Experimental methods of determination

Most chemical substance manufacturers systematically submit their new substances (or preparations) to tests that enable them to evaluate the decomposition risks. There are many types of apparatus that are used to test the effect of the different physical causes of instability. The most important are the mechanical and thermal sensitivity tests. The methods listed below are simply intended to give an idea of the available experimentel possibilities. 

How easily a substance can spontaneously decompose or explode under the influence of shock or friction is analysed. These are some of the most frequent causes of explosive decomposition of unstable substances related to common handling stirring, breaking, sieving, etc, or the accidental dropping of a substance or the opening of a flask etc. 

A small quantity of substance is placed on a porcelain plate. Then an hemispheric mass of porcelain is placed on the substance with a weight that can be adjusted and then proceed to a displacement of the porcelain plate. The weight that is necessary to obtain a probability of decomposition of 50% by doing a series of thirty tests is determined m-nitrobenzene gives 0% at 36 kgf (327N). 

200mg of substance is put in a test tube, which is kept open, and which is then placed vigorously in an oil or melted metal bath. The temperature at which the substance is burnt up or explodes is thus determined. With this test m-dinitrobenzene combusts at 400°C. 

20 g of the substance is placed in a cylindrical steel socket of diameter of 24 mm and height 75 mm. This socket is closed with a lid equipped with a light that has a calibrated diameter. It is placed in an enclosure, which contains four burners three laterally and one on the lower part. The socket is then heated vigorously and the limiting diameter of the light with which an explosion of the socket is obtained after three tests is determined. The limiting diameter with m-dinitrobenzene is found to be less than 1 mm. 

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The experimental methods of determining phase diagrams will be only briefly commented upon, in order to give an idea of the problems involved and of the connection between phase diagram science and other disciplines. A few special points will be considered in Chapter 6, dedicated to the preparation of intermetallics. 

Concern about fission-product release from coated reactor fuel particles and fission-product sorption by fallout particles has provided stimulus to understand diffusion. In a fallout program mathematics of diffusion with simple boundary conditions have been used as a basis for (1) an experimental method of determining diffusion coefficients of volatile solutes and (2) a calculational method for estimating diffusion profiles with time dependent sources and. time dependent diffusion coefficients. The latter method has been used to estimate the distribution of fission products in fallout. In a fission-product release program, a numerical model which calculates diffusion profiles in multi-coated spherical particles has been programmed, and a parametric study based on coating and kernel properties has provided an understanding of fission product release. 

Determination of macromolecules conformations is one of the basic problems of science about polymers. Simultaneously with development of theory [4-6] the perfection and enrichment of experimental methods of determination of macromolecules conformations in various phase and aggregate states occurs. However the method of neutron scattering was almost the only one method allowing reliable determination of polymer chains conformation in solid amorphous state until now [7], Not long ago they begun to use with this aim also the method based on measurement of rate of electron excitement transfer between molecules of chromophores covalent bonded with polymer chain [8],... 

The coefficient of expansion generally increases, if it varies at all, with the temperature, but by amounts which vary for different substances. It would not be worth while to discuss the numerical data here, but we may mention that there appears to be a distinct parallelism between the coefficient of expansion and the specific heat. The experimental methods of determining the coefficient of expansion will be found in most text-books on physics. 

When only one sohd phase is present, the total concentration of the solution is indeterminate, and may be altered by addition of the other simple salt or of the double salt. The solubility of a salt is therefore not affected by the addition of a salt with a common ion. For the graphical representation of the equihbria in a three-component system, it is convenient to use a three-dimensional system of coordinates, of which the axes are the temperature and the concentrations of the two simple salts. Each point in the space corresponds to a definite vapour pressure. Monovariant equilibria are represented by lines, and bivariant equihbria by surfaces in the space model. (See van t Hoff, Bildung und Spaltung von Doppelsalzen, Leipzig 1897 also van t Hoff u. Meyerhoffer, Zeitschr. /. physikcd. Chemie, 30, 64 (1899), and others. Experimental methods of determining the transition point are also described there.)... 

This is one of the most important equations in chemical thermodynamics it shows that the equilibrium constant is determined entirely by the standard free energy change. At the same time it provides another experimental method of determining standard free energies. 

The quality of fit of these USER models is excellent and the error is comparable to the uncertainties in experimental methods of determining solubility, and has been claimed to have "reached the level of exhaustive fit" ( . 

Experimental methods of determining the various parameters are described in standard electrochemical engineering texts. We use the values of Goodridge and Scott (1995) ... 

I he development of experimental methods of determining the spinodal, the interaction parameter x (or g), and other critical parameters has promoted the appearance of the third approximation of h lory-IIuggins lattice theory where the dependence of the interaction parameter g on the polymer molecular weight (or MWD) and the peculiar features of dilute polymer solutions or of polymer-depleted phetse at phase separation arc taken into account. 

EXPERIMENTAL METHOD OF DETERMINATION OF THE GROWTH SPECinC RATE VARIATIONS... 

Figure 9.Experimental method of determination of the growth specific rate variations with oxygen partial pressure...

One of the most powerful experimental methods of determining short-range order in polymers utilizes birefringence (6). Birefringence measures orientation in the axial direction. The birefringence of a sample is defined by... 

If the product, 8 X d, has a value of 3.34 X 10 coulomb meter (C m), the dipole moment, p., has a value called 1 debye, D (pronounced duh-bye). One experimental method of determining dipole moments is based on the behavior of polar molecules in an electric field, suggested in Figure 10-15. 

A thin film of water spreads up the inside walls of the capillary because of strong adhesive forces between water and glass (water wets glass). The pressure below the meniscus falls slightly. Atmospheric pressure then pushes a column of water up the tube to eliminate the pressure difference. The smaller the diameter of the capillary, the higherthe liquid rises. Because its magnitude is also directly proportional to surface tension, capillary rise provides a simple experimental method of determining surface tension, described in Exercise 122. 

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