scholarly journals Comparison of the Board of Trade ampere-standard balance with the Ayrton-Jones current-weigher; with an appendix on the electromotive forces of standard cells

1908 ◽  
Vol 80 (540) ◽  
pp. 383-389 ◽  
Keyword(s):  
Technical College ◽  
National Physical Laboratory ◽  
Current Strength ◽  
Physical Laboratory ◽  
The Difference ◽  
Set Up ◽  
High Degree ◽  
A Current ◽  
Fair Degree

When the Board of Trade ampere balance was set up and verified in 1894, the platinum weight (marked A) used with the instrument was adjusted so that a current which deposited silver from a 15-per-cent. solution of silver nitrate at the rate of 1·118 milligrammes per second produced, on reversal, a change of force equal to the weight of A. At that period such a current was believed to represent the ampere , viz., 1/10 of a C. G. S. unit, with a fair degree of accuracy. During the last few years a new current weigher, designed at the Central Technical College, has been constructed at the National Physical Laboratory with a precision previously not obtained in any instrument for the absolute determination of current strength, and by means of it the electrochemical equivalent of silver has been determined to a very high degree of accuracy. We therefore considered it of interest to determine the difference between the units of current as measured by the two balances, and at the same time ascertain how nearly the ampere, as measured by the Board of Trade balance, deposits silver at the rate of 1·118 milligrammes per second.

scholarly journals On the determination of the absolute unit of resistance by alternating current methods

1912 ◽  
Vol 87 (597) ◽  
pp. 391-414 ◽  
Keyword(s):  
Lower Order ◽  
Alternating Current ◽  
National Physical Laboratory ◽  
Mutual Inductance ◽  
Electrical Circuits ◽  
Physical Laboratory ◽  
Absolute Measure ◽  
The Absolute ◽  
Set Up

1. Introductory .—Recently at the National Physical Laboratory we have constructed a standard of mutual inductance of novel type, whose value has been accurately calculated from the dimensions. This inductance has formed the basis for the determination of the unit of resistance in absolute measure by two different methods, in both of which alternating current is employed. Although there is no doubt that the accuracy attainable by these methods could be increased by greater elaboration of the apparatus used, the results already obtained seem to be of sufficient interest to warrant publication. It should be mentioned that the accuracy here aimed at was of a considerably lower order than that contemplated in the determination of the ohm by the Lorenz apparatus which is at present being carried out in the laboratory. For the experiments here described, no apparatus was specially constructed, but use was made of instruments which had already been designed and set up for the measurement of inductance and capacity. I shall first give a brief description of the standard inductance and then pass on to the methods and results. 2. Standard Mutual Inductance .—The design of the mutual inductance has already been described. The electrical circuits have the form and arrange­ment shown in section in fig. 1.

AN IMPROVED INTERFEROMETER FOR DETERMINING PARALLELISM ERRORS IN LONG END-GAUGES

1947 ◽  
Vol 25f (3) ◽  
pp. 242-259
Author(s):  
L. Graham Turnbull
Keyword(s):  
Mechanical Design ◽  
National Physical Laboratory ◽  
Physical Laboratory ◽  
Specialized Technique ◽  
End Gauges ◽  
The Difference

This paper describes an interferometer designed for the determination of the parallelism of the working faces of end-gauges up to 24 in. in length. An instrument for this purpose, but which required somewhat highly specialized technique in the course of its construction, had been previously designed by the National Physical Laboratory. Using optical principles the same as those of the British instrument, another of an entirely new mechanical design has been constructed by the National Research Laboratories, Ottawa. This new interferometer incorporates kinematic principles and a number of interesting features to permit easy adjustment and operation to the very fine limits necessary. By the addition of a sensitive level vial to this instrument, the difference in length of nominally equal end-gauges can be determined to an accuracy of 1 or 2 × 10−6 in.

scholarly journals Amplitude response of a telemetered seismic system from seismometers to digital acquisition system

1995 ◽  
Vol 38 (1) ◽  
Author(s):  
R. Di Giovambattista ◽  
S. Barba ◽  
A. Marchetti
Keyword(s):  
Digital Signals ◽  
Amplitude Response ◽  
Automatic Mode ◽  
Steady State Method ◽  
Sinusoidal Current ◽  
Fully Automatic ◽  
The Difference ◽  
High Degree ◽  
Seismic System

Automated amplitude response of the complete seismometer, telemetry and recording system js obtaiued trom sinusoidal inputs to the calibration coil. Custom-built software was designed to perform fully automatic cali- bration analyses of the digital signals. In this paper we describe the signals used for calibration and interactive and batch procedures designed to obtain calibration functions in automatic mode. By using a steady-state method we reach a high degree of accuracy in the determination of both the frequency and amplitude of the \ignal. The only parameters required by this procedure are the seismometer mass, the calibration-coil constant and the intensity of the current injected into the calibration coil. This procedure is applicable to telemetered seismic systems and represents an optimization of the processing time. The software was designed to requjre no modification" jf the device used to generate the sinusoidal current should change. In particular, it is possi- ble to changc the number of monotrequcncy packages transmitted to the calibration coil with the on]y restric- tion that the difference between the frequency of two consecutjve packages be greater than 5%; for these rea- sons the procedure is expected to be usefu] for the seismological community. The paper inc]udes a generaI de- scription of thc designing criteria, and of the hardware and software architecture, as well as an account of thc system's performancc during a two year period of operation.

scholarly journals Gordon Brims Black McIvor Sutherland, 8 April 1907 - 27 June 1980

1982 ◽  
Vol 28 ◽  
pp. 589-626 ◽  
Keyword(s):  
Molecular Structure ◽  
Critical Time ◽  
Active Role ◽  
The United States ◽  
National Physical Laboratory ◽  
Andrews University ◽  
Left Behind ◽  
Active Life ◽  
Physical Laboratory

As a scientist Gordon Sutherland made, at a critical time, a major contribution to the transformation of infrared spectroscopy from a research technique practised in few laboratories into a powerful and widely used method for analysis and for the determination of molecular structure. A physicist by training, he was happy to be described as a chemical physicist or a biophysicist in relation to different aspects of his researches. Later in his career he was a successful Director of the National Physical Laboratory and then Master of Emmanuel College, Cambridge. He played an active role in British science policy. He died on 27 June 1980, in his seventy-third year, some 3 years after his retirement from the Mastership of Emmanuel College. Although after his graduation from St Andrews University Sutherland spent most of his active life in England or in the United States, he always retained the accent of a Scot, and a very deep affection for his native country. In a characteristically thoughtful way, Sutherland left behind a brief account in his own words of the earlier part of his life and career. A number of substantial quotations from his autobiographical document are included in this memoir.

scholarly journals The thermal and electrical conductivity of a single crystal of aluminium

1927 ◽  
Vol 115 (770) ◽  
pp. 236-241 ◽  
Keyword(s):  
Electrical Conductivity ◽  
Single Crystals ◽  
Test Specimen ◽  
Average Diameter ◽  
National Physical Laboratory ◽  
Present Communication ◽  
Uniform Size ◽  
The Third ◽  
Physical Laboratory

The recent work of Carpenter and Elam on the growth of single crystals of large dimensions has rendered possible the study of the physical constants of single crystals of the commoner metals, and the present communication describes the determination of the thermal and electrical conductivity of aluminium in the form of an isolated crystal. The form of the crystal investigated is shown in fig. 1. This crystal had been prepared at the National Physical Laboratory employing the technique described by Carpenter in “Nature,” p. 266, August 21, 1926, which briefly is as follows:— The test specimen is machined and subjected to three treatments, thermal, mechanical, and thermal. The first treatment is necessary to soften the metal completely and produce new equiaxed crystals of so far as possible uniform size, the average diameter being 1/150 inch. The second consists in straining these crystals to the required amount, and the third in heating the strained crystals to the requisite temperature, so that the potentiality of growth conferred by strain could be brought fully into operation.

Address of the President, Professor P. M. S. Blackett, C.H., at the Anniversary Meeting, 30 November 1966

1967 ◽  
Vol 167 (1006) ◽  
Keyword(s):  
National Physical Laboratory ◽  
Simple Approach ◽  
Ionic Crystals ◽  
X Ray Diffraction ◽  
Complete Structure ◽  
Principal Role ◽  
X Ray ◽  
Physical Laboratory ◽  
Royal Institution

The Copley Medal is awarded to Sir Lawrence Bragg, O.B.E., M.C., F.R.S. Bragg’s career has precisely coincided with the growth of a major field of science—the X-ray diffraction analysis of crystal structures. This had its beginning in his own early researches, and he has throughout played a principal role by his leadership at a series of laboratories, at Manchester, at the National Physical Laboratory, at Cambridge and at the Royal Institution, and in many other ways. He was the first to determine the atomic arrangement in a crystal (sodium chloride), and this work marked the introduction of a technique which has since been successfully applied to increasingly complicated molecules, culminating in the complete structure determination of the protein lysozyme at the Royal Institution a year before his retirement. Bragg has been prominent in the development of methods, beginning with the Law named after him; he also pioneered or encouraged the application of these methods in several fields—ionic crystals, elementary oxides, silicates, metals and proteins. The striking characteristic of Bragg as a scientist has been his direct and simple approach to complicated physical situations; his solutions of problems have a lucidity and simplicity which, in retrospect, make one forget how baffling they often seemed in advance.

scholarly journals National Physical Laboratory Radiocarbon Measurements II

Radiocarbon ◽  
1964 ◽  
Vol 6 ◽  
pp. 25-30 ◽  
Author(s):  
W. J. Callow ◽  
M. J. Baker ◽  
Daphne H. Pritchard
Keyword(s):  
Standard Deviation ◽  
Standard Error ◽  
Half Life ◽  
Research Programme ◽  
National Physical Laboratory ◽  
Reference Standard ◽  
Best Value ◽  
Physical Laboratory ◽  
The Difference ◽  
Absolute Age

The following list comprises measurements made since those reported in NPL I and is complete to the end of November 1963.Ages are relative to a.d. 1950 and are calculated using a half-life of 5568 yr. The measurements have been corrected for fractionation and referred to 0.950 times the activity of the NBS oxalic acid as a contemporary reference standard. The quoted uncertainty is one standard deviation derived from a proper combination of the parameter variances, viz. those of the standard and background measurements over a rolling twenty-week period, of the sample measurements from at least three independent fillings, of the δC13 measurements and of the de Vries effect (assumed to add an additional uncertainty equivalent to a standard deviation of 80 yr). Any uncertainty in the half-life has been excluded so that relative C14 ages may be correctly compared. Absolute age assessments, however, should be made using the accepted best value for the half-life and the appropriate uncertainty included. If the net sample activity is less than 4 times the standard error of the difference between the sample and background activities, a lower limit to the age is reported equivalent to a sample activity of 4 times the standard error of this difference.The description of each sample is based on information provided by the person submitting the sample to the Laboratory.The work reported forms part of the research programme of the Laboratory and is published by permission of the Director.

Voltammetric determination of Al(III) with adsorptive preconcentration of the pyrocatechol violet complex

1991 ◽  
Vol 69 (9) ◽  
pp. 1418-1426 ◽  
Author(s):  
Dragic V. Vukomanovic ◽  
John A. Page ◽  
Gary W. Vanloon
Keyword(s):  
Metal Species ◽  
Aqueous Samples ◽  
Linear Calibration ◽  
Pyrocatechol Violet ◽  
Key Words Aluminium ◽  
Standard Additions ◽  
The Difference ◽  
A Current ◽  
Good Agreement

A method is described for the determination of aluminium in aqueous samples by linear scan voltammetry after adsorptive accumulation of the pyrocatechol violet (PCV) complex. A pH 6.5 triethanolamine/perchloric acid electrolyte is used for the determination with adsorption onto a mercury drop electrode at −0.50 V (vs a Ag/AgCl/satd KCl reference). Scanning cathodically after adsorption gave a current peak at −0.70 V for reduction of adsorbed PCV and a peak at −0.90 V for reduction of the adsorbed Al-PCV complex. The peaks were well resolved. Using 1.0 μM PCV and a 60 s adsorption period gave linear calibration curves for Al in the range 1 to 25 ng mL−1 Al. The detection limit was 0.1 ng mL−1 Al. For analysis, calibration by the method of standard additions is required. Most other metal species do not interfere, but vanadium (V(IV) and V(V)) forms a complex with PCV that is adsorbed and reduced at the same potential as Al–PCV. The interference may be eliminated by complexation of the V with citrate. Al and V present together may be determined by analysis in the absence of citrate (total: Al + V) and in the presence of citrate (Al); V is determined as the difference in the two values.The analysis of a range of samples with Al concentrations from 6 ng mL−1 to 3 μg mL−1 gave results which were in good agreement with those obtained by other methods. Key words: aluminium, pyrocatechol violet, adsorption, voltammetry, environmental.

Molecular Weight and Polydispersivity of Rubber by Diffusion Measurements

1947 ◽  
Vol 20 (2) ◽  
pp. 377-379
Author(s):  
A. G. Pasynskii ◽  
T. V. Gatovskaya
Keyword(s):  
Molecular Weight ◽  
Natural Rubber ◽  
Average Value ◽  
Type Iv ◽  
Average Diffusion Coefficient ◽  
Average Diffusion ◽  
The Difference ◽  
Diffusion Curves ◽  
Fair Degree

Abstract The study of diffusion in solutions of natural rubber (light crepe) by Lamm's method showed that even with a concentration of 0.1 per cent the normalized experimental diffusion curves diverge from the ideal Gaussian curve (Figure 1), in that they are characterized by a marked asymmetry and an excess of the maximal ordinate. It follows from an analysis of the experimental curves by the method of moments (up to moments of the fourth order) that they belong to Type IV Pearson curves, that is, to asymmetrical distribution curves with asymptotic branches. The determination of the perturbation multiplier enables us to calculate the course of the experimental curves with a fair degree of accuracy. The physical cause of asymmetry of the diffusion curves is the difference in the rate of diffusion to both sides of the interface (of the polymer into the solvent and back) due to a marked intermolecular interaction in the solution of the polymer at a given concentration. With a decrease of the concentration or of the molecular weight of the dissolved substance, the asymmetry of the diffusion curves becomes less pronounced. However, this asymmetry does not preclude the computation of the average diffusion coefficient D from the standard deviation of the curve. It can, indeed, be shown that the probable error does not exceed 1 per cent. The average value found for natural rubber in carbon tetrachloride is D20°=0.71×10−7 sq. cm. per sec.

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