I. Contact theory of voltaic action. Parts I and II

1878 ◽  
Vol 27 (185-189) ◽  
pp. 196-238 ◽  
Keyword(s):  
Electromotive Force ◽  
Zinc Sulphate ◽  
Copper Plate ◽  
Contact Theory ◽  
Metallic Contact ◽  
A Value ◽  
A Cell ◽  
The Difference ◽  
Voltaic Cell

The contact theory of voltaic action seems to have undergone no development since the date of Sir W. Thomson’s experiment, which consisted in connecting a plate of zinc and a plate of copper by means, of a drop of water, when it was found that the metals were brought to the same electric potential, although when metallically connected they were at different potentials. He believed that any electrolyte would behave in exactly the same way as the water of his experiment, equalizing the potentials of any two metals connected by it. The electromotive force of a simple cell, ought, in accordance with the theory, to be equal to the difference of potentials between zinc and copper in; contact. A test founded on this deduction was very difficult to apply, because there was no exact determination of the difference of potential of zinc and copper in contact, Sir W. Thomson, in his experiment, having really measured the difference of potential between air at the surface of a zinc plate, and air at the surface of a copper plate. In the absence of this test, the equality of the electromotive forces of simple cells in which zinc and copper are the metals (the liquids being water, dilute sulphuric acid, and sulphate of zinc) was held as a proof of the theory. Now it is known that when two pieces of the same metal are dipped into any two liquids, which are diffusing into one another, a difference of potentials is established between the metals, and the electromotive force of a cell of this kind can in no way depend on a difference of potentials due to metallic contact. So that although in such a cell there is an action which is somewhat the same as the action in a simple voltaic cell, the theory took no account of it whatever. In fact, the explanation of voltaic action given in the latest treatises on electricity is felt to be incomplete, even by the writers of such treatises, and the present investigation has been entered upon in consequence. Sir W. Thomson’s result, and our own experiments lead us to magine that when zinc and copper are immersed in water there are three successive states to be noticed:—At the instant of immersion the zinc and copper may be reduced to the same potential, so that the electromotive force of the voltaic cell E is equal to the difference of potential ZC — between zinc and copper in contact; the zinc now becomes negative to the copper, so that E reaches a limit which is greater than ZC — ; lastly, if a current passes, polarization occurs and the zinc becomes gradually less negative to the copper, E diminishing, therefore, from its maximum value# But when a saturated solution of zinc sulphate is employed instead of water, the first state, if it exists at all, exists for so short a time that practically, zinc and copper in zinc sulphate are never at the same potential. Thus (see Table X ) when care is taken to keep the zinc and copper in a water cell well insulated from one another, E is found to increase from a value very little greater than ZC — , the electromotive force of contact of zinc and copper, to a limit, but in a zinc sulphate cell no such great increase is observed.

THE MAINTENANCE OF A STANDARD OF ELECTROMOTIVE FORCE: NOTES ON STANDARD WESTON CELLS

1930 ◽  
Vol 3 (5) ◽  
pp. 473-489
Author(s):  
A. Norman Shaw ◽  
H. E. Reilley
Keyword(s):  
Electromotive Force ◽  
Essential Feature ◽  
Mean Deviation ◽  
Entire Group ◽  
Standard Cells ◽  
Characteristics Analysis ◽  
A Cell ◽  
The Mean ◽  
The Difference

A detailed procedure for the maintenance of a standard of voltage to within one or two parts in a million is described.In so far as these investigations have proceeded, neutral saturated cells have been found to be superior to acid cells as independent standards for a period of many years, though the latter are preferable for purposes of ordinary precision or shorter periods. The recommended code of procedure is briefly as follows: a number of cells should be constructed according to standard specifications with the new requirements of uniformity of container and speed of preparation, and observations made upon them every few days for a period of three months. The differences in electromotive force (at constant temperature) should be determined between each cell in the group and any one of them chosen arbitrarily as reference cell, and certain new selection and rejection rules applied. In accordance with these rules a cell should be rejected: (a) if its deviation from the mean electromotive force of the group has increased or decreased by 10 microvolts or more during the preceding two weeks; or (b) if it differs in electromotive force from the mean of the group by more than 10 +d microvolts where d is the mean deviation of the cells of the group. If d exceeds 20 microvolts the entire group should be considered untrustworthy. The selected cells should be observed for three additional months, the rejection rules again applied and if a specified proportion survive elimination, the initial reference mean of the laboratory may be established.At intervals of several months additional groups of cells, neutral and acid, should be constructed and exchanges made with laboratories possessing cells of known characteristics. Analysis of the resulting observations determines: (a) the constants in the aging* equation for the reference batch, and (b) the difference between the initial reference mean of the laboratory and the estimated value of the international reference mean.Examples of the analysis of cell observations are given, illustrating the establishment of the initial reference mean, the recapture of this value when the aging coefficients are known, and the preliminary determination of the aging equation for a given group of cells. The use of the aging equation is found to be the essential feature in the attainment of increased precision.A summary of data on standard cells is included.

scholarly journals Determination of the H<sub>2</sub>O content in minerals, especially zeolites, from their refractive indices based on mean electronic polarizabilities of cations

2020 ◽  
Vol 32 (1) ◽  
pp. 27-40
Author(s):  
Reinhard X. Fischer ◽  
Manfred Burianek ◽  
Robert D. Shannon
Keyword(s):  
Thermal Analyses ◽  
Refractive Indices ◽  
Formula Unit ◽  
Electronic Polarizability ◽  
Hydrous Minerals ◽  
A Value ◽  
Small Crystals ◽  
Zeolite Type ◽  
The Difference

Abstract. It is shown here that the H2O content of hydrous minerals can be determined from their mean refractive indices with high accuracy. This is especially important when only small single crystals are available. Such small crystals are generally not suitable for thermal analyses or for other reliable methods of measuring the amount of H2O. In order to determine the contribution of the H2O molecules to the optical properties, the total electronic polarizability is calculated from the anhydrous part of the chemical composition using the additivity rule for individual electronic polarizabilities of cations and anions. This anhydrous contribution is then compared with the total observed electronic polarizability calculated from the mean refractive index of the hydrous compound using the Anderson–Eggleton relationship. The difference between the two values represents the contribution of H2O. The amount can be derived by solving the equation αcalc=∑iniαicat+∑jαjo×10-NjVm1.2×nj+nW1.2+nw×αW for the number nw of H2O molecules per formula unit (pfu), with the electronic polarizabilities αcat for cations, the values N and αo describing the anion polarizabilities, the number n of cations and anions, and the molar volume Vm, using a value of αW=1.62 Å3 for the electronic polarizability of H2O. The equation is solved numerically, yielding the number nw of H2O molecules per formula unit. The results are compared with the observed H2O content evaluating 157 zeolite-type compounds and 770 non-zeolitic hydrous compounds, showing good agreement. This agreement is expressed by a factor relating the calculated to the observed numbers being close to 1 for the majority of compounds. Zeolites with occluded anionic or neutral species (SO3, SO4, CO2, or CO3) show unusually high deviations between the calculated and observed amount of H2O, indicating that the polarizabilities of these species should be treated differently in zeolites and zeolite-type compounds.

scholarly journals THE RATE OF EXCHANGE OF TRITIATED WATER ACROSS THE HUMAN RED CELL MEMBRANE

1957 ◽  
Vol 41 (2) ◽  
pp. 259-277 ◽  
Author(s):  
C. V. Paganelli ◽  
A. K. Solomon
Keyword(s):  
Reaction Rate ◽  
Tritiated Water ◽  
Red Cell ◽  
Red Cell Membrane ◽  
Equivalent Radius ◽  
A Value ◽  
Cylindrical Pores ◽  
The Difference ◽  
Human Red Cell Membrane

The flow method of reaction rate measurement has been adapted to the determination of the rate of diffusion of water into the human red cell. In seven experiments the half-time for diffusion exchange has been found to be 4.2 ± 1.1 msec., which is equivalent to a diffusion flow of 8.6 x 10–9 ml. H2O/(sec., red cell). This figure has been compared with the rate of water entrance under an osmotic pressure gradient, and has been found to be smaller by a factor of 2.5. The difference between these two rates of water entrance has been interpreted as indicating the presence of water-filled channels in the membrane. An estimate of the equivalent radius of these channels (on the assumption of uniform right cylindrical pores) leads to a value of 3.5 Å, which is viewed as an operational description of the resistance offered by the membrane to the passage of water.

scholarly journals Value stock and growth stock on Indonesia stock exchange after global crisis

2018 ◽  
Vol 1 (1) ◽  
pp. 8
Author(s):  
Muhammad Fadhil Rabbani ◽  
Harjum Muharam
Keyword(s):  
Financial Crisis ◽  
Stock Exchange ◽  
High Ratio ◽  
Sharpe Ratio ◽  
Value Stocks ◽  
A Value ◽  
The World ◽  
Before And After ◽  
The Difference

This study was conducted to determine whether there are differences between the stock return of value stocks and growth stock in Indonesia before and after the world financial crisis that occurred in 2008. To investigate the difference, the stocks formed into a portfolio that is based on the 2002 calculated in 2002 and 2009 when the world financial crisis has ended. The formation of the portfolio based on stocks that have gone public before 2000 and have the complete data during the study period. For the determination of the categories of stocks used Price-to-Earnings ratio, price-to-book ratio and price-to-cash flow ratio. Shares of stock that has a very high ratio will be eliminate to avoid bias that may occur if the stocks are still included. Similarly, the stocks of which are negative because they do not meet the criteria as a value stock. Then ANOVA test conducted to determine differences in returns and Sharpe ratio on the portfolio which was formed in 2002 and in 2009. Results from this studies are not found differences in returns and Sharpe ratio on both the portfolio. This indicates that the formation of the portfolio by value stocks and growth stock can not be used as a guide to get a high return.

scholarly journals VIII. The variations of electromotive force of cells consisting of certain metals, platinum, and nitric acid

1891 ◽  
Vol 182 ◽  
pp. 319-339 ◽  
Keyword(s):  
Nitric Acid ◽  
Nitrous Acid ◽  
Electromotive Force ◽  
Chemical Change ◽  
Division Of Labour ◽  
Contact Theory ◽  
Necessary Condition ◽  
Continuous Formation ◽  
High Degree ◽  
Voltaic Cell

The experiments described by one of us in another paper have established that the necessary condition for the chemical reactions between nitric acid and the metals copper, mercury, and bismuth, is the presence and continuous formation of nitrous acid. These results confirm the previous observations of Russell in the case of the metal silver. Further, it has been shown that when these metals are introduced into purified nitric acid, no apparent change takes place at first, but after some time gas bubbles are seen to rise from the surface of the metal, and the liquid then contains an amount of nitrous acid which can be detected by the more delicate reagents. The amount of this acid increases up to a maximum and constant point, while concomitantly the amount of metal dissolved per unit of time equally increases to a maximum and constant value. It seemed, therefore, desirable to ascertain if these phenomena determined by the balance are correlated with any alteration of electromotive force. To avoid any misunderstanding, however, it would be advisable at the outset to state that this paper is separated from that of one of us “On the Condition of Chemical Change between certain Metals and Nitric Acid,” rather on account of division of labour than of difference of subject. The idea of measuring the electromotive force of cells consisting of platinum, certain metals, and nitric acid occurred to the latter of us, while the apparatus and method of measurement finally adopted are due solely to the former. Previous Investigations . Many years ago Faraday pointed out that neither nitrogen peroxide nor nitric acid are conductors when pure, but that the addition of water to the former, or of nitrous acid to the latter, produces the property of conductivity “in a very high degree among electrolytes.” Thus the presence of nitrous acid is the necessary condition that nitric acid should become an electrolyte. Again, Faraday proved that the electric position of certain pairs of metals in nitric acid is varied according to the conditions of concentration and temperature; in fact, experiments on this point were considered by him to be of especial importance in confirming the chemical and disproving the contact theory of the voltaic cell.

scholarly journals IV. A determination of the electromotive force of the weston normal cell in semi-absolute volts

1914 ◽  
Vol 214 (509-522) ◽  
pp. 147-198 ◽  
Keyword(s):  
Electromotive Force ◽  
Order Of Accuracy ◽  
Absolute Determination ◽  
A Value ◽  
Great Progress ◽  
The Mean ◽  
The Absolute ◽  
The Times ◽  
Made In

The measurement of the E. M. F. of the Weston cell affords the best means of comparing the performances of different methods and instruments for the absolute determination of the ampere. Great progress has been made in the last six years, but the most recent determinations by independent methods, giving equal promise of accuracy, still show discrepancies covering a range of 2 parts in 10,000, which must be debited for the most part to the difficulty of the absolute determination of current. Each method in itself appears to give an order of accuracy of repetition approaching, or even exceeding, 1 in 100,000. It is therefore of special interest and importance to compare the results of methods differing as widely as possible in experimental details in endeavouring to arrive at a value comparatively free from the constant errors which may beset any particular type of method. The measurements described by Mr. Shaw in the following paper were made by the method of the Weber bifilar electrodynamometer, as modified by Clerk Maxwell and Latimer Clark, which has not hitherto been employed for work of the highest accuracy, and which merits attention on account of its many fundamental points of difference from recent methods. The instrument originally supplied to McGill College for this purpose was a faithful copy of Clerk Maxwell’s instrument at Cambridge, of which the theory is given together with a figure and description in his ‘ Electricity and Magnetism,’ vol, 2, p. 367. The chief sources of error in this instru­ment were (1) the uncertainty of insulation of the coils, which proved to be of the order of nearly one half of 1 per cent.; (2) the difficulty of determining the mean radii of the coils, which were wound with silk-covered wire; (3) the want of rigidity of the pulley arrangement for equalising the tensions of the suspending wires, and the imperfect elasticity of the control, which depended too much on torsion, and made it impossible to obtain readings consistent to 1 in 1000 for the deflections or the times of oscillation. These defects were so fatal to accurate work even of the order of 1 in 10,000, which was all that it was originally contemplated, that it was found necessary to reconstruct the instrument entirely until nothing remained of the original except the frame, and even that required stiffening to a material extent.

A thermocouple method of following the non-stationary state of chemical reactions V. The evaluation of velocity coefficients for the propagation and termination reactions for the heterogeneous polymerization of acrylonitrile

1961 ◽  
Vol 260 (1301) ◽  
pp. 205-217 ◽  
Keyword(s):  
Stationary State ◽  
Bulk Polymerization ◽  
Polymer Chains ◽  
Polymerization Reaction ◽  
Kinetic Chain ◽  
A Value ◽  
Thermocouple Method ◽  
The Difference ◽  
Made In

An attempt has been made to evaluate the velocity coefficients for the propagation and termination reactions in the bulk polymerization of acrylonitrile using the thermocouple non-stationary-state method. The reaction has been studied at 25 °C, and 1. 1'-azo-bis- cyclo -hexane carbonitrile has been employed as a photosensitizer. In the very early stages of the reaction (< 0.1 % conversion) when there is very little dead polymer present, the intensity exponent is 0.5, which indicates that the termination reaction proceeds by the interaction of growing polymer chains. The values obtained for the propagation and termination velocity coefficients (namely, 52 and 5.0 × 10 6 1. mole -1 s- 1, respectively) are lower than those reported in the literature for the polymerization of acrylonitrile in dimethylformamide solution. The difference has been attributed to environmental factors. Measurements of rates and lifetimes of the kinetic chain have also been made in the region of 1 to 7% conversion. By means of a suitably designed dilatometer which could be centrifuged, the effects of polyacrylonitrile on the polymerization reaction was studied. It was shown that the presence of polymer produced an enormous increase in the lifetime of the kinetic chain, while the rate decreased a little probably due to the scattering of initiating irradiation by the precipitated polymer. The intensity exponent appeared to increase to a value of 0.7, but this may not have been a true effect, as errors in the determination of the rate may have arisen due to difficulties in maintaining adiabatic conditions throughout the non-stationary state. The results in general are in keeping with the occlusion theory suggested by previous workers to explain some peculiar characteristics of the bulk polymerization of acrylonitrile.

scholarly journals XI. A determination of the specific heat of water in terms of the international electric units

1895 ◽  
Vol 186 ◽  
pp. 415-467 ◽  
Keyword(s):  
Specific Heat ◽  
Electromotive Force ◽  
Good Deal ◽  
Great Accuracy ◽  
Important Research ◽  
Science And Art ◽  
The Wire ◽  
The Difference ◽  
Work Done

This research was originally undertaken by Professor Schuster and Mr. H. Hadley before the authors were aware that Mr. E. H. Griffiths was engaged on a similar investigation. After a number of preliminary experiments, and just as the final arrangements for the conduct of the measurements were being definitely made, Mr. Hadley, on his appointment to the Head Mastership of the School of Science and Art, Kidderminster, had to leave Manchester. In the meantime Mr. Griffiths’ important research was published; and we had to consider whether our own work, which was designed on a smaller scale, could compete with it in accuracy. We decided to complete the investigation, principally for the reason that, although we both aimed at determining what is commonly called the mechanical equivalent of heat through the heating of a certain mass of water by means of an electric current, the details of the experiments differed very materially, so that our two ways of dealing with the problem seemed to afford a useful test of the amount of agreement which may be obtained at present. Our investigation touches only a small part of that treated by Mr. Griffiths, as we did not attempt to measure the changes in the specific heat of water due to change of temperature. On the other hand, the more modest limits within which we have confined ourselves, allowed us to use a much simpler apparatus. On Mr. Hadley’s departure, Mr. W. Gannon took his place. From the former gentleman we received a good deal of help in the devising and construction of some important parts of the apparatus. The principle of the method we have used is extremely simple. The electrical work done in a conductor being measured by ∫EC dt , where E is the difference of potential at the ends of the conductor, C the current and t the time, we keep the electromotive force constant, and measure ∫C dt directly by a silver voltameter. We do not therefore require to know the resistance of the wire, and we thus avoid the difficulty of having to estimate the excess of temperature of the wire over that of the water in which it is placed. We also gain the advantage of not having to measure time, and therefore are able to complete the experiment more quickly than we could have safely done if the length of time during which the current passed had to be measured with great accuracy.

scholarly journals Dielectrophoretic Characterisation of Mammalian Cells above 100 MHz

2019 ◽  
Vol 2 (1) ◽  
pp. 64-71 ◽  
Author(s):  
Colin Chung ◽  
Martin Waterfall ◽  
Steve Pells ◽  
Anoop Menachery ◽  
Stewart Smith ◽  
...  
Keyword(s):  
Dielectric Properties ◽  
Cell Separation ◽  
Mammalian Cells ◽  
Uniform Electric Field ◽  
Cell Diameter ◽  
Label Free ◽  
Myeloma Cells ◽  
A Value ◽  
A Cell

Abstract Dielectrophoresis (DEP) is a label-free technique for the characterization and manipulation of biological particles - such as cells, bacteria and viruses. Many studies have focused on the DEP cross-over frequency fxo1, where cells in a non-uniform electric field undergo a transition from negative to positive DEP. Determination of fxo1 provides a value for the membrane capacitance from the cell diameter, the means to monitor changes in cell morphology and viability, and the information required when devising DEP cell separation protocols. In this paper we describe the first systematic measurements of the second DEP cross-over frequency fxo2 that occurs at much higher frequencies. Theory indicates that fxo2 is sensitive to the internal dielectric properties of a cell, and our experiments on murine myeloma cells reveal that these properties exhibit temporal changes that are sensitive to both the osmolality and temperature of the cell suspending medium.

Determination of yielding and debonding in Al–Cu thin films from residual stress measurements via diffraction

1991 ◽  
Vol 6 (5) ◽  
pp. 950-956 ◽  
Author(s):  
C.J. Shute ◽  
J.B. Cohen
Keyword(s):  
Thin Films ◽  
Residual Stress ◽  
Film Thickness ◽  
Void Formation ◽  
Thickness Dependence ◽  
A Value ◽  
The Difference ◽  
Thin Polycrystalline ◽  
Si Wafer

The yield strength and interfacial bonding are properties of interest for understanding void formation in thin film interconnect and subsequent failure of VLSI devices. A method is presented to examine the mechanical properties of thin polycrystalline films attached to substrates by measuring the change in thermal residual stress, due to the difference in coefficient of expansion between the film and substrate, as a function of decreasing temperature of the sample. The yield strengths of passivated 0.5, 1.0, and 2.0 μm thin films of Al–2% Cu on oxidized Si wafer substrates have been determined with this method to be 325, 170, and 120 MPa, respectively. Unpassivated films of the same thicknesses were also examined, but yielding did not occur for these films even though the residual stress reached a value of over 400 MPa. The lack of yielding in the unpassivated samples and the thickness dependence of the passivated samples is attributed to the grain size of these materials, which is less than the film thickness for the unpassivated case and greater than the film thickness after passivation. Debonding occurred in the 2 μm unpassivated sample but in none of the others, indicating a thickness dependence of the energy for delamination.

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