Electrical methods of determining

An electrical resistance methods which directly measures loss of metal from a probe installed in the corrosive system under study is described in Section 19.3. It is reported that corrosion equivalent to a thickness loss of as little as 2-5 X 10 cm can be detected . This technique is most useful as a means of monitoring steps taken to reduce corrosion, e.g. by inhibitors, or to detect changes in the corrosivity of process streams. Electrical methods of determining corrosion rates are considered subsequently. 

In Vol I the electrical method of determining the solubility of a salt such as silver chromate by measurement of the conductivity has already been described In the case of a salt like silver chlonde the solubility is so very small that the conductivity method would be a somewhat inaccurate one By means of electromotive force measurements, however, the solubility of this salt can be determined with a high degree of accuracy Thus if the following concentration cell be set up—... 

Electrical methods of determining the end-point of titrations are widely used some of the advantages of the technique are obvious, such as the ability to titrate coloured solutions where the change of a visual indicator would be difficult or impossible to detect and the ability to carry out titrations for which no suitable visual indicator exists. Electrometric endpoints may often be employed with greater accuracy than visual ones and with greater sensitivity. It should always be remembered, however, that where a suitable visual method of end-point detection is available, it is usually more rapid and more economical to use. Electrometric methods may be classified into potentiometric, conductometric and amperometric methods. 

Millikan R A A new modification of the cloud method of determining the elementary electrical charge and the most probable value of that charge Phil. Mag. 19 209-28... 

Acceleration is perhaps the best method of determining the force resulting from machine vibration. Accelerometers use piezoelectric crystals or films to convert mechanical energy into electrical signals and Figure 43.23 is a schematic of such a device. Data acquired with this type of transducer are relative... 

Electrical methods of analysis (apart from electrogravimetry referred to above) involve the measurement of current, voltage or resistance in relation to the concentration of a certain species in solution. Techniques which can be included under this general heading are (i) voltammetry (measurement of current at a micro-electrode at a specified voltage) (ii) coulometry (measurement of current and time needed to complete an electrochemical reaction or to generate sufficient material to react completely with a specified reagent) (iii) potentiometry (measurement of the potential of an electrode in equilibrium with an ion to be determined) (iv) conductimetry (measurement of the electrical conductivity of a solution). 

The method of determination from measurements of cell potentials depends on the possibility of carrying out a transformation reversibly in an electrical cell. (See Fig. 7.2.) In this case, the spontaneous tendency of the transformation wUl be opposed by an opposing potential just sufficient to balance the potential in the electrical ceU produced by that spontaneous tendency. The potential observed under such circumstances is related to the change of the Gibbs function for the reaction by Equation (7.84)... 

TITRATION. A method of determining volumetrically the concentration of a substance in solution by adding a standard solution of known volume and strength until a change in an indicator is noted or by electrical measurements. 

One method of determining nuclear quadrupole moment Q is by measuring the quadrupole coupling constant, given by eqQ/h, where e is the charge of the electron and q the electric field gradient due to the electrons at the atomic nucleus. The extraction of Q depends on an accurately calculated q. As a test of our finite-field relativistic coupled cluster approach, preliminary results for Cl, Br, and I are presented. 

Free ions occurring in a solution will move under the influence of a homogeneous electric field, the negative ions going to the positive pole, and the positive ions to the negative one. Measurement of the electrical conductivity of such solutions is the best method of determining the number and kinds of ions present, even when the ions are associated with solvent molecules. Molecules of the solvent will, of course, be transported with the ions, and special experiments can be made to determine the quantity being transported and hence arrive at the number of molecules of solvent associated with each ion. 

Electrical methods of measuring coal moisture involve determination of the capacitances or resistances or the dielectric constant of coal from which the... 

Possible methods of determining the extent of protonation include absorption spectroscopy at a wavelength for which species with n and fir-1 protons have different extinction coefficients, freezing point depression, and electrical conductivity (15). Of these, we have utilized only spectroscopy, which has the disadvantage that only the equilibrium constants for the most highly protonated states are accessible if, as is usual, the species with low protonation are insoluble. In this method, the extinction coefficient c of the compound is determined as a function of the H2SO4 content in the sulfuric acid solvent and correlated with the Hammet acidity function H0 (18) to give the pKB value of the protonated species,... 

A convenient method of determining the temperature of a luminous flame consists 3 in inserting a thin wire of incorrodible metal, such as gold or platinum, into the flame and estimating the temperature with a pyrometer. The loss of heat occasioned by insertion of the wire is compensated for by raising the wire to the temperature of the flame by an electric current. When the wire has reached the same temperature as the flame there is no deposition of carbon. The wires should not exceed 1 mm. in diameter. 

The second group consists of properties that are important at very high electric field strengths, such as electric discharge, dielectric breakdown and arc resistance. They may be regarded as the ultimate electrical properties. Properties of the first group are directly related to the chemical structure of the polymer those of the second are greatly complicated by additional influences in the methods of determination. 

Ed. 1 Section 3 Method of determining the minimum ignition energy of dust-air mixtures Electrical apparatus for use in the presence of combustible dust... 

R.O. James, G.A. Parks, Characterization of Aqueous Colloids by Their Electrical Double Layer and Intrinsic Surface Chemical Properties, in Surface and Colloid Science, Vol. 12, E. Matijevlc, Ed., Plenum Press (1982) 119. (Review emphasizing methods of determining intrinsic binding constants, mostly for latices and oxides.)... 

The Coulter technique is a method of determining the number and size distribution of particles suspended in an electrolyte by causing them to pass through a small orifice on either size of which is immersed an electrode. The changes in electrical impedance as particles pass through the orifice generate pulses whose amplitudes are proportional to the volumes of the particles. The pulses are fed to a pulse height analyzer where they are scaled and counted and, from the derived data, the size distribution of the suspended phase is determined. 

In the wake of earlier methods of determining electric dipole moments of polar molecules, recent developments have led to methods permitting the determination of electric moments of higher orders quadrupoles,... 

In 1907 Sir j. J. Thomson developed a method of determining the ratio of charge to mass of an ionized atom (or ionized gas molecule) by measuring the deflection of a beam of the ionized atoms in electric and magnetic fields. The apparatus is called a mass spectrograph. 

Electrical methods. The electrical methods of measuring temperature are based on two facts, firstly, that the resistance of a conductor varies with the temperature, and secondly, that the electromotive force which is produced at a point of contact between two different metals or alloys is hkewise a function of the temperature. If, therefore, we close a circuit consisting of two wires of different metals, so that there are two joints in the circuit where two metals meet, a current will flow in general so long as these joints are not at the same temperature. If the temperature of the one joint is known, a measurement of the electromotive force enables us to determine the temperature of the other. On account of the great sensibility of electrical measurements, it is possible to measure very small differences of temperature by either of these methods. They have the further advantage over the first and second methods, that we are enabled by their means to measure very high and very low temperatures in a most convenient manner. The small bulk occupied by a thermocouple is often important from an experimental point of view, and for this reason thermocouples are preferable in some cases to all other forms of thermometer. 

The method of determining the specific heat which was used by Nemst and his collaborators was devised by Eucken. The substance was immersed in a suitable bath, such as liquid hydrogen, or Hquid air, in a vacuum vessel, and was then heated by a known electric current. The heating wire also served as a resistance thermometer. As the rise in temperature was always very small, the true specific heat was obtained directly. The following table shows the more or less rapid decrease of the specific heat with the temperature for a number of substances f... 

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