal electrolytic current in CaF2 appears to be carried by the negative ions. Thus climb of dislocations is difficult to produce as a result of processes inducing electrolytic flow. It is proposed that the positive ions carry a larger component of the current near 1200°c and that maintenance of the electrolytic currents induced during additive coloration produce what might be termed mild climb. Under this climb dislocations having a strong screw component are induced to assume a helical or spiral prismatic form as proposed earlier by Seitz. The model of F-centres in CaF2 and their equilibrium characteristics are discussed. It is pointed out that helical dislocations should be generated in many materials under a wide variety of circumstances in which climb occurs and that such dislocations are, in principle at lead, capable of generating whiskers when they occur sufficiently near the surface. Such whiskers would grow from the base and should possess many of the attributes found in the whiskers of this type which are observed in practice. It is proposed that controlled climb of any material may be produced with the use of an appropriate temperature gradient if the production or annihilation of lattice defects at the dislocations engenders climb and if the production lies in an attainable temperature range.

Films of omega-branched fatty acids

This investigation deals with the effect of terminal branching upon the behavior of long-chain aliphatic acids. Monomolecular layers of these compounds, spread on buffer solutions, are characterized by determination of the force/area relationship. On the basis of their minimum molecular area in condensed films, the tilt of the molecule against the surface was computed and various possibilities for the conformation of the terminal groups were evaluated. The capability of building up polylayer films on a solid surface and the character of such films reflects the shape of the molecule and its deviations from the prismatic form. A number of surface phenomena such as contact angles, surface reflection, and skeletonization by dissolving the free fatty acids in the film are treated. Although films of branched fatty acids resemble those of normal fatty acids in several points, a striking difference is revealed by their enormous surface volatility. Molecular Sublimation of branched fatty acids across blankets of stearic acid, several hundred Angström units thick, is an important manifestation of the dynamic state prevailing in crystalline polymolecular films.

新巻鮭に見られた燐酸塩結晶に就て

Studies on the struvites in canned marine products were frequenfly reported, but little is known about the presence of sodium phosphate in fisheries products. In the present paper, an occurrence of sodium phosphate (Na2HPO4•12H2O) in mild-cured salmon is described. The writer found a small quantity of transparent prismatic crytals, which resemled pieces of ice, deposited on superficial skin near the dorsal and ventral fins and sometimes on the thin membranes of abdominal cavities of the fishes, which were commercialy processed and kept in cold store-house, Tokyo, in the winter of 1942. (Plate 1) Probably owing to dehydration, transparency of the crystal was gradually reduced under atmospheric condition. By the recrystallisation, usually prismatic form could not be reappeared and it took a rhombic shape or a parallelogram. (Plate 2) The optical characters tested by a petrographic microscope were as follows: the crystalline system is monoclinic, as both straight and oblique extinction can be observed; angle of extinction is 31°; and sign of elongation is negative. The writer confirmed that these characteristics as well as analytical data were quite identical with those of the pure specimens of sodium phosphate examined simultaneously. It is not yet clear what sort of conditions have favoured the deposition of sodium phosphate in mild-cured salmon instead of struvite.

Prismatic cleavage and steep rhombohedral form in α-quartz

As is well known, quartz rarely shows well-defined cleavages. Kenngott has shown that quartz that has suddenly been cooled, after strong heating, has a tendency to break up in the directions of rhombohedron faces. Breithaupt (cf. Hintze, Min., 1904, vol. 1, p. 1273) mentions ‘cleavage following the primary rhombohedron and the prism, rarely well defined, often passing into conchoidal fracture’.It may be useful to put on record an example of clear rock-crystal in which cleavage is developed in all three 60° directions of the prism faces. The specimen was originally in the Daimeries collection, in Brussels, having been bought years ago at Idar, near Oberstein on the Nahe, by A. Daimeries. I obtained it from Mr. A. G. F. Gregory, who had bought the Daimeries collection. The locality from which it came is, unfortunately, unknown.

A new polarizing system for spectrophotometers

The effect of scattered light in the nicol prism and an improved form of prism in which scattered light is much reduced is described. An improved polarizing system for spectrophotometers is described consisting of three nicols in tandem, the first and last being stationary and arranged to transmit light polarized in the same plane, the second prism being arranged to rotate. In such a system it is shown that the ratio of intensity follows the law I1/I2 = tan4 θ. The theoretical advantages of the system as compared with the usual system consisting of one fixed and one rotating nicol in which the ratio of intensity follows the tan2 θ law, are also discussed.

Theory of a new form of the chamber crank chain

This particular crank mechanism in which the crank itself is fixed and the two arms rotate about the fixed crank ends, named by Reuleaux the “rotating slider crank” (“rotirende kurbelschiefe”) and by Kennedy the “turning block,” has been, as Reuleaux pointed out, the basis of more attempted applications than any other mechanism. Notwithstanding all these attempts it has had little if any practical success, at any rate for rotary pumps or motors. The reason for this want of success is largely due to the difficulty of making running joints for holding the pressure of fluids with any device except lower pairs of either the revolute or the cylindrical prism form. The following note gives the theory of a new modification of this mechanism, which, apart from any useful practical application it may have, appears to be of some scientific interest.

Dispersion of light by Potassium Vapour

Anomalous dispersion in the region of the red lines of potassium was first observed by Ebert in 1904. The method adopted for Ebert’s experiments was a modified form of the crossed prism method used by Wood in the investigation of the corresponding phenomena in the case of sodium. Potassium was heated in a tube through which two currents of hydrogen passed from each end to a central outlet. The cool hydrogen kept the potassium vapour in a prismatic form, so that light passing along the length of the tube suffered deviation and dispersion by the potassium vapour prism. The author of the present communication has shown that there is no need for the hydrogen streams. If the tube be kept cool on its upper surface the metallic vapour takes of itself a prismatic form or is arranged in layers of decreasing density, and so behaves in a similar way to a prism of homogeneous vapour. The present communication deals with quantitative results from the measurement of dispersions at different wave-lengths, and it appears that the deviation due to potassium vapour is observable over the whole of the visible spectrum and for a considerable distance in the ultra-violet. Strong absorption takes place at the lines of the principal series and for wave-lengths near these series lines we have "anomalous" dispersion. This phenomenon has been observed at seven of the pairs forming the principal series lines for potassium—as the pairs of lines in this series get closer and closer together with diminishing wave-length, the dispersion effects after the first two pairs are only observable outside the lines forming a pair, but there appears a lack of symmetry in the observed dispersion curves corresponding to the different intensities of the lines forming the pair. The dispersion to be observed may then be regarded as that corresponding to the principal series absorption lines; no other absorption region seems to affect the dispersion —at any rate at low densities of vapour.

Peculiar Ice Formation

IN reply to Mr. James Foulds's inquiry in NATURE (March 15, p. 464) whether the prismatic forms of ice such as he has recently observed in Lancashire have been observed elsewhere, it may suffice to refer him to previous volumes of NATURE, more particularly to vols. xxxi. and xlvii., for letters from Messrs. Woodd-Smyth and McGee, also from myself. In the latter volume is an account by me of a more extended series of observations on these “crystallites” than previous observers appear to have made. Friability of soils is due to interstitial water.

Sextant-Telescopes

I RECENTLY made the attempt to attach one of the prism forms of binocular to a sextant in place of the ordinary telescope, and it seemed that such an adaptation would materially increase the usefulness of the instrument and add to the accuracy of its records. In the sextant which I used there was no provision for rigorous attachment, and only a device of a temporary character could be adopted; but a very slight modification in the construction of the instrument or of the so-called “up and down piece” would overcome this drawback.

A Note on a New Form of Fluid Prism.

A Note on a New Form of Fluid Prism.