The Structure of Gutta-Percha Based on Studies with Electron Rays

1934 ◽  
Vol 7 (4) ◽  
pp. 603-607 ◽  
Author(s):  
G. Bruni ◽  
G. Natta
Keyword(s):  
Organic Compounds ◽  
Structural Investigations ◽  
X Ray ◽  
Molecular Weights ◽  
Vegetable Fibers ◽  
Gutta Percha ◽  
Natural Organic Compounds ◽  
Ray Methods ◽  
Identity Period

Abstract Among the natural organic compounds with high molecular weights which have been the object of roentgenographic investigations with a view to determining their intimate constitution, rubber and other hydrocarbons of similar constitution such as gutta-percha and balata have been extensively studied in recent years. The results obtained with these substances by x-ray methods have however not been so complete and reliable as in the case of other products with high molecular weights, such as cellulose, found in nature in ramie and in certain vegetable fibers in forms which are particularly well oriented, which is of enormous advantage in structural investigations. Nevertheless, the roentgenographic results on rubber are of the greatest interest because from them it is possible to show that the molecules of rubber are oriented when the rubber is stretched or frozen, so that it can be proved that under these special conditions it has a sort of crystalline structure which is characterized by definite identity periods. The determination of the identity period in the direction of the fibers, which is 8.1 A. U., is particularly reliable.

A Review of Bromine Determination in Foods

1975 ◽  
Vol 58 (4) ◽  
pp. 711-716 ◽  
Author(s):  
Milton E Getzendaner
Keyword(s):  
Neutron Activation Analysis ◽  
Activation Analysis ◽  
Neutron Activation ◽  
Organic Compounds ◽  
Methyl Bromide ◽  
Ethylene Dibromide ◽  
X Ray ◽  
Instrumental Methods ◽  
Bromine Determination

Abstract Organic compounds containing bromine, including methyl bromide, ethylene dibromide, and l,2-dibromo-3-chloropropane, have been used extensively for the fumigation of foods, or soils in which foods grow, making it necessary to determine residues of bromine and bromine-containing organic compounds. A large number of methods for the determination of bromine in foods, as organic, inorganic, and combined total bromide, have been developed. In methods for organic bromide, the bromine is converted to the inorganic form for measurement by titration, photometry, or other means. In recent years, instrumental methods have been developed in which the total bromine in the sample is determined, regardless of the state in which it exists. X-ray fluorescence and neutron activation analysis are the 2 instrumental methods used most widely. Residue data are presented for some typical bromine-containing samples.

Detection Confirmation and Determination of Trace Amounts of Selenium by X-Ray Methods

1963 ◽  
Vol 7 ◽  
pp. 542-554
Author(s):  
Frank L. Chan
Keyword(s):  
Matrix Effects ◽  
Hexagonal Structure ◽  
Elemental Selenium ◽  
X Ray Diffraction ◽  
X Ray ◽  
Yellow Color ◽  
The Matrix ◽  
Ray Methods ◽  
Tetravalent State

AbstractRecently, interest in the determination of selenium in trace amounts has been greatly intensified because of the nutritional aspects of this element. It has been reported that selenium in the amount of 13 μg in the form of sodium selenite in 100 g of feed has an effect similar to that of vitamin E. In the field of semiconductors, the detection and determination of trace amounts of selenium in arsenic, antimony, and small single crystals of solid solution of cadmium selenide and sulfide are of considerable importance in semiconductor performance.In the Aerospace Research Laboratories, 4,5 diamino-6-tbiopyi-imidine has been successfully adopted as a reagent for the spectrophotometric determination of selenium. The reaction of 4,5 diamino-6-thiopyrimidine and tetxavalent selenium produces a yellow color with the formation of elemental selenium. It is possible to determine elemental selenium by collecting it in a thin layer. The selenium deposited in this layer may then be determined by an X-ray fluorescence method. A procedure of this nature has the advantage of eliminating the matrix effects commonly encountered in X-ray fluorescence. Furthermore, the slow generation of selenium affords a convenient means of detection and confirmation of this element by the use of X-ray diffraction procedures. By this technique selenium is first converted to its tetravalent state and is then reacted with 4,5 diamino-6-thiopyrimidine. On standing, the selenium is reduced to a red precipitate of elemental selenium which can be dissolved in carbon disulfide. Finally, the selenium can be converted into its hexagonal structure by annealing at 205-207°C.

Determination of minerals in platinum concentrates from the Transvaal by X-ray methods

1932 ◽  
Vol 23 (138) ◽  
pp. 188-206 ◽  
Author(s):  
F. A. Bannister
Keyword(s):  
Solid Solution ◽  
New Mineral ◽  
Early Analysis ◽  
Aqua Regia ◽  
X Ray ◽  
Ray Methods ◽  
Platinum Mineral ◽  
Insoluble Portion

Concentrates from the platiniferous norites of the Bushveld, Transvaal, are not completely soluble in aqua regia. The insoluble portion consists of steel-grey fragments first analysed chemically by R. A. Cooper and considered by him to be a new platinum mineral represented by the formula Pt(As,S)2. The name cooperite was proposed for the new mineral by F. Wartenweiller, and after further work Cooper decided that the arsenic found in the early analysis was due to the presence of sperrylite, and he changed the formula to PtS2. H. Schneiderhöhn observed simple twinning and, less frequently, polysynthetie lamellae on polished sections of mineral grains from the same deposits, and he suggested that cooperite is probably orthorhombic and isomorphous with marcasite. The latest account of the new mineral has been published by H. R. Adam who gave several analyses of cooperite from the Rustenburg and Potgietersrust districts and concluded that the ‘mineral is PtS2 with a small amount of excess metal (platinum, palladium, and nickel) present in solid solution’.

scholarly journals Crystallographic studies of meteoric iron

1939 ◽  
Vol 238 (794) ◽  
pp. 393-421 ◽  
Keyword(s):  
Crystal Structures ◽  
X Ray ◽  
Cubic Lattice ◽  
Principal Axes ◽  
Ray Methods

The first study of meteoric iron by X-ray methods was undertaken at the instigation of Professor S. W. J. Smith, F.R.S. some years ago. This research (Young 1926) resulted not only in the determination of the crystal structures of two of the main constituents, kamacite and taenite, but also in the important discovery of the nature of the mutual orientations of these constituents when the meteorite exhibits a Widmanstätten structure. As is well known, the Widmanstätten figures in meteorites arise from the arrangement of kamacite lamellae on the planes of an octahedron, and for that reason a meteorite exhibiting these figures is generally referred to as an octahedrite. The kamacite lamellae, therefore, fix the {I I I}-planes of a hypothetical cubic lattice whose principal axes, XYZ , will be referred to as “ the axes of the octahedrite”.

Molecular Weight and Chain-Length of Natural and Synthetic Rubber

1934 ◽  
Vol 7 (1) ◽  
pp. 34-39 ◽  
Author(s):  
A. J. Wildschut
Keyword(s):  
Chain Length ◽  
Freezing Point ◽  
Specific Viscosity ◽  
Molecular Weights ◽  
Gutta Percha ◽  
Synthetic Rubber ◽  
The Subject ◽  
Molecular Substances ◽  
Very High

Abstract The determination of the chain-length of high molecular substances, as, e.g., rubber and gutta-percha, has lately been the subject of many investigations, though as yet the problem has not been definitely solved. The ordinary methods—measurements of the raising of the boiling point and of the depression of the freezing point—can be used only for molecular weights of some thousands, and there always remains a large gap between these compounds and the far greater natural ones. To bridge over this gap Staudinger has developed a supposition according to which it is possible to determine very high molecular weights by means of a viscosimetric method. This method depends on the known fact that for dilute solutions, in which the molecules do not hinder each other (so-called sol-solutions), the specific viscosity is proportional to the length of the molecule. For homologs we have:

Determination of the thickness of polycrystalline thin films by using X-ray methods

2015 ◽  
Vol 591 ◽  
pp. 215-218 ◽  
Author(s):  
S. Daniš ◽  
Z. Matĕj ◽  
L. Matĕjová ◽  
M. Krupka
Keyword(s):  
Thin Films ◽  
X Ray ◽  
Polycrystalline Thin Films ◽  
Ray Methods
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