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An x‐ray microscope is described in which the mirrors are thin optical flats. These flats are mechanically bent to obtain the radius of curvature necessary to focus the image. The adjustable curvature increases the flexibility of the microscope and the ease of focusing the image. The difficulties of grinding and polishing concave cylindrical surfaces are avoided.The degree of smoothness of reflecting surfaces was studied, and the anelastic properties of various mirror materials were investigated to find a material suitable for bending. Highly polished tungsten carbide was found to be an excellent mirror material and does not require an evaporated surface coating of high density metal.The x‐ray microscope promises to be a valuable research instrument.

An investigation of the effects of rolling and annealing on the orientation of individual grains in silicon ferrite strip yielded results which led to the formulation of a theory for the appearance of the ``magnetic'' orientation in the final processed strip. It is proposed that, in a fine‐grained strip of silicon ferrite, those grains which are already in the ``magnetic'' orientation before rolling will keep that mean orientation during rolling but become more highly strained than other grains, and therefore, they will become the portions of the cold‐rolled strip with highest free energy. In the annealing process these highest energy regions will recrystallize first, becoming lowest energy regions which will be able to consume the now higher energy regions surrounding them. Since these nuclei have the ``magnetic'' orientation, the final product also attains the ``magnetic'' orientation.

An x‐ray analysis shows that crystalline hydrazinium difluoride is built upon a rhombohedral unit cell having a0=5.43A, α=38°10′, containing one molecular formula. The positions of the atoms have been determined and correspond to trans‐hydrazinium ions which form linear hydrogen bonds to fluoride ions at the corners of an elongated octahedron. Each fluoride ion forms three hydrogen bonds to different hydrazinium ions, and condenses the octahedra into continuous layers. As a result of the packing of these layers to build up the structure, each nitrogen atom comes in contact with an ``extra'' fluoride ion and thereby assumes a coordination number of 5. Analysis of the N–N and N–H≡F distances of 1.42A and 2.62A, respectively, shows that each atom in the hydrazinium ion bears approximately ¼ of a unit of positive charge. The bearing of the structure of the ion on the adjacent charge rule is discussed. Some of the properties of the ion are interpreted in terms of the structure.

A simple method is described for making replicas of surfaces for study in the electron microscope. The surface to be studied is cleaned and then coated with a very thin slightly wedge‐shaped film of polyvinyl formal having a range in thickness from about 500 to 750A in 2.5 cm. This film is formed by dipping the prepared surface into a 0.5‐percent solution of the resin dissolved in dioxane or ethylene dichloride and permitting the solvent to evaporate while the surface is held in a vertical position. The replica film is removed by placing the coated surface under water and peeling the film from it. A description of this technique is given in detail. A graph is presented which shows the thickness of resin films obtainable from various concentrations of resin in dioxane, and a table gives the interference effects which may be used for determining approximate thicknesses of thin resin films. Several easy procedures are described for checking the thickness of such films. A technique is described for preparing strong films having a thickness of 100A and an area of 3 cm2 when mounted in air. Such films are very useful when working with the electron microscope and several methods are described for mounting specimens on them, including a conditioning treatment—useful in mounting water suspensions—which makes one surface very hydrophilic. Five micrographs show the results obtainable with the techniques described.

It is shown that the three‐dimensional Patterson method can be so simplified by the use of the symmetry properties of the crystal under consideration that its use in determining the positions of atoms in crystals is practicable. This method is then used to determine the positions of the heavy atoms in proustite, Ag3AsS3. The positions of the sulfur atoms are found by the use of the covalent atomic radii and assumptions concerning bond directions. The structure so derived is found to be compatible with the observed data. Proustite is found to contain pyramidal AsS3′′′ groups and silver atoms forming two bonds to sulfur in almost opposed directions. Pyrargyrite, Ag3SbS3, is found to have almost the same structure as proustite. The analytical statement of the structures is as follows:— The space group, C3v6 — R3c, is common to both proustite and pyrargyrite. The special positions of C3v6 are (in hexagonal axes) (2a)0,0,Z;0,0,12+Z;(6b)X,Y,Z;Y¯,X−Y,Z;Y−X,X¯,Z;Y¯,X¯,12+Z;X,X−Y,12+Z;Y−X,Y,12+Z; and positions der...

A device for measuring x‐ray diffractions from a single crystal is described. The heart of the apparatus is an ``Eulerian Cradle,'' so named because it permits rotation of the crystal about each of the Eulerian axes. It is used for orienting single crystals in an x‐ray beam, in order to bring each reciprocal lattice point into the equatorial plane for Geiger counter measurement of the intensity. It eliminates the need for raising the Geiger tube out of the equatorial plane and suggests that the reciprocal lattice be surveyed by either ``zone'' or ``cone'' schemes. These are described, and the ``cone'' scheme is shown to permit a complete hemisphere of the reciprocal lattice to be surveyed with only a single mounting of any crystal. Fine points concerning the use of the apparatus in the precise orientation of a crystal, and for the measurement of integrated intensities at single settings, are given. All angular motions are controlled by worm wheels and worms with dials for direct reading to 0.01°. Data collection is further facilitated by computing appropriate angular coordinates for reciprocal lattice points from an accurate set of lattice parameter measurements (readily obtained with the same instrument) and setting the various circles accordingly. The long spacings, characteristic of protein crystals, require both the high precision of this instrument and computed coordinates for the many thousands of reflections that must be measured.

A nickel‐molybdenum alloy containing about 20 atom percent of molybdenum exists above 900°C as a cubic close‐packed structure. If this alloy is quenched and then held at temperatures below 840°C, an ordering reaction occurs which results in a slight tetragonal distortion of the cubic structure. This ordered structure requires for its description a tetragonal cell with 2.5 times the volume of the distorted face‐centered cubic cell. The completely ordered structure can be described analytically as follows: space group: C4h5—I4/m; dimensions of unit cell: a0=5.720A, c0=3.564A, c/a=0.6231; atomic positions: 2 Mo in 2(a), 8 Ni in 8(h), x=0.200. y=0.400.